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Authors:
James F. Kurose, Keith W. Ross
Chapter:
Multimedia Networking
Exercise:
Problems
Question:15 | ISBN:9780132856201 | Edition: 6

Question

a. Suppose we send into the Internet two IP datagrams, each carrying a differ- ent UDP segment. The first datagram has source IP address A1, destination IP address B, source port P1, and destination port T. The second datagram has source IP address A2, destination IP address B, source port P2, and des- tination port T. Suppose that A1 is different from A2 and that P1 is different from P2. Assuming that both datagrams reach their final destination, will the two UDP datagrams be received by the same socket? Why or why not?

b. Suppose Alice, Bob, and Claire want to have an audio conference call using SIP and RTP. For Alice to send and receive RTP packets to and from Bob and Claire, is only one UDP socket sufficient (in addition to the socket needed for the SIP messages)? If yes, then how does Alice’s SIP client distinguish between the RTP packets received from Bob and Claire?

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Answer

a)

 

Given data:

  • Assume the Internet have two IP datagrams.
  • The first datagram has source IP address A1, destination IP address B, source port P1, and destination port T.
  • The second datagram has source IP address A2, destination IP address B, source port P2, and des- tination port T. Suppose that A1 is different from A2 and that P1 is different from P2. 

Suppose that both datagrams reach their final destination, then the receiving host always directs each segment to the appropriate socket through port number and segment’s destination IP(Internet Protocol).

 

Hence, the two UDP( User Datagram Protocol) datagrams be received by the same socket.

 

b)

 

Given data:

  • Assume Alice, Bob, and Claire want to have an audio conference call using SIP(Session Initiation Protocol) and RTP(Real-time Transport Protocol).
  • For Alice to send and receive RTP packets to and from Bob and Claire, is only one UDP( User Datagram Protocol) socket.

The following steps are Alice’s SIP client distinguish between the RTP packets received from Bob and Claire:

  • It depends on their respective IP(Internet Protocol) address. 
  • Bob and Claire will choose different SSRC’s (Synchronization source identifier). 
  • Alice choose only one socket IP address.

 

Hence, only one UDP socket is enough for Alice to send and receive RTP packets to and from Bob and Claire.

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