Internet
Raghudathesh G P
Asst Professor
MULTIMEDIA COMMUNICATION COMMUNICATION (VTU) - 10EC841 1 0EC841 U N I T – 6:
The Internet: Introduction, IP Datagram, Fragmentation, IP Address, ARP and RARP, QoS Support, IPv6. 7 Hours TEXT BOOK:
1. Multimedia Communications: Applications, Networks, Protocols and Standards , Fred Halsall, Pearson Education, Asia, Second Indian reprint 2002. REFERENCE BOOKS:
1. “Multimedia Fundamentals: Vol 1 - Media Coding and Content Processing” , Ralf Steinmetz, Klara Narstedt, Pearson Education, 2004. Special Thanks To:
1. Ramisuniverse for providing providing free e-material. e-material. 2. Gururaj E for providing Images in this material. PREPARED PREP ARED BY:
RAGHUDATHESH G P Asst Professor ECE Dept, GMIT Davangere 577004 Cell: +917411459249 Mail:
[email protected]
Quotes from Great People :
The future belongs to those who believe in the beauty of their dreams.
Have a heart that never hardens, and a temper that never tires, and a touch that never hurts.
The next best thing to solving a problem is finding some humor in it.
The greatest barrier to success is the fear of failure.
Keep challenging yourself to think better, do better and be better.
The ordinary person spends their best hours on entertainment and extraordinary person spends them on self-education.
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Internet
Raghudathesh G P
Asst Professor
THE INTERNET INTRODUCTION (Operation of Internet):
It’s a global network that supports a variety of interpersonal and interactive multimedia
applications.
User gains access to these t hese applications applications by means of an end system referred as host.
Ex.: Multimedia PC, a network computer, or a workstation
Internet comprises a large number of different access networks which are interconnected together by means of a global internetwork.
Gateway:
1. Associated with each access network – ISP ISP network, intranet, enterprise network, site/campus site/campus LAN and so on. o n. 2. Is a regional, national, and international, networks all of which are interconnected together using high bi b it rate leased lines and devices (known as routing gateways or routers).
Internet: Operates in a packet-switched mode Figure below Shows the protocol stack
associated with it.
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Asst Professor
interface card in all hosts that are attached attached to an access Assumption (in Fig.): Network interface network communicate with other ot her hosts using using the TCP/IP T CP/IP protocol stack.
In general various access networks have different operational parameters associated with them: 1. Bit rate 2. Frame format 3. Maximum frame size 4. Type of o f addresses that that are used
a token ring LAN uses a different bit rate, frame Ex.: In the case of a site/campus LAN – a format, and maximum frame size from an Ethernet LAN. Therefore, since, bridges can only be used to interconnect LAN segments of the same type; they cannot be used to perform the network interconnection interconnection function. function.
Functions of Network Layer:
1. Routing 2. Forwarding
As in figure to transfer packets of information from one host to another – IP IP in two hosts and IP in each Internet gateway and router involved, that performs the routing and other coordination coordination functions functions necessary.
Internet address (IP address): IP in each host that communicates directly over the
Internet has a unique Internet-wide address assigned to it.
Each IP has 2 parts:
1. network identifier (netid) 2. host identifier (hosted)
InterNIC (Internet Network Information Center):
1. Allocates netids and is managed centrally. 2. Each access network has a unique netid assigned to it.
Ex.: Each campus/site LAN is assigned a single netid.
IP address of a host attached to an access network contains the unique netid of the access network and a unique hosted.
Local administrator of the access network to which host is attached centrally allocated hosted by this time.
IP provides a connectionless best-effort service to the transport layer .
Transport layer has two protocol protoco l associated with with it: 1. Transmission Transmission Control Contro l Protocol (TCP) 2. User Datagram Protocol (UDP)
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Raghudathesh G P
Asst Professor
When either protocol has a block of information to transfer – it is send to the local IP together with the IP address of the intended recipient. recipient.
Operation of Source IP:
1. Source IP Adds the destination and source IP addresses to the head of the block, together with the indication of the source protocol (TCP or UDP), which forms IP datagram. 2. IP then sends datagram to its local gateway datagram is here called as packet.
Every Access gateway is attached to an internetwork router and at regular intervals IP in these routers exchange routing information.
After this each router build the routing table which enables to route a packet/datagram to any of the t he other networks/netids networks/netids that make up the Internet.
On receipt of a packet , router simply simply reads the destination netid from the packet header and uses the contents of its routing table to forward the packet on the path/route through the global internetwork first to the destination internetwork router and, from there, to the destination destination access gateway.
Assumption: Size of the packet is equal to or less than the maximum frame size of the
destination access network.
On receipt of the packet, destination gateway reads the hosted part of the destination IP address and forwards the packet to the local host identified by the hosted part.
IP in the host then strips off the header from the packet and passes the block o f information information contained within it called payload to the peer transport layer protocol indicated in the packet header.
If size of the packet > maximum frame size ( Max. Transmission Unit – MTU – MTU) of the destination access network IP in the destination gateway proceeds to divide the block of information contained in the packet into a number of smaller blocks each known as fragment .
Each fragment fragment is forwarded to the t he IP in the destination host in a separate packet the length of which is determined by the MTU of the access network.
Destination IP then, reassembles the fragments of the information from each received packet to form the t he original submitted block block of information information and passes this to the peer transport layer protocol indicated in the packet header.
Adjunct protocols : IP uses a number these protocols to perform its functions Figure below
Shows these adjunct adjunct protocols: protocols:
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1. ARP and RARP ( Address Resolution Protocol and reverse ARP):
Used by the IP in hosts that are attached to a broadcast LAN (such as an Ethernet or token ring) to determi d etermine ne the physical MAC address of a host or or gateway given its IP address (ARP) and
For RARP, the reverse function.
2. OSPF protocol (Open Shortest Path First):
Example of a routing protocol.
Used in the global internetwork. Such protocols are present in each internetwork router.
Utilized to build up the contents of the routing table, used to route packets across the global internetwork.
3. ICMP (Internet control Message Protocol):
Used by the IP in a host or gateway.
Used to exchange error and other control messages with the IP in another host or gateway.
4. IGMP (Internet Group Management Protocol):
Used with multicasting.
Used to enable a host to send a copy of a datagram to the other hosts that are part of the same multicast multicast group.
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Asst Professor
IP DATAGRAMS:
IP is a connectionless protocol.
All user information is transferred in the payload part called datagram.
Header of datagram contains a number of fields – format format is shown in Figure below.
Version field:
1. Contains the version of the IP used to create the datagram. 2. Ensures that all systems – gateway, routers, and hosts, that process the datagram/packet during its transfer across the Internet to the destination host interpret the various fields correctly IPv4 (IP version 4) is current version number. 3. Header can be of variable length.
IHL (Intermediate Header Length) field:
1. Specifies the actual length of the header in multiples multiples of o f 32-bit words. 2. Minimum length without options is 5. 3. If datagram contains options these are multiples of 32 bits with any unused bytes filled with padding bytes. 4. IHL field is 4 bits so, maximum permissible length is 15.
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TOS (type of service) field:
1. Allows an application protocol/process to specify the relative priority (precedence) of the application data and the preferred attributes associated with the path to be followed. 2. Used by each gateway and router during the transmission and routing of the packet to transmit packets of higher priority first and to select a line/route that has the specified attributes should a choice be available. 3. For Ex.: If a route with a minimum delay is specified then given a choice of routes the line with the smallest delay associated with it should be chosen.
Total length filed:
1. Defines the total length of the initial datagram including the header and payload parts 16-bit field and hence, maximum length is 65535 bytes. 2. If the contents of the initial datagram need to be transferred in multiple smaller packets then the value in this t his field is used by the destination host to reassemble the t he payload contained within each smaller packet known as fragment into the original payload.
Identification field:
1. Each smaller packet contains the same value in this to enable the destination host to relate each received packet fragment to the same original datagram.
Flag bits:
Next 3 bits are flag bits of which 2 are currently used 1. don’t fragment or D-bit D -bit: First bit
Set by source host and is examined by routers.
Set of D-bit indicates packet should be transferred in its entirely or not at all.
2. more fragment or M-bit : Second bit
Used during the reassembly procedure associated with data transfers involving multiple smaller packets/fragments
Set to 1: In all but the t he last packet/fragment in which it is set to 0
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Raghudathesh G P
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Fragment offset:
1. Used by the same procedure to indicate the position of the first bye of the fragment contained within a smaller packet in relation to the original packet payload. 2. All fragments except the last one are in multiples of 8 bytes.
Time-to-live field:
1. Value of it defines the maximum time for which a packet can be in transit across the Internet. 2. Value is in second and is set by the IP in the source host. 3. It is then decremented in each gateway and router by a defined amount and when the value become zero, the packet is discarded. 4. This procedure allows the destination IP to wait a known maximum time for an outstanding packet fragment during the reassembly procedure. 5. In practice it is used primarily by routers to detect packets that are caught in loops. loo ps. 6. For the above reason therefore value is normally a hop way/router visited and should the value is zero discarding of packet.
protocol field:
1. Used to enable the destination IP to pass the payload within each received packet to the same (peer) protocol that sent the data. 2. This is an internal network layer protocol – such such as, ICMP, or a higher-layer protocol such as TCP or UDP.
Header Checksum:
1. Applies just to the header part of o f the datagram. 2. Is a safeguard against corrupted packets packet s being routed to incorrect destination. 3. Computed by treating each block of 16 bits as an integer and adding them all together using 1s complement arithmetic. 4. Checksum is then, the complement co mplement (inverse) of the 1s complement sum.
Source address and destination address:
1. Are internet wide IP addresses – of of the source and destination hosts respectively. respectively.
Options field:
add itional information information relating to: Used in selected datagram’s to carry additional
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Raghudathesh G P
Asst Professor
1. Security: Payload may be encrypted or be made accessible only to a specified user group contains fields to enable the destination to decrypt the payload and authenticate the sender. 2. Source routing: If known the actual path/route to be followed through the Internet may be specified in this field as a list list of o f gateways/router addresses 3. Loose source routing: Used to specify preferred routers in a path. pat h. 4. Route recording field: Used by each gateway/router visited during the passage of a packet through the Internet to record its address. Resulting list of addresses addres ses can then be used. 5. Stream identification: This field and source and destination addresses in the datagram header enables each gateway/router along the path followed by the packet to identify the stream/flow to which the packet belongs and, if necessary, give the packet precedence over other packets Ex.: include streams containing samples of speech or compressed video. 6. Time-stamp: If present, used by each gateway/router along the path followed by the packet to record the time it processed the packet.
FRAGMENT FRAGM ENTA ATION AND REASSEMBLY:
Fragmentation:
When the size of the packet is greater than the MTU of the destination access network or an intermediate network in the global internetwork the IP in the destination gateway or intermediate router divides the information received in the packet into a numb number er o f smaller blocks called as a s fragments. Each Fragment then, forwarded to the IP in the destination destination host ho st in a separate packet t he length of which is determined by the MTU of the access/intermediate access/intermediate network.
Reassembly:
IP in the destination host then, reassembles reassembles the fragments fragments of information information from each received packet to form the original submitted block of information. information. It then, passes this to peer transport layer protocol indicated in the protocol field of the packet header.
Various fields in the packet header are used to perform fragmentation and reassembly.
Scenario:
Consider the transport protocol in a host that is attached to a token ring LAN transferring a block of 7000 bytes including the transport protocol header over the Internet to the transport protocol in host that is attached to an Ethernet LAN.
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Raghudathesh G P
Asst Professor
Assume that MTU associated with the token ring LAN is 4000 bytes and that of Ethernet LAN 1500 bytes . Header of each IP datagram requires 20 bytes.
Steps taken to transfer the complete block of o f 7000 bytes are shown in Figure below.
Operational Steps:
Header of each datagra datagram m requires requires 20 bytes.
Maximum usable data in each token ring frame 4000 – 20 20 = 3980 398 0 bytes.
In each of Ethernet frame: 1500 – 20 20 = 1480 bytes.
All fragments of user data except the t he last one must be in multiples multiples of 8 bytes thus, Maximum user data in each packet transferred over the token ring to 3976 bytes.
For Ethernet LAN 1480 is divisible by 8 and so this value can be used unchanged.
For 7000 700 0 bytes data to transfer: transfer:
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Over token ring LAN – requires requires 2 datagrams.
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a) One with 3976 bytes of user data dat a and b) Second 7000 – 3976 3976 = 3024 bytes
Values for the various fields associated with the fragmentation and reassembly procedures in each datagram header are shown in in figure.
Value in the identification field:
Same in all fragments and is used by the destination IP to relate each fragment fragment to the t he same original block of information
Ex.: Assume a value of 20 has been allocated by the IP in the source host
Total length:
is the number of bytes in the initial datagram including 20-byte header
Since, 20 is subtracted from the maximum user data value associated with each LAN this is known as 7000
Note: It’s the same in all datagram fragments
Hence, the destination IP can readily determine when all fragments have been received. received.
Fragment offset:
Indicates the position of the user in each fragment in multiples of 8 bytes relative relative to the start of o f the initial initial datagram.
More fragments (M bit):
is 1 in each fragment and
0 in the final fragment
datagrams/packets created by the source IP are transferred over Assumption: Two datagrams/packets the global internetwork unchanged; on reaching the access gateway gat eway attached to the Ethernet LAN the smaller maximum user data value of 1480 bytes means that both packets must be be further further fragmented.
As in figure both packets must be fragmented into 3 smaller packets.
First into 2 maximum sized packets of 1480 bytes and a further packet containing containing 3976-2(1480)=1016 bytes and
The second containing 2 maximum sized packets and a further packet containing containing 3024-2(1480)=64 30 24-2(1480)=64 bytes. bytes.
IP in the destination destination host then reassembles the user data in each of the six packets it receives into the original 7000 byte block of information and delivers this to the peer transport transport protocol. protocol.
Time-to-live field:
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in each packet header and fragment header is present.
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To avoid packets endlessly looping around the Internet (normally as a result of routing table inconsistencies) and also to set a maximum limit on the time a host needs to wait for a delayed/corrupted/ discarded datagram fragment.
So, even though use of fragmentation would appear to be relatively straightforward there are drawbacks associated with w ith its use.
Ex.: With the TCP transport protocol if an acknowledgement of correct receipt of a
submitted block is not received within a defined maximum time limit, the source TCP will retransmit the complete block.
So, as in figure it only needs one of o f the six datagram fragments fragments to be delayed delayed or discarded to trigger the t he retransmission retransmission of the complete 7000-byte 7000-byte block. b lock.
As a result therefore, most TCP implementations avoid the possibility of fragmentation occurring by limiting the maximum submitted block size including transport protocol header to 1048 bytes or, in some instances, 556 bytes.
Alternatively it’s possible for the source IP prior to sending any transport protocol user data to determine the MTU of the path to be followed followed through the Internet. Then, if this is smaller than the submitted user data source IP fragments the data using this MTU and no further fragmentation should be necessary during the transfer of the packets through the global internetwork.
IP address:
The "IP" part of IP address stands for "Internet Protocol." The "address" part refers to a unique number that gets linked to all online activity you do.
Each host, gateway, and router has unique Internetwide IP address assigned to it.
IP address comprises a netid and a hostid part.
For gateways and routers: which interconnect 2 or more networks together each gateway/router port also referred to as an interface has a different netid associated with it.
To have for flexibility in assigning netids INIC (Internet Network Information Center) provides 3 different different address formats for unicast addresses as shown in the figure below. They are: 1. Class A 2. Class B 3. Class C
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Each of these classes is intended for use with a different size of network.
Ex.: At one extreme a large national network netwo rk and at the other a small site LAN.
Class to which an address belongs to can be determined determined from the position of the first zero bit bit in the first first four bits.
Remaining Remaining bits then, specifies the netid and hostid parts with the boundary separating separating the 2 parts located on byte boundaries boundaries to simplify simplify decoding.
Class A:
If the MSB bit (32nd ) is 0 then the address belongs to class A.
Have 7 bits for netid and 24 bits for hosted.
Intended for use with with networks that have a large large number of attached hosts hosts up to 224.
It covers 50% of the address space.
Range (dotted decimal): 0.0.0.0 to 127.0.0.0
Ex: large national network.
Class B:
If the first first 2 MSB bits are 1 and 0 then the address belongs to class class B.
Have 14 bits for netid and 16 bits for hosted.
Allows for a medium size networks each with number of attached hosts up to 16K.
It covers 25% of the address space.
Range (dotted decimal):128.0.0.0 to 191.0.0.0
Ex:
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Class C:
If the first 3 MSB bits are 1, 1 and 0 then the address belongs to class C.
Have 21 bits for netid and 8 bits for hosted.
Allows Allows for a large number of networks each with a small number of attached hosts up to 256.
It covers 12.5% of the address space.
Range (dotted decimal): 192.0.0.0 to 223.0.0.0
Ex: Small site LAN
Netid and hostids hosti ds comprising either all 0s or all 1s have special meaning:
An address with a hostid of all 0s is used to refer to the network in the netid part rather than a host
An address with with a netid of all 0s implies the same network as the source network/netid
An address of all 1s means broadcast the packet over the source network
An address with a host id of all 1s means broadcast the packet over the destination network in the netid part
A class A address with a netid of all 1s is used for test purposes within within the protocol proto col stack of the source host it is known as, loopback address
Dotted decimal notation:
To make it easier for communication 32 bits are first broken into 4 bytes. Each byte is then converted into its equivalent decimal form. Total IP address is represented – as the 4 decimal numbers with a dot (period) between each. Ex.: 00001010 00000000 0000000 0 00000000 00000000 = 10.0.0.0. = class A, netid 10 10000000 00000011 00000010 00000011 = 128.3.2.3 = class B, netid 128.3, hostid 2.3 11000000 00000000 00000001 11111111 = 192.0.1.255 = class C,all hosts broadcast broadcast on netid netid 192.0.1
Class D addresses:
Reserved for multicasting.
LAN in a frame can be sent to an individual, individual, broadcast, or group address. Group address is used by a station to send a copy of the frame to all stations that are members of the same multicast group and hence, have the same multicast address.
For the case o f LANs group address is a MAC address and the class D IP address format format is provided to enable enable this mode mode of working working to be extended extended over the complete complete Internet. Internet.
Unlike 3 unicast address classes 28-bit multicast group addresses has no further structure.
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IANA (Internet Assigned Numbers Authority) assign, the multicast group addresses.
Most of these assignments are dynamically dynamically (for conferences and so on) o n)
identify specific groups Permanent multicast group addresses: addresses are reserved to identify of hosts and/or routers.
Ex.: 224.0.0.1 – means means all hosts and routers on the same broadcast network
224.0.0.2 – means means all routers on the same site network
Subnets
The basic structure is adequate for most o f the addressing addressing purposes.
Introduction Introduction of multiple multiple LANs at each site can mean unacceptably high overheads in terms of routing.
MAC bridges are used to interconnect LAN segments of the same type.
This solution is attractive attractive for routing purposes since, the combined combined LAN then, behaves like a single network Interconnection of dissimilar LAN types the differences in frame format and frame length mean that routers are normally used since, the fragmentation and reassembly of packets/frames is a function of the network layer rather than the MAC sublayer.
Use of routers means with the basic address formats each LAN must have its own netid. For large sites there may be a significant number of such LANs.
With the basic addressing scheme all the routers relating to a site need to take part in the overall Internet routing function.
Efficiency of any routing scheme is strongly influenced by the number of routing nodes that make up the Internet. Internet.
Subnets: Concepts have been introduced to decouple the routers, and hence, routing
associated with a single site from the overall o verall routing function in the global internetwork.
Essentially Essentially instead of each LAN associated assoc iated with a site having its won netid only the site is allocated a netid, each LAN is then known as a subnet and the identity of each LAN subnet then forms part of the hostid field refined this address format is shown in Figure below (1)
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Same address classes and associated structure are used. Netid now relates relates to a complete complete site rather rather than to a single single subnet. Hence, since, only a single gateway/router gat eway/router attached to a site site performs internetwide routing the netid is considered as the Internet part.
For a single single netid with a number of associated subnets hostid hostid part consists consists of 2 subfields: subfields: 1. Sub-netid part 2. Local hostid part
These have only a local significance significance are known collecti co llectively vely as local part
To discriminate between the routers in the global internetwork and those in a local site network the latter are known as subnet routers.
Possibility Possibility of wide range of subnets associated with different different site networks no attempt has been made to define define rigid.
Subaddress boundaries for the local address part.
Address mask instead can be used for it.
Used to define the subaddress boundary for a particular network and hence netid.
Is kept by the site gateway and all the subnet routers at the site.
Consists of binary 1s in those bit positions that contain a network address including the netid and subnetid and binary 0s in positions that contain the hostid
Hence an address addre ss mask of
111111 111 11111 11 111 111111 11111 11 111 111111 11111 11 00000000 00000 000 means that the first first
3 bytes (octets) contain a network/subnet identifier and the fourth byte contains the host identifier.
For Ex.: If the mask relates to a class B address a 0 bit in the second bit position this is
readily interpreted as the first 2 bytes are the internetwide netid, next byte the subnetid, and last byte the hostid on the subnet.
Figure below (2) shows such an address
Dotted decimal is used to define the address masks hence, above mask is written: 255.255.255.0
Byte boundaries are no normally rmally chosen to simplify simplify address decoding
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With With this mask and assuming, the netid was say, say, 128.10, then all the hosts attached to this network would have this same netid.
Presence of a possibly large number o f subnets and associated subnet routers is transparent to all the other Internet gateways and routers for routing routing purposes.
ARP AND RARP:
These protocols are used by IP in hosts that are attached to a broadcast LAN. ARP:
Abbreviated as Address Resolution Protocol.
ARP Used to determine the MAC address of another host or gateway that is attached to
the same LAN given the IP address of the host gateway.
It is defined in RFC 826.
Each host is associated with 2 addresses: addresses: 1. IP address also known as logical address. 2. MAC address which, is assigned to the MAC integrated circuit when it is manufactured is known as the host’s hardware (or physical) address.
Normally, Normally, both addresses addresses are stored stored in the configuration configuration field field of the host on the hard disk. disk. describe the operati o peration on of o f the ARP. ARP. Figure below Shows the LAN topology to describe
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It comprises 3 Ethernet Ethernet hubs (H1, H2, and H3) which are interconnected by means of a 4th hub H4 and site gateway G are co nnected. nnected.
Assumption:
1. All the hubs are simple repeater hubs. 2. All hosts have just been switched on and hence, have sent no frames.
ARP cache(Definition): Routing table associated with each ARP.
ARP cache contains a list of the IP/MAC address-pairs of those hosts with which host A has recently communicated, and when the host is first switched on, it contains no entries.
Steps taken by ARP to send datagram in same and different LAN:
Two Scenarios:
Host A to send a datagram to another host on the same LAN host B and then to a host B on a different LAN via the gateway.
Scenarios1: host A sends a datagram to host B on the same LAN:-
1. On reception of first datagram from the IP in host A, ARP in A reads the destination IP address of B contained in the datagram header and determines it is not in its cache. Hence, it broadcasts an ARP request message in a broadcast frame over the LAN and waits for a reply. 2. Request message contains both its own IP/MAC address-pair and the (target) IP address of the destination, host B. This broadcast frame is received by the ARP in all hosts attached to the t he LAN. 3. ARP in host B recognizes its own IP address in the request message and proceeds to process it. An ARP first check to see whether the address-pair of the source is within its own cache and, if not, enters them. 4. Above is done, since it is highly probable that the destination host will require MAC address of the source when the higher-layer protocol responds to the message contained within the datagram payload. 5. ARP in host B then responds by returning an ARP reply message containing its own MAC address to the ARP in host A using the latter’s MAC address contained in the request message. 6. On receipt of the reply message: ARP in host A makes an entry of the requested IP/MAC address-pair in its own cache and then passes the waiting datagram to either the LLC sublayer (if one is present) present) or (if not) to the MAC sublayer together with the MAC address of host B which indicates where it should be sent. 7. At B the datagram is passed directly to the IP for processing. 8. Being on the same broadcast network as all the site hosts the LAN port of the gateway receives a cop y of all broadcast frames containing containing ARP request and reply messages.
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9. On receipt of each message the ARP first checks to see if it has the IP/MAC address-pair(s) contained in the message in its cache and if not, adds them to the cache. 10. In this way site gateway gat eway learns the address-pair of all the hosts that are attached to the site LAN.
Scenario 2: Datagram to send from host A to a host on a different LAN via the gateway:-
1. For this case the netid of the t he ARP in A broadcasts the request message. 2. Here on receipt of the message, the gateway determines that the netid part of the destination IP address relates to a different network and responds by returning a reply message containing its own address-pair. 3. Thus, A makes an entry of this in its cache and proceeds to forward the datagram to the gateway as if it was the destination host. 4. The gateway then forwards the datagram/packet over the Internet using one of the global internetwork routing protocols. 5. The ARP in the gate-way is known as a proxy ARP since it is acting as an agent for the ARP in the destination host. 6. When the gateway receives the response packet from the destination host, it reads the destination IP address from the header host A and obtains from its cache the MAC address of A. 7. It then transfers the packet to the IP in A using the services provided by the MAC sublayer. 8. A similar procedure is followed for bridged LANs and for router based LANs except that with the latter, the ARP in the subnet router that is connected to the same subnet as the source host acts as the proxy ARP. 9. In order to allow for hosts to change their network point of attachments, entries in the ARP cach timeout after a predefined time interval. RARP:
Abbreviated as Reverse Address Resolution Protocol.
Generally the IP/MAC address pair of a host is stored in the configuration file of the host on its hard disk.
But with diskless hosts, clearly this is not possible and hence the only address that is known is the MAC address of the MAC chipset. In such cases, therefore, the alternative reverse address resolution protocol (RARP) is used.
The server associated with a set of diskless hosts has a copy of the IP/MAC address-pair of all the hosts it serves in a configuration file.
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Asst Professor
When a diskless host first comes into service, it broadcasts a RARP request message containing the MAC address of the host ho st onto its local LAN segment.
Being a broadcast message, the server receives this and, on determining it is a RARP message, the MAC/LLC sublayer passes the message to the RARP.
The latter first uses the MAC address within it to obtain the related IP address from the configuration file and then proceeds to create a RARP reply message containing the IP address of the host and also a lso its own address-pair.
The server then sends the reply message back to the host and, once its own address-pair is known, the ARP in the diskless host can proceed as before.
ARP/RARP message formats and transmission:
As show in the figure above, the format of the ARP and RARP request and reply messages are the same both having a fixed length of 28 bytes.
Hardware address is used to refer to a MAC address.
Target is used to reffer the recipient of a request.
The hardware type field specifies the type of hardware (MAC) address contained within the message, for example 0001 (hex) in the case of an Ethernet.
The ARP and RARP can be used with other network protocols (as well as the IP) .
The protocol type indicates the type of network address being resolved.
Ex.: 0800 (hex) is used for IP addresses.
Department ECE,GMIT
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Page No - 20
Internet
Raghudathesh G P
Asst Professor
The HLEN and PLEN fields specify the size in bytes of the hardware (MAC) and protocol (IF) address lengths respectively. respectively.
Ex.: 06 (hez) for an Et hernet and 04 (ha) for the IP.
The operation field indicates whether the message (resolution operation) is an ARP request (0001) or reply (0002) or a RARP request (0003) or reply (0004).
The next four fields specify the hardware (MAC)/IP address-pair of the sender (source) and the target (destination).
Ex.: in an ARP request message just the address-pair of the sender is used while in the reply message all four addresses are used.
Both the ARP and RAM are integral parts of IP inasmuch as, once the MAC address relating to an IP address is present in the ARP cache, the IP can use this to initiate the transmission transmission of o f a datagram to its intended recipient directly.
Thus, on receipt of a frame, the receiving MAC/LLC sublayer must be able to determine to which protocol the frame contents should be sent: IP, ARP, or RARP.
To achieve above, when each of the protocols passes a message/datagram to the LLC/MAC sublayer for transmission, in addition to the MAC address of the intended recipient, it specifies the name of the (peer) protocol in the destination (IP/ARP/RARP) to which the message/datagram should be passed. pa ssed.
A two-byte type field which immediately precedes the message/datagram in the user data field of the MAC frame, the LLC sublayer is not used with the original Ethernet MAC standard and hence the type t ype field immediately follows the MAC source address (SA).
For 802.3 MAC standard, standard, the LLC sublayer is present and hence the field field immediately follows follows the 6 bytes required for the LLC protocol. protoco l.
The maximum frame length associated with the 802.3 standard (1500 bytes) means that the length indicator value in the header is always different from the three type field values.
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Page No - 21
Internet
Raghudathesh G P
Asst Professor
The receiving MAC sublayer can readily determine which of the two standards is being used and, therefore, where the type field is located. With a token ring LAN, since there is only one standard: this problem does not arise.
QoS support: Definition: Quality of Service (QoS) refers to the capability of a network to provide better
service to selected network traffic over various technologies, including Frame Relay, Asynchronous Transfer Mode (ATM), Ethernet and 802.1 networks, SONET, and IP-routed networks that may use any or all of these underlying technologies. Congestion arises within a network when the demand for a network resource exceeds the level
that is provided. E.x: if a burst of packets arrive at a router on a number of different input lines that all require the same output line, then the output line will become congested if the rate of arrival of packets a greater than the rate they can be output. In order to allow for above possibility each carpal one his a Fenno IMO/ queue anociated web a which is used to hold a defined packets that are mast* outpat on that Sr Hence, providing the born a relathelt shoo duration and the umber of o f packets to be queued is that the number of o f packet buffers availabk, the convince co nvince ma be ' and the t he ode effect *add be a mad Manor in the astkownd earlexperienced by each packet sting that Got. In the meet of a longer however, then an the packet butlers may become full madam a rank mans win have to he dneardcd Sart, at a nerwocknide km1. since the Istenset is a besteSott necticakm nemorL be global internerwork become osigetted 1( a sustained period. the aggregate rate at ittikh packets are etnining intereetymek exceeds it total capacity la term$ of transmission bshddf and packet toners. At ace an in Section 133. asocial! with each ail defined set of parameters inch form what is called the seitimunt gdtg strike IQoS) ropairensents for the call. For example. with a path rat bed network hie the Internet. these include a defined minima as packet throoehput raw and a maximum endtownd packet transfer del Hoare. las a remit of congestion thew requiremeatt sir me MO, dace gumbo of the ca!I ram no longer be acceptable to the tact This a dr with appbeaboos ntsolven real-use media streams, for example. loth Lawmen tek-pbom As we can conclude from he above. two loth Cl congestion control required. one that operates as the global interretuvek fief and the ad that ormases at the rouser kw+ The am of the first a to Inst the aggrrs rate at winch packet an entering the &OW, miernetevelt to Mime ita tat 1716113 rate. and the ate of the second n w masimae the Bow of pock through each mina la the fodomne subsernons ve dictum wend eo the schemes that are toed to per form these functions LI Integrated services Mon raft 11)0(31•00s of the Internet late tat hued and berate enenserne to
deb. a/Anne faanaks include FT? and email, both a can tokrate the added deans incurred ty the me of a hoetotem non emu& mechanism to overcome the effect of lost paclwo reatiiing fa the
Department ECE,GMIT
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Page No - 22
Internet
Raghudathesh G P
Asst Professor
ben-thou service provided by LP Other tee bad applications, ap plications, hoed cannot okra the dem de m caused by tereamaismons but omen/tries ngu naiumal packet loses (templet of rho ripe of appbcasim ate those nee to network coney:, More remedy a number of interpersonal applications involving pad toed vetch and video nor introduced Thew require the packet that generated at tbe sower to be crinderred owe the Internet aid pined the destinabon in real new Dm means that the tanowaisace of km sir
Question Bank(VTU): 1. With With respect to IP datagram datagram/packe /packett format, explain explain the role role of the following following fields: fields: a. IHL b. TOS c. To Tota tall Leng ength d. Flag bi bits. ts.
May/June 2010 (08 M)
2. What What is the meaning meaning of IP address address class? class? With With the help of a diagram diagram,, explai e xplain n the different different types of IP address formats.
May/June 2010 (08 M)
3. Explain Explain how RARP is used used to enable a diskles disklesss host to determi determine ne its own IP address address from from its local server.
May/June 2010 (04 M)
4. Write Write a protocol protocol stack stack of various various adjunct adjunct protocols protocols that is is used used by IP. December 2010 (05 M)
5. Explain Explain IP address address classes, classes, with with the help of a neat diagram. diagram. Identify Identify a particul particular ar application for each class.
December 2010 (05 M)
6. Descri Describe be the the operati operations ons of ARP ARP and RARP RARP.. December 2010 (10 M), June 2013 (10 M) 7. Explain Explain the operation operation of internet internet with with a neat diagram of protocol protocol associate associated d networking networking component. Also, explain IP adjunct protocols, protoco ls, with a neat diagram. December 2011 (10 M)
8. What What is QoS support support for internet internet applicati application? on? Explain Explain the control mechanism mechanism used used in each class to meet QoS requirement. req uirement.
December 2011 (08 M)
9. The administrator of a campus LAN is assigned a single class B IP address 150.10.0.0.
Assuming the LAN comprises 100 subnets, each of which is connected to FDDI backbone network, using a subnet su bnet router, define a suitable address mask for the site if the maximum number of hosts connected to each subnet is 70. December 2011 (02 M) 10. Explain Explain datagram, datagram, format format of IPV6.
June 2012 (10 M)
11. With example, explain fragmentation fragmentation and reassembly in in the internet. internet. June 2012 (10 M), June 2013 (10 M), December 2013 (10 M)
12. Explain IP datagram with packet format format and header fields. fields. December 2013 (10 M)
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Page No - 23
