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Question

Which of the following statements is true ? S1 : Source to destination delivery is the functionality that must be implemented by network layer above data­link layer. S2 : Packet delivery in correct order is the functionality that must be implemented by network layer above data­link layer. Which of the following is correct ?

a. Only S1 is true

b. Only S2 is true

c. Both S1 and S2 are true

d. Neither of S1 or S2 is true

Comments

example : 

TCP is a transport layer protocol that create a process-to-process communication.

And 

Network layer protocols are responsible for source-to-destination node (or machine) delivery.

Answer 1

Option A)

S2:

 If IP packets should be received and accepted in order, then this is done by one of transport layer protocols

S1:

Network layer takes care of routing the packets from source to destination. But Transport layer is responsible for process to process delivery. Since the statement does not say anything about process to process delivery I think its correct.

Comments

Flow control ensures proper order of frames. For eg in Stop and Wait and Go back N all out of order frames are discarded. And in selective repeat as the receiver window size is equal to sender window size out of order frames are saved in a buffer and is arranged in proper order before it is sent to network layer for processing.

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If i am wrong please correct me and if you have any reference links add it..

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They are asking packet delivery order but not frame delivery order. If IP packets should be received and accepted in order, then this is done by one of transport layer protocols. Because of this $S2$ is false.