The length of the TCP header is specified here. This helps the receiving end to identify where the header ends and the data starts from.
📝 Note The header length is represented by 4 bits, i.e., the numbers
0000
→
1111
0000→1111
or
0
→
15
0→15
in decimal which is not enough to represent the potential 60 bytes of the header. Hence, this number is multiplied by 4 upon receiving. So
1111
1111
would represent
60
60
. In other words, the way the 4-bit header length field is used to represent a maximum header length of 60, is that this field represents the number of 4-byte words in the header