TCP segment is the unit of data
transfer between any two devices that use TCP. The segment is divided into two
parts. The part is called as header part and other one is called is data part.
TCP header format:
1) Source Port Address:
- It defines the application program in the source computer
and is 16 bit wide.
2) Destination Port
Address: - The destination port address
defines the application program in the destination computer. It is also 16 bit
wide.
3) Sequence Number: - A stream of data from the application program may be
divided into two or more TCP segment.
4) Acknowledgement
number: - The 32 bit acknowledgement
number is used acknowledge the receipt of data from the other communicating
device.
5) Header Length: - The 4- bit header length field indicates the number of 32
bit (4 byte) words in the TCP header.
6) Unused: - The 6 bit field is reserved for future use.
7) Control: - Each bit of the 6 bit control field functions individually
and independently. A bit can either define the use of a segment.
Control Field:
URG
|
ACK
|
PSH
|
RST
|
SYN
|
FIN
|
i.
URG: - Urgent
pointer is valid.
ii.
ACK:-Acknowledgement
is valid.
iii.
PSH: - Push the
data.
iv.
RST:-Reset the
connection.
v.
SYN:-Synchronize
sequence numbers during the connection FIN.
vi.
FIN:-Terminate the connection.
8) Window size: - The field defines the size of the window in bytes. The
length of this field is 16 bits, which means the maximum size of the window is
65,535 bytes.
9) Checksum: - The 16 bit contains the checksum. It is generally used in
error detection.
10)
Urgent pointer: - The 16 bit
field, which is valid only if the urgent flag is set. In this the pointer
defines the end of the urgent data and the start of the normal data.
11)
Options:-There can
be up to 40 bytes of optional information in the TCP header. They are used to
conventional additional information to the receiver or for alignment purpose.
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