A user wishes to transmit a file of size 12 MBytes (1M = 10^6). The source TCP e

Question

A user wishes to transmit a file of size 12 MBytes (1M = 10^6). The source TCP entity generates segments with MSS (Maximum Segment Size) of 4000 bytes. These segments go through an Ethernet with an MTU of 1500 bytes. Assume that the Ethernet header is of size 18 bytes, the IP header is 20 bytes, and the TCP header is 20 bytes. (a) How many IP datagrams are transmitted through the Ethernet? (b) What is the total number of header bytes (including TCP, IP, and Ethernet headers) transmitted? What is the percentage overhead of header bytes in transmitting this file through this network?

Explanation / Answer

(a)

The user wishes to transmit 12 Mb = 12000000 bytes.

Ethernet can send maximum unit of 1500 bytes of data but along with the Ethernet header 18 bytes, IP header 20 bytes and TCP header 20 bytes. so only data can be send through Ethernet =(1500-(18+20+20)) bytes = 1442 bytes.

Now total amount of data = 12000000 bytes

at a time ethernet can send data = 1442 bytes

so total number of datagrams are to be transmitted = 12000000/1442 = 8322.

(b) It is already given that header file need for one transmitions = (18+20+20)= 58 bytes

Total number of header bytes transmitted = (total number of block x 1500 - total message length)=(8322 x 1500 - 12000000)= 483000 bytes.

(c) Percentage of overhead of header bytes is transmitting this file through this network = {(number of header bytes) x 100} / 12000000 = 4.025 %.

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