TCP Connection Establishment and Termination

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Timeout of connection establishment
Look at the TCP Timeout (Telnet).cap file, and mind the time interval.
MSS:
The maximum segment size (MSS) is the largest "chunk" of data that TCP will send to the other end. When a connection is established, each end can announce its MSS. The values we've seen have all been 1024. The resulting IP datagram is normally 40 bytes larger: 20 bytes for the TCP header and 20 bytes for the IP header.
Some texts refer to this as a "negotiated" option. It is not negotiated in any way. When a connection is established, each end has the option of announcing the MSS it expects to receive. (An MSS option can only appear in a SYN segment.) If one end does not receive an MSS option from the other end, a default of 536 bytes is assumed. (This default allows for a 20-byte IP header and a 20-byte TCP header to fit into a 576-byte IP datagram.)
In general, the larger the MSS the better, until fragmentation occurs. A larger segment size allows more data to be sent in each segment, amortizing the cost of the IP and TCP headers. When TCP sends a SYN segment, either because a local application wants to initiate a connection, or when a connection request is received from another host, it can send an MSS value up to the outgoing interface's MTU, minus the size of the fixed TCP and IP headers.
TCP Half-Close
TCP provides the ability for one end of a connection to terminate its output, while still receiving data from the other end. This is called a half-close.
TCP State Transition Diagram
Please look th Figure on book.
2MSL Wait State
The TIME_WAIT state is also called the 2MSL wait state. Every implementation must choose a value for the maximum segment lifetime (MSL). It is the maximum amount of time any segment can exist in the network before being discarded. We know this time limit is bounded, since TCP segments are transmitted as IP datagrams, and the IP datagram has the TTL field that limits its lifetime.
Given the MSL value for an implementation, the rule is: when TCP performs an active close, and sends the final ACK, that connection must stay in the TIME_WAIT state for twice the MSL. This lets TCP resend the final ACK in case this ACK is lost (in which case the other end will time out and retransmit its final FIN).
Another effect of this 2MSL wait is that while the TCP connection is in the 2MSL wait, the socket pair defining that connection (client IP address, client port number, server IP address, and server port number) cannot be reused. That connection can only be reused when the 2MSL wait is over.
Reset Segments
Look at the file TCP Reset (Telnet).cap
TCP Options
What we often see is MSS.
# 2009-09-22  22:42
               
               
               

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