A Web-Based Introduction to Computer Networks for Non-Majors

Transport Layer: Error Control and Automatic Repeat Request Protocols

Caveats and References

Error Control in TCP is based on Go-Back-N Continuous RQ. Thus, the Selective Repeat simulations of this applet is similar but not exactly the same as the basic behavior of TCP. There are a number of further simplifications. Chapters 17-24 of Richard Stevens [4] give a more accurate description of the behavior of TCP. Page 308 of Richard Stevens [4] is an example of a real TCP packet exchange that illustrates error control. Here are a few of the simplifications.

• The sequence number used in the acknowledgment packets is not actually the number of the next expected data packet.
• The trigger of retransmission is not necessarily a pure timeout. For example, a certain number, say three, of duplicate acknowledgment packets received in a row could trigger a retransmission.
• TCP has a number of features for flow control; that is, stopping the sender from sending data packets if the network or the receiver are too busy. The flow control features combine with error control to determine when the sender sends data packets or retransmits data packets.

[1] D. Bertsekas and R. Gallager, Data Networks, Second Edition, Prentice-Hall, Englewood Cliffs, NJ, 1992.

[2] F. Halsall, Data Communications, Computer Networks, and Open Systems, Fourth Edition, Addison-Wesley, Reading, MA, 1996.

[3] W. Stallings, Data and Computer Communications, Fifth Edition, Prentice-Hall, Upper Saddle River, NJ, 1997.

[4] W. R. Stevens, TCP/IP Illustrated, Volume 1, Addison-Wesley, Reading, MA, 1994.

Acknowledgements and Developer Information

Copyright notice (C) 1996 Mark A. Holliday. All rights reserved.