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+26 votes

Which of the following functionality must be implemented by a transport protocol over and above the network protocol?

  1. Recovery from packet losses
  2. Detection of duplicate packets
  3. Packet delivery in the correct order
  4. End to end connectivity
asked in Computer Networks by Veteran (52k points) | 3.5k views
can someone explain the other options?
here why we are comparing transport and udp layer ,question is about network layer and tcp

and for tcp and network only tcp has end to end connectivity
Just additional question -

Let us assume TCP is not handling whatever is mentioned in option A, B and C. Then which layer would be best for handling these functionality ? (and How could it be handled ?)
@chhotu which layer will handle all these functionalities..

6 Answers

+35 votes
Best answer

Answer(D) TCP and UDP are transport layer protocols.

Question is asking which service must be provided by transport layer so that source can successfully communicate to destination. UDP is a connection-less protocol but it's a transport layer protocol so that from here we can say that reliability is not a service that MUST be provided by transport layer protocols. with that same argument cut all those options in which such a service is mentioned which UDP doesn't provide so only (D) remain so it's the answer..

other way to answer is ' for Process to Process delivery transport layer service is MUST otherwise there is no way to deliver the data to right process'.. if reliability is in danger data can survive (Data link layer also take care about errors so we can compromise error recovery at transport layer), if there are duplicate packets , yet data can survive ,only bandwidth is wasted, if packets are delivered out of order data can survive but if data of process A is delivered to process B , data can't survive.... "to Assigning port numbers" Transport layer service is MUST...

answered by Boss (13.7k points)
edited by
very nicely explained!!
Thanks reena.
Yeah, all options from (a)-(c) can be done by the data link layer, but end-to-end connectivity is provided by the transport layer.
great rupendra thanks bhai

@Rupendra Choudhary packet loss is maintained by NL by sending ICMP then what is the reason to implement packet loss at TL by using TCP and UDP?


@Ayush Upadhyaya 

sir how can data link layer habdles out of order packets (option C)??

if the datagram is fragmented then it can be arranged by network layer ..  Am i right?



@Verma Ashish_yes I think I am wrong there.

+23 votes
End to end connectivity is the required functionality provided by Trnasport protocol. UDP of transport layer protocol that doesn't implement other three functionalities, they are implemented only in TCP.
answered by Loyal (8.1k points)
Packet delivery in the correct order is the common functionality which is implemented by both TCP and UDP. Other  functionalities as mentioned in the options are only implemented by TCP and not UDP. Hence, option C, must be implemented by the transport layer.

in question , trasport protocol is compared to network not [email protected] Imteyazmohsin 


Imteyazmohsin Since UDP is unreliable protocol and connectionless protocol,how come the packet's in UDP come in order.

+6 votes
Service point addressing is an important functionalities of transport layer That's why End to End connection or Socket to Socket connection is must gifted properties of Transport layer.
answered by Loyal (9.7k points)
+5 votes
D. Transport layer protocol is called end to end connecting layer.
answered by Active (1.6k points)
+4 votes
Transport protocols are mainly for providing end to end connections by making sockets.
Recovery from packet loss & delivery in correct order, duplication is checked by Data link layer.
Hence (D) is correct option.
answered by Active (1.2k points)
–3 votes

Answer: D

answered by Active (1.4k points)

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