Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide


NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

Searchable, convenient, complete TCP/IP information.
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Transport Layer Protocols
           9  Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)
                9  TCP/IP Transmission Control Protocol (TCP)
                     9  TCP Basic Operation: Connection Establishment, Management and Termination

Previous Topic/Section
TCP Connection Establishment Process: The "Three-Way Handshake"
Previous Page
Pages in Current Topic/Section
12
3
Next Page
TCP Connection Management and Problem Handling, the Connection Reset Function, and TCP "Keepalives"
Next Topic/Section

TCP Connection Establishment Sequence Number Synchronization and Parameter Exchange
(Page 3 of 3)

TCP Parameter Exchange

In addition to initial sequence numbers, SYN messages also are designed to convey important parameters about how the connection should operate. TCP includes a flexible scheme for carrying these parameters, in the form of a variable-length Options field in the TCP segment format that can be expanded to carry multiple parameters. Only a single parameter is defined in TCP 793 to be exchanged during connection setup: Maximum Segment Size (MSS). The significance of this parameter is explained in the TCP data transfer section.

Each device sends the other the MSS that it wants to use for the connection, if it wishes to use a non-default value. When receiving the SYN, the server records the MSS value that the client sent, and will never send a segment larger than that value to the client. The client does the same for the server. The client and server MSS values are independent, so a connection can be established where the client can receive larger segments than the server or vice-versa.

Later RFCs have defined additional parameters that may be exchanged during connection setup. Some of these include:

  • Window Scale Factor: Allows a pair of devices to specify larger window sizes than would normally be possible given the 16-bit size of the TCP Window field.

  • Selective Acknowledgment Permitted: Allows a pair of devices to use the optional selective acknowledgment feature to allow only certain lost segments to be retransmitted.

  • Alternate Checksum Method: Lets devices specify an alternative method of performing checksums than the standard TCP mechanism.

Previous Topic/Section
TCP Connection Establishment Process: The "Three-Way Handshake"
Previous Page
Pages in Current Topic/Section
12
3
Next Page
TCP Connection Management and Problem Handling, the Connection Reset Function, and TCP "Keepalives"
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.