Transmission Control Protocol (TCP) is a
connection-oriented Layer 4 (transport layer) protocol that provides reliable
full-duplex
data transmission. TCP is part of the TCP/IP protocol stack.
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Following are the definitions of the
fields in the TCP segment:
- source port -- number of the calling port
- destination port -- number of the called port
- sequence number -- number used to ensure correct
sequencing of the arriving data
- acknowledgment number - next expected TCP octet
- HLEN -- number of 32-bit words in the header
- reserved -- set to zero
- code bits -- control functions (such as setup and
termination of a session)
- window -- number of octets that the sender is willing
to accept
- checksum -- calculated checksum of the header and
data fields
- urgent pointer -- indicates the end of the urgent
data
- option-one option -- maximum TCP segment size
- data -- upper-layer protocol data
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