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TCP Segments
TCP slices (dices?) the incoming byte-stream data into
segments for transmission across the Internet. A
segment is a highly-structured data package consisting of an
administrative header and some application
data.
- Source and Destination Port Numbers
- We have already seen that TCP server processes wait for
connections at a pre-agreed port number. At connection
establishment time, TCP first allocates a client port
number -- a port number by which the client, or
initiating, process can be identified. Each segment contains both
port numbers.
- Segment and Acknowledgement Numbers
- Every transmitted segment is identified with a 32-bit
Sequence number[2],
so that it can be explicitly acknowledged by the receipient. The
Aknowledgement Number identifies the last segment recived by the
originator of this segment.
- Application Data
- Optional because some segments convey only control
information -- for example, an ACK segment has a valid
aknowledegement number field, but no data. The data field can be
any size up to the currently configured MSS for
the whole segment.
[2] The sequence
number actually identifies the last byte of data
contained in this segment.
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