COLOR-CODE STANDARDS STANDARDS FOR NETWORK CABLE
Again, please bear with me... me... Let's start with with simple pin-out diagrams diagrams of the two types of UTP Ethernet cables and watch how committees can make a can of worms out of them. them. Here are the diagrams: diagrams:
Note that the TX (transmitter) pins are connected to corresponding RX (receiver) pins, plus to plus plus and minus minus to minus. minus. And that you must must use a crossover cable to connect units units with identical interfaces. interfaces. If you use a straight-through straight-through cable, one of the two units must, in effect, perform the crossover function. Two wire color-code standards apply: EIA/TIA 568A and EIA/TIA 568B. The codes are commonly depicted with RJ-45 jacks as follows (the view is from the front of the jacks):
If we apply the 568A color code and show all eight wires, our pin-out looks like this:
Note that pins 4, 5, 7, and 8 and the blue and brown pairs are not used in either standard. standard. Quite contrary to what you may read elsewhere, elsewhere, these pins and wires are not used or required to implement 100BASE-TX duplexing--they are just plain wasted. However, the actual actual cables are not physically that that simple. In the diagrams, the orange orange pair of wires are not not adjacent. adjacent. The blue pair is upside-down. upside-down. The right ends match RJ-45 jacks and the left ends do do not. If, for example, we invert the left side of the 568A "straight"-thru cable to match a 568A jack--put one 180° twist in the entire cable from end-to-end--and twist together and rearrange the appropriate pairs, we get the following can-of-worms: This further emphasizes, I hope, the importance of the word "twist" in making network cables which will work. You cannot cannot use an flatuntwisted telephone cable for a network cable. Furthermore, you must use a pair of twisted wires to connect a set of transmitter transmitter pins to their corresponding corresponding receiver pins. pins. You cannot use a wire from one pair and another wire from a different pair. Keeping the above principles in mind, we can simplify the diagram for a 568A straight-thru cable by by untwisting the wires, except the 180° twist in the entire cable, and bending bending the ends upward. upward. Likewise, if we exchange exchange the green and orange pairs in the 568A diagram we will get a simplified diagram for a 568B straight-thru cable. cable. If we cross the green and orange orange pairs in the 568A diagram we will arrive arrive at a simplified simplified diagram for for a crossover cable. cable. All three are shown below.
HOW TO MAKE YOUR OWN CAT CAT 5 TWISTED-PAIR NETWORK CABLES Last updated: 1/18/2001
INTRODUCTION. The purpose of this article is to show you how to make the
two kinds of cables which can be used to network two or more computers together to form quick and simple home or small office local area networks (LANs). These instructions instructions can also be be used to make make patch cables cables for networks with more complex infrastructure wiring. The two most common unshielded twisted-pair (UTP) network standards are the10 Mhz 10BASE-T Ethernet and the 100Mhz 100BASE-TX Fast Ethernet. The 100BASE-TX standard is quickly becoming the predominant LAN standard. If you are starting from scratch, to build a small home or office network, this is clearly the standard you should choose. choose. This article will show you how how to make cables which will work with both standards. LANS SIMPLIFIED. A LAN can be as simple as
two computers, each having a network interface card (NIC) or network adapter and running network software, connected together with a crossover cable . The next step up would be a network consisting of three or more computers and a hub. Each of the computers is plugged into the hub with a straight-thru cable (the crossover function is performed by the hub).
Registered jack (R J – 45)
A registered jack (RJ) is a standardized physical network interface — both jack construction and wiring pattern — for connecting telecommunications or data equipment to a service provided by a local exchange carrier or long distance carrier . The standard designs for these connectors and their wiring are named RJ11, RJ14,RJ21, RJ48, etc. Many of these interface standards are commonly used in North America, though some interfaces are used world-wide. The physical connectors that registered jacks use are mainly of the modular connector and 50pin miniature ribbon connector types. For example, RJ11 uses a 6 position 4 conductor (6P4C) modular plug and jack, while RJ21 uses a 50-pin miniature ribbon connector.
Left to right, RJ connectors:
an eight-contact 8P8C plug (used for RJ49, RJ61 and others, but often called "RJ45" because of its outward
semblance to the true RJ45)
six-contact RJ25 plug
four-contact RJ14 plug (often also used instead of two-pin RJ11)
a four-contact handset plug (also popularly, though incorrectly, called "RJ22", "RJ10", or "RJ9")
RJ25 and RJ14 can be plugged into the same standard six-pin jack, pictured.
Naming confusion Strictly, "registered jack" refers to both the female physical connector (modular connector ) and its wiring, but the term is often used loosely to refer to modular connectors regardless of wiring, such as in Ethernet over twisted pair . There is much confusion over these connection standards. The six-position plug and jack commonly used for telephone line connections may be used for RJ11, RJ14 or even RJ25, all of which are actually names of interface standards that use this physical connector. The RJ11 standard d ictates a 2-wire connection, while RJ14 uses a 4-wire configuration, and RJ25 uses all six wires. The RJ abbreviations, though, only pertain to the wiring of the jack (hence the name " registered jack"); it is commonplace but not strictly correct to refer to an unwired plug connector by any of these names. Plugs and jacks of this type are often called modular connectors, which originally distinguished them from older telephone connectors, which were very bulky or wired directly to the wall and therefore not accommodating of modular systems. A common nomenclature for modular connectors is e.g. "6P" to indicate a six-position modular plug or jack. Sometimes the nomenclature is expanded to indicate the number of positions that contain conductors. For example, a six-position modular plug with conductors in the middle two positions and the other four positions unused is called a 6P2C. RJ11 uses a 6P plug; furthermore, it often uses a 6P2C. (The connectors could be supplied more pins, but if more pins are actually wired, the interface is no longer an RJ11.) Registered jacks were created by the FCC to be the standard interface between a telephone company and a customer. The wired communications provider (telephone company) is responsible for de livery of services to a minimum point of entry (MPOE) (physically a utility box) which connects the telephone/network wiring on the customer's property (CPE - Customer-premises equipment) to the communication provider's network. The customer is responsible for jacks, wiring, and equipment on their side of the MPOE. The intent is to establish a universal standard for wiring and interfaces, and to separate ownership of in-home (or in-office) telephone wiring away from (North America's)Bell Systems and relinquish ownership of wiring in an entity's owned structure to that entity. The various interfaces created due to this regulation were numbered and integrated into the telecommunications' order system by adopting them as Universal Service Order Codes (USOC). USOCs are commonly passed to the communications provider by large businesses for a variety of services. Because there are many standardized interface options available to the customer, the customer must specify the type of interface required, by RJ/USOC. And for a multi-line interface such as the RJ21, they must denote which position(s) of the interface are to be used. If there are multiple RJ21 connectors, they are numbered sequentially and the customer must advise the communications provider of which one to use.
Twisted pair See also: Category 5 cable and TIA/EIA-568-B While the plugs are generally used with a flat cable (a notable exception being Ethernet twisted-pair cabling used with the 8P8C modular plug), the long cables feeding them in the building wiring and the phone network before them are normally twisted pair . Wiring conventions were designed to take full advantage of the physical compatibility ensuring that using a smaller plug in a larger socket would pick up complete pairs not a (relatively useless) two half pairs but here again there has been a problem. The original concept was that the centre two pins would be one pair, the ne xt two out the second pair, and so on until the outer pins of an e ight-pin connector would be the fourth twisted pair. Additionally, signal shielding was optimised by alternating the “live” (hot) and “earthy” (ground) pins of each pair. This standard for the eight-pin connector is the USOC-defined pinout, but the outermost pair are then too far apart to meet the electrical requirements of high-speed LAN protocols. Two variations known as T568A and T568B overcome this by using adjacent pairs of the outer four pins for the third and fourth pairs. For T568A, the inner four pins are wired identically to those in RJ14. In the T568B variant, different pairs are assigned to different pins, so a T568B jack is incompatible with the wiring pattern of RJ14. In connecting cables, however, the performance differences between the pairs that are assigned to different pins are minimal, and in general use T568A and T568B patch cables are interchangeable.
History and authority For more details on this topic, see Interconnection. Under the Bell System monopoly (following the Communications Act of 1934), the Bell System owned the phones and did not allowinterconnection of separate phones or other terminal equipment; a popular saying was "Ma Bell has you by the calls". Phones were generally hardwired, or at times used proprietary Bell System connectors. This began to change with the case Hush-A-Phone v. United States [1956] and the FCC's Carterfone [1968] decision, which required Bell to a llow some interconnection, which culminated in registered jacks. Registered jacks were introduced by the Bell System in the 1970s under a 1976 FCC order ending the use of protective couplers. They replaced earlier, bulkier connectors. The Bell System issued specifications for the modular connectors and their wiring as Universal Service Ordering Codes (USOC), which were the only standard at the time.
When the US telephone industry was opened to more competition in the 1980s, the specifications were made a matter of US law, ordered by the Federal Communications Commission (FCC) and codified in the Code of Federal Regulations, 47 CFR 68, subpart F. In January 2001, the FCC turned over responsibility for standardizing connections to the telephone network to a new private industry organization, the Administrative Council for Terminal Attachment (ACTA). The FCC removed Subpart F from the CFR and added Subpart G, which delegates the task to the ACTA. The ACTA published a standard called TIA/EIA-IS-968 which contained the information that was formerly in the CFR. The current version of that standard, called TIA-968-A, specifies the modular connectors at length, but not the wiring. Instead, TIA-968-A incorporates a standard called T1.TR5-1999 by reference to specify the wiring. Note that a registered jack name such as RJ11 identifies both the physical connectors and the wiring (pinout) of it (see above).
International use The modular jack was chosen as a candidate for ISDN systems. In order to be considered, the connector system had to be defined under international standards. In turn this led to ISO 8877. Under the rules of the IEEE 802 standards project, international standards are to be preferred over national standards so the modular connector was chosen for IEEE 802.3i-1990, the original 10BASE-T twisted-pair wiring version of Ethernet.
Registered jack types It has been suggested that RJ11, RJ14, RJ25, RJ21, RJ48 and RJ61 be merged into this article or section. (Discuss) It has been suggested that this section be split into a new article titled List of registered jacks. (Discuss)
The most familiar registered jack is probably the RJ11. This is a 6 position modular connector wired for one phone line, and is found in most homes and offices in North America for single line telephones. RJ14 and RJ25 are also fairly common, using the same size connector as RJ11, but with two and three phone lines, respectively, connected. Essentially all one, two, and three line analog telephones made today (2009) are meant to plug into RJ11, RJ14, or RJ25 jacks, respectively. The true RJ45(S) is an extremely uncommon registered jack, but the name "RJ45" is also used quite commonly to refer to any 8P8C modular connector .
Many of the basic names have suffixes that indicate subtypes:
C: flush-mount or surface mount
W: wall-mount
S: single-line
M: multi-line
X: complex jack
For example, RJ11 comes in two forms: RJ11W is a jack from which you can hang a wall telephone, while RJ11C is a jack designed to have a cord plugged into it. (You can plug a cord into an RJ11W as well, but it usually doesn't look as nice as a cord plugged into an RJ11C.)
RJ2MB: 50-pin miniature ribbon connector, 2-12 telephone lines with make-busy
RJ11C/RJ11W: 6P2C, for one telephone line (6P4C with power on second pair)
RJ12C/RJ12W: 6P6C, for one telephone line ahead of the key system (key telephone system)
RJ13C/RJ13W: 6P4C, for one telephone line behind the key system (key telephone system)
RJ14C/RJ14W: 6P4C, for two telephone lines (6P6C with power on third pair)
RJ15C: 3-pin weatherproof, for one telephone line
RJ18C/RJ18W : 6P6C, for one telephone line with make-busy arrangement
RJ21X: 50-pin miniature ribbon connector, for up to 25 lines
RJ25C/RJ25W: 6P6C, for three telephone lines
RJ26X: 50-pin miniature ribbon connector, for multiple data lines, universal
RJ27X: 50-pin miniature ribbon connector, for multiple data lines, programmed
RJ31X: 8P8C (although usually only 4C are used), Often incorrectly stated as allowing alarm (fire
and intrusion) equipment to seize a phone line, the jack is actually used to disconnect the equipment from the phone line while allowing the phone circuit to continue to the site phones.
RJ38X: 8P8C, similar to RJ31X, with continuity circuit
RJ41S: 8P8C keyed, for one data line, universal
RJ45S: 8P2C + keyed, for one data line with programming resistor
RJ48S: 8P8C, for four-wire data line (DDS)
RJ48C: 8P8C, for four-wire data line (DSX-1)
RJ48X: 8P8C with shorting bar, for four-wire data line (DS1)
RJ49C: 8P8C, for ISDN BRI via NT1
RJ61X: 8P8C, for four telephone lines
RJ71C: 12 line series connection using 50 pin connector (with bridging adapter) ahead of
customer equipment. Mostly used for call sequencer equipment.
"Unofficial" (incorrect) plug names These "RJ" names do not really refer to truly existing ACTA RJ types:
"RJ9", "RJ10", "RJ22": 4P4C or 4P2C, for telephone handsets. Since telephone handsets do not
connect directly to the public network, they have no registered jack code whatsoever.
"RJ45": 8P8C, informal designation for T568A/T568B, including Ethernet; not the same as the
true RJ45/RJ45S
"RJ50": 10P10C, for data
RJ -45
RJ45 pin numbering Before we start with the discussion of wiring schemes for modular jacks, it is good to know how pins are numbered on RJ45 and other modular jacks. The following scheme shows the exact pin numbering on both male and female RJ45 connectors. RJ45 pin numbering
All other modular jacks—like RJ11—start counting at the same side of the connector. In the wiring diagrams with modular jacks on this site we prefer to use a picture of the jack upside down, with the hook underneath.
The straight through RJ45 network cable, EIA/TIA 568B The most common wiring for RJ45 cables is the straight through cable. In this cable layout, all pins are wired one-to-one to the other side. The pins on the RJ45 connector are assigned in pairs, and every pair carries one differential signal. Each line pair has to be twisted. If UTP or FTP cable is used, the pairs have orange, brown, blue and green colors. The wiring of these cables to RJ45 to make a straight through cable is defined by EIA/TIA 568B. The RJ45 connectors on both ends are wired in the same way. The color scheme is shown below. Straight through RJ45 color coding - EIA/TIA 568B
The cross over RJ45 network cable, EIA/TIA 568A The straight through RJ45 cable is commonly used to connect network cards with hubs on 10Base-T and 100Base-Txnetworks. On network cards, pair 1-2 is the transmitter, and pair 3-6 is the receiver. The other two pairs are not used. On hubs pair 1-2 is the receiver and 3-6 the transmitter. Because of this a straight through RJ45 cable can be used to connect network cards to hubs. In very small network configurations where only two computers have to be connected, the use of a hub is not necessary. The straight through RJ45 cable cannot be used in that situation. Also when two hubs have to be connected to increase the number of nodes on a
network segment, this cable is not appropriate. In both situations a cross over RJ45 cable is necessary, where the transmit and receive lines on both RJ45 connectors are cross connected. The color coding for the cross over RJ45 cable has been defined in the EIA/TIA 568A standard. Please note: One RJ45 connector has to be wired as EIA/TIA 568B, the other as EIA/TIA 568A. When wiring both ends as EIA/TIA 568A, the resulting cable is a straight through cable again. Cross over RJ45 color coding - EIA/TIA 568A
Common data and voice wiring schemes Depending of the situation where modular cables are used, the wiring schemes with modular jacks differ. The most common wiring schemes can be seen in the picture below. Common modular jack wiring schemes
Female connector, looking from the open e nd
Introduction A computer network allows computers to communicate with many other computers and to share resources and information. The Advanced Research Projects Agency (ARPA) funded the design of the "Advanced Research Projects Agency Network" (ARPANET) for the United States Department of Defense. It was the first operational computer n etwork in the world.[1] Development of the network began in 1969, based on designs developed during the 1960s.
Network classification What is networking? The following list presents categories used for classifying networks. In the world of computers, networking is the practice of linking two or more computing devices together for the purpose of sharing data. Networks are built with a mix of computer hardware and computer software
Connection method What is Networking? In the world of computers, networking is the practice of linking two or more computing devices together for the purpose of sharing data. Networks are built with a mix of computer hardware and computer software. Computer networks can also be classified according to the hardware and software technology that is used to interconnect the individual devices in the network, such as Optical fiber , Ethernet,Wireless LAN, HomePNA, Power line communication or G.hn. Ethernet uses physical wiring to connect devices. Frequently deployed devices include hubs, switches, bridges and/or routers. Wireless LAN technology is designed to connect devices without wiring. These devices useradio waves or infrared signals as a transmission medium. ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed (up to 1 Gigabit/s) local area network. Wired Technologies
Twisted-Pair Wire - This is the most widely used medium for telecommunication. Twisted-pair wires are ordinary telephone wires which consist of two insulated copper wires twisted into pairs and are used for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed range from 2 million bits per second to 100 million bits per second.
Coaxial Cable – These cables are widely used for cable television systems, office buildings, and other worksites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating
layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second.
Fiber Optics – These cables consist of one or more thin filaments of glass fiber wrapped in a protective layer. It transmits light which can travel over long distance and higher bandwidths. Fiber-optic cables are not affected by electromagnetic radiation. Transmission speed could go up to as high as trillions of bits per second. The speed of fiber optics is hundreds of times faster than coaxial cables and thousands of times faster than twisted-pair wire. Wireless Technologies
Terrestrial Microwave – Terrestrial microwaves use Earth-based transmitter and receiver. The equipment look similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx. 30 miles apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks.
Communications Satellites – The satellites use microwave radio as their telecommunications medium which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically 22,000 miles above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.
Cellular and PCS Systems – Use several radio communications technologies. The systems are divided to different geographic area. Each area has low-power transmitter or radio relay antenna device to relay calls from one area to the next area.
Wireless LANs – Wireless local area network use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless L ANS use spread spectrum technology to enable communication between multiple devices in a limited area. Example of open-standard wireless radio-wave technology is IEEE 802.11b.
Bluetooth – A short range wireless technology. Operate at approx. 1Mbps with range from 10 to 100 meters. Bluetooth is an open wireless protocol for data exchange over short distances.
The Wireless Web – The wireless web refers to the use of the World Wide Web through equipments like cellular phones, pagers,PDAs, and other portable communications devices. The wireless web service offers anytime/anywhere connection.
Scale Networks are often classified as Local Area Network (LAN), Wide Area Network (WAN), Metropolitan Area Network (MAN), Personal Area Network (PAN), Virtual Private Network (VPN), Campus Area
Network (CAN), Storage Area Network (SAN), etc. depending on their scale, scope and purpose. Usage, trust levels and access rights often differ between these types of network - for example, LANs tend to be designed for internal use by an organization's internal systems and employees in individual physical locations (such as a building), while WANs may connect physically separate parts of an organization to each other and may include connections to third parties.
Functional relationship (network architecture) Computer networks may be classified according to the functional relationships which exist among the elements of the network, e.g., Active Networking, Client-server and Peer-to-peer (workgroup) architecture.
Network topology Computer networks may be classified according to the network topology upon which the network is based, such as bus network, star network,ring network, mesh network, star-bus network, tree or hierarchical topology network. Network topology signifies the way in which devices in the network see their logical relations to one another. The use of the term "logical" here is significant. That is, network topology is independent of the "physical" layout of the network. Even if networked computers are physically placed in a linear arrangement, if they are connected via a hub, the network has a Star topology, rather than a bus topology. In this regard the visual and o perational characteristics of a network are distinct; the logical network topology is not necessarily the same as the physical layout. Networks may be classified based on the method of data used to convey the data, these include digital and analog networks.
Types of networks Below is a list of the most common types of computer networks in order of scale.
Personal area network A personal area network (PAN) is a computer network used for communication among computer devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles. Such a PAN may include wired and wireless connections between devices. The reach of a PAN is typically at least about 20-30 feet (approximately 6-9 meters), but this is expected to increase with technology improvements.
Local area network A local Area Network (LAN) is a computer network covering a small physical area, like a home, office, or small group of buildings, such as a school, or an airport. Current wired LANs are most likely to be based on Ethernet technology, although new standards like ITU-T G.hn also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines)[2].
For example, a library may have a wired or wireless LAN for users to interconnect local devices (e.g., printers and servers) and to connect to the internet. On a wired LAN, PCs in the library are typically connected by category 5 (Cat5) cable, running the IEEE 802.3 protocol through a system of interconnected devices and eventually connect to the Internet. The cables to the servers are typically on Cat 5e enhanced cable, which will support IEEE 802.3 at 1 Gbit/s. A wireless LAN may exist using a different IEEE protocol, 802.11b, 802.11g or possibly 802.11n. The staff computers (bright green in the figure) can get to the color printer, checkout records, and the academic network and the Internet. All user computers can get to the Internet and the card catalog. Each workgroup can get to its local printer. Note that the printers are not accessible from outside their workgroup.
Typical library network, in a branching tree topology and controlled access to resources
All interconnected devices must understand the network layer (layer 3), because they are handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the central router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand IP. It would be more correct to call them access routers, where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers. The defining characteristics of LANs, in contrast to WANs (Wide Area Networks), include their higher data transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE has projects investigating the standardization of 40 and 100 Gbit/s.[3]
Campus area network A campus area network (CAN) is a computer network made up of an interconnection of local area networks (LANs) within a limited geographical area. It can be considered one form of a metropolitan area network, specific to an academic setting.
In the case of a university campus-based campus area network, the network is likely to link a variety of campus buildings including; academic departments, the university library and student residence halls. A campus area network is larger than a local area network but smaller than a wide area network (WAN) (in some cases). The main aim of a campus area network is to facilitate students accessing internet and university resources. This is a network that connects two or more LANs but that is limited to a specific and contiguous geographical area such as a college campus, industrial complex, office building, or a military base. A CAN may be considered a type of MAN (metropolitan area network), but is generally limited to a smaller area than a typical MAN. This term is most often used to discuss the implementation of networks for a contiguous area. This should not be confused with a Controller Area Network. A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings.
Metropolitan area network A metropolitan area network (MAN) is a network that connects two or more local area networks or campus area networks together but does not extend beyond the boundaries of the immediate town/city. Routers, switches and hubs are connected to create a metropolitan area network.
Wide area network A wide area network (WAN) is a computer network that covers a broad area (i.e. any network whose communications links cross metropolitan, regional, or national boundaries [1]). Less formally, a WAN is a network that uses routers and public communications links. Contrast with personal area networks (PANs), local area networks (LANs), campus area networks (CANs), or metropolitan area networks (MANs), which are usually limited to a room, building, campus or specific metropolitan area (e.g., a city) respectively. The largest and most well-known example of a WAN is the Internet. A WAN is a data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI model|OSI reference model: the physical layer, the data link layer, and the network layer.
Global area network A global area networks (GAN) (see also IEEE 802.20) specification is in development by several groups, and there is no common definition. In general, however, a GAN is a model for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key
challenge in mobile communications is "handing o ff" the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial WIRELESS local area networks (WLAN).[4]
Virtual private network A virtual private network (VPN) is a computer network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network (e.g., the Internet) instead of by physical wires. The data link layer protocols of the virtual network are said to be tunneled through the larger network when this is the case. One common application is secure communications through the public Internet, but a VPN need not have explicit security features, such as authentication or content encryption. VPNs, for example, can be used to separate the traffic of different user communities over an underlying network with strong security features. A VPN may have best-effort performance, or may have a defined service level agreement (SLA) between the VPN customer and the VPN service provider. Generally, a VPN has a topology more complex than point-to-point. A VPN allows computer users to appear to be editing from an IP address location other than the one which connects the actual computer to the Internet.
Internetwork An Internetwork is the connection of two or more distinct computer networks or network segments via a common routing technology. The result is called an internetwork (often shortened to internet). Two o r more networks or network segments connect using devices that operate at layer 3 (the 'network' layer) of the OSI Basic Reference Model, such as a router. Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork. In modern practice, interconnected networks use the Internet Protocol. There are at least three variants of internetworks, depending on who administers and who participates in them:
Intranet
Extranet
Internet
Intranets and extranets may or may not have connections to the Internet. If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization. The Internet is not considered to be a part of the intranet or extranet, although it may serve as a portal for access to portions of an extranet.
Intranet An intranet is a set of networks, using the Internet Protocol and IP-based tools such as web browsers and file transfer applications, that is under the control of a single administrative entity. That administrative entity closes the intranet to all but specific, authorized users. Most commonly, an intranet is the internal network of an organization. A large intranet will typically have at least one web server to provide users with organizational information.
Extranet An extranet is a network or internetwork that is limited in scope to a single organization or entity and also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (e.g., a company's customers may be given access to some part of its intranet creating in this way an extranet, while at the same time the customers may not be considered 'trusted' from a security standpoint). Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although, by definition, an extranet cannot consist of a single LAN; it must have at least one connection with an external network.
Internet The Internet consists of a worldwide interconnection of go vernmental, academic, public, and private networks based upon the networking technologies of the Internet Protocol Suite. It is the successor of the Advanced Research Projects Agency Network (ARPANET) developed byDARPA of the U.S. Department of Defense. The Internet is also the communications backbone underlying the World Wide Web (WWW). The 'Internet' is most commonly spelled with a capital 'I' as a proper noun, for historical reasons and to distinguish it from other generic internetworks. Participants in the Internet use a diverse array of methods of several hundred documented, and often standardized, protocols compatible with the Internet Protocol Suite and an addressing system (IP Addresses) administered by the Internet Assigned Numbers Authority and address registries. Service providers and large enterprises exchange information about the reachability of their address spaces through the Border Gateway Protocol (BGP), forming a redundant worldwide mesh of transmission paths.
Basic hardware components All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.12) or optical cable ("optical fiber "). An Ethernet card may also be required.
Network interface cards A network card, network adapter, or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It p rovides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses.
Repeaters A repeater is an electronic device that receives a signal and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable which runs longer than 100 meters.
Hubs A network hub contains multiple ports. When a packet arrives at one port, it is copied unmodified to all ports of the hub for transmission. The destination address in the frame is not changed to a broadcast address.[5]
Bridges A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address only to that port. Bridges do send broadcasts to all ports except the one on which the broadcast was received.
Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a po rt, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived. Bridges come in three basic types: 1.
Local bridges: Directly connect local area networks (LANs)
2.
Remote bridges: Can be used to create a wide area network (WAN) link between LANs.
Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers. 3.
Wireless bridges: Can be used to join LANs or connect remote stations to LANs
Switches A network switch is a device that forwards and filters OSI layer 2 datagrams (chunk of data communication) between ports (connected cables) based on the MAC addresses in the packets.[6] This is distinct from a hub in that it only forwards the packets to the ports involved in the communications rather than all ports connected. Strictly speaking, a switch is not capable of routing traffic based on IP address (OSI Layer 3) which is necessary for communicating between network segments or within a large or complex LAN. Some switches are capable of routing based on IP addresses but are still called switches as a marketing term. A switch normally has numerous ports, with the intention being that most or all of the network is connected directly to the switch, or another switch that is in turn connected to a switch. [7] Switch is a marketing term that encompasses routers and bridges, as well as devices that may distribute traffic on load or by application content (e.g., a Web URL identifier). Switches may operate at one or more OSI model layers, including physical, data link, network, or transport (i.e., end-to-end). A device that operates simultaneously at more than one of these layers is called a multilayer switch. Overemphasizing the ill-defined term "switch" often leads to confusion when first trying to understand networking. Many experienced network designers and operators recommend starting with the logic of devices dealing with only one protocol level, not all of which are covered by OSI. Multilayer device selection is an advanced topic that may lead to selecting particular implementations, but multilayer switching is simply not a real-world design concept.
Routers A router is a networking device that forwards packets between networks using information in protocol headers and forwarding tables to determine the best next router for each packet. Routers work at the Network Layer (layer 3) of the OSI model and the Internet Layer of TCP/IP.
Wireless access point In computer networking, a wireless access point (WAP) is a device that allows wireless communication devices to connect to a wireless network using Wi-Fi, Bluetooth or related standards. The WAP usually connects to a wired network, and can relay data between the wireless devices (such as co mputers or printers) and wired devices on the network. In industrial wireless networking, the design is rugged with a metal cover, a Din-Rail mount, and a wider temperature range during operations, high humidity and exposure to water, dust, and oil. Wireless security includes: WPA-PSK, WPA2, IEEE 802.1x/RADIUS, WDS, WEP, TKIP, and CCMP (AES) encryption. Unlike home consumer models, industrial wireless access points can also be used as a bridge, router, or a client.
Planet WsAP-4000 Wireless Access Point
Introduction
Linksys WAP54G 802.11g Wireless Access Point
embedded RouterBoard 112 withU.FL-RSMA pigtail and R52 mini PCIWi-Fi card widely used by wirelessInternet service providers (WISPs) across the world
Prior to wireless networks, setting up a computer network in a business, home, or school o ften required running many cables through walls and ceilings in order to deliver network access to all of the networkenabled devices in the building. With the advent of the Wireless Access Point, network users are now able to add devices that access the network with few or no cables. Today's WAPs are built to support a standard for sending and receiving data using radio frequencies rather than cabling. Those standards, and the frequencies they use are defined by the IEEE. Most WAPs use IEEE 802.11 standards.
Common WAP Applications A typical corporate use involves attaching several WAPs to a wired network and then providing wireless access to the office LAN. The wireless access points are managed by a WLAN Controller which handles automatic adjustments to RF power, channels, authentication, and security. Further, controllers can be combined to form a wireless mobility group to allow inter-controller roaming. The controllers can be pa rt of a mobility domain to allow clients a ccess throughout large or regional office locations. This saves the clients time and administrators overhead because it can automatically re-associate or re-authenticate. Further, multiple controllers and all of the hundreds of access points attached to those controllers can be managed by a software called Cisco Wireless Control System Which handles the same functions as a controller yet adds the bonus features of mapping user or RFID locations to an uploaded map, upgrading controllers and access point firmware, and rogue detection/handling. In this instance, the WAP functions as a gateway for clients to access the wired network. A Hot Spot is a common public application of WAPs, where wireless clients can connect to the Internet without regard for the particular networks to which they have attached for the moment. The concept has become common in large cities, where a combination of coffeehouses, libraries, as well as privately owned open access points, allow clients to stay more or less continuously connected to the Internet, while moving around. A collection of connected Hot Spots can be referred to as a lily-pad network.
The majority of WAPs are used in Home wireless networks.[citation needed ] Home networks generally have only one WAP to connect all the computers in a home. Most are wireless routers, meaning converged devices that include the WAP, a router , and, often, an ethernet switch. Many also include a broadband modem. In places where most homes have their own WAP within range of the neighbors' WAP, it's possible for technically savvy people to turn off their encryption and set up a wireless community network, creating an intra-city communication network without the need of wired networks. A WAP may also act as the network's arbitrator, negotiating when each nearby client device can transmit. However, the vast majority of currently installed IEEE 802.11 networks do not implement this, using a distributed pseudo-random algorithm called CSMA/CA instead.
Wireless Access Point vs. Ad-Hoc Network Some people confuse Wireless Access Points with Wireless Ad-Hoc networks. An Ad-Hoc network uses a connection between two or more devices without using an access point: the devices communicate directly. An Ad-Hoc network is used in situations such as a quick data exchange or a multiplayer LAN game because it is easy to set up and does not require an access point. Due to its peer-to-peer layout, Ad-Hoc connections are similar to Bluetooth ones and are generally not recommended for a permanent installation. Internet access via Ad-Hoc networks, using features like Windows' Internet Connection Sharing, may work well with a small number of devices that are close to each other, but Ad-Hoc networks don't scale well. Internet traffic will converge to the nodes with direct internet connection, potentially congesting these nodes. For internet-enabled nodes, Access Points have a clear advantage, being designed to handle this load.
Limitations One IEEE 802.11 WAP can typically communicate with 30 client systems located within a radius of 100 m.[citation needed ] However, the actual range of communication can vary significantly, depending on such variables as indoor or outdoor placement, height above ground, n earby obstructions, other electronic devices that might actively interfere with the signal by broadcasting on the same frequency, type of antenna, the current weather, ope rating radio frequency, and the power output of devices. Network designers can extend the range of WAPs through the use of repeaters and reflectors, which can bounce or amplify radio signals that ordinarily would go un-received. In experimental conditions, wireless networking has operated over distances of several kilometers.[citation needed ]
Most jurisdictions have only a limited number of frequencies legally available for use by wireless networks. Usually, adjacent WAPs will use different frequencies (Channels) to communicate with their clients in order to avoid interference between the two nearby systems. Wireless devices can "listen" for data traffic on other frequencies, and can rapidly switch from one frequency to another to achieve better reception. However, the limited number of frequencies becomes problematic in crowded downtown areas with tall buildings using multiple WAPs. In such an environment, signal overlap becomes an issue causing interference, which results in signal dropage and data errors. Wireless networking lags behind wired networking in terms of increasing bandwidth and throughput. While (as of 2004) typical wireless devices for the consumer market can reach speeds of 11 Mbit/s (megabits per second) (IEEE 802.11b) or 54 Mbit/s (IEEE 802.11a, IEEE 802.11g), wired hardware of similar cost reaches 1000 Mbit/s (Gigabit Ethernet). One impediment to increasing the speed of wireless communications comes from Wi-Fi's use of a shared communications medium, so a WAP is only able to use somewhat less than half the actual over-the-air rate for data throughput. Thus a typical 54 MBit/s wireless connection actually carries TCP/IP data at 20 to 25 Mbit/s. Users of legacy wired networks expect faster speeds, and people using wireless connections keenly want to see the wireless networks catch up. As of 2007 a new standard for wireless, 802.11n is awaiting final certification from IEEE. This new standard operates at speeds up to 540 Mbit/s and at longer distances (~50 m) than 802.11g. Use of legacy wired networks (especially in consumer applications) is e xpected[by whom? ] to decline sharply as the common 100 Mbit/s speed is surpassed and users no longer need to worry about running wires to attain high bandwidth.[citation needed ] By the year 2008 draft 802.11n based access points and client devices have already taken a fair share of the market place but with inherent problems integrating products from different vendors.
Security Main article: Wireless LAN Security Wireless access has special security considerations. Many wired networks base the security on physical access control, trusting all the users on the local network, but if wireless access points are connected to the network, anyone on the street or in the ne ighboring office could connect. The most common solution is wireless traffic encryption. Modern access points come with built-in encryption. The first generation encryption scheme WEP proved easy to crack; the second and third generation schemes, WPA and WPA2, are considered secure if a strong enoughpassword or passphrase is used.
Some WAPs support hotspot style authentication using RADIUS and other authentication servers.
Active networking Active networking is a communication pattern that a llows packets flowing through a telecommunications network to dynamically modify the operation of the network.
How it works Active network architecture is composed of execution environments (similar to a unix shell that can execute active packets), a node operating system capable of supporting one or more execution environments. It also consists of active h ardware, capable of routing or switching as well as executing code within active packets. This differs from the traditional network architecture which seeks robustness and stability by attempting to remove complexity and the ability to change its fundamental operation from underlying network components. Network processorsare one means of implementing active networking concepts. Active networks have also been implemented as overlay networks.
What does it offer? Active networking allows the possibility of highly tailored and rapid "real-time" changes to the underlying network operation. This enables such ideas as sending code along with packets of information allowing the data to change its form (code) to match the ch annel characteristics. The smallest program that can generate a sequence of data can be found in the definition of Kolmogorov Complexity. The use of realtime genetic algorithms within the network to compose network services is also enabled by active networking.
Fundamental Challenges Active network research addresses the nature of how best to incorporate extremely dynamic capability within networks[1]. In order to do this, active network research must address the problem of optimally allocating computation versus communication within communication networks[2]. A similar problem related to the compression of code as a measure of complexity is addressed via algorithmic information theory.
Nanoscale Active Networks
As the limit in reduction of transistor size is reached with current technology, active networking concepts are being explored as a more efficient means accomplishing computation and communication[3] [4].
Bluetooth This article is about the electronic protocol. For the medieval King of Denmark, see Harald I of Denmark .
Bluetooth logo.
Bluetooth is an open wireless protocol for exchanging data over short distances (using short length radio waves) from fixed and mobile devices, creating personal area networks (PANs). It was originally conceived as a wireless alternative to RS-232 data cables. It can connect several devices, overcoming problems of synchronization.
Name and logo The word Bluetooth is an anglicised version of Danish Blåtand , the epithet of the tenth-century king Harald I of Denmark and Norway who united dissonant Danish tribes into a single kingdom. The implication is that Bluetooth does the same with communications protocols, uniting them into one universal standard.[1][2][3] Although blå in modern Scandinavic languages means blue, during the Viking age it also could mean black.So a historically correct translation of Old Norse Harald Blátönn would rather be Harald Blacktooth than Harald Bluetooth. The Bluetooth logo is a bind rune merging the Germanic runes
(Gebo) and
(Berkanan).
[edit]Implementation Bluetooth uses a radio technology called frequency-hopping spread spectrum, which chops up the data being sent and transmits chunks of it on up to 79 frequencies. In its basic mode, the modulation is Gaussian frequency-shift keying (GFSK). It can achieve a gross data rate of 1Mb/s. Bluetooth provides a way to connect and exchange information between devices such as mobile phones, telephones, laptops, personal computers, printers, Global Positioning System (GPS) receivers, digital cameras, and video game consoles through a secure, globally unlicensed Industrial, Scientific and Medical (ISM) 2.4 GHz short-range radio frequency bandwidth. The Bluetooth specifications
are developed and licensed by the Bluetooth Special Interest Group (SIG). The Bluetooth SIG consists of companies in the areas of telecommunication, computing, networking, and consumer electronics.[4] [edit]Uses Bluetooth is a standard and a communications protocol primarily designed for low power consumption, with a short range (power-class-dependent: 100m, 10m and 1m, but ranges vary in practice; see table below) based on low-cost transceiver microchips in each device.[5]Bluetooth makes it possible for these devices to communicate with each other when they are in range. Because the devices use a radio (broadcast) communications system, they do not have to be in line of sight of each other.[4]
Class
Maximum Permitted Power Range mW (dBm) (approximate)
Class 1 100 mW (20 dBm)
~100 metres
Class 2 2.5 mW (4 dBm)
~22 metres
Class 3 1 mW (0 dBm)
~6 metres
In most cases the effective range of class 2 devices is extended if they connect to a class 1 transceiver, compared to a pure class 2 network. This is accomplished by the h igher sensitivity and transmission power of Class 1 devices. Version
Data Rate
Version 1.2
1 Mbit/s
Version 2.0 + EDR
3 Mbit/s
[edit]Bluetooth profiles
Main article: Bluetooth profile In order to use Bluetooth, a device must be compatible with certain Bluetooth profiles. These define the possible applications and uses of the technology. [edit]List
of applications
A typical Bluetooth mobile phone headset.
More prevalent applications of Bluetooth include:
Wireless control of and communication between a mobile phone and a hands-free headset. This
was one of the earliest applications to become popular.
Wireless networking between PCs in a confined space and where little bandwidth is required.
Wireless communication with PC input and output de vices, the most common being
themouse, keyboard and printer .
Transfer of files, contact details, calendar appointments, and reminders between devices
with OBEX.
Replacement of traditional wired serial communications in test equipment, GPS receivers,
medical equipment, bar code scanners, and traffic control devices.
For controls where infrared was traditionally used.
For low bandwidth applications where higher [USB] bandwidth is n ot required and cable-free
connection desired.
Sending small advertisements from Bluetooth-enabled advertising hoardings to other,
discoverable, Bluetooth devices[6].
Wireless bridge between two Industrial Ethernet (e.g., PROFINET) networks.
Two seventh-generation game consoles, Nintendo's Wii[7] and Sony's PlayStation 3, use
Bluetooth for their respective wireless controllers.
Dial-up internet access on personal computers or PDAs using a data-capable mobile phone as a
wireless modem like Novatel Mifi.
Short range transmission of health sensor data from medical devices to mobile phone, set-top
box or dedicated telehealthdevices[8]. [edit]Bluetooth
vs. Wi-Fi IEEE 802.11 in networking
Bluetooth and Wi-Fi have many applications in today's offices, homes, and on the move: setting up networks, printing, or transferring presentations and files from PDAs to computers. Both are versions of unlicensed wireless technology. Wi-Fi is intended for resident equipment and its applications. The category of applications is outlined as WLAN, the wireless local area networks. Wi-Fi is intended as a replacement for cabling for general local area network access in work areas. Bluetooth is intended for non resident equipment and its applications. The category of applications is outlined as the wireless personal area network (WPAN). Bluetooth is a replacement for cabling in a variety of personally carried applications in any ambience. [edit]Bluetooth devices
A Bluetooth USB dongle with a 100 m range.
Bluetooth exists in many products, such as telephones, the Wii, PlayStation 3, PSP Go, Lego Mindstorms NXT and recently in some high definition watches[citation needed ], modems and headsets. The technology is useful when transferring information between two or more devices that are near each other in lowbandwidth situations. Bluetooth is commonly used to transfer sound data with telephones (i.e., with a Bluetooth headset) or byte data with hand-held computers (transferring files). Bluetooth protocols simplify the discovery and setup o f services between devices. Bluetooth devices can advertise all of the services they provide. This makes using services easier because more of the security, network address and permission configuration can be automated than with many other network types. [edit]Wi-Fi
Main article: Wi-Fi Wi-Fi is a traditional Ethernet network, and requires configuration to set up shared resources, transmit files, and to set up audio links (for example, headsets and hands-free devices). Wi-Fi uses the same radio frequencies as Bluetooth, but with higher power, resulting in a stronger connection. Wi-Fi is sometimes called "wireless Ethernet." This description is accurate, as it also provides an indication of its relative
strengths and weaknesses. Wi-Fi requires more setup but is better suited for operating full-scale networks; it enables a faster connection, better range from the base station, and better security than Bluetooth. [edit]Computer
requirements
A typical Bluetooth USB dongle.
An internal notebook Bluetooth card (14×36×4 mm).
A personal computer must have a Bluetooth adapter in order to communicate with other Bluetooth devices (such as mobile phones, mice and keyboards). While some desktop computers and most recent laptops come with a built-in Bluetooth adapter, others will require an external one in the form of a dongle. Unlike its predecessor, IrDA, which requires a separate adapter for each device, Bluetooth allows multiple devices to communicate with a computer over a single adapter.
Operating system support For more details on this topic, see Bluetooth stack . Apple has supported Bluetooth since Mac OS X v10.2 which was released in 2002.[9]
For Microsoft platforms, Windows XP Service Pack 2 and later releases have native support for Bluetooth. Previous versions required users to install their Bluetooth adapter's own drivers, which were not directly supported by Microsoft.[10] Microsoft's own Bluetooth dongles (packaged with their Bluetooth computer devices) have no external drivers and thus require at least Windows XP Service Pack 2. Linux has two popular Bluetooth stacks, BlueZ and Affix. The BlueZ[11] stack is included with most Linux kernels and was originally developed by Qualcomm. The Affix stack was developed by Nokia. FreeBSD features Bluetooth support since its 5.0 release. NetBSD features Bluetooth support since its 4.0 release. Its Bluetooth stack has been ported to OpenBSD as well.
Mobile phone requirements A mobile phone that is Bluetooth enabled is able to pair with many devices. To ensure the broadest support of feature functionality together with legacy device support, the Open Mobile Terminal Platform (OMTP) forum has recently published a recommendations paper, entitled "Bluetooth Local Connectivity"; see external links below to download this paper.
Specifications and features The Bluetooth specification was developed in 1994 by Jaap Haartsen and Sven Mattisson, who were working for Ericsson Mobile Platforms inLund, Sweden.[12][citation needed ] The specification is based on frequency-hopping spread spectrum technology. The specifications were formalized by the Bluetooth Special Interest Group (SIG). The SIG was formally announced on May 20, 1998. Today it has a membership of over 11,000 companies worldwide. It was established by Ericsson, IBM, Intel, Toshiba, and Nokia, and later joined by many other companies.
Bluetooth 1.0 and 1.0B Versions 1.0 and 1.0B had many problems, and manufacturers had difficulty making their products interoperable. Versions 1.0 and 1.0B also included mandatory Bluetooth hardware device address (BD_ADDR) transmission in the Connecting process (rendering anonymity impossible at the protocol level), which was a major setback for certain services planned for use in Bluetooth environments.
Bluetooth 1.1
Ratified as IEEE Standard 802.15.1-2002.
Many errors found in the 1.0B specifications were fixed.
Added support for non-encrypted channels.
Received Signal Strength Indicator (RSSI).
Bluetooth 1.2 This version is backward compatible with 1.1 and the major enhancements include the following:
Faster Connection and Discovery
Adaptive frequency-hopping spread spectrum (AFH), which improves resistance to radio
frequency interference by avoiding the use of crowded frequencies in the hopping sequence.
Higher transmission speeds in practice, up to 721 kbit/s, than in 1.1.
Extended Synchronous Connections (eSCO), which improve voice quality of audio links by
allowing retransmissions of corrupted packets, and may optionally increase audio latency to provide better support for concurrent data transfer.
Host Controller Interface (HCI) support for three-wire UART.
Ratified as IEEE Standard 802.15.1-2005.
Introduced Flow Control and Retransmission Modes for L2CAP.
Bluetooth 2.0 + EDR This version of the Bluetooth specification was released on November 10, 2004. It is backward compatible with the previous version 1.2. The main difference is the introduction of an Enhanced Data Rate (EDR) for faster data transfer . The nominal rate of EDR is about 3 megabits per second, although the practical data transfer rate is 2.1 megabits per second.[13] The additional throughput is obtained by using a different radio technology for transmission of the data. Standard, or Basic Rate, transmission uses Gaussian Frequency Shift Keying (GFSK) modulation of the radio signal with a g ross air data rate of 1 Mbit/s. EDR uses a combination of GFSK and Phase Shift Keying modulation (PSK) with two variants, π/4DQPSK and 8DPSK. These have gross air data rates of 2, and 3 Mbit/s respectively. [14] According to the 2.0 + EDR specification, EDR provides the following benefits:
Three times the transmission speed (2.1 Mbit/s) in some cases.
Reduced complexity of multiple simultaneous connections due to additional bandwidth.
Lower power consumption through a reduced duty cycle.
The Bluetooth Special Interest Group (SIG) published the specification as "Bluetooth 2.0 + EDR" which implies that EDR is an optional feature. Aside from EDR, there are other minor improvements to the 2.0 specification, and products may claim compliance to "Bluetooth 2.0" without supporting the higher data rate. At least one commercial device, the HTC TyTN Pocket PC phone, states "Bluetooth 2.0 without EDR" on its data sheet.[15]
Bluetooth 2.1 + EDR Bluetooth Core Specification Version 2.1 + EDR is fully backward compatible with 1.2, and was adopted by the Bluetooth SIG on July 26, 2007.[14] It supports theoretical data transfer speeds of up to 3 Mb/s. This specification includes the following features: Extended inquiry response (EIR) Provides more information during the inquiry procedure to allow better filtering of devices before connection. This information may include the name of the device, a list of services the device supports, the transmission power level used for inquiry responses, and manufacturer defined data. Sniff subrating Reduces the power consumption when devices are in the sniff low-power mode, especially on links with asymmetric data flows. Human interface devices (HID) are expected to benefit the most, with mouse and keyboard devices increasing their battery life by a factor of 3 to 10. [citation needed ]
It lets devices decide how long they will wait before sending keepalive messages to one
another. Previous Bluetooth implementations featured keep alive message frequencies of up to several times per second. In contrast, the 2.1 + EDR specification allows pairs of devices to negotiate this value between them to as infrequently as once every 10 seconds. Encryption pause/resume (EPR) Enables an encryption key to be changed with less management required by the Bluetooth host. Changing an encryption key must be done for a role switch of an encrypted an ACL link, or every 23.3 hours (one Bluetooth day) encryption is enabled on an ACL link. Before this feature was introduced, when an encryption key is refreshed the Bluetooth host would be notified of a brief gap in encryption while the new key was generated; so the Bluetooth host was required to handle pausing data transfer (however data requiring encryption may already have been sent before the notification that encryption is disabled has been received). With EPR, the Bluetooth host is not notified of the gap, and the Bluetooth controller ensures that no unencrypted data is transferred while they key is refreshed.
Secure simple pairing (SSP) Radically improves the pairing experience for Bluetooth devices, while increasing the use and strength of security. See the section onPairing below for more details. It is expected that this feature will significantly increase the use of Bluetooth.[16] Near field communication (NFC) cooperation Automatic creation of secure Bluetooth connections when NFC radio interface is also available. This functionality is part of SSP where NFC is one way of exchanging pairing information. For example, a headset should be paired with a Bluetooth 2.1 + EDR phone including NFC just by bringing the two devices close to each other (a few centimeters). Another example is automatic uploading of photos from a mobile phone or camera to a digital picture frame just by bringing the phone or camera close to the frame.[17][18] Non-Automatically-Flushable Packet Boundary Flag (PBF) Using this feature L2CAP may support both isochronous (A2DP media Streaming) and asynchronous data flows (AVRCP Commands) over the same logical link by marking packets as automatically-flushable or non-automatically-flushable by setting the appropriate value for the Packet_Boundary_Flag in the HCI ACL Data Packet
Bluetooth 3.0 + HS The 3.0 + HS specification[14] was adopted by the Bluetooth SIG on April 21, 2009. It supports theoretical data transfer speeds of up to 24 Mb/s. Its main new feature is AMP (Alternate MAC/PHY), the addition of 802.11 as a high speed transport. Two technologies had been anticipated for AMP: 802.11 and UWB, but UWB is missing from the specification.[19]
Alternate MAC/PHY Enables the use of alternative MAC and PHYs for transporting Bluetooth profile data. The Bluetooth Radio is still used for device discovery, initial connection and profile configuration, however when lots of data needs to be sent, the high speed alternate MAC PHY (802.11, typically associated with Wi-Fi) will be used to transport the data. This means that the proven low power connection models of Bluetooth are used when the system is idle, and the low power per bit radios are used when lots of data needs to be sent.
Unicast connectionless data Permits service data to be sent without establishing an explicit L2CAP channel. It is intended for use by applications that require low latency between user action and reconnection/transmission of data. This is only appropriate for small amounts of data. Read encryption key size Introduces a standard HCI command for a Bluetooth host to query the encryption key size on an encrypted ACL link. The encryption key size used on a link is required for the SIM Access Profile, so generally Bluetooth controllers provided this feature in a proprietary manner. Now the information is available over the standard HCI interface. Enhanced Power Control
Updates the power control feature to remove the open loop power control, and also to clarify ambiguities in power control introduced by the new modulation schemes added for EDR. Enhanced power control removes the ambiguities by specifying the behaviour that is expected. The feature also adds closed loop power control, meaning RSSI filtering can start as the response is received. Additionally, a "go straight to maximum power" request has been introduced, this is expected to deal with the headset link loss issue typically observed when a user puts their phone into a pocket on the opposite side to the headset.
Bluetooth low energy Main article: Bluetooth low energy On April 20, 2009, Bluetooth SIG presented the new Bluetooth low energy as an entirely additional protocol stack, compatible with other existing Bluetooth protocol stacks. The preceding naming as Wibree and Bluetooth ULP (Ultra Low Power) has not been adopted as the final naming. The soon to be launched version of the Bluetooth core specification is being referred to as Bluetooth low energy . On June 12, 2007, Nokia and Bluetooth SIG had announced that Wibree will be a part of the Bluetooth specification, as an ultra-low power Bluetooth technology. [20]
Expected use cases include watches displaying Caller ID information, sports
sensors monitoring the wearer's heart rate during exercise, and medical devices. The Medical Devices Working Group is also creating a medical devices profile and
associated protocols to enable this market. Bluetooth low energy technology is designed for devices to have a battery life of up to one year.
Future Broadcast channel Enables Bluetooth information points. This will drive the adoption of Bluetooth into mobile phones, and enable advertising models based around users pulling information from the information points, and not based around the object push model that is used in a limited way today. Topology management Enables the automatic configuration of the piconet topologies especially in scatternet situations that are becoming more common today. This should all be invisible to users of the technology, while also making the technology "just work." improvements Enable audio and video data to be transmitted at a higher quality, especially when best effort traffic is being transmitted in the samepiconet.
UWB for AMP Main article: ultra-wideband The high speed (AMP) feature of Bluetooth 3.0 is based on 802.11, but the AMP mechanism was designed to be usable with other radios as well. It was originally intended for UWB, but the WiMedia Alliance, the body responsible for the flavor of UWB intended for Bluetooth, announced in March 2009 that it was disbanding. On March 16, 2009, the WiMedia Alliance announced it was entering into technology transfer agreements for the WiMedia Ultra-wideband(UWB) specifications. WiMedia will transfer all current and future specifications, including work on future high speed and power optimized implementations, to the Bluetooth Special Interest Group (SIG), Wireless USB Promoter Group and the USB Implementers Forum. After the successful completion of the technology transfer, marketing and related administrative items, the WiMedia Alliance will cease operations.[21]
In October 2009 the Bluetooth Special Interest Group has dropped development of UWB as part of the alternative MAC/PHY, Bluetooth 3.0/High Speed solution. A small, but significant, number of former WiMedia members had not and would not sign up to the necessary agreements for the IP transfer. The Bluetooth group is now in the process of evaluating other options for its longer term roadmap.[22]
Technical information Bluetooth protocol stack Main articles: Bluetooth stack and Bluetooth protocols "Bluetooth is defined as a layer protocol architecture consisting of core protocols, cable replacement protocols, telephony control protocols, and adopted protocols."[23] Mandatory protocols for all Bluetooth stacks are: LMP, L2CAP and SDP. Additionally, these protocols are almost universally supported: HCI and RFCOMM.
LMP (Link Management Protocol) Used for control of the radio link between two devices. Implemented on the controller.
L2CAP (Logical Link Control & Adaptation Protocol) Used to multiplex multiple logical connections between two devices using different higher level protocols. Provides segmentation and reassembly of on-air packets. In Basic mode, L2CAP provides packets with a payload configurable up to 64kB, with 672 bytes as the default MTU, and 48 bytes as the minimum mandatory supported MTU. In Retransmission & Flow Control modes, L2CAP can be configured for reliable or isochronous data per channel by performing retransmissions and CRC checks. Bluetooth Core Specification Addendum 1 adds two add itional L2CAP modes to the core specification. These modes effectively deprecate original Retransmission and Flow Control modes: Enhanced Retransmission Mode (ERTM): This mode is an improved version of the original retransmission mode. This mode provides a reliable L2CAP channel.
Streaming Mode (SM): This is a very simple mode, with no retransmission or flow control. This mode provides an unreliable L2CAP channel. Reliability in any of these modes is optionally and/or additionally guaranteed by the lower layer Bluetooth BDR/EDR air interface by configuring the number of retransmissions and flush timeout (time after which the radio will flush packets). Inorder sequencing is guaranteed by the lower layer. Only L2CAP channels configured in ERTM or SM may be operated over AMP logical links.
ISDP (Service Discovery Protocol) Used to allow devices to discover what services each other support, and what parameters to use to connect to them. For example, when connecting a mobile phone to a Bluetooth headset, SDP will be used to determine which Bluetooth profiles are supported by the headset (Headset Profile, Hands Free Profile, Advanced Audio Distribution Profile etc) and the protocol multiplexer settings needed to connect to each of them. Each service is identified by a Universally Unique Identifier (UUID), with official services (Bluetooth profiles) assigned a short form UUID (16 bits rather than the full 128)
HCI (Host/Controller Interface) Standardised communication between the host stack (e.g., a PC or mobile phone OS) and the controller (the Bluetooth IC). This standard allows the host stack or controller IC to be swapped with minimal adaptation. There are several HCI transport layer standards, each using a different hardware interface to transfer the same command, event and data packets. The most commonly used are USB (in PCs) and UART (in mobile phones and PDAs). In Bluetooth devices with simple functionality (e.g., headsets) the host stack and controller can be implemented on the same microprocessor. In this case the HCI is optional, although often implemented as an internal software interface.
RFCOMM (Cable replacement protocol) Radio frequency communications (RFCOMM) is the cable replacement protocol used to create a virtual serial data stream. RFCOMM provides for binary data
transport and emulates EIA-232 (formerly RS-232) control signals over the Bluetooth baseband layer. RFCOMM provides a simple reliable data stream to the user, similar to TCP. It is used directly by many telephony related profiles as a carrier for AT commands, as well as being a transport layer for OBEX over Bluetooth. Many Bluetooth applications use RFCOMM because of its widespread support and publicly available API on most operating systems. Additionally, applications that used a serial port to communicate can be quickly ported to use RFCOMM.
BNEP (Bluetooth Network Encapsulation Protocol) BNEP is used to transfer another protocol stack's data via an L2CAP channel. Its main purpose is the transmission of IP packets in the Personal Area Networking Profile. BNEP performs a similar function to SNAP in Wireless LAN.
AVCTP (Audio/Visual Control Transport Protocol) Used by the remote control profile to transfer AV/C commands over an L2CAP channel. The music control buttons on a stereo headset use this protocol to control the music player
AVDTP (Audio/Visual Data Transport Protocol) Used by the advanced audio distribution profile to stream music to stereo headsets over an L2CAP channel. Intended to be used by video distribution profile.
Telephone control protocol Telephony control protocol-binary (TCS BIN) is the bit-oriented protocol that defines the call control signaling for the establishment of voice and data calls between Bluetooth devices. Additionally, "TCS BIN defines mobility management procedures for handling groups of Bluetooth TCS devices." TCS-BIN is only used by the cordless telephony profile, which failed to attract implementers. As such it is only of historical interest.
Adopted protocols Adopted protocols are defined by other standards-making organizations and incorporated into Bluetooth’s protocol stack, allowing Bluetooth to create protocols only when necessary. The adopted protocols include: Point-to-Point Protocol (PPP)
Internet standard protocol for transporting IP datagrams over a point-to-point link TCP/IP/UDP Foundation Protocols for TCP/IP protocol suite Object Exchange Protocol (OBEX) Session-layer protocol for the exchange of objects, providing a model for object and operation representation Wireless Application Environment/Wireless Application Protocol (WAE/WAP) WAE specifies an application framework for wireless devices and WAP is an open standard to provide mobile users access to telephony and information services.[23]
Communication and connection A master Bluetooth device can communicate with up to seven devices in a Wireless User Group. This network group of up to eight devices is called a piconet. A piconet is an ad-hoc computer network, using Bluetooth technology protocols to allow one master device to interconnect with up to seven active devices. Up to 255 further devices can be inactive, or parked, which the master device can bring into active status at any time. At any given time, data can be transferred between the master and one other device, however, the devices can switch roles and the slave can become the master at any time. The master switches rapidly from one device to another in a round-robin fashion. (Simultaneous transmission from the master to multiple other devices is possible, but not used much.) The Bluetooth specification allows connecting two or more p iconets together to form a scatternet, with some devices acting as a bridge by simultaneously playing the master role in one piconet and the slave role in another. Many USB Bluetooth adapters are available, some of which also include an IrDA adapter. Older (pre-2003) Bluetooth adapters, however, have limited services, offering only the Bluetooth Enumerator and a less-powerful Bluetooth Radio incarnation. Such devices can link computers with Bluetooth, but they do not offer much in the way of services that modern adapters do.
Baseband Error Correction
Three types of error correction are implemented in Bluetooth systems, 1/3 rate forward error correction (FEC) 2/3 rate FEC Automatic repeat-request (ARQ)
Computer networking
Network cards such as this one can transmit and receive data at high rates over various types of network cables. This card is a 'Combo' card which supports three cabling standards.
This article is about computer networking, the disciplin e of engineering computer networks. For the article on computer networks, see Computer network . "Datacom" redirects here. For other uses, see Datacom (disambiguation). Computer networking is the engineering discipline concerned with communication betweencomputer systems or devices. Networking, routers, routing protocols, and networking over the public Internet have their specifications defined in documents called RFCs.[1] Computer networking is sometimes considered a sub-discipline of telecommunications, computer science, information technology and/or computer engineering. Computer networks rely heavily upon the theoretical and practical application of these scientific and engineering disciplines. There are three types of networks: 1.Internet. 2.Intranet. 3.Extranet. A computer network is any set of computers or devices connected to each other with the ability to exchange data. [2]
Examples of different networks are:
Local area network (LAN), which is usually a small n etwork constrained to
a small geographic area. An example of a LAN would be a computer network within a building.
Metropolitan area network (MAN), which is used for medium size area.
examples for a city or a state.
Wide area network (WAN) that is usually a larger network that covers a
large geographic area.
Wireless LANs and WANs (WLAN & WWAN) are the wireless equivalent of
the LAN and WAN. All networks are interconnected to allow communication with a variety of different kinds of media, including twisted-pair twisted-pair copper copper wire cable, cable,coaxial cable, cable, optical fiber , power lines and various wireless technologies.[3] The devices can be separated by a few meters (e.g. via Bluetooth Bluetooth)) or nearly unlimited distances (e.g. via the interconnections of the Internet[4]).
Views of networks Users and network administrators often have d ifferent views of their networks. Often, users who share printers and some servers form a workgroup, which usually means they are in the same geographic location and are on the same LAN. A community of interest has less of a connection of being in a local area, and should be thought of as a set of arbitrarily located users who share a set of servers, and possibly also communicate via peer-to-peer peer-to-peer technologies. technologies. Network administrators see networks from both physical and logical perspectives. The physical perspective involves geographic locations, physical cabling, and the network elements (e.g., routers routers,, bridges and application layer gateways that interconnect the physical media. Logical networks, called, in the TCP/IP architecture, subnets subnets,, map onto one or more physical media. For example, a common practice in a campus of buildings is to make a set of LAN cables in each building appear to be a common subnet, using virtual LAN (VLAN) technology. Both users and administrators will be aware, to varying extents, of the trust and scope characteristics of a network. Again u sing TCP/IP architectural terminology, terminology, an intranet is a community of interest under private administration usually by an enterprise, and is only accessible by authorized users (e.g. employees). employees).[5] Intranets
do not have to be connected to the Internet, but generally have a limited connection. An extranet extranetiis an extension of an intranet that allows secure communications to users outside of the intranet (e.g. business partners, customers).[5] Informally, the Internet is the set of users, enterprises,and content providers that are interconnected by Internet Service Providers (ISP). From an engineering standpoint, the Internet is the set of subnets, and aggregates of subnets, which share the registered IP address space and exchange information about the reachability of those IP addresses using the Border Gateway Protocol. Protocol. Typically, the human-readable names of servers are translated to IP addresses, transparently to users, via the directory function of the Domain Name System (DNS). Over the Internet, there can be business-to-business (B2B), (B2B), business-to-consumer (B2C) and consumer-to-consumer (C2C) communications. Especially when money or sensitive information is exchanged, the communications are apt to be secured by some form of communications of communications security mechanism. Intranets and extranets can be securely superimposed onto the Internet, without any access by general Internet users, using secure Virtual Private Network (VPN) technology. When used for gaming one computer will have to be the server while the others play through it. [edit edit]]History
of Computer Networks
Before the advent of computer networks that were based upon some type of telecommunications of telecommunications system, communication between calculation machines and history of computer hardware early computers was performed by human users by carrying instructions between them. Many of the social behavior seen in today's Internet was demonstrably present in nineteenth-century and arguably in even earlier networks using visual signals.The Victorian Internet In September 1940 George Stibitz used a teletype machine to send instructions for a problem set from his Model at Dartmouth College in New Hampshire to his Complex Number Calculator in New York and received results back by the same means. Linking output systems like teletypes to computers was an interest at the Advanced Research Projects Agency (ARPA) when, in 1962, J.C.R. Licklider was hired and developed a working group he called the "Intergalactic Network", a precursor to the ARPANet.
In 1964, researchers at Dartmouth developed the Dartmouth Time Sharing System for distributed users of large computer systems. The same year, at MIT MIT,, a research group supported by General Electric and Bell Labs used a computer DEC's to route and manage telephone connections. Throughout the 1960s Leonard Kleinrock,Paul Baran and Donald Davies independently conceptualized and developed network systems which u sed datagrams or Packet information technology that could be used in a network between computer systems. 1965 Thomas Merrill and Lawrence G. Roberts created the first wide area network (WAN WAN). ). The first widely used PSTN switch that used true computer control was the Western Electric introduced in 1965. In 1969 the University of California at Los Angeles, SRI (in Stanford), University of California at Santa Barbara, and the University of Utah were connected as the beginning of the ARPANet network using 50 kbit/s circuits. Commercial services using X.25 were deployed in 1972, and later used as an underlying infrastructure for expanding TCP/IP networks. Computer networks, and the technologies needed to connect and communicate through and between them, continue to drive computer hardware, software, and peripherals industries. This expansion is mirrored by growth in the numbers and types of users of networks from the researcher to the home user. Today, computer networks are the core of modern communication. All modern aspects of the Public Switched Telephone Network (PSTN) are computercontrolled, and telephony increasingly runs over the Internet Protocol, although not necessarily the public Internet. The scope of communication has increased significantly in the past decade and this boom in communications would not have been possible without the progressively advancing computer network.
Networking methods One way to categorize computer networks is by their geographic scope, although many real-world networks interconnect Local Area Networks(LAN) Networks(LAN) via Wide Area Networks (WAN) and wireless networks (WWAN). These three (broad) types are:
Local area network (LAN) A local area network is a network that spans a relatively small space and p rovides services to a small number of people. A peer-to-peer or client-server method of networking may be used. A peer-to-peer network is where each client shares their resources with other workstations in the network. Examples of peer-to-peer networks are: Small office networks where resource use is minimal and a home network. A client-server network is where every client is connected to the server and each o ther. Client-server networks use servers in different capacities. These can be classified into two types: 1. Single-service servers 2. Print server The server performs one task such as file server, while other servers can not only perform in the capacity of file servers and print servers, but also can conduct calculations and use them to provide information to clients (Web/Intranet Server). Computers may be connected in many different ways, including Ethernet cables, Wireless networks, or other types of wires such as power lines or phone lines. The ITU-T G.hn standard is an example of a technology that provides high-speed (up to 1 Gbit/s) local area networking over existing home wiring (power lines, phone lines and coaxial cables).
Wide area network (WAN) A wide area network is a network where a wide variety of resources are deployed across a large domestic area or internationally. An example of this is a multinational business that uses a WAN to interconnect their offices in different countries. The largest and best example of a WAN is the Internet, which is a network composed of many smaller networks. The Internet is considered the largest network in the world. [6]
. The PSTN(Public Switched Telephone Network) also is an extremely large
network that is converging to use Internet technologies, although not necessarily through the public Internet. A Wide Area Network involves communication through the use of a wide range of different technologies. These technologies include Point-to-Point WANs such as Point-to-Point Protocol (PPP) and High-Level Data Link Control (HDLC), Frame
Relay, ATM (Asynchronous Transfer Mode) and Sonet (Synchronous Optical Network). The difference between the WAN technologies is based on the switching capabilities they perform and the speed at which sending and receiving bits of information (data) occur.
Metropolitan area network (MAN) A metropolitan network is a network that is too large for even the largest of LAN's but is not on the scale of a WAN. It also integrates two or more LAN networks over a specific geographical area ( usually a city ) so as to increase the network and the flow of communications. The LAN's in question would usually be connected via " backbone " lines. For more information on WANs, see Frame Relay, ATM and Sonet.
Wireless networks (WLAN, WWAN)
A wireless network is basically the same as a LAN or a WAN but there are no wires between hosts and servers. The data is transferred over sets of radio transceivers. These types of networks are beneficial when it is too costly or inconvenient to run the necessary cables. For more information, see Wireless LAN and Wireless wide area network. The media access protocols for LANs come from the IEEE. The most common IEEE 802.11 WLANs cover, depending on antennas, ranges from hundreds of meters to a few kilometers. For larger areas, either communications satellites of various types, cellular radio, or wireless local loop (IEEE 802.16) all have advantages and disadvantages. Depending on the type of mobility needed, the relevant standards may come from the IETF or the ITU.
Network topology The network topology defines the way in which computers, printers, and other devices are connected, physically and logically. A network topology describes the layout of the wire and devices as well as the p aths used by data transmissions. Network topology has two types:
Physical
logical
Commonly used topologies include:
Bus
Star
Tree (hierarchical)
Linear
Ring
Mesh
partially connected
fully connected (sometimes known as fully redundant )
The network topologies mentioned above are only a general representation of the kinds of topologies used in computer network and are considered basic topologies. As a matter of fact networking is defined by the standard of OSI (Open Systems Interconnection) reference for communications. The OSI model consists of seven layers. Each layer has its own function. The OSI model layers are Application, Presentation, Session, Transport, Network, Data Link, and Physical. The upper layers (Application, Presentation, Session) of the OSI model concentrate on the application while the lower layers (transport, network, data link, and physical) focus on signal flow of data from origin to destination. The Application layer defines the medium that communications software and any applications need to communicate to other computers. Layer 6 which is the presentation layer focuses on defining data formats such as text, jpeg, gif, and binary. An example of this layer would be displaying a picture that was received in an e-mail. The 5th Layer is the session layer which establishes how to start, control, and end links or conversations. The transport layer includes protocols that allow it to provide functions in many different areas such as: error recovery, segmentation, and reassembly. The network layers primary job is the end to end delivery of data packets. To do this, the network layer relies on logical addressing so that the origin and destination point can both be recognized. An example of this would be, ip running in a router’s job is to examine the destination address, compare the address to the ip routing table, separate the packet into smaller chunks for transporting purposes, and then deliver the packet to the correct receiver. Layer 2 is the data link layer, which sets the standards for data being delivered across a link or medium. The 1st layer is the physical layer which deals with the physical characteristics of the transmission of data such as the
network card and network cable type. An easy way to remember the layers of OSI is to remember All People Seem To Need Data Processing (Layers 7 to 1).
Computer networking device A full list of Computer networking devices are units that mediate data in a computer network. Computer networking devices are also called network equipment, Intermediate Systems (IS) or InterWorking Unit (IWU). Units which are the last receiver or generate data are called hosts or data terminal equipment. [edit]List
of computer networking devices
Common basic networking devices:
Gateway: device sitting at a network node for interfacing with another
network that uses different protocols. Works on OSI layers 4 to 7.
Router : a specialized network device that determines the next network
point to which to forward a data packet toward its destination. Unlike a gateway, it cannot interface different protocols. Works on OSI layer 3.
Bridge: a device that connects multiple network segments along the data
link layer . Works on OSI layer 2.
Switch: a device that allocates traffic from one network segment to certain
lines (intended destination(s)) which connect the segment to another network segment. So unlike a hub a switch splits the network traffic and sends it to different destinations rather than to all systems on the network. Works on OSI layer 2.
Hub: connects multiple Ethernet segments together making them act as a
single segment. When using a hub, every attached device shares the same broadcast domain and the same collision domain. Therefore, only one computer connected to the hub is able to transmit at a time. Depending on the network topology, the hub provides a basic level 1 OSI model connection among the network objects (workstations, servers, etc). It provides bandwidth which is shared among all the objects, compared to switches, which provide a dedicated connection between individual nodes. Works on OSI layer 1.
Repeater : device to amplify or regenerate digital signals received while
setting them from one part of a network into another. Works on OSI layer 1.
Some hybrid network devices:
Multilayer Switch: a switch which, in addition to switching on OSI layer 2,
provides functionality at higher protocol layers.
Protocol Converter : a hardware device that converts between two different
types of transmissions, such as asynchronous and synchronous transmissions.
Bridge Router (Brouter): Combine router and bridge functionality and are
therefore working on OSI layers 2 and 3.
Digital media receiver : Connects a computer network to a home theatre
Hardware or software components that typically sit on the connection point of different networks, e.g. between an internal network and an external network:
Proxy: computer network service which allows clients to make indirect
network connections to other network services
Firewall: a piece of hardware or software put on the network to prevent
some communications forbidden by the n etwork policy
Network Address Translator : network service provide as hardware or
software that converts internal to external network addresses and vice versa Other hardware for establishing networks or dial-up connections:
Multiplexer : device that combines several electrical signals into a single
signal
Network Card: a piece of computer hardware to allow the attached
computer to communicate by network
Modem: device that modulates an analog "carrier" signal (such as sound),
to encode digital information, and that also demodulates such a carrier signal to decode the transmitted information, as a computer communicating with another computer over the telephone network
ISDN terminal adapter (TA): a specialized gateway for ISDN
Line Driver : a device to increase transmission distance by amplifying the
signal. Base-band networks only.mohit
Network Device Connectivity
Home network A home network or home area network (HAN) is a residential local area network. It is used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a cable tv or Digital Subscriber Line (DSL) provider. More recently telephone companies such as AT&T and British Telecom have been using home networking to provide triple play services (voice, video and data) to customers. These use IPTVto provide the video service. The home network usually operates over the existing home wiring (coax in North America, phone wires in multi dwelling units (MDU) and powerline in Europe). These h ome networks are often professionally installed and managed by the telco. The ITU-TG.hn standard, which provides high-speed (up to 1 Gbit/s) local area networking over existing home wiring (power lines, phone lines and coaxial cables), is an example of a home networking technology designed specifically for IPTV delivery.
Network devices
home network may consist of the following components:
A broadband modem for connection to the internet (either a DSL
modem using the phone line, or cable modem using the cable internetconnection).
A residential gateway (sometimes called a router) connected between the
broadband modem and the rest of the network. This enables multiple devices to connect to the internet simultaneously. Residential gateways, hubs/switches, DSL modems, and wireless access points are often combined.
A PC, or multiple PCs including laptops
A wireless access point, usually implemented as a feature rather than a
separate box, for connecting wireless devices
Entertainment peripherals - an increasing number of devices can be
connected to the home network, including DVRs like TiVo, digital audio players, games machines, stereo system, and IP set-top box.
Internet Phones (VoIP)
A network bridge connects two networks together, often giving a wired
device, e.g. Xbox, access to a wireless network.
A network hub/switch - a central networking hub containing a number
of Ethernet ports for connecting multiple networked devices
A network attached storage (NAS) device can be used for storage on the
network.
A print server can be used to share printers among computers on the
network. Older devices may not have the appropriate connector to the network. USB and PCI network controllers can be installed in some devices to allow them to connect to networks. Network devices may also be configured from a computer. For e xample, broadband modems are often configured through a web client on a networked PC. As networking technology evolves, more electronic devices and home appliances are becoming Internet ready and accessible through the home network. Set-top boxes from cable TV providers already have USB and Ethernet ports "for future use".
Network media Ethernet cables are the standard medium for networks. However, homes are often more difficult to wire than office environments, and other technologies are being developed which don't require new wires. Home networking may use
Ethernet Category 5 cable, Category 6 cable - for speeds of 10 Mbit/s, 100
Mbit/s, or 1 Gbit/s.
Wi-Fi Wireless LAN connections - for speeds up to 248 Mbit/s, dependent
on signal strength and wireless standard.
Coaxial cables (TV antennas) - for speeds of 270 Mbit/s (see Multimedia
over Coax Alliance or 320 Mbit/s see HomePNA)
Electrical wiring - for speeds of 14 Mbit/s to 200 Mbit/s (see Power line
communication)
Phone wiring - for speeds of 160 Mbit/s (see HomePNA)
Fiber optics - although rare, new homes are beginning to include fiber
optics for future use. Optical networks generally use Ethernet.
All home wiring (coax, powerline and phone wires) - future standard for
speeds up to 1 Gbit/s being developed by the ITU-T (see G.hn) Ethernet and Wireless are the most common standards. As the demand for home networks has increased, the other alliances have formed to produce standards for networking alternatives.
IP address An Internet Protocol (IP) address is a numerical label that is assigned to devices participating in a computer network utilizing the Internet Protocol for communication between its nodes.[1] An IP address serves two principal functions in networking: host or network interfaceidentification and location addressing. The role of the IP address has also been characterized as follows: "A name indicates what we seek.
An address indicates where it is. A route indicates how to get there." [2] The original designers of TCP/IP defined an IP address as a 32-bit number [1] and this system, known as Internet Protocol Version 4 or IPv4, is still in use today. However, due to the enormous growth of the Internet and the resulting depletion of available addresses, a new addressing system (IPv6), using 128 bits for the address, was developed in 1995[3] and last standardized by RFC 2460 in 1998. [4]
Although IP addresses are stored as binary numbers, they are usually displayed
in human-readable notations, such as 208.77.188.166 (for IPv4), and 2001:db8:0:1234:0:567:1:1 (for IPv6). The Internet Protocol also has the task of routing data packets between networks, and IP addresses specify the locations of the source and destination nodes in the topology of the routing system. For this purpose, some of the bits in an IP address are used to designate asubnetwork. The number of these bits is indicated in CIDR notation, appended to the IP address, e.g., 208.77.188.166/24. With the development of private networks and the threat of IPv4 address exhaustion, a group of private address spaces was set aside by RFC 1918. These private addresses may be used by anyone on private networks. They are often used with network address translators to connect to the global public Internet.
The Internet Assigned Numbers Authority (IANA) manages the IP address space allocations globally. IANA works in cooperation with fiveRegional Internet Registries (RIRs) to allocate IP address blocks to Local Internet Registries (Internet service providers) and other entities.
IP versions Two versions of the Internet Protocol (IP) a re currently in use (see IP version history for details), IP Version 4 and IP Version 6. Each version defines an IP address differently. Because of its prevalence, the generic term IP address typically still refers to the addresses defined by IPv4.
An illustration of an IP address (version 4), in both dot-decimal notation and binary.
IP version 4 addresses Main article: IPv4#Addressing IPv4 uses 32-bit (4-byte) addresses, which limits the address space to 4,294,967,296 (232) possible unique addresses. IPv4 reserves some addresses for special purposes such as private networks (~18 million addresses) or multicast addresses (~270 million addresses). This reduces the number of addresses that can be allocated to end users and, a s the number of addresses available is consumed, IPv4 address exhaustion is inevitable. This foreseeable shortage was the primary motivation for developing IPv6, which is in various deployment stages around the world and is the only strategy for IPv4 replacement and continued Internet expansion. IPv4 addresses are usually represented in dot-decimal notation (four numbers, each ranging from 0 to 255, separated by d ots, e.g. 208.77.188.166). Each part represents 8 bits of the address, and is therefore called an octet . In less common
cases of technical writing, IPv4 addresses may be presented inhexadecimal, octal, or binary representations. In most representations each octet is converted individually.
IPv4 subnetting In the early stages of development of the Internet Protocol,[1] network administrators interpreted an IP address in two parts, network number portion and host number portion. The highest order octet (most significant eight bits) in an address was designated the network number and the rest of the bits were called the rest
field or host identifier and were used for host numbering within a network. This method soon proved inadequate as additional networks developed that were independent from the existing networks already designated by a network number. In 1981, the Internet addressing specification was revised with the introduction of classful network architecture.[2] Classful network design allowed for a larger number of individual network assignments. The first three bits of the most significant octet of an IP address was defined as the class of the address. Three classes (A, B, and C ) were defined for universal unicast addressing. Depending on the class derived, the network identification was based on octet boundary segments of the entire address. Each class used successively additional octets in the network identifier, thus reducing the possible number of hosts in the higher order classes (B and C ). The following table gives an overview of this now obsolete system. Historical classful network architecture
Class First octet in binary
Range of first octet
Network ID Host ID Number of networks Number of addresses
A
0XXXXXXX
0 - 127
a
b.c.d
27 = 128
224 = 16,777,216
B
10XXXXXX
128 - 191
a.b
c.d
214 = 16,384
216 = 65,536
C
110XXXXX
192 - 223
a.b.c
d
221 = 2,097,152
28 = 256
The articles 'subnetwork' and 'classful network' explain the details of this design. Although classful network design was a successful developmental stage, it proved unscalable in the rapid expansion of the Internet and was abandoned when Classless Inter-Domain Routing (CIDR) was created for the allocation of IP address blocks and new rules of routing protocol packets using IPv4 addresses. CIDR is based on variable-length subnet masking (VLSM) to allow allocation and routing on arbitrary-length prefixes. Today, remnants of classful network concepts function only in a limited scope as the default configuration parameters of some network software and hardware components (e.g. netmask), and in the technical jargon used in network administrators' discussions.
IPv4 private addresses Main article: Private network Early network design, when global end-to-end connectivity was envisioned for communications with all Internet hosts, intended that IP addresses be uniquely assigned to a particular computer or device. However, it was found that this was not always necessary as private networks developed and public address space needed to be conserved (IPv4 address exhaustion). Computers not connected to the Internet, such as factory machines that communicate only with each other via TCP/IP, need not have globally-unique IP addresses. Three ranges of IPv4 addresses for private networks, one range for each class (A, B, C ), were reserved in RFC 1918. These addresses are not routed on the Internet and thus their use need not be coordinated with an IP address registry. Today, when needed, such private networks typically connect to the Internet through network address translation (NAT). IANA-reserved private IPv4 network ranges
Start
24-bit Block (/8 prefix, 1 x A)
10.0.0.0
End
10.255.255.255
No. of addresses
16,777,216
20-bit Block (/12 prefix, 16 x B) 172.16.0.0
172.31.255.255 1,048,576
16-bit Block (/16 prefix, 256 x C) 192.168.0.0 192.168.255.255 65,536
Any user may use any of the reserved blocks. Typically, a network administrator will divide a block into subnets; for example, many home routers automatically use a default address range of 192.168.0.0 - 192.168.0.255 (192.168.0.0/24).
IPv4 address depletion Main article: IPv4 address exhaustion The IP version 4 address space is rapidly nearing exhaustion of available, officially assignable address blocks.
IP version 6 addresses Main article: IPv6 Addresses
An illustration of an IP address (version 6), in hexadecimaland binary.
The rapid exhaustion of IPv4 address space, despite conservation techniques, prompted the Internet Engineering Task Force (IETF) to explore new technologies to expand the Internet's addressing capability. The permanent solution was deemed to be a redesign of the Internet Protocol itself. This next generation of the Internet Protocol, aimed to replace IPv4 on the Internet, was eventually named Internet Protocol Version 6 (IPv6) in 1995[3][4] The address size was increased from 32 to 128 bits or 16 octets, which, even with a generous assignment of network blocks, is deemed sufficient for the foreseeable future. Mathematically,
the new address space provides the potential for a maximum of 2128, or about 3.403 × 1038 unique addresses. The new design is not based on the goal to provide a sufficient quantity of addresses alone, but rather to allow efficient aggregation of subnet routing prefixes to occur at routing nodes. As a result, routing table sizes are smaller, and the smallest possible individual allocation is a subnet for 264 hosts, which is the size of the square of the size of the entire IPv4 Internet. At these levels, actual address utilization rates will be small on any IPv6 network segment. The new design also provides the opportunity to separate the addressing infrastructure of a network segment—that is the local administration of the segment's available space—from the addressing prefix used to route external traffic for a network. IPv6 has facilities that automatically change the routing prefix of entire networks should the global connectivity or the routing policy change without requiring internal redesign or renumbering. The large number of IPv6 addresses allows large blocks to be assigned for specific purposes and, where appropriate, to be aggregated for efficient routing. With a large address space, there is not the need to have complex address conservation methods as used in classless inter-domain routing (CIDR). All modern desktop and enterprise server operating systems include native support for the IPv6 protocol, but it is not yet widely deployed in other devices, such as home networking routers, voice over Internet Protocol (VoIP) and multimedia equipment, and network peripherals. Example of an IPv6 address: 2001:0db8:85a3:08d3:1319:8a2e:0370:7334
IPv6 private addresses Just as IPv4 reserves addresses for private or internal networks, there are blocks of addresses set aside in IPv6 for private addresses. In IPv6, these are referred to as unique local addresses (ULA). RFC 4193 sets aside the routing prefix fc00::/7 for this block which is divided into two /8 blocks with different implied policies (cf. IPv6) The addresses include a 40-bit pseudorandom number that minimizes the risk of address collisions if sites merge or packets are misrouted.
Early designs (RFC 3513) used a different block for this purpose (fec0::), dubbed site-local addresses. However, the definition of what constituted sites remained unclear and the poorly defined addressing policy created ambiguities for routing. The address range specification was abandoned and must no longer be used in new systems. Addresses starting with fe80: — called link-local addresses — are assigned only in the local link area. The addresses are generated usually automatically by the operating system's IP layer for each network interface. This provides instant automatic network connectivity for any IPv6 host and means that if several hosts connect to a common hub or switch, they have an instant communication path via their link-local IPv6 address. This feature is used extensively, and invisibly to most users, in the lower layers of IPv6 network administration (cf. Neighbor Discovery Protocol). None of the private address prefixes may be routed in the public Internet.
IP subnetworks Main article: Subnetwork The technique of subnetting can operate in both IPv4 and IPv6 networks. The IP address is divided into two parts: the network address and thehost identifier . The subnet mask (in IPv4 only) or the CIDR prefix determines how the IP address is divided into network and host parts. The term subnet mask is only used within IPv4. Both IP versions however use the Classless Inter-Domain Routing (CIDR) concept and notation. In this, the IP address is followed by a slash and the number (in decimal) of bits used for the network part, also called the routing prefix . For example, an IPv4 address and its subnet mask may be 192.0.2.1 and 255.255.255.0, respectively. The CIDR notation for the same IP address and subnet is 192.0.2.1/24, because the first 24 bits of the IP address indicate the network and subnet.
Static and dynamic IP addresses
When a computer is configured to use the same IP address each time it powers up, this is known as a Static IP address. In contrast, in situations when the computer's IP address is assigned automatically, it is known as a Dynamic IP address.
Method of assignment Static IP addresses are manually assigned to a computer by an administrator. The exact procedure varies according to platform. This contrasts with dynamic IP addresses, which are assigned either by the computer interface or host software itself, as in Zeroconf , or assigned by a server using Dynamic Host Configuration Protocol (DHCP). Even though IP addresses assigned using DHCP may stay the same for long periods of time, they can generally change. In some cases, a network administrator may implement dynamically assigned static IP addresses. In this case, a DHCP server is used, but it is specifically configured to always assign the same IP address to a particular computer. This allows static IP addresses to be configured centrally, without having to specifically configure each computer on the network in a manual procedure. In the absence or failure of static or stateful (DHCP) address configurations, an operating system may assign an IP address to a network interface using state-less autoconfiguration methods, such as Zeroconf .
Uses of dynamic addressing Dynamic IP addresses are most frequently assigned on LANs and broadband networks by Dynamic Host Configuration Protocol (DHCP) servers. They are used because it avoids the administrative burden of assigning specific static addresses to each device on a network. It also allows many devices to share limited address space on a network if only some of them will be online at a particular time. In most current desktop operating systems, dynamic IP configuration is e nabled by default so that a user does not need to manually enter any settings to connect to a network with a DHCP server. DHCP is not the only technology used to assigning dynamic IP addresses. Dialup and some broadband networks use dynamic address features of the Point-to-Point Protocol.
Sticky dynamic IP address
A sticky dynamic IP address or sticky IP is an informal term used by cable and DSL Internet access subscribers to describe a dynamically assigned IP address that does not change often. The addresses are usually assigned with the DHCP protocol. Since the modems are usually powered-on for extended periods of time, the address leases are usually set to long periods and simply renewed upon expiration. If a modem is turned off and powered up again before the next expiration of the address lease, it will most likely receive the same IP address.
Address autoconfiguration RFC 3330 defines an address block, 169.254.0.0/16, for the special use in linklocal addressing for IPv4 networks. In IPv6, every interface, whether using static or dynamic address assignments, also receives a local-link address automatically in the fe80::/10 subnet. These addresses are only valid on the link, such as a local network segment or point-to-point connection, that a host is connected to. These addresses are not routable and like private addresses cannot be the source or destination of packets traversing the Internet. When the link-local IPv4 address block was reserved, no standards existed for mechanisms of address autoconfiguration. Filling the void,Microsoft created an implementation that called Automatic Private IP Addressing (APIPA). Due to Microsoft's market power, APIPA has been deployed on millions of machines and has, thus, become a de facto standard in the industry. Many years later, the IETF defined a formal standard for this functionality, RFC 3927, entitled Dynamic Configuration of IPv4 Link-Local Addresses.
Uses of static addressing Some infrastructure situations have to use static a ddressing, such as when finding the Domain Name System host that will translate domain names to IP addresses. Static addresses are also convenient, but not absolutely necessary, to locate servers inside an enterprise. An address obtained from a DNS server comes with a time to live, or caching time, after which it should be looked up to confirm that it has not changed. Even static IP addresses do change as a result of network administration (RFC 2072)
Modifications to IP addressing IP blocking and firewalls Main articles: IP blocking and Firewall Firewalls are common on today's Internet. For increased network security, they control access to private networks based on the public IP of the client. Whether using a blacklist or a whitelist, the IP address that is blocked is the p erceived public IP address of the client, meaning that if the client is using a proxy server or NAT, blocking one IP address might block many individual people.
IP address translation Main article: Network Address Translation Multiple client devices can appear to share IP addresses: either because they are part of a shared hosting web server environment or because an IPv4 network address translator (NAT) or proxy server acts as an intermediary agent on behalf of its customers, in which case the real originating IP addresses might be hidden from the server receiving a request. A common practice is to have a NAT hide a large number of IP addresses in a private network. Only the "outside" interface(s) of the NAT need to have Internet-routable addresses[5]. Most commonly, the NAT device maps TCP or UDP port numbers on the outside to individual private addresses on the inside. Just as a telephone number may have site-specific extensions, the port numbers are site-specific extensions to a n IP address. In small home networks, NAT functions usually take place in a residential gateway device, typically one marketed as a "router". In this scenario, the computers connected to the router would have 'private' IP addresses and the router would have a 'public' address to communicate with the Internet. This type of router allows several computers to share one public IP address.
Ethernet hub A network hub or repeater hub is a device for connecting multiple twisted pair or fiber optic Ethernet devices together and thus making them act as a single network segment. Hubs work at the physical layer (layer 1) of the OSI model.
The device is thus a form of multiport repeater . Repeater hubs also participate in collision detection, forwarding a jam signal to all ports if it detects a collision. Hubs also often come with a BNC and/or AUI connector to allow connection to legacy10BASE2 or 10BASE5 network segments. The availability of lowpriced network switches has largely rendered hubs obsolete but they are still seen in older installations and more specialized applications.
.4-port Ethernet hub
Technical information A network hub is a fairly unsophisticated broadcast device. Hubs do not manage any of the traffic that comes through them, and any packet entering any port is broadcast out on all other ports. Since every packet is being sent out through all other ports, packet collisions result—which greatly impedes the smooth flow of traffic. The need for hosts to be able to detect collisions limits the number of hubs and the total size of the network. For 10 Mbit/s networks, up to 5 segments (4 hubs) are allowed between any two end stations. For 100 Mbit/s networks, the limit is reduced to 3 segments (2 hubs) between any two end stations, and even that is only allowed if the hubs are of the low delay variety. Some hubs have special (and generally manufacturer specific) stack ports allowing them to be combined in a way that allows more hubs than simple chaining through Ethernet cables, but even so, a large Fast Ethernet network is likely to require switches to avoid the chaining limits of hubs. Most hubs (intelligent hubs) detect typical problems, such as excessive collisions on individual ports, and partition the port, disconnecting it from the shared medium. Thus, hub-based Ethernet is generally more robust than coaxial cable-based Ethernet, where a misbehaving device can disable the entire collision domain. Even
if not partitioned automatically, an intelligent hub makes troubleshooting easier because status lights can indicate the possible problem source or, as a last resort, devices can be disconnected from a hub one at a time much more easily than a coaxial cable. They also remove the need to troubleshoot faults on a huge cable with multiple taps. Hubs classify as Layer 1 devices in the OSI model. At the physical layer, hubs can support little in the way of sophisticated networking. Hubs do not read any of the data passing through them and are not aware of their source or destination. Essentially, a hub simply receives incoming packets, possibly amplifies the electrical signal, and broadcasts these packets out to all devices on the network including the one that originally sent the packet. Technically speaking, three different types of hubs exist: 1. Passive (A hub which does not need an external power source, because it does not regenerate the signal and therefore falls as part of the cable, with respect to maximum cable lengths) 2. Active (A hub which regenerates the signal and therefore needs an external power supply) 3. Intelligent (A hub which provides error detection (e.g. excessive collisions) and also does what an active hub does) Passive hubs do not amplify the electrical signal of incoming packets before broadcasting them out to the network. Active hubs, on the other hand, do perform this amplification, as does a different type of dedicated network device called a repeater. Another, not so common, name for the term concentrator is referring to a passive hub and the term multiport repeater is referred to an active hub. Intelligent hubs add extra features to an active hub that are of particular importance to businesses. An intelligent hub typically is stackable (built in such a way that multiple units can be placed one on top of the other to conserve space). It also typically includes remote management capabilities via Simple Network Management Protocol (SNMP) and virtual LAN (VLAN) support.
Uses
Historically, the main reason for purchasing hubs rather than switches was their price. This has largely been eliminated by reductions in the price of switches, but hubs can still be useful in special circumstances:
For inserting a protocol analyzer into a network connection, a hub is an
alternative to a network tap or port mirroring.
Some computer clusters require each member computer to receive all of
the traffic going to the cluster.[citation needed ] A hub will do this naturally; using a switch requires special configuration.
When a switch is accessible for end users to make connections, for
example, in a conference room, an inexperienced or careless user (or saboteur ) can bring down the network by connecting two ports together, causing a loop. This can be prevented by using a hub, where a loop will break other users on the hub, but not the rest of the network. (It can also be prevented by buying switches that can detect and deal with loops, for example by implementing the Spanning Tree Protocol.)
A hub with a 10BASE2 port can be used to connect devices that only
support 10BASE2 to a modern network. The same goes for linking in an old thicknet network segment using an AUI port on a hub (individual devices that were intended for thicknet can be linked to modern Ethernet by using an AUI-10BASE-T transceiver ).
Network switch A network switch is a computer networking device that connects network segments. The term commonly refers to a network bridge that processes and routes data at the data link layer (layer 2) of the OSI model. Switches that additionally process data at the network layer (layer 3 and above) are often referred to as Layer 3 switches or multilayer switches. The term network switch does not generally encompass unintelligent or passive network devices such as hubs and repeaters. The first Ethernet switch was introduced by Kalpana in 1990.[1]
Typical SOHO network switch.
Back view of Atlantis network switch withEthernet ports.
Function The network switch, packet switch (or just switch) plays an integral part in most Ethernet local area networks or LANs. Mid-to-large sized LANs contain a number of linked managed switches. Small office/home office (SOHO) applications typically use a single switch, or an all-purposeconverged device such as gateway access to small office/home broadband services such as DSL router or cable Wi-Fi router . In most of these cases, the end user device contains a router and components that interface to the particular physical broadband technology, as in the Linksys 8-port and 48-port devices. User devices may also include a telephone interface to VoIP. In the context of a standard 10/100 Ethernet switch, a switch operates at the datalink layer of the OSI model to create a different collision domain per switch port. If you have 4 computers A/B/C/D on 4 switch ports, then A and B can transfer data between them as well as C and D at the same time, and they will never interfere
with each others' conversations. In the case of a "hub" then they would all have to share the bandwidth, run in Half duplex and there would be collisions and retransmissions. Using a switch is called micro-segmentation. It allows you to have dedicated bandwidth on point to point connections with every computer and to therefore run in Full duplex with no collisions.
Role of switches in networks Network switch is a marketing term rather than a technical one.[citation needed ] Switches may operate at one or more OSI layers, includingphysical includingphysical,, data link, link, network network,, or transport or transport (i.e., end-to-end). end-to-end). A device that operates simultaneously at more than one of these layers is called amultilayer amultilayer switch, switch, although use of the term is diminishing.[citation needed ] In switches intended for commercial use, built-in or modular interfaces make it possible to connect different types of networks, includingEthernet includingEthernet,, Fibre Channel,, ATM Channel ATM,, ITU-T G.hn and 802.11 802.11.. This connectivity can be at any of the layers mentioned. While Layer 2 functionality is adequate for speed-shifting within one technology, interconnecting technologies such as Ethernet and token ring are easier at Layer 3. Interconnection of different Layer 3 networks is done by routers routers.. If there are any features that characterize "Layer-3 switches" as oppo sed to general-purpose routers, it tends to be that they are optimized, in larger switches, for high-density Ethernet connectivity. In some service provider and other environments where there is a need for a great deal of analysis of network performance and security, switches may be connected between WAN routers as places for analytic modules. Some vendors [2][3] [3] provide firewall firewall,,[2] network intrusion detection, detection,[4] and performance analysis
modules that can plug into switch ports. Some of these functions may be on combined modules.[5] In other cases, the switch is used to create a mirror image of data that can go to an external device. Since most switch port mirroring provides only one mirrored stream, network hubs can be useful for fanning out data to several read-only analyzers, such as intrusion detection systemsand systemsand packet sniffers. sniffers.
Layer-specific Layer-specific functionality
A modular network switch with three network modules (a total of 24 Ethernet and 14 Fast Ethernet ports) and one power supply.
While switches may learn about topologies at many layers layers,, and forward at one or more layers, they do tend to have common features. Other than for highperformance applications, modern commercial switches use primarily Ethernet interfaces, which can have different input and output speeds of 10, 100, 1000 or 10,000 megabits per second. second. Switch ports almost always default to Full duplex operation, unless there is a requirement for interoperability with devices that are strictly Half duplex. duplex. Half duplex means that the device can only send or receive at any given time, whereas Full duplex can send and receive at the same time. At any layer, a modern switch may implement power over Ethernet (PoE), which avoids the need for attached devices, such as an IP telephone or wireless or wireless access point,, to have a separate power supply. Since switches can have redundant p ower point circuits connected touninterruptible touninterruptible power supplies, supplies, the connected device can continue operating even when regular office power fails.
Layer-1 hubs versus higher-layer switches A network hub, hub, or repeater, is a fairly unsophisticated network device. Hubs do not manage any of the traffic that comes through them. Any packet entering a port is broadcast out or "repeated" on every other port, except for the port of entry. Since
every packet is repeated on every other port, packet collisions result, which slows down the network. There are specialized applications where a hub can be useful, such as copying traffic to multiple network sensors. High end switches ha ve a feature which does the same thing called port mirroring. mirroring. There is no longer any significant price difference between a hub and a low-end switch.[6]
Layer 2 A network bridge, bridge, operating at the Media Access Control (MAC) sublayer of the data link layer, may interconnect a small number of devices in a home or office. This is a trivial case of bridging, in which the bridge learns the MAC address of each connected device. Single bridges also can provide extremely high performance in specialized applications such as storage area networks. networks. Classic bridges may also interconnect using a spanning tree protocol that disables links so that the resulting local area network is a tree treewithout without loops. In contrast to routers, spanning tree bridges must have topologies with only one active path between two points. The older IEEE older IEEE 802.1D spanning tree protocol could be quite slow, with forwarding stopping for 30 seconds while the spanning tree would reconverge. A Rapid Spanning Tree Protocol was introduced as IEEE 802.1w 802.1w,, but the newest edition of IEEE of IEEE 802.1D-2004, 802.1D-2004, adopts the 802.1w extensions as the base standard. The IETF is specifying the TRILL protocol, which is the application of link-state routing technology to the layer-2 bridging problem. Devices which implement TRILL, called RBridges RBridges,, combine the best features of both routers and bridges. While "layer 2 switch" remains more of a marketing term than a technical term,[citation needed ]
the products that were introduced as "switches" tended to
use microsegmentation and Full duplex to prevent collisions among devices connected to Ethernets. By using an internal forwarding plane much faster than any interface, they give the impression of simultaneous paths among multiple devices. Once a bridge learns the topology through a spanning tree protocol, it forwards data link layer frames using a layer 2 forwarding method. There are four forwarding methods a bridge can use, of which the second through fourth method were performance-increasing methods when used on "switch" products with the same input and output port speeds:
1.
Store and forward: The switch buffers and, typically, performs
a checksum on each frame before forwarding it on.
2.
Cut through: The switch reads only up to the frame's hardware
address before starting to forward it. There is no error checking with this method.
3.
Fragment free: A method that attempts to retain the benefits of
both "store and forward" and "cut through". Fragment free checks the first 64 bytes of the frame, where addressing information is stored. According to Ethernet specifications, collisions should be detected during the first 64 bytes of the frame, so frames that are in error because of a collision will not be forwarded. This way the frame will always reach its intended destination. Error checking of the actual data in the packet is left for the end device in Layer 3 or Layer 4 (OSI), typically a router .
4.
Adaptive switching: A method of automatically switching between
the other three modes. Cut-through switches have to fall back to store and forward if the outgoing port is busy at the time the packet arrives. While there are specialized applications, such as storage area networks, where the input and output interfaces are the same speed, this is rarely the case in general LAN applications. In LANs, a switch used for end user access typically concentrates lower speed (e.g., 10/100 Mbit/s) into a higher speed (at least 1 Gbit/s). Alternatively, a switch that provides access to server ports usually connects to them at a much higher speed than is used by end user devices.
Layer 3 Within the confines of the Ethernet physical layer, a layer 3 switch can perform some or all of the functions normally performed by a router . A true router is able to forward traffic from one type of network connection (e.g., T1, DSL) to another (e.g., Ethernet, WiFi). The most common layer-3 capability is a wareness of IP multicast. With this awareness, a layer-3 switch can increase efficiency by delivering the traffic of a multicast group only to ports where the attached device has signaled that it wants to listen to that group. If a switch is not aware of multicasting and broadcasting, frames are also forwarded on all ports of each broadcast domain, but in the case of
IP multicast this causes inefficient use of bandwidth. To work around this problem some switches implement IGMP snooping.[7]
Layer 4 While the exact meaning of the term Layer-4 switch is vendor-dependent, it almost always starts with a capability for network address translation, but then adds some type of load distribution based on TCP sessions.[8] The device may include a stateful firewall, a VPN concentrator, or be an IPSec security gateway.
Layer 7 Layer 7 switches may distribute loads based on URL or by some installationspecific technique to recognize application-level transactions. A Layer-7 switch may include a web cache and participate in a content delivery network.[9]
Rack-mounted 24-port 3Com switch
Types of switches Form factor
Desktop, not mounted in an enclosure, typically intended to be used in a
home or office environment outside of a wiring closet
Rack mounted
Chassis — with swappable "switch module" cards. e.g. Alcatel's
OmniSwitch 7000; CiscoCatalyst switch 4500 and 6500; 3Com 7700, 7900E, 8800.
Configuration options
Unmanaged switches — These switches have no configuration interface or
options. They are plug and play. They are typically the least expensive switches, found in home, SOHO, or small businesses. They can be desktop or rack mounted.
Managed switches — These switches have one or more methods to modify
the operation of the switch. Common management methods include: a serial console or command line interface accessed via telnet or Secure Shell, an embedded Simple Network Management Protocol (SNMP) agent allowing management from a remote console or management station, or a web interface for management from a web browser. Examples of configuration changes that one can do from a managed switch include: enable features such as Spanning Tree Protocol, set port speed, create or modify Virtual LANs (VLANs), etc. Two sub-classes of managed switches are marketed today:
Smart (or intelligent) switches — These are managed switches
with a limited set of management features. Likewise "web-managed" switches are switches which fall in a market niche between unmanaged and managed. For a price much lower than a fully managed switch they provide a web interface (and usually no CLI access) and allow configuration of basic settings, such as VLANs, port-speed and duplex.[10]
Enterprise Managed (or fully managed) switches — These have a
full set of management features, including Command L ine Interface, SNMP agent, and web interface. They may have additional features to manipulate configurations, such as the ability to display, modify, backup and restore configurations. Compared with smart switches, enterprise switches have more features that can be customized or optimized, and are generally more expensive than "smart" switches. Enterprise switches are typically found in networks with larger number of switches and connections, where centralized management is a significant savings in administrative time and effort. Astackable switch is a version of enterprise-managed switch.
Traffic monitoring on a switched network Unless port mirroring or other methods such as RMON or SMON are implemented in a switch,[11] it is difficult to monitor traffic that is bridged using a switch because all ports are isolated until one transmits data, and even then only the sending and receiving ports can see the traffic. These monitoring features rarely are present on consumer-grade switches. Two popular methods that are specifically designed to allow a network analyst to monitor traffic are:
Port mirroring — the switch sends a copy of network packets to a
monitoring network connection.
SMON — "Switch Monitoring" is described by RFC 2613 and is a protocol
for controlling facilities such as port mirroring. Another method to monitor may be to connect a Layer-1 hub between the monitored device and its switch port. This will induce minor delay, but will provide multiple interfaces that can be used to monitor the individual switch port.
Typical switch management features
Linksys 48-port switch
A rack-mounted switch with network cables
Turn some particular port range on or off
Link speed and duplex settings
Priority settings for ports
MAC filtering and other types of "port security" features which prevent MAC
flooding
Use of Spanning Tree Protocol
SNMP monitoring of device and link health
Port mirroring (also known as: port monitoring, spanning port, SPAN port,
roving analysis port or link mode port)
Link aggregation (also known as bonding , trunking or teaming )
VLAN settings
802.1X network access control
IGMP snooping
Link aggregation allows the use of multiple ports for the same connection achieving higher data transfer speeds. Creating VLANs can serve security and performance goals by reducing the size of the broadcast domain.
Local area network "LAN" redirects here. For other uses, see LAN (disambiguation). A local area network (LAN) is a computer network covering a small physical area, like a home, office, or small group of buildings, such as a school, or an airport. The defining characteristics of LANs, in contrast to wide-area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, and lack of a need for leased telecommunication lines. ARCNET, Token Ring and many other technologies have been used in the past, and G.hn may be used in the future, but Ethernet over twisted pair cabling, and WiFi are the two most common technologies currently in use.
History As larger universities and research labs obtained more computers during the late 1960s, there was increasing pressure to provide high-speed interconnections. A report in 1970 from the Lawrence Radiation Laboratory detailing the growth of their "Octopus" network[1][2] gives a good indication of the situation. Cambridge Ring was developed at Cambridge University in 1974[3] but was never developed into a successful commercial product. Ethernet was developed at Xerox PARC in 1973–1975,[4] and filed as U.S. Patent 4,063,220. In 1976, after the system was deployed at PARC, Metcalfe and Boggs published their seminal paper, "Ethernet: Distributed Packet-Switching For Local Computer Networks."[5] ARCNET was developed by Datapoint Corporation in 1976 and announced in 1977.[6] It had the first commercial installation in December 1977 at Chase Manhattan Bank in New York.[7]
Standards evolution
The development and proliferation of CP/M-based personal computers from the late 1970s and then DOS-based personal computers from 1981 meant that a single site began to have dozens or even hundreds of computers. The initial attraction of networking these was generally to share disk space and laser printers, which were both very expensive at the time. There was much enthusiasm for the concept and for several years, from about 1983 onward, computer industry pundits would regularly declare the coming year to be “the year of the LAN”. In practice, the concept was marred by proliferation of incompatible physical Layer and network protocol implementations, and a plethora of methods of sharing resources. Typically, each vendor would have its own type of network card, cabling, protocol, and network operating system. A solution appeared with the advent of Novell NetWare which provided even-handed support for dozens of competing card/cable types, and a much more sophisticated operating system than most of its competitors. Netware dominated[8] the personal computer LAN business from early after its introduction in 1983 until the mid 1990s when Microsoft introduced Windows NT Advanced Server and Windows for Workgroups. Of the competitors to NetWare, only Banyan Vines had comparable technical strengths, but Banyan never gained a secure base. Microsoft and3Com worked together to create a simple network operating system which formed the base of 3Com's 3+Share, Microsoft's LAN Manager and IBM's LAN Server . None of these were particularly successful. In this same timeframe, Unix computer workstations from vendors such as Sun Microsystems, Hewlett-Packard, Silicon Graphics, Intergraph,NeXT and Apollo were using TCP/IP based networking. Although this market segment is now much reduced, the technologies developed in this area continue to be influential on the Internet and in both Linux and Apple Mac OS X networking—and the TCP/IP protocol has now almost completely replaced IPX, AppleTalk, NBF and other protocols used by the early PC LANs.
Cabling Early LAN cabling had always been based on various grades of co-axial cable, but IBM's Token Ring used shielded twisted pair cabling of their own design, and in 1984 StarLAN showed the potential of simple Cat3 unshielded twisted pair —the same simple cable used for telephone systems. This led to the development
of 10Base-T (and its successors) and structured cabling which is still the basis of most LANs today. In addition, fiber-optic cabling is increasingly used.
Technical aspects Switched Ethernet is the most common Data Link Layer implementation on local area networks. At the Network Layer , the Internet Protocol has become the standard. However, many different options have been used in the history of LAN development and some continue to be popular in niche applications. Smaller LANs generally consist of one or more switches linked to each other—often at least one is connected to a router ,cable modem, or ADSL modem for Internet access. Larger LANs are characterized by their use of redundant links with switches using the spanning tree protocol to prevent loops, their ab ility to manage differing traffic types via quality of service (QoS), and to segregate traffic with VLANs. Larger LANS also contain a wide variety of network devices such as switches, firewalls, routers, load balancers, and sensors.[9] LANs may have connections with other LANs via leased lines, leased services, or by tunneling across the Internet using virtual private networktechnologies. Depending on how the connections are established and secured in a LAN, and the distance involved, a LAN may also be classified as metropolitan area network (MAN) or wide area networks (WAN).
LAN switching This article addresses packet switching in computer networks. LAN switching is a form of packet switching used in local area networks. Switching technologies are crucial to network design, as they allow traffic to be sent only where it is needed in most cases, using fast, hardware-based methods.
Layer 2 switching Layer 2 switching is hardware based, which means it uses the media access control address (MAC address) from the host's network interface cards (NICs) to decide where to forward frames. Switches use application-specific integrated circuits (ASICs) to build and maintain filter tables (also known as MAC address tables). One way to think of a layer 2 switch is as a multiport bridge. Layer 2 switching provides the following
Hardware-based bridging (MAC)
Wire speed
High speed
Low latency
Low cost
Layer 2 switching is highly efficient because there is no modification to the data packet, only to the frame encapsulation of the packet, and only when the data packet is passing through dissimilar media (such as from Ethernet to FDDI). Layer 2 switching is used for workgroup connectivity and network segmentation (breaking up collision domains). This allows a flatter network design with more network segments than traditional10BaseT shared networks. Layer 2 switching has helped develop new components in the network infrastructure
Server farms — Servers are no longer distributed to physical locations
because virtual LANs can be created to create broadcast domains in a switched internetwork. This means that all servers can be placed in a central location, yet a certain server can still be part of a workgroup in a remote branch, for example.
Intranets — Allows organization-wide client/server communications based
on a Web technology. These new technologies allow more data to flow off from local subnets and onto a routed network, where a router's performance can become the bottleneck.
Limitations Layer 2 switches have the same limitations as bridge networks. Remember that bridges are good if a network is designed by the 80/20 rule: users spend 80 percent of their time on their local segment. Bridged networks break up collision domains, but the network remains one large broadcast domain. Similarly, layer 2 switches (bridges) cannot break up broadcast domains, which can cause performance issues and limits the size of your network. Broadcast and multicasts, along with the slow convergence of spanning tree, can cause major problems as the network grows. Because of these problems, layer 2 switches cannot completely replace routers in the internetwork.
Layer 3 switching The only difference between a layer 3 switch and router is the way the administrator creates the physical implementation. Also, traditional routers use microprocessors to make forwarding decisions, and the switch performs only hardware-based packet switching. However, some traditional routers can have other hardware functions as well in some of the higher-end models. Layer 3 switches can be placed anywhere in the network because they handle highperformance LAN traffic and can cost-effectively replace routers. Layer 3 switching is all hardware-based packet forwarding, and all packet forwarding is handled by hardware ASICs. Layer 3 switches really are no different functionally than a traditional router and perform the same functions, which are listed here
Determine paths based on logical addressing
Run layer 3 checksums (on header only)
Use Time to Live (TTL)
Process and respond to any option information
Update Simple Network Management Protocol (SNMP) managers
with Management Information Base (MIB) information
Provide Security
The benefits of layer 3 switching include the following
Hardware-based packet forwarding
High-performance packet switching
High-speed scalability
Low latency
Lower per-port cost
Flow accounting
Security
Quality of service (QoS)
Layer 4 switching
Layer 4 switching is considered a hardware-based layer 3 switching technology that can also consider the application used (for example, Telnet or FTP). Layer 4 switching provides additional routing above layer 3 by using the port numbers found in the Transport layer header to make routing decisions. These port numbers are found in Request for Comments (RFC) 1700 and reference the upper-layer protocol, program, or application. Layer 4 information has been used to help make routing decisions for quite a while. For example, extended access lists can filter packets based on layer 4 port numbers. Another example is accounting information gathered by NetFlow switching in Cisco's higher-end routers. The largest benefit of layer 4 switching is that the network administrator can configure a layer 4 switch to prioritize data traffic by application, which means a QoS can be defined for each user. For example, a number of users can be defined as a Video group and be assigned more priority, or band-width, based on the need for video conferencing.
Multi-layer switching (MLS) Main article: Multilayer switch Multi-layer switching combines layer 2, 3, and 4 switching technologies and provides high-speed scalability with low latency. It accomplishes this high combination of high-speed scalability with low latency by using huge filter tables based on the criteria designed by the network administrator. Multi-layer switching can move traffic at wire speed and also provide layer 3 routing, which can remove the bottleneck from the network routers. This technology is based on the idea of "route once, switch many". Multi-layer switching can make routing/switching decisions based on the following
MAC source/destination address in a Data Link frame
IP source/destination address in the Network layer h eader
Protocol field in the Network layer header
Port source/destination numbers in the Transport layer header
There is no performance difference between a layer 3 and a layer 4 switch because the routing/switching is all hardware based.
Router A router , pronounced /ˈraʊtər/ in the United States, Canada, and Australia, and / ˈruːt ər/
in the UK andIreland (to differentiate it from the tool used to rout wood), is
an electronic device used to connect two or more computers or other electronic devices to each other, and usually to the Internet, by wire or radiosignals. This allows several computers to communicate with each other and to the Internet at the same time. If wires are used, each computer is connected by its own wire to the router. Modern wired-only routers designed for the home or small business typically have one "input" port (to the Internet) and four "output" ports, one or more of which can be connected to other computers. A typical modern home wireless router , in addition to having four wired ports, also allows several devices to connect with it wirelessly. Most modernpersonal computers are built with a wired port (almost always an Ethernet type), which allows them to connect to a router with the addition of just a cable (typically a Category 5e type). To connect with a wireless router, a device must have an adapter . This is sometimes, but not a lways, included with the computer at manufacture. Some electronic games, including handheld electronic games, have an adapter built-in, or one can be added later. More technically, a router is a networking device whose software and hardware are usually tailored to the tasks of routing and forwarding information. Routers connect two or more logical subnets, which do not necessarily map one-to-one to the physical interfaces of the router.[1] The term "layer 3 switching" is often used interchangeably with routing, but switch is a general term without a rigorous technical definition. In marketing usage, a switch is generally optimized for Ethernet LAN interfaces and may not have other physical interface types. In comparison, the network hub (predecessor of the "switch" or "switching hub") does not do any routing, instead every packet it receives on one network line gets forwarded to all the other network lines. Routers operate in two different planes:[2]
Control plane, in which the router learns the outgoing interface that is most
appropriate for forwarding specific packets to specific destinations,
Forwarding plane, which is responsible for the actual process of sending a
packet received on a logical interface to an outbound logical interface.
Cisco 1800 Router
Nortel ERS 8600
For the pure Internet Protocol (IP) forwarding function, router design tries to minimize the state information kept on individual packets. Once a packet is forwarded, the router should no longer retain statistical information about it. It is the sending and receiving endpoints that keeps information about such things as errored or missing packets. Forwarding decisions can involve decisions at layers other than the IP internetwork layer or OSI layer 3. Again, the marketing term switch can be applied to devices that have these capabilities. A function that forwards based on data link layer , or OSI layer 2, information, is properly called a bridge. Marketing literature may call it a layer 2 switch, but a switch has no p recise definition.
Among the most important forwarding decisions is deciding what to do when congestion occurs, i.e., packets arrive at the router at a rate higher than the router can process. Three policies commonly used in the Internet are Tail drop, Random early detection, and Weighted random early detection. Tail drop is the simplest and most easily implemented; the router simply drops packets once the length of the queue exceeds the size of the buffers in the router. Random early detection (RED) probabilistically drops datagrams early when the queue exceeds a configured size. Weighted random early detection requires a weighted average queue size to exceed the configured size, so that short bursts will not trigger random drops. A router uses a routing table to decide where the packet should be sent so if the router cant find the preferred address then it will look down the routing table and decide which is the next best address to send it to.
Types of routers
Routers may provide connectivity inside enterprises, between enterprises and the Internet, and inside Internet Service Providers (ISPs). The largest routers (for example the Cisco CRS-1 or Juniper T1600) interconnect ISPs, are used inside ISPs, or may be used in very large enterprise networks. The smallest routers provide connectivity for small and home offices.
Routers for Internet connectivity and internal use Routers intended for ISP and major enterprise connectivity will almost invariably exchange routing information with the Border Gateway Protocol (BGP). RFC 4098[3] defines several types of BGP-speaking routers:
Edge Router: Placed at the edge of an ISP network, it speaks
external BGP (eBGP) to a BGP speaker in another provider or large enterprise Autonomous System(AS).
Subscriber Edge Router: Located at the edge of the subscriber's network, it
speaks eBGP to its provider's AS(s). It belongs to an end user (enterprise) organization.
Inter-provider Border Router: Interconnecting ISPs, this is a BGP speaking
router that maintains BGP sessions with other BGP speaking routers in other providers' ASes.
Core router: A router that resides within the middle or backbone of the LAN
network rather than at its periphery. Within an ISP: Internal to the provider's AS, such a router speaks internal BGP (iBGP) to that provider's edge routers, other intra-provider core routers, or the provider's inter-provider border routers. "Internet backbone:" The Internet does not have a clearly identifiable backbone, as did its predecessors. See default-free zone (DFZ). Nevertheless, it is the major ISPs' routers that make up what many would consider the core. These ISPs o perate all four types of the BGP-speaking routers described here. In ISP usage, a "core" router is internal to an ISP, and used to interconnect its edge and bo rder routers. Core routers may also have specialized functions in virtual private networks based on a combination of BGP and Multi-Protocol Label Switching (MPLS).[4] Routers are also used for port forwarding for private servers.
Small Office Home Office (SOHO) connectivity Main article: Residential gateway Residential gateways (often called routers) are frequently used in homes to connect to a broadband service, such as IP over cable or DSL. Such a router may also include an internal DSL modem. Residential gateways and SOHO routers typically provide network address translationand port address translation in addition to routing. Instead of directly presenting the IP addresses of local computers to the remote network, such a residential gateway makes multiple local computers appear to be a single computer.
SOHO routers may also support Virtual Private Network tunnel functionality to provide connectivity to an enterprise network..
Enterprise routers All sizes of routers may be found inside enterprises. The most powerful routers tend to be found in ISPs and academic & research facilities. Large businesses may also need powerful routers. A three-layer model is in common use, not all of which need be present in smaller networks.[5]
Access Access routers, including SOHO, are located at customer sites such as branch offices that do not need hierarchical routing of their own. Typically, they are optimized for low cost.
Distribution Distribution routers aggregate traffic from multiple access routers, either at the same site, or to collect the data streams from multiple sites to a major enterprise location. Distribution routers often are responsible for enforcing quality of service across a WAN, so they may have considerable memory, multiple WAN interfaces, and substantial processing intelligence. They may also provide connectivity to groups of servers or to external networks. In the latter application, the router's functionality must be carefully considered as part of the overall security architecture. Separate from the router may be a Firewalled or VPN concentrator, or the router may include these and other security functions. When an enterprise is primarily on one campus, there may not be a distinct distribution tier, other than perhaps off-campus access. In such cases, the access routers, connected to LANs, interconnect via core routers.
Core In enterprises, a core router may provide a "collapsed backbone" interconnecting the distribution tier routers from multiple buildings of a
campus, or large enterprise locations. They tend to be optimized for high bandwidth. When an enterprise is widely distributed with no central location(s), the function of core routing may be subsumed by the WAN service to which the enterprise subscribes, and the distribution routers become the highest tier.
History
Leonard Kleinrock and the first IMP.
A Cisco ASM/2-32EM router deployed at CERN in 1987.
The very first device that had fundamentally the same functionality as a router does today, i.e a packet switch, was the Interface Message Processor (IMP); IMPs were the devices that made up the ARPANET, the first packet switching network. The idea for a router (although they were called "gateways" at the time) initially came about through an international group of computer networking researchers called the International Network Working Group (INWG). Set up in 1972 as an informal group to consider the technical issues involved in connecting different networks, later that year it became a subcommittee of theInternational Federation for Information Processing. [6]
These devices were different from most previous packet switches in two ways. First, they connected dissimilar kinds of networks, such as serial lines and local area networks. Second, they wereconnectionless devices, which had no role in assuring that traffic was delivered reliably, leaving that entirely to the hosts (although this particular idea had b een previously pioneered in the CYCLADES network). The idea was explored in more detail, with the intention to produce a real prototype system, as part of two contemporaneous programs. One was the initial DARPA-initiated program, which created the TCP/IParchitecture of today. [7] The other was a program at Xerox PARC to explore new networking technologies, which produced the PARC Universal Packet system, although due to corporate intellectual property concerns it received little attention outside Xerox until years later.
[8]
The earliest Xerox routers came into o peration sometime after early 1974. The first true IP router was developed by Virginia Strazisar at BBN, as part of that DARPA-initiated effort, during 1975-1976. By the end of 1976, three PDP11-based routers were in service in the experimental prototype Internet. [9] The first multiprotocol routers were independently created by staff researchers at MIT and Stanford in 1981; the Stanford router was done by William Yeager , and the MIT one by Noel Chiappa; both were also based on PDP11s. [10] [11] [12] [13] As virtually all networking now uses IP at the network layer, multiprotocol routers are largely obsolete, although they were important in the early stages of the growth of computer networking, when several protocols other than TCP/IP were in widespread use. Routers that handle both IPv4 and IPv6 arguably are multiprotocol, but in a far less variable sense than a router that processed AppleTalk, DECnet, IP, and Xerox protocols. In the original era of routing (from the mid-1970s through the 1980s), generalpurpose mini-computers served as routers. Although general-purpose computers can perform routing, modern high-speed routers are highly specialized computers, generally with extra hardware added to accelerate both common routing functions such as packet forwarding and specialised functions such as IPsec encryption.
