1. Ensuring the Reliability of Data Delivery © 2004 Cisco Systems, Inc. All rights reserved. Understanding How UDP and TCP Work INTRO v2.0—6-1

2. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-2 Outline Overview Transport Layer Functions Reliable vs. Best Effort UDP and TCP UDP and TCP Port Numbers UDP and TCP Header Formats Summary

3. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-3 Transport Layer Session multiplexing Segmentation Flow control (when required) Connection-oriented (when required) Reliability (when required)

4. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-4 Reliable vs. Best Effort Comparison

5. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-5 TCP/IP Protocol Stack

6. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-6 UDP Characteristics

7. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-7 TCP Characteristics

8. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-8 Port Numbers

9. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-9 UDP Header

10. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-10 TCP Header

11. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-11 Summary The transport layer operates between the network layer and the application layer and provides communication services directly to the application processes running on different hosts. UDP is a best-effort, connectionless protocol used for applications that do not require error checking or sequence numbering, such as voice and video streaming. TCP is a reliable, connection-oriented protocol that ensures delivery of packets without error and in correct order.

12. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-12 Summary (Cont.) UDP and TCP use ports to support multiple conversations between different network devices. UDP delivers TFTP, SNMP, and RIP. TCP delivers FTP, Telnet, and SMTP. The UDP header length is always 64 bits. The TCP header follows the Internet header, supplying information specific to the TCP protocol. This division allows for the existence of host level protocols other than TCP.