In the given network system, station A needs to send a payload of 1600B from its network layer to station B. If fragmentation is done, then the actual data size to be transmitted is?
this is the solution that is given.
@Somoshree Datta 5 It should be 456+20 ,Anyways it does not change the final answer! But my doubt is that Network 1 is transferring datagrams to Network 2, then network 2 has to transfer to destination....Why network 2 does not add any header here?
How are you getting the same answer as that given in the solution? If the question is trying to ask the total number of bytes that are being sent to B, then I am getting answer as 1700 B.
1st fragment: 456B data+20B header
2nd fragment: 456B data+20B header
3rd fragment: 456B data+20B header
4th fragment: 112B data+20B header
5th fragment: 120B data+20B header
So total number of bytes that are being sent= 1600+(20*5)= 1700B
Shouldnt this be the answer?
@Somoshree Datta 5 Why are you taking 112 B and 120 B data separately, you can take 232 B data in 4th fragment itself.
Because we are already fragmenting the packet into 2 fragments of size 1480B+20B as the first fragment and 120B+20B while passing through the network having MTU of 1500B. As we dont recombine fragments in intermediate routers, so we cant combine 120B and 112B and form a fragment of 232B. Reassemby of all fragments take place at the final destination and not at the intermediate routers.
@Somoshree Datta 5 I think we are supposed to take bottleneck MTU. Here minimum MTU = 480 B
@gauravkc The explanation they have provided is wrong. We cannot add more bytes to 460
Solution provided by made easy is wrong.
we consider the bottleneck MTU only when we discover the path MTU using ICMP packets. Otherwise we don't consider it. How is host A supposed to know the bottleneck MTU unless and until it uses path MTU discovery technique?
@Somoshree Datta 5 Correct. But I thought that it is always assumed that minimum MTU is known (using MTU discovery technique). Maybe I will have to look other questions of similar kind, to clear the doubt.Did you see any such other question?