The size of TCP header varies from 20 bytes to 60 bytes.

Header length:

It is of 4 bits and it contains the length of the TCP header and useful in determining the actual size of the data.

The length of the TCP header varies from 20 bytes to 60 bytes.

The option field can vary from 0 to 40 bytes.

Scaling factor for header length:

• Since the header length is 4 bits so the range of decimal value can vary from [0 to 15]
• But the header length varies from [20 to 60]
• So scaling factor of 4 is used to represent the header length.
• Header length = Header length field value * 4

Note: Header length field value and header length are not same.

Example:

If the header length field contains value 5(represented as 0101) then

header length = 5 * 4 =20 bytes

Categories: Networking