PROJECT REPORT ON COMPUTER NETWORKING
at NHPC LIMITED
Report Submitted by: ANIRUDH SANGWAN 7105
Report for 6 Weeks Summer Training after 6th Semester.
ACKNOWLEDGEMENT
I take great privilege in conveying my heartiest gratitude to Mr. Girish Sharma for givi giving ng me the the oppor opportu tuni nity ty to under underta take ke this this proj projec ectt work work in thei theirr comp compan any. y. The The successful successful completion completion of the project work rendered was made possible possible by the valuable guidance of the supervision. I am grateful to him for his active and warm interest, which encouraged me to overcome difficulties encountered in preparation of this project.
Last but not the least, I would like to thank the staff members of the NHPC Limited who cooperated with me during the entire project.
ANIRUDH 7105(ECE 6th SEM.)
© 2007 INDUS. All rights reserved
Network 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.
Area Networks Networks can be categorized in several different ways. One approach defines the type of network according to the geographic area it spans. Local area networks (LANs), for example, typically reach across a single home, whereas wide area networks (WANs), reach across cities, states, or even across the world. The Internet is the world's largest public WAN.
Network Design Computer networks also differ in their design. The two types of high-level network design are called clientserver and peer-to-peer . Client-server networks feature centralized server computers that store email, Web pages, files and or applications. On a peer-to-peer network, conversely, all computers tend to support the same functions. Client-server networks are much more common in business and peer-to-peer networks much more common in homes. A network topology represents its layout or structure from the point of view of data flow. In so-called bus networks, for example, all of the computers share and communicate across one common conduit, whereas in a star network, all data flows through one centralized device. Common types of network topologies include bus, star, ring and mesh.
Network Protocols In networking, the communication language used by computer devices is called the protocol. Yet another way to classify computer networks is by the set of protocols they support. Networks often implement multiple protocols to support specific applications. Popular protocols include TCP/IP, the most common protocol found on the Internet and in home networks.
Wired vs Wireless Networking Many of the same network protocols, like TCP/IP, work in both wired and wireless networks. Networks with Ethernet cables predominated in businesses, schools, and homes for several decades. Recently, however, wireless networking alternatives have emerged as the premier technology for building new computer networks Wireless networks utilize radio waves and/or microwaves to maintain communication channels between computers. Wireless networking is a more modern alternative to wired networking that relies on copper and/or fiber optic cabling between network devices. A wireless network offers advantages and disadvantages compared to a wired network. Advantages of wireless include mobility and elimination of unsightly cables. Disadvantages of wireless include the potential for radio interference due to weather, other wireless devices, or obstructions like walls. Wireless is rapidly gaining in popularity for both home and business networking. Wireless technology continues to improve, and the cost of wireless products continues to decrease. Popular wireless local area networking (WLAN) products conform to the 802.11 "Wi-Fi" standards.
OSI Model Definition: The OSI model defines internetworking in terms of a vertical stack of seven layers. The upper layers of the OSI model represent software that implements network services like encryption and
connection management. The lower layers of the OSI model implement more primitive, hardware-oriented functions like routing, addressing, and flow control. In the OSI model, data communication starts with the top layer at the sending side, travels down the OSI model stack to the bottom layer, then traveses the network connection to the bottom layer on the receiving side, and up its OSI model stack. The OSI model was introduced in 1984. Although it was designed to be an abstract model, the OSI model remains a practical framework for today's key network technologies like Ethernet and protocols like IP.
Standard network layer architecture The Open Systems Interconnection (OSI) reference model has been an essential element of computer network design since its ratification in 1984. The OSI is an abstract model of how network protocols and equipment should communicate and work together (interoperate). The OSI model is a technology standard maintained by the International Standards Organization (ISO). Although today's technologies do not fully conform to the standard, it remains a useful introduction to the study of network architecture.
Network topology is the study of the arrangement or mapping of the elements (links, nodes, etc.) of a network, especially the physical (real) and logical (virtual) interconnections between nodes. [1] [2] [3]
A local area network (LAN) is one example of a network that exhibits both a physical topology and a logical topology. Any given node in the LAN will have one or more links to one or more other nodes in the network and the mapping of these links and nodes onto a graph results in a geometrical shape that determines the physical topology of the network. Likewise, the mapping of the flow of data between the nodes in the network determines the logical topology of the network. It is important to note that the physical and logical topologies might be identical in any particular network but they also may be different . Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes. LAN Network Topology is, therefore, technically a part of graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical [2].
Basic types of topologies The arrangement or mapping of the elements of a network gives rise to certain basic topologies which may then be combined to form more complex topologies (hybrid topologies). The most common of these basic types of topologies are (refer to the illustration at the top right of this page): • • • •
• • •
Bus (Linear, Linear Bus) Star Ring Mesh partially connected mesh (or simply 'mesh') o fully connected mesh o Tree Hybrid Point to Point
Point-to-point The simplest topology is a permanent link between two endpoints. Switched point-to-point topologies are the basic model of conventional telephony. The value of a permanent point-to-point network is the value of guaranteed, or nearly so, communications between the two endpoints. The value of an on-demand point-to-point connection is proportional to the number of potential pairs of subscribers, and has been expressed as Metcalfe's Law. Permanent (dedicated) Easiest to understand, of the variations of point-to-point topology, is a point-to-point communications channel that appears, to the user, to be permanently associated with the two endpoints. Children's "tin-can telephone" is one example, with a microphone to a single public address speaker is another. These are examples of physical dedicated channels. Within many switched telecommunications systems , it is possible to establish a permanent circuit. One example might be a telephone in the lobby of a public building, which is programmed to ring only the number of a telephone dispatcher. "Nailing down" a switched connection saves the cost of running a physical circuit between the two points. The resources in such a connection can be released when no longer needed, as, for example, a television circuit from a parade route back to the studio. Switched: Using circuit-switching or packet-switching technologies, a point-to-point circuit can be set up dynamically, and dropped when no longer needed. This is the basic mode of conventional telephony.
Bus Linear bus
The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has exactly two endpoints (this is the 'bus', which is also commonly referred to as the backbone, or trunk) – all data that is transmitted between nodes in the network is transmitted over this common transmission medium and is able to be received by all nodes in the network virtually simultaneously (disregarding propagation delays)[1][3]. Note: The two endpoints of the common transmission medium are normally terminated with a device called a terminator that exhibits the characteristic impedance of the transmission medium and which dissipates or absorbs the energy that remains in the signal to prevent the signal from being reflected or propagated back onto the transmission medium in the opposite direction, which would cause interference with and degradation of the signals on the transmission medium (See Electrical termination). Distributed bus The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has more than two endpoints that are created by adding branches to the main section of the transmission medium – the physical distributed bus topology functions in exactly the same fashion as the physical linear bus topology (i.e., all nodes share a common transmission medium). Notes: 1.) All of the endpoints of the common transmission medium are normally terminated with a device called a 'terminator' (see the note under linear bus). 2.) The physical linear bus topology is sometimes considered to be a special case of the physical distributed bus topology – i.e., a distributed bus with no branching segments. 3.) The physical distributed bus topology is sometimes incorrectly referred to as a physical tree topology – however, although the physical distributed bus topology resembles the physical tree topology, it differs from the physical tree topology in that there is no central node to which any other nodes are connected, since this hierarchical functionality is replaced by the common bus.
Star The type of network topology in which each of the nodes of the network is connected to a central node with a point-to-point link in a 'hub' and 'spoke' fashion, the central node being the 'hub' and the nodes that are attached to the central node being the 'spokes' (e.g., a collection of point-to-point links from the peripheral nodes that converge at a central node) – all data that is transmitted between nodes in the network is transmitted to this central node, which is usually some type of device that then retransmits the data to some or all of the other nodes in the network, although the
central node may also be a simple common connection point (such as a 'punch-down' block) without any active device to repeat the signals. Notes: 1.) A point-to-point link (described above) is sometimes categorized as a special instance of the physical star topology – therefore, the simplest type of network that is based upon the physical star topology would consist of one node with a single point-to-point link to a second node, the choice of which node is the 'hub' and which node is the 'spoke' being arbitrary [1]. 2.) After the special case of the point-to-point link, as in note 1.) above, the next simplest type of network that is based upon the physical star topology would consist of one central node – the 'hub' – with two separate point-topoint links to two peripheral nodes – the 'spokes'. 3.) Although most networks that are based upon the physical star topology are commonly implemented using a special device such as a hub or switch as the central node (i.e., the 'hub' of the star), it is also possible to implement a network that is based upon the physical star topology using a computer or even a simple common connection point as the 'hub' or central node – however, since many illustrations of the physical star network topology depict the central node as one of these special devices, some confusion is possible, since this practice may lead to the misconception that a physical star network requires the central node to be one of these special devices, which is not true because a simple network consisting of three computers connected as in note 2.) above also has the topology of the physical star. 4.) Star networks may also be described as either broadcast multi-access or nonbroadcast multi-access (NBMA), depending on whether the technology of the network either automatically propagates a signal at the hub to all spokes, or only addresses individual spokes with each communication. Extended star A type of network topology in which a network that is based upon the physical star topology has one or more repeaters between the central node (the 'hub' of the star) and the peripheral or 'spoke' nodes, the repeaters being used to extend the maximum transmission distance of the point-to-point links between the central node and the peripheral nodes beyond that which is supported by the transmitter power of the central node or beyond that which is supported by the standard upon which the physical layer of the physical star network is based. Note: If the repeaters in a network that is based upon the physical extended star topology are replaced with hubs or switches, then a hybrid network topology is created that is referred to as a physical hierarchical star topology, although some texts make no distinction between the two topologies. Distributed Star A type of network topology that is composed of individual networks that are based upon the physical star topology connected together in a linear
fashion – i.e., 'daisy-chained' – with no central or top level connection point (e.g., two or more 'stacked' hubs, along with their associated star connected nodes or 'spokes').
Ring The type of network topology in which each of the nodes of the network is connected to two other nodes in the network and with the first and last nodes being connected to each other, forming a ring – all data that is transmitted between nodes in the network travels from one node to the next node in a circular manner and the data generally flows in a single direction only. Dual-ring The type of network topology in which each of the nodes of the network is connected to two other nodes in the network, with two connections to each of these nodes, and with the first and last nodes being connected to each other with two connections, forming a double ring – the data flows in opposite directions around the two rings, although, generally, only one of the rings carries data during normal operation, and the two rings are independent unless there is a failure or break in one of the rings, at which time the two rings are joined (by the stations on either side of the fault) to enable the flow of data to continue using a segment of the second ring to bypass the fault in the primary ring.
Mesh The value of fully meshed networks is proportional to the exponent of the number of subscribers, assuming that communicating groups of any two endpoints, up to and including all the endpoints, is approximated by Reed's Law. Full Fully connected The type of network topology in which each of the nodes of the network is connected to each of the other nodes in the network with a point-to-point link – this makes it possible for data to be simultaneously transmitted from any single node to all of the other nodes. Note: The physical fully connected mesh topology is generally too costly and complex for practical networks, although the topology is used when there are only a small number of nodes to be interconnected [3]. Partial Partially connected The type of network topology in which some of the nodes of the network are connected to more than one other node in the network with a point-topoint link – this makes it possible to take advantage of some of the redundancy that is provided by a physical fully connected mesh topology without the expense and complexity required for a connection between every node in the network.
Note: In most practical networks that are based upon the physical partially connected mesh topology, all of the data that is transmitted between nodes in the network takes the shortest path (or an approximation of the shortest path) between nodes, except in the case of a failure or break in one of the links, in which case the data takes an alternate path to the destination. This requires that the nodes of the network possess some type of logical 'routing' algorithm to determine the correct path to use at any particular time.
Tree (also known as hierarchical): The type of network topology in which a central 'root' node (the top level of the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level) with a point-to-point link between each of the second level nodes and the top level central 'root' node, while each of the second level nodes that are connected to the top level central 'root' node will also have one or more other nodes that are one level lower in the hierarchy (i.e., the third level) connected to it, also with a point-to-point link, the top level central 'root' node being the only node that has no other node above it in the hierarchy – the hierarchy of the tree is symmetrical, each node in the network having a specific fixed number, f, of nodes connected to it at the next lower level in the hierarchy, the number, f, being referred to as the 'branching factor' of the hierarchical tree. Notes: 1.) A network that is based upon the physical hierarchical topology must have at least three levels in the hierarchy of the tree, since a network with a central 'root' node and only one hierarchical level below it would exhibit the physical topology of a star. 2.) A network that is based upon the physical hierarchical topology and with a branching factor of 1 would be classified as a physical linear topology. 3.) The branching factor, f, is independent of the total number of nodes in the network and, therefore, if the nodes in the network require ports for connection to other nodes the total number of ports per node may be kept low even though the total number of nodes is large – this makes the effect of the cost of adding ports to each node totally dependent upon the branching factor and may therefore be kept as low as required without any effect upon the total number of nodes that are possible. 4.) The total number of point-to-point links in a network that is based upon the physical hierarchical topology will be one less than the total number of nodes in the network. 5.) If the nodes in a network that is based upon the physical hierarchical topology are required to perform any processing upon the data that is transmitted between nodes in the network, the nodes that are at higher levels in the hierarchy will be required to perform more processing
operations on behalf of other nodes than the nodes that are lower in the hierarchy.
Hybrid network topologies The hybrid topology is a type of network topology that is composed of one or more interconnections of two or more networks that are based upon different physical topologies or a type of network topology that is composed of one or more interconnections of two or more networks that are based upon the same physical topology, but where the physical topology of the network resulting from such an interconnection does not meet the definition of the original physical topology of the interconnected networks (e.g., the physical topology of a network that would result from an interconnection of two or more networks that are based upon the physical star topology might create a hybrid topology which resembles a mixture of the physical star and physical bus topologies or a mixture of the physical star and the physical tree topologies, depending upon how the individual networks are interconnected, while the physical topology of a network that would result from an interconnection of two or more networks that are based upon the physical distributed bus network retains the topology of a physical distributed bus network). Star-bus A type of network topology in which the central nodes of one or more individual networks that are based upon the physical star topology are connected together using a common 'bus' network whose physical topology is based upon the physical linear bus topology, the endpoints of the common 'bus' being terminated with the characteristic impedance of the transmission medium where required – e.g., two or more hubs connected to a common backbone with drop cables through the port on the hub that is provided for that purpose (e.g., a properly configured 'uplink' port) would comprise the physical bus portion of the physical starbus topology, while each of the individual hubs, combined with the individual nodes which are connected to them, would comprise the physical star portion of the physical star-bus topology. Star-of-stars Hierarchical star A type of network topology that is composed of an interconnection of individual networks that are based upon the physical star topology connected together in a hierarchical fashion to form a more complex network – e.g., a top level central node which is the 'hub' of the top level physical star topology and to which other second level central nodes are attached as the 'spoke' nodes, each of which, in turn, may also become the central nodes of a third level physical star topology. Notes: 1.) The physical hierarchical star topology is not a combination of the physical linear bus and the physical star topologies, as cited in some texts,
as there is no common linear bus within the topology, although the top level 'hub' which is the beginning of the physical hierarchical star topology may be connected to the backbone of another network, such as a common carrier, which is, topologically, not considered to be a part of the local network – if the top level central node is connected to a backbone that is considered to be a part of the local network, then the resulting network topology would be considered to be a hybrid topology that is a mixture of the topology of the backbone network and the physical hierarchical star topology. 2.) The physical hierarchical star topology is also sometimes incorrectly referred to as a physical tree topology, since its physical topology is hierarchical, however, the physical hierarchical star topology does not have a structure that is determined by a branching factor, as is the case with the physical tree topology and, therefore, nodes may be added to, or removed from, any node that is the 'hub' of one of the individual physical star topology networks within a network that is based upon the physical hierarchical star topology. 3.) The physical hierarchical star topology is commonly used in 'outside plant' (OSP) cabling to connect various buildings to a central connection facility, which may also house the 'demarcation point' for the connection to the data transmission facilities of a common carrier, and in 'inside plant' (ISP) cabling to connect multiple wiring closets within a building to a common wiring closet within the same building, which is also generally where the main backbone or trunk that connects to a larger network, if any, enters the building. Star-wired ring A type of hybrid physical network topology that is a combination of the physical star topology and the physical ring topology, the physical star portion of the topology consisting of a network in which each of the nodes of which the network is composed are connected to a central node with a point-to-point link in a 'hub' and 'spoke' fashion, the central node being the 'hub' and the nodes that are attached to the central node being the 'spokes' (e.g., a collection of point-to-point links from the peripheral nodes that converge at a central node) in a fashion that is identical to the physical star topology, while the physical ring portion of the topology consists of circuitry within the central node which routes the signals on the network to each of the connected nodes sequentially, in a circular fashion. Note: In an 802.5 Token Ring network the central node is called a Multistation Access Unit (MAU). Hybrid mesh A type of hybrid physical network topology that is a combination of the physical partially connected topology and one or more other physical topologies the mesh portion of the topology consisting of redundant or alternate connections between some of the nodes in the network – the physical hybrid mesh topology is commonly used in networks which require a high degree of availability..
What is Network Cabling? Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network. The following sections discuss the types of cables used in networks and other related topics. • • • • • •
Unshielded Twisted Pair (UTP) Cable Shielded Twisted Pair (STP) Cable Coaxial Cable Fiber Optic Cable Wireless LANs Cable Installation Guides
Unshielded Twisted Pair (UTP) Cable Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks (See fig. 1).
Fig.1. Unshielded twisted pair
The quality of UTP may vary from telephone-grade wire to extremely high-speed cab le. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot. The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated five categories of wire.
Categories of Unshielded Twisted Pair
Type
Use
Category 1
Voice Only (Telephone Wire)
Category 2
Data to 4 Mbps (LocalTalk)
Category 3
Data to 10 Mbps (Ethernet)
Category 4
Data to 20 Mbps (16 Mbps Token Ring)
Category 5
Data to 100 Mbps (Fast Ethernet)
Buy the best cable you can afford; most schools purchase Category 3 or Category 5. If you are designing a 10 Mbps Ethernet network and are considering the cost savings of buying Category 3 wire instead of Category 5, remember that the Category 5 cable will provide more "room to grow" as transmission technologies increase. Both Category 3 and Category 5 UTP have a maximum segment length of 100 meters. In Florida, Category 5 cable is required for retrofit grants. 10BaseT refers to the specifications for unshielded twisted pair cable (Category 3, 4, or 5) carrying Ethernet signals. Category 6 is relatively new and is used for gigabit connections.
Unshielded Twisted Pair Connector The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector (See fig. 2). A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.
Fig. 2. RJ-45 connector
Shielded Twisted Pair (STP) Cable A disadvantage of UTP is that it may be susceptible to radio and electrical frequency interference. Shielded twisted pair (STP) is suitable for environments with electrical interference; however, the extra shielding can make the cables quite bulky. Shielded twisted pair is often used on networks using Token Ring topology.
Coaxial Cable Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield (See fig. 3). The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers.
Fig. 3. Coaxial cable
Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial cabling are thick coaxial and thin coaxial. Thin coaxial cable is also referred to as thin net. 10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to the approximate maximum segment length being 200 meters. In actual fact the maximum segment length is 185 meters. Thin coaxial cable is popular in school networks, especially linear bus networks. Thick coaxial cable is also referred to as thick net. 10Base5 refers to the specifications for thick coaxial cable carrying Ethernet signals. The 5 refers to the maximum segment length being 500 meters. Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. This makes thick coaxial a great choice when running longer lengths in a linear bus network. One disadvantage of thick coaxial is that it does not bend easily and is difficult to install.
Coaxial Cable Connectors The most common type of connector used with coaxial cables is the Bayone-NeillConcelman (BNC) connector (See fig. 4). Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid problems with your network, always use the BNC connectors that crimp, rather than screw, onto the ca ble.
Fig. 4. BNC connector
Fiber Optic Cable Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials (See fig. 5). It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between bu ildings, due to its immunity to the effects of moisture and lighting. Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling; however, it is more difficult to install and modify. 10BaseF refers to the specifications for fiber optic cable carrying Ethernet signals.
Fig.5. Fiber optic cable
Facts about fiber optic cables: • • • •
Outer insulating jacket is made of Teflon or PVC. Kevlar fiber helps to strengthen the cable and prevent breakage. A plastic coating is used to cushion the fiber center. Center (core) is made of glass or plastic fibers.
Fiber Optic Connector The most common connector used with fiber optic cable is an ST connector. It is barrel shaped, similar to a BNC connector. A newer connector, the SC, is becoming more popular. It has a squared face and is easier to connect in a confined space.
Ethernet Cable Summary
Specification
Cable Type
Maximum length
10BaseT
Unshielded Twisted Pair
100 meters
10Base2
Thin Coaxial
185 meters
10Base5
Thick Coaxial
500 meters
10BaseF
Fiber Optic
2000 meters
100BaseT
Unshielded Twisted Pair
100 meters
100BaseTX
Unshielded Twisted Pair
220 meters
10Mbps Networking Standard
Cable Type
Segment Length
Connector Topology
10Base2
Thin Coaxial
185 meters
BNC
Physical bus
10BaseT
Category 3, 4, 5 twisted pair
100 meters
RJ-45
Physical star
2000 meters
SC/ST
Physical star
10BaseFL Fiber-optic
IEEE Standard
803.2a
Notes on 10Base2 10Base2 networks follow the 5-4-3 rule whereby there is a maximun of 5 network segments allowed, using a maximum of 4 repeaters. Only 3 of the 5 permitted segments may be populated. Each populated 10Base2 segment is limited to a maximum of 30 attached nodes.
Notes on 10BaseT 10BaseT networks follow the 5-4-5 rule whereby there is a maximum of 5 network segments allowed, using a maximum of 4 repeaters. All 5 segments may be populated with nodes.
Fast Ethernet Networking Fast Ethernet defines a group of standards for networking speed of 100 Mbps
Standard
Cable Type
Segment Length
Connector Topology
IEEE Standard
100BaseTX Category 5 UTP 100 meters
RJ-45
Physical Star
802.3u
Category 3, 4, 5 100 meters UTP
RJ-45
Physical Star
802.3u
412 meters / Multimode fiber 10000 meters / Single-mode fiber
SC, ST
Physical Star
802.3u
2000 meters
SC, ST
Dual Ring ANSI FDDI
100BaseT4
Multimode 100BaseFX Single-mode fiber-optic
FDDI
Fiber Optic / Twisted Pair (CDDI)
Gigabit Ethernet Networking Standard
1000BaseLX
Cable Type
Segment Length
Multimode/Singlemode fiber
1000BaseSX Multimode fiber
Connector
IEEE Standard
550/multimode 5000/Single-mode
Fiber connectors 802.3z
550 meters with 50 micron multimode fiber
Fiber connectors 802.3z
1000BaseCX Sheilded Twisted Pair 25 meters
9-pin shielded connector 8-pin fiber channel type 2 connector
802.3z
1000BaseT
75 meters
802.3ab
UTP Category 5
75 meters
10 Gigabit Ethernet Standard
Transmission Type
Distance
Cable type
Connector
IEEE Standard
10GBBaseSR Baseband
33m / 300m
50 micron / 62.5 Fiber micron multimode connectors
802.3ae
10GBBaseLR Baseband
10000 meters
Single-mode fiber
Fiber connectors
802.3ae
10GBBaseER Baseband
40000 meters
Single-mode fiber
Fiber connectors
802.3ae
Retrieved from "http://www.techotopia.com/index.php/Network_Cable_Types_and_Specifications"
LAN - Local Area Network A LAN connects network devices over a relatively short distance. Sponsored Links SS7 Signaling SolutionComplete SS7 development & deployment environment based on SS7www.ulticom.com Planning WAN Re-design?Deploy, Upgrade your network Speak to IBM, call 1800 425 3333www.IBM.com/expressadvantage/in Networking Lan Wan ManMeet the new Windows Server 2008 The Server Unleashed. Learn More...Microsoft.com/WindowsServer2008 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. In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet. In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization. They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring.
WAN - Wide Area Network As the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth. A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address. A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances.
LAN, WAN and Home Networking Residences typically employ one LAN and connect to the Internet WAN via an Internet Service Provider (ISP) using a broadband modem. The ISP provides a WAN IP address to the modem, and all of the computers on the home network use LAN (so-called private) IP addresses. All computers on the home LAN can communicate directly with each other but must go through a central gateway, typically a broadband router , to reach the ISP.
Other Types of Area Networks
• •
•
•
While LAN and WAN are by far the most popular network types mentioned, you may also commonly see references to these others: Wireless Local Area Network - a LAN based on WiFi wireless network technology Metropolitan Area Network - a network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity such as a government body or large corporation. Campus Area Network - a network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus. Storage Area Network - connects servers to data storage devices through a technology like Fibre Channel.
•
System Area Network - links high-performance computers with high-speed connections in a cluster configuration. Also known as Cluster Area Network.
The 7 Layers of the OSI
Model
The OSI, or O pen S ystem I nterconnection, model defines a networking framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.
Application (Layer 7)
Presentation (Layer 6)
Session (Layer 5)
Transport (Layer 4)
Network (Layer 3)
Data Link (Layer 2)
This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer. This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer . This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination. This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer. This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing. At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls ho w a computer on the network gains access to the data and permission to transmit it. The
LLC layer controls frame synchronization, flow control and error checking.
Physical (Layer 1)
This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.
The five-layer TCP/IP model 5. Application layer
DHCP · DNS · FTP · Gopher · HTTP · IMAP4 · IRC · NNTP · XMPP · POP3 · RTP · SIP · SMTP · SNMP · SSH · TELNET · RPC · RTCP · RTSP · TLS (and SSL) · SDP · SOAP · GTP · STUN · NTP · (more) 4. Transport layer TCP · UDP · DCCP · SCTP · RSVP · ECN · (more) 3. Network/internet layer IP (IPv4 · IPv6) · OSPF · IS-IS · BGP · IPsec · ARP · RARP · RIP · ICMP · ICMPv6 · IGMP · (more) 2. Data link layer
802.11 (WLAN) · 802.16 · Wi-Fi · WiMAX · ATM · DTM · Token ring · Ethernet · FDDI · Frame Relay · GPRS · EVDO · HSPA · HDLC · PPP · PPTP · L2TP · ISDN · ARCnet · LLTD · (more) 1. Physical layer Ethernet physical layer · RS-232 · SONET/SDH · G.709 · Optical fiber · Coaxial cable · Twisted pair ·
INTERNET The Internet, sometimes called simply "the Net," is a worldwide system of computer networks - a network of networks in which users at any one computer can, if they have permission, get information from any other computer (and sometimes talk directly to users at other computers). It was conceived by the Advanced Research Projects Agency (ARPA) of the U.S. government in 1969 and was first known as the ARPANET. The original aim was to create a network that would allow users of a research computer at one university to be able to "talk to" research computers at other universities. A side benefit of ARPANet's design was that, because messages could be routed or rerouted in more than one direction, the network could continue to function even if parts of it were destroyed in the event of a military attack or other disaster. Today, the Internet is a public, cooperative, and self-sustaining facility accessible to hundreds of millions of people worldwide. Physically, the Internet uses a portion of the total resources of the currently existing public telecommunication networks. Technically, what distinguishes the Internet is its use of a set of protocols called TCP/IP (for Transmission Control Protocol/Internet Protocol). Two recent adaptations of Internet technology, the intranet and the extranet, also make use of the TCP/IP protocol. For many Internet users, electronic mail (e-mail) has practically replaced the Postal Service for short written transactions. Electronic mail is the most widely used application on the Net. You can also carry on live "conversations" with other computer users, using Internet Relay Chat (IRC). More recently, Internet telephony hardware and software allows real-time voice conversations. The most widely used part of the Internet is the World Wide Web (often abbreviated "WWW" or called "the Web"). Its outstanding feature is hypertext, a method of instant cross-referencing. In most Web sites, certain words or phrases appear in text of a different color than the rest; often this text is also underlined. When you select one of these words or phrases, you will be transferred to the site or page that is relevant to this word or phrase. Sometimes there are buttons, images, or portions of images that are "clickable." If you move the pointer over a spot on a Web site and the pointer changes into a hand, this indicates that you can click and be transferred to another site. Using the Web, you have access to millions of pages of information. Web browsing is done with a Web browser , the most popular of which are Microsoft Internet Explorer and Netscape Navigator. The appearance of a particular Web site may vary slightly depending on the browser you use. Also, later versions of a particular browser are ab le to
render more "bells and whistles" such as animation, virtual reality, sound, and music files, than earlier versions.
INTRANET - An intranet is a private network that is contained within an enterprise. It may consist of many interlinked local area networks and also use leased lines in the wide area network . Typically, an intranet includes connections through one or more gateway computers to the outside Internet. The main purpose of an intranet is to share company information and computing resources among employees. An intranet can also be used to facilitate working in groups and for teleconferences. An intranet uses TCP/IP, HTTP, and other Internet protocols and in general looks like a private version of the Internet. With tunneling, companies can send private messages through the public network, using the public network with special encryption/decryption and other security safeguards to connect one part of their intranet to another. Typically, larger enterprises allow users within their intranet to access the public Internet through firewall servers that have the ability to screen messages in bo th directions so that company security is maintained. When part of an intranet is made accessible to customers, partners, suppliers, or others outside the company, that part bec omes part of an extranet.
Bandwidth Bandwidth can mean different things in the related fields of computer networks, communication theory, signal processing, and linear algebra. (The first two meanings are related by the Shannon–Hartley theorem.) •
• •
Bandwidth (signal processing) – a measure of the width of a range of frequencies, measured in hertz Bandwidth (computing) – a rate of data transfer, measured in bits per second Bandwidth of a sparse matrix – the distribution of nonzero terms around the diagonal of a matrix
IP address The five-layer TCP/IP model
5. Application layer
DHCP · DNS · FTP · Gopher · HTTP · IMAP4 · IRC · NNTP · XMPP · POP3 · RTP · SIP · SMTP · SNMP · SSH · TELNET · RPC · RTCP · RTSP · TLS (and SSL) · SDP · SOAP · GTP · STUN · NTP · (more) 4. Transport layer TCP · UDP · DCCP · SCTP · RSVP · ECN · (more) 3. Network/internet layer IP (IPv4 · IPv6) · OSPF · IS-IS · BGP · IPsec · ARP · RARP · RIP · ICMP · ICMPv6 · IGMP · (more) 2. Data link layer 802.11 (WLAN) · 802.16 · Wi-Fi · WiMAX · ATM · DTM · Token ring · Ethernet · FDDI · Frame Relay · GPRS · EVDO · HSPA · HDLC · PPP · PPTP · L2TP · ISDN · ARCnet · LLTD · (more) 1. Physical layer Ethernet physical layer · RS-232 · SONET/SDH · G.709 · Optical fiber · Coaxial cable · Twisted pair · (more) This box: view • talk • edit
An IP address (or Internet Protocol address) is a unique address that certain electronic devices use in order to identify and communicate with each other on a computer network utilizing the Internet Protocol standard (IP)—in simpler terms, a computer address. Any participating network device—including routers, switches, computers, infrastructure servers (e.g., NTP, DNS, DHCP, SNMP, etc.), printers, Internet fax machines, and some telephones —can have its own address that is unique within the scope of the specific network. Some IP addresses are intended to be unique within the scope of the global Internet, while others need to be unique only within the scope of an enterprise. The IP address acts as a locator for one IP device to find another and interact with it. It is not intended, however, to act as an identifier that always uniquely identifies a particular device. In current practice, an IP address is not always a unique identifier, due to technologies such as dynamic assignment and network address translation. IP addresses are managed and created by the Internet Assigned Numbers Authority (IANA). The IANA generally allocates super-blocks to Regional Internet Registries, who in turn allocate smaller blocks to Internet service providers and enterprises.
IP versions The Internet Protocol (IP) has two versions currently in use (see IP version history for details). Each version has its own definition of an IP address. Because of its prevalence, "IP address" typically refers to those defined by IPv4.
An illustration of an IP address (version 4), in both dot-decimal notation and binary.
IP version 4 addresses IPv4 only uses 32- bit (4- byte) addresses, which limits the address space to 4,294,967,296 (232) possible unique addresses. However, many are reserved 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 as public Internet addresses, and as the number of addresses available is consumed, an IPv4 address shortage appears to be inevitable in the long run. This limitation has helped stimulate the push towards IPv6, which is currently in the early stages of deployment and is currently the only contender to replace IPv4. IPv4 addresses are usually represented in dotted-decimal notation (four numbers, each ranging from 0 to 255, separated by dots, e.g. 147.132.42.18). Each range from 0 to 255 can be represented by 8 bits, and is therefore called an octet . It is possible, although less common, to write IPv4 addresses in binary or hexadecimal. When converting, each octet is treated as a separate number. (So 255.255.0.0 in dot-decimal would be FF.FF.00.00 in hexadecimal.)
IPv4 address networks Currently, three classes of networks are commonly used. These classes may be segregated by the number of octets used to identify a single network, and also by the range of numbers used by the first octet. •
•
•
Class
Class A networks (the largest) are identified by the first octet, which ranges from 1 to 126.(127 is reserved for loopback) Class B networks are identified by the first two octets, the first of which ranges from 128 to 191. Class C networks (the smallest) are identified by the first three octets, the first of which ranges from 192 to 223.
Range of first octet
Network
Host Possible number of Possible number
ID
ID
networks
of hosts
A
1 - 126 (127 is reserved a for loopback)
b.c.d
126 = (2 - 2)
16,777,214 = (224 2)
B
128 - 191
a.b
c.d
16,382 = (214 - 2)
65,534 = (216 - 2)
C
192 - 223
a.b.c
d
2,097,150 = (221 - 2) 254 = (28 - 2)
7
Some first-octet values have special meanings: •
•
First octet 127 represents the local computer, regardless of what network it is really in. This is useful when testing internal operations. First octet 224 and above are reserved for special purposes such as multicasting.
Octets 0 and 255 are not acceptable values in some situations, but 0 can be used as the second and/or third octet (e.g. 10.2.0.100). A class A network does not necessarily consist of 16 million machines on a single network, which would excessively burden most network technologies and their administrators. Instead, a large company is assigned a class A network, and segregates it further into smaller sub-nets using Classless Inter-Domain Routing. However, the class labels are still commonly used as broad descriptors.
IPv4 private addresses Machines not connected to the outside world (e.g. factory machines that communicate with each other via TCP/IP) need not have globally-unique IP addresses. Three ranges of IPv4 addresses for private networks, one per class, were standardized by RFC 1918; these addresses will not be routed, and thus need not be coordinated with any IP address registrars.
IANA Reserved Private Network Ranges Start of range
End of range
The 24-bit Block
10.0.0.0
10.255.255.255
The 20-bit Block
172.16.0.0
172.31.255.255
The 16-bit Block
192.168.0.0
192.168.255.255
Each block is not necessarily one single network, although it is possible. Typically the 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).
An illustration of an IP address (version 6), in hexadecimal and binary.
IP version 6 addresses IPv6 is a new standard protocol intended to replace IPv4 for the Internet. Addresses are 128 bits (16 bytes) wide, which, even with a generous assignment of netblocks, will more than suffice for the foreseeable future. In theory, there would be exactly 2128, or about 3.403 × 1038 unique host interface addresses. Further, this large address space will be sparsely populated, which makes it possible to ag ain encode more routing information into the addresses themselves. Example: 2001:0db8:85a3:08d3:1319:8a2e:0370:7334 Writing for Technology Review in 2004, Simson Garfinkel wrote notes that there will exist "roughly 5,000 addresses for every square micrometer of the Earth's surface".[1] This enormous magnitude of available IP addresses will be sufficiently large for the indefinite future, even though mobile phones, cars and all types of personal devices are coming to rely on the Internet for everyday purposes. The above source, however, involves a common misperception about the IPv6 architecture. Its large address space is not intended to provide unique addresses for every possible point. Rather, the addressing architecture is such that it allows large blocks to be assigned for specific purposes and, where appropriate, aggregated for providing 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). Windows Vista, Apple Computer 's Mac OS X, and an increasing range of Linux distributions include native support for the protocol, but it is not yet widely deployed elsewhere.
IPv6 private addresses Just as there are addresses for private, or internal networks in IPv4 (one example being the 192.168.0.0 - 192.168.255.255 range), there are blocks of addresses set aside in IPv6 for private addresses. Addresses starting with FE80: are called link-local addresses and are routable only on your local link area. This means that if several hosts connect to each other through a hub or switch then they would communicate through their link-local IPv6 address. Early designs specified an address range used for "private" addressing, with prefix FEC0. These are called site-local addresses (SLA) and are routable within a particular site, analogously to IPv4 private addresses. Site-local addresses, however, have been deprecated by the IETF, since they create the same problem that does the existing IPv4 private address space (RFC 1918). With that private address space, when two sites need to communicate, they may have duplicate addresses that "combine". In the IPv6 architecture, the preferred method is to have unique addresses, in a range not routable on the Internet, issued to organizations (e.g., enterprises). The preferred alternative to site-local addresses are centrally assigned unique local unicast addresses (ULA). In current proposals, they will start with the prefix FC00. Neither ULO nor SLA nor link-local address ranges are routable over the internet.
IP address subnetting Both IPv4 and IPv6 addresses utilize subnetting, or dividing the IP address into two parts: the network address and the host address. By using a subnet mask , the computer can determine where to split the IP address.
Static and dynamic IP addresses When a computer uses the same IP address every time it connects to the network, it is known as a Static IP address. In contrast, in situations when the computer's IP ad dress changes frequently (such as when a user logs on to a network through dialup or through shared residential cable) it is called a Dynamic IP address.
Classful network Classful networking is the name given to the first round of changes to the structure of the IP address in IPv4.
Classful networking is obsolete on the modern Internet. There is no longer any such thing as a class A/B/C network. The correct modern representation for what would have been referred to as a "Class B" prior to 1993 would be "a set of /16 addresses", under the Classless Inter-Domain Routing (CIDR) system.
Before Classes The prototype Internet in 1982; note that all the networks (the ovals) have addresses which are single integers; the rectangles are switches. Originally, the 32-bit IPv4 address consisted simply of an 8-bit network number field (which specified the particular network a host was attached to), and a rest field, which gave the address of the host within that network. This format was picked before the advent of local area networks (LANs), when there were only a few, large, networks such as the ARPANET. This resulted in a very low count (256) of network numbers being available, and very early on, as LANs started to appear, it became obvious that that would not be enough.
Classes As a kludge, the definition of IP addresses was changed in 1981 by RFC 791 to allow three different sizes of the network number field (and the associated rest field), as specified in the table below:
Class
Leading Bit String
Size of Network Size of Rest Bit field Number Bit field
Class A
0
8
24
Class B
10
16
16
Class C
110
24
8
Class D (multicast)
1110
not defined
not defined
Class E (reserved)
1111
not defined
not defined
This allowed the following population of network n umbers (excluding addresses consisting of all zeros or all ones, which are not allowed):
Class Leading Bit String Number of Networks Addresses Per Network
Class A
0
127
16,777,214
Class B
10
16,384
65,534
Class C
110
2,097,152
254
The number of valid networks and hosts available is always 2 N - 2 (where N is the number of bits used, and the subtraction of 2 adjusts for the invalidity of the first and last addresses). Thus, for a class C address with 8 bits available for hosts, the number of hosts is 254. The larger network number field allowed a larger number of networks, thereby accommodating the continued growth of the Internet. The IP address netmask (which is so commonly associated with an IP address today) was not required because the mask length was part of the IP address itself. Any network device could inspect the first few bits of a 32-bit IP address to see which class the address belonged to. The method of comparing two IP address's physical networks did not change, however (see subnet). For each address, the network number field size and its subsequent value were determined (the rest field was ignored). The network numbers were then compared. If they matched, then the two addresses were on the same network.
Class ranges The address ranges used for each class are given in the following table, in the standard dotted decimal notation.
Class
Leading bits
Start
CIDR equivalent
End
Default subnet mask
Class A
0
0.0.0.0 127.255.255.255 /8
255.0.0.0
Class B
10
128.0.0.0 191.255.255.255 /16
255.255.0.0
Class C
110
192.0.0.0 223.255.255.255 /24
255.255.255.0
Class D (multicast)
1110
224.0.0.0 239.255.255.255 /4
not defined
Class E (reserved)
1111
240.0.0.0 255.255.255.255 /4
not defined
Special ranges Some addresses are reserved for special uses (RFC 3330).
Addresses
0.0.0.0 0.255.255.255
10.0.0.0 10.255.255.255
127.0.0.0 127.255.255.255
169.254.0.0 169.254.255.255
CIDR Equivalent
Purpose
RFC
Class
Total # of addresses
0.0.0.0/8
Zero Addresses
RFC 1700 A
16,777,216
10.0.0.0/8
Private IP addresses
RFC 1918 A
16,777,216
127.0.0.0/8
Localhost Loopback Address
RFC 1700 A
16,777,216
169.254.0.0/16 Zeroconf /
RFC 3330 B
65,536
APIPA
172.16.0.0 172.31.255.255
192.0.2.0 192.0.2.255
192.88.99.0 192.88.99.255
192.168.0.0 192.168.255.255
198.18.0.0 198.19.255.255
224.0.0.0 239.255.255.255
240.0.0.0 255.255.255.255
172.16.0.0/12 *
Private IP addresses
RFC 1918 B
1,048,576
192.0.2.0/24
Documentation and Examples
RFC 3330 C
256
192.88.99.0/24
IPv6 to IPv4 relay Anycast
RFC 3068 C
256
RFC 1918 C
65,536
192.168.0.0/16 Private IP * addresses
198.18.0.0/15 *
Network Device RFC 2544 C Benchmark
131,072
224.0.0.0/4
Multicast
RFC 3171 D
268,435,456
Reserved
RFC 1700, Fuller 240/4 E space draft[1]
268,435,456
240.0.0.0/4
*
Note that these ranges listed were originally defined as consecutive network blocks and their "CIDR Equivalent" notation makes them appear to be in the wrong "Class". While nowadays CIDR allows to use this range as a Class B subnet, some network hard- and software still has hard-coded limitations which still prevent use of subnets other than Class C size.
HUB A network hub or concentrator is a device for connecting multiple twisted pair or fiber optic Ethernet devices together, making them act as a single network segment. Hubs
work at the physical layer (layer 1) of the OSI model, and the term layer 1 switch is often used interchangeably with hub. The device is thus a form of multiport repeater . Network hubs are also responsible for 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 legacy 10BASE2 or 10BASE5 network segments. The availability of low-priced network switches has largely rendered hubs obsolete but they are still seen in older installations and more specialized applications.
A hubbed Ethernet network behaves like a shared-medium, that is, only one device can successfully transmit at a time and each host remains responsible for collision detection and retransmission. With 10BASE-T and 100BASE-T links (which generally account for most or all of the ports on a hub) there are separate pairs for transmit and receive but they are used in half duplex mode in which they still effectively behave like shared medium links (See 10BASE-T for the pins specifications) A network hub or repeater, is a fairly unsophisticated broadcast device. Hubs do n ot manage any of the traffic that comes through them, and any packet entering any port is broadcast out on every other port (other than the port of entry). Since every packet is being sent out through every other port, 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 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 segment. Even if not partitioned automatically, a 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.
Uses Historically, the main reason for purchasing hubs rather than switches was its price. This has largely been eliminated by reductions in the price of switches, but hubs can still be useful in special circumstances: •
•
•
•
A protocol analyser connected to a switch does not always receive all the desired packets since the switch separates the ports into different segments. Connecting the protocol analyzer to a hub allows it to see all the traffic on the segment. (Expensive switches can be configured to allow one port to listen in on traffic on another port. This is called port mirroring. However, these cost much more than a hub.) Some computer clusters require each member computer to receive all of the traffic going to the cluster. A hub will do this naturally; using a switch requires implementing special tricks. 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 cheap hub with a 10BASE2 port is probably the cheapest and easiest way to connect devices that only support 10BASE2 to a modern network (cheap switches don't tend to come with 10BASE2 ports). 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 AUI10BASE-T transceiver ).
Network switch
A network switch is a computer networking device that connects network segments. In the past, it was faster to use Layer 2 techniques to switch, when only MAC addresses could be looked up in content addressable memory (CAM). With the advent of ternary CAM (TCAM), it was equally fast to look up an IP address or a MAC address. TCAM is expensive, but very appropriate for enterprise switches that use default routes plus a moderate number of other routes. For routers that need a full Internet routing table, TCAM may not be cost-effective. The first Ethernet switch was introduced by Kalpana in 1989. [1]
Function As with hubs, Ethernet implementations of network switches support either 10/100 Mbit/s or 10/100/1000 Mbit/s ports Ethernet standards. Large switches may have 10 Gbit/s ports. Switches differ from hubs in that they can have ports of different speed. 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-purpose converged device such as gateway access to small office/home office broadband services such as DSL router or cable, WiFi 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.
Role of switches in networks Network switch is a marketing term rather than a technical one. Switches may operate at one or more OSI layers, including physical, data link , network , or transport (i.e., end-toend). A device that operates simultaneously at more than one of these layers is called a multilayer switch, although use of the term is diminishing. In switches intended for commercial use, built-in or modular interfaces makes it possible to connect different types of networks, for example Ethernet, Fibre Channel, ATM, and 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. Again, "switch" is principally a marketing term; interconnection of different Layer 3 networks is done by routers. If there are any features that characterize "Layer-3 switches" as opposed 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 much analysis of network performance and security, switches may be connected between WAN routers as places for analytic modules. Some vendors provide firewall,[2][3] network intrusion 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 systems and packet sniffers.
Managed or unmanaged switching This option determines the level of control you can have over your network, including the degree of security that your business wants for its networked data and communications. Managed switches offer more control; they also usually require more technical expertise. If you have multiple LANs and switches, you may decide to manage some of them and not others. Unmanaged switches are preconfigured to satisfy most small business needs and can be set up quickly, making them appropriate for simple LAN connections. Managed switches provide control capabilities that can increase LAN security and performance, and let you segment traffic. For example, you could allow only certain employees access to your finance applications. You could also give certain ap plications more bandwidth, or ensure that video and voice communications take priority over other types of traffic.
Router A router (pronounced /'rautər/ in the USA and Australia, and pronounced /'ru:tər/ in the UK) is a computer whose software and hardware are usually tailored to the tasks of routing and forwarding information. Routers generally contain a specialized operating system (e.g. Cisco's IOS or Juniper Networks JUNOS and JUNOSe or Extreme Networks XOS), RAM, NVRAM, flash memory, and one or more processors. High-end routers contain many processors and specialized Application-specific integrated circuits (ASIC) and do a great deal of parallel processing. Chassis based systems like the Nortel MERS8600 or ERS-8600 routing switch, (pictured right) have multiple ASICs on every module and allow for a wide variety of LAN, MAN, METRO, and WAN port technologies or other connections that are customizable. Much simpler routers are used where cost is important and the demand is low, for example in providing a home internet service. With appropriate software (such as SmoothWall, XORP or Quagga), a standard PC can act as a router. 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 switch often is used interchangeably with router, but switch is really a general term without a rigorous technical definition. In marketing usage, it is generally optimized for Ethernet LAN interfaces and may not have other physical interface types. 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 send ing a packet received on a logical interface to an outbound logical interface.
Modem Modem (from modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used over any means of transmitting analog signals, from driven diodes to radio.
The most familiar example is a voiceband modem that turns the digital 1s and 0s of a personal computer into sounds that can be transmitted over the telephone lines of Plain Old Telephone Systems (POTS), and once received on the other side, converts those 1s and 0s back into a form used by a USB, Serial, or Network connection. Modems are generally classified by the amount of data they can send in a given time, normally measured in bits per second, or "bps". They can also be classified by Baud, the number of times the modem changes its signal state per second. Baud is NOT the modem's speed. The baud rate varies, depending on the modulation technique used. Original Bell 103 modems used a modulation technique that saw a change in state 300 times per second. They transmitted 1 bit for every baud, and so a 300 bit/s modem was also a 300-baud modem. However, casual computerists confused the two. A 300 bit/s modem is the only modem whose bit rate matches the baud rate. A 2400 bit/s modem changes state 600 times per second, but due to the fact that it transmits 4 bits for each baud, 2400 bits are transmitted by 600 baud, or changes in states. Faster modems are used by Internet users every day, notably cable modems and ADSL modems. In telecommunications, "radio modems" transmit repeating frames of data at very high data rates over microwave radio links. Some microwave modems transmit more than a hundred million bits per second. Optical modems transmit data over optical fibers. Most intercontinental data links now use optical mode ms transmitting over undersea optical fibers. Optical modems routinely have data rates in excess of a billion (1x109) bits per second. One kilobit per second (kbit/s or kb/s or kbps) as used in this article means 1000 bits per second and not 1024 bits per second. For example, a 56k modem can transfer data at up to 56,000 bits per second over the phone line.
Straight - Cross - Rollover Cable Straight - Cross - Rollover Cable Straight-through cable A straight-through cable is the standard network cable connection and is used to connect the source and destination computers through an internetworking device.
Specifically, you can use it to connect a host to a hub or switch. Crossover cable In a crossover cable, the standard RJ-45 cable between the source and destination computers is cross-connected. A crossover cable can be used to connect: * Two computers * Two hubs * A hub to a switch * A cable modem to a router * Two router interfaces Rollover cable These Cisco proprietary cables used to connect to a router or switch console port. In a rollover cable (8 pins), RJ-45 connectors are usually present at each ends and are used to connect router and computer ports. Pin 1 on one end of cable connects to Pin 8 at the other end of the cable, similarly, Pin 2 connects Pin 7, and so on.
What is a Leased Line A leased line is a permanent, always on connection between two locations. It is a dedicated, private line and only carries communications and traffic from your company, resulting in a guaranteed level of service. The line can be used for data, video and voice and is most effective when sharing bandwidth hungry applications between different offices. High speed connections up to 1Gig are available.
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Companies with separate office locations that regularly share a lot of data
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Companies with separate office locations who want to use VoIP
What benefits would a Leased Line bring my business? •
Cost effective for heavy Internet users
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High speed data throughput
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Private point-to-point connection, with no contention ratios
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Fixed charges regardless of usage, allowing accurate budgeting
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A guaranteed high level of service with vastly reduced latency and jitter
ISDN ISDN [I*SD'N] n. 1. Integrated Services Digital Network. 2. A digital telephone service that provides fast, accurate data transmission over existing copper telephone wiring. 3. The way fast way to go online. The Basics
ISDN is based on a number of fundamental building blocks. First, there are two types of ISDN "channels" or communication paths: •
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B-channel The Bearer ("B") channel is a 64 kbps channel which can be used for voice, video, data, or multimedia calls. B-channels can be aggregated together for even higher bandwidth applications. D-channel The Delta ("D") channel can be either a 16 kbps or 64 kbps channel used primarily for communications (or "signaling") between switching equipment in the ISDN network and the ISDN equipment at your site.
These ISDN channels are delivered to the user in one of two pre-defined configurations: •
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Basic Rate Interface (BRI) BRI is the ISDN service most people use to connect to the Internet. An ISDN BRI connection supports two 64 kbps B-channels and one 16 kbps D-channel over a standard phone line. BRI is often called "2B+D" referring to its two B-channels and one D-channel. The D-channel on a BRI line can even support low-speed (9.6 kbps) X.25 data, however, this is not a very popular application in the United States. Primary Rate Interface (PRI) ISDN PRI service is used primarily by large organizations with intensive communications needs. An ISDN PRI connection supports 23 64 kbps B-channels and one 64 kbps D-channel (or 23B+D) over a high speed DS1 (or T-1) circuit. The European PRI configuration is slightly different, supporting 30B+D.
BRI is the most common ISDN service for Internet access. A single BRI line can support up to three calls at the same time because it is comprised of three channels (2B+D). Two voice, fax or data "conversations," and one packet switched data "conversation" can take place at the same time. Multiple channels or even multiple BRI lines can be combined into a single faster connection depending on the ISDN equipment you have. Channels can be combined as needed for a specific application (a large multimedia file transfer, for example), then broken down and reassembled into individual channels for different applications (normal voice or data transmissions). What Do I Use It For?
