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Old 27th August 2012
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jggimi jggimi is offline
More noise than signal
Join Date: May 2008
Location: USA
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Default Chapter 8: Session states

Stateless protocols do not keep track of conversation status, they do not manage sessions. Protocols that track state, such as TCP, are known as Stateful protocols. Endpoints may be in any of ten states at any time, covering three general communication phases: a) establishing a session, b) data transfer, and c) ending a session.

TCP requires three packets to be sent and received -- a "3-way handshake" to establish a session. Once established, the session remains as a communication channel until an endpoint initiates a session teardown sequence, which may take as many as 4 packets to complete. Along with port numbers and sequence numbers, checksums are added to the packets to permit error recovery.

State management has overhead, but the overhead provides value: error detection and recovery, packet reordering (when the arrivals are out-of-order), confirmation of receipt, and flow controls to manage network congestion or latency effects.

Other protocols may manage state. For example, HTTP tracks state with application specific content called a "cookie".

Last edited by jggimi; 31st August 2012 at 05:20 PM.
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