View Source: TCP - Waikato Linux Users Group

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TCP is an [Acronym] of TransmissionControlProtocol. It is part of the [TCP/IP] protocol stack.

TCP is connection-oriented: before two parties can communicate, they must ''open'' a common connection; after they have finished communicating, they ''close'' the connection. The initiation of the connection is ''asymmetric'': one end needs to ''listen'' for connection attempts, while the other end initiates a connection during this time. However, once the connection is opened, it is ''symmetric'' and ''full-duplex''--both ends are equally capable of transmitting arbitrary information at arbitrary times.

TCP is an ordered stream--data sent from one end will arrive at the other end in the same order. Communication is ''reliable''--all transmissions are automatically acknowledged, with timeouts and retries if any lower-level packets are lost, including automatic sequencing to detect duplicates (as can happen when a lower-level packet wasn't "lost", but simply took too long to arrive).  Compare [XCP] and [DCCP].

Someone who's done 312 recently want to write a big long discussion about Nagle, Slow start, backoff, congestion control, window sizes etc?

We have separate pages discussing TcpStates, and the TcpWindow.

!!TCP Header:

|00|01|02|03|04|05|06|07|08|09|10|11|12|13|14|15|16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31
||||||||||||||||||||||||||||||||^[IPv4]/[IPv6] Header
||||||||||||||||Source Port |||||||||||||||| Destination Port
|||||||||||||||||||||||||||||||| Sequence Number
|||||||||||||||||||||||||||||||| Acknowledgement
||||Data Offset||||Reserved|[CWR]|[ECE]|[URG]|[ACK]|[PSH]|[RST]|[SYN]|[FIN]||||||||||||||||Window
||||||||||||||||Checksum||||||||||||||||Urgent Pointer
||||||||||||||||||||||||||||||||Optional Options / Padding
||||||||||||||||||||||||||||||||v Data

!!TCP Options:

! End of option list
|00|01|02|03|04|05|06|07
|||||||| 0

! No Op (Padding)
|00|01|02|03|04|05|06|07
|||||||| 1


! Maximum Segement Size
|00|01|02|03|04|05|06|07|08|09|10|11|12|13|14|15|16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31
|||||||| 2 |||||||| length (4) |||||||||||||||| MSS
|||||||||||||||| MSS (Continued) ||||||||||||||||

! Window Scale Option
|00|01|02|03|04|05|06|07|08|09|10|11|12|13|14|15|16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31
|||||||| 3 |||||||| length (3) |||||||| Shift Count ||||||||


! [SACK]
|00|01|02|03|04|05|06|07|08|09|10|11|12|13|14|15
|||||||| 4 |||||||| length (2)

! [SACK] Information
|00|01|02|03|04|05|06|07|08|09|10|11|12|13|14|15|16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31
|||||||| 5 |||||||| length |||||||||||||||| Left edge of first block
|||||||||||||||| Left edge of first block (continued) |||||||||||||||| Right edge of first block
|||||||||||||||| Right edge of first block (continued) |||||||||||||||| .....
|||||||||||||||| ....... |||||||||||||||| Left edge of last block
|||||||||||||||| left edge of last block (continued) |||||||||||||||| Right edge of last block
|||||||||||||||| Right edge of last block (continued)


! TCP Timestamps
|00|01|02|03|04|05|06|07|08|09|10|11|12|13|14|15|16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31
|||||||| 8 |||||||| length (10) |||||||||||||||| TS Value
|||||||||||||||| TS Value (Continued) |||||||||||||||| TS Echo Reply
|||||||||||||||| TS Echo Reply (Continued) ||||||||||||||||

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See also:
* [A very nice cheat sheet | http://www.sans.org/newlook/resources/tcpip.pdf] for [TCP/IP]
* [assigned tcp options|http://www.iana.org/assignments/tcp-parameters]
* [Linux Congestion Control | http://www.cs.helsinki.fi/u/sarolaht/papers/linuxtcp.pdf ]
* TcpTuning

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CategoryProtocols, CategoryNetworking
46 pages link to TCP:
Last edited on Friday, May 5, 2006 10:08:06 pm by LawrenceDoliveiro
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