TCP Header Format (3)


Header format has some limitations.
Sequence Number 
From 0 to (2^32 -1) bytes
Port Number
From 0 to (2^16-1)
Window Size
From 0 to (2^16-1) bytes.
Header length 
From 0 to 15 in 32bit words.
Max TCP header size is limited to 60 bytes
Since normal header has 20 bytes, TCP can have another 40 bytes for options.
Reserved bit
6 bits are reserved for future extension