1. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Chapter 3 Transport Layer

2. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Understand the position of the transport layer in the Internet model. Understand the rationale for the existence of the transport layer. Understand the concept of application-to-application delivery. Understand the duties of the transport layer: packetizing, addressing, connection creation, and reliable delivery. After reading this chapter, the reader should be able to: O BJECTIVES Know which application layer program can use UDP and which can use TCP. Distinguish between the two transport-layer protocols used in the Internet: UDP and TCP.

3. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. APPLICATION-TO-APPLICATIONDELIVERYAPPLICATION-TO-APPLICATIONDELIVERY 3.1

4. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 3-1 Transport layer in the Internet model

5. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 3-2 Application-to-application delivery

6. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. DUTIESDUTIES 3.2

7. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 3-3 Duties of the transport layer

8. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 3-4 Connection establishment

9. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 3-5 Connection termination

10. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Connection is closely related to reliability: A connectionless protocol cannot be reliable because the relationship between packets provides reliability. Note:

11. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 3-6 Application programs

12. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. The addresses of client and server programs are defined at the transport layer. These addresses are local to the computer running the programs. The addresses must be unique locally but not universally. Note:

13. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 3-7 Port numbers

14. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Technical Focus: Range of Port Numbers The port numbers range from 0 to 65535 and are divided into three ranges: Well-known ports: 0 to 1023 Temporary ports: 49,152 to 66,535 Registered ports: 1,024 to 49,151

15. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Business Focus: Well-Known Ports Some well-known port numbers are shown below: SMTP: 25 TFTP: 69 HTTP: 80 FTP: 20 and 21 TELNET: 23

16. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. A client uses a temporary port number; a server uses a well-known port number. Note:

17. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 3-8 Damage control

18. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. For reliable service, the transport layer needs to number packets belonging to a connection using sequence numbers. Note:

19. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. A reliable transport protocol provides damage control, loss control, order control, and duplicate control even if the underlying networking technology and lower-level protocols are not reliable. This is done through sequence numbers, timers, error detection, and retransmission. Note:

20. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. INTERNETPROTOCOLSINTERNETPROTOCOLS 3.3

21. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 3-9 UDP and TCP in the Internet model

22. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 3-10 User datagram

23. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Technical Focus: User Datagram The fields in a user datagram are as follows: Source port number Length Destination port number Checksum

24. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 3-11 Segment

25. McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Technical Focus: Segment The fields in a segment are as follows: Source port number Destination port number Sequence number Header length Control flags Checksum Option Urgent pointer