Data Communication Networks Lec 7

TCP/IP

Physical and Data Link Layers Do not define specific protocols. It supports all standards.

Network Layer TCP/IP supports internetworking protocols. ARP, RARP, ICMP and IGMP

Internetworking Protocol(IP) unreliable and connectionless protocol. No error checking or tracking. Data in packets called datagram. Can travel different routes and can arrive out-of-order.

Address Resolution Protocol(ARP) Use to associate logical address with physical address. In LAN , each device on link is identified by physical address. ARP is used to find the physical address of the node when its internet address is known.

Reverse Address Resolution Protocol(RARP) Allow a host to discover its internet address when it knows only its physical address.

Internet Control Message Protocol(ICMP) Use to send notifications of datagram problems back to the sender.

Internet Group Message Protocol(IGMP) Transmissions of a message to a group of recipients.

Transport Layer UDP TCP SCTP

Application Layer Combined session , presentation and application layer .

Addressing

Addresses in TCP/IP

Physical Address

Logical Address

Logical Address For universal communication that are independent of underlying physical networks. Physical addresses not adequate. Universal address needed. Fig show with two routers connecting three LANs. Each device , pair of addresses(logical and physical) Each router has three pair of addresses, one for each connection. Separate physical for each connection, and logical address(routing)

Logical Address Data to be send from A/10 to P/95. Sender encapsulate its data in a packet at network layer and address to logical address (A and P).

Logical Address The network layer find the physical address of the next hop before packet is delivered. N/L consult routing table, find logical address of next hop (router 1 ) to be F. ARP finds physical address of router 1 that corresponds to logical address of 20. Passed it to data link layer, which encapsulate the packet with physical destination address 20 and physical source address 10.

Logical Address Frame is received by every device on LAN 1, all discard except router1 , because destination physical address matches. The router decapsulates the packet to read logical destination address P. As logical address do not match with router logical address so need to be forwarded. The router consult its routing table and ARP to find physical address of the next hop(router2), create frame, encapsulate packet and send to router 2.

Logical Address Note, the source address changes from 10 to 99, and destination physical address changes from 20 (router 1 PA) to 33(router 2 PA). The logical source and destination addresses must remain same , otherwise packet will be lost.

Logical Address Router 2 same scenario. Physical address changed and new frame is send to destination computer. Destination logical address P matches the logical address of the computer. Data is decapsulated and delivered to upper layer.

Logical Address The physical address will change from hop to hop but the logical address usually remain same.

Port Address Computer A can communicate with computer C using TELNET At the same time, computer A communicate with computer B using FTP.

Port Address The transport layer encapsulates data from application layer in a packet and adds two source and destination port addresses. This packet will again encapsulated in another packet at network layer with logical S and D address. Finally S and D , addresses at data link layer.

Port Address

Port Address The physical addresses change from hop to hop, but the logical and port addresses usually remain the same.

Specific Address E-mail address URL (Universal Resource Locator) Recipient and WWW