Question

A 5,000 bit Application Layer packet being transmitted is encapsulated with a 20-byte TCP header (including the checksum), a 20-byte IP header and a 14-byte Ethernet header plus the 4-byte checksum. What percentage overhead do the headers and checksum take up, i.e. what % of bandwidth used is taken up by these overheads?

Answer 1

8 bits = 1 byte

Therefore 5000 bits = 5000/8 = 625 bytes.

Payload (the packet size that is being transmitted) is 625 bytes.

Payload = 625 bytes

Overheads:

TCP = 20 bytes

IP = 20 bytes

Ethernet =14 bytes

Checksum = 4 bytes

Total overheads = 20+20+14+4 = 58 bytes

Formula for calculating percentage overhead of the headers and checksum take up (or) % of bandwidth taken up by these overheads is:

= Payload / ( Payload + Total overheads )

= 625 / (625+58)

= 625 / 683

= 0.91

= 91%