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TCP Connections

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• Identifying a TCP Connection
  • TCP connection:

    A TCP connection is a logical connection between 2 TCP ports.

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  • Packets of a TCP connection are uniquely identified by these 4 values:

    The Source IP-Address The Source TCP port number The Destination IP-Address The Destination TCP port number           Graphically: (Source-IP-Addr, SourcePort#, Dest-IP-Addr, DestPort#)

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  • Note:

    A TCP connection is uni-directional Example: (Source-IP-Addr, SourcePort#, Dest-IP-Addr, DestPort#) and (Dest-IP-Addr, DestPort#, Source-IP-Addr, SourcePort#) are 2 different TCP connections !!!

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• The state of a TCP connection
  • Fact:

    Each TCP connection has a state (We say that TCP is state-full protocol)

  • The state information of the (uni-directional) TCP connection are:

    The current (send) sequence number of the sliding window The current acknowledgement number of the sliding window

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  • Note:

    In a bi-directional TCP connection: Each (uni-directional) TCP connection has its own send sequence number and ACK number

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• Comment on stateful protocols
  • Consequence of state-fullness of TCP:

    When a computer crashes: he state of a TCP connection is lossed (and cannot be recovered) Consequently: TCP connections must be reset when the source/receiver crashes (I.e.: your program will exit when the other party crashes....)

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  • Note:

    In contrast, the UDP protocol is a stateless protocol              Your program (using UDP will not exit if the other party crashes !!!