Test by Bikram | Computer Networks | Test 1 | Question: 28

Question

Which among the following services is provided by the transport layer?

• A. Recovery from message loss.
• B. End to end delivery of individual messages.
• C. Correct order message delivery.
• D. All of the above.

Comments

Correct order paket delivery is also the service of transport layer so why not answer given is D as well

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@shivesh

Thanks for the correction.

Actually  option b) end to end delivery of individual packets without guarantee is perform by network layer  

and option d) correct order packet delivery is done by Transport Layer [1]

• The Network layer is responsible for end-to-end (also named source-to-destination) delivery of individual packets across multiple networks, without guarantees. [2]

Where as:

• The Transport layer is responsible for end-to-end delivery of entire message. [2]
• Transport layer Provides end-to-end connectivity,
• Transport layer allows data to be transferred reliably (for example, with a guarantee that it will be delivered in the same order that it was sent )

See this link as Reference:

1. http://www.rhyshaden.com/osi.htm
2. http://www.techexams.net/forums/network/281-quick-question-layer-defines-end-end-delivery.html

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in tcp packets can go in out of order also but they are ordered at reciever end

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What if UDP is taken into consideration? It does only end to end delivery and not any of a,c,d.

Answer 1

Though option (d) is a part of services provided by Transport Layer but I think (b) should be correct answer end to end delivery, Network layer does host to host delivery. Following screenshot is taken from Forozuan's CN book:

Now decide yourself which one is correct answer!

Comments

But UDP is also a transport layer protocol, and it does not provide correct order packet delivery. Where am I wrong??

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@Manu is right.

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Corrected the question

Answer 2

 Correct order packet delivery is done by Transport Layer [1]

The Network layer is responsible for end-to-end (also named source-to-destination) delivery of individual packets across multiple networks, without guarantees. [2]

Where as:

• The Transport layer is responsible for end-to-end delivery of entire message. [2]
• Transport layer Provides end-to-end connectivity,
• Transport layer allows data to be transferred reliably (for example, with a guarantee that it will be delivered in the same order that it was sent )

 References:

1. http://www.rhyshaden.com/osi.htm
2. http://www.techexams.net/forums/network/281-quick-question-layer-defines-end-end-delivery.html

Answer 3

Transport Layer provides flow and error control for messages (Data link layer provides the same for frames). But this does not mean that every Transport layer protocol provides these - UDP for example does not give these. 

https://gateoverflow.in/?qa=blob&qa_blobid=15275542168689172988