Problem 15
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?
Problem 16
True or false: a. If stored video is streamed directly from a Web server to a media player, then the application is using TCP as the underlying transport protocol. b. When using RTP, it is possible for a sender to change encoding in the middle of a session. c. All applications that use RTP must use port 87. d. If an RTP session has a separate audio and video stream for each sender, then the audio and video streams use the same SSRC. e. In differentiated services, while per-hop behavior defines differences in performance among classes, it does not mandate any particular mechanism for achieving these performances. f. Suppose Alice wants to establish an SIP session with Bob. In her INVITE message she includes the line: m=audio 48753 RTP/AVP 3 (AVP 3 denotes GSM audio). Alice has therefore indicated in this message that she wishes to send GSM audio. g. Referring to the preceding statement, Alice has indicated in her INVITE message that she will send audio to port 48753. h. SIP messages are typically sent between SIP entities using a default SIP port number. i. In order to maintain registration, SIP clients must periodically send REGISTER messages. j. SIP mandates that all SIP clients support G.711 audio encoding.
Problem 17
Suppose that the WFQ scheduling policy is applied to a buffer that supports three classes, and suppose the weights are 0.5, 0.25, and 0.25 for the three classes. a. Suppose that each class has a large number of packets in the buffer. In what sequence might the three classes be served in order to achieve the WFQ weights? (For round robin scheduling, a natural sequence is 123123123 . . .). b. Suppose that classes 1 and 2 have a large number of packets in the buffer, and there are no class 3 packets in the buffer. In what sequence might the three classes be served in to achieve the WFQ weights?
Problem 18
Give an example of a scheduling discipline that is not work conserving.
