A) Suppose we send into the Internet two IP datagrams, each carrying a different

Question

A) Suppose we send into the Internet two IP datagrams, each carrying a different 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 destination 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?

Explanation / Answer

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A) Suppose we send into the Internet two IP datagrams, each carrying a different 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 destination 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?

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Answer:
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   Given
      
       ---------------------------
       The first datagram has
       ---------------------------
           source IP address A1
           destination IP address B  
           source port P1
           destination port T
       ---------------------------  
       The second datagram
       ---------------------------

           source IP address A2
           destination IP address B
           source port P2
           destination port T  

   UDP sockets are   identified by the two-tuple consisting of destination IP address and destination port number.
So the two packets will indeed pass through the same socket because UDP sockets are identified by two tuples destination IP and port.

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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:
---------
   Alice to send and receive RTP packets to and from Bob
   Claire is only one UDP socket.
   By using another protocol on top of it to establish the connection and distinguish the packets, RTP+SIP
by which Alice’s SIP client distinguish between the RTP packets received from Bob and Claire.
  
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