Multimedia Networks

Extra Credit

  1. Kurose & Ross, Chapter 9, Problem P1.

    Consider the figure below.

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    Similar to our discussion of Figure 9.1, suppose that video is encoded at a fixed bit rate, and thus each video block contains video rames that are to be played out over the same fixed amount of time, Δ. The server transmits the first video block at t0, the second block at t0 + Δ, the third at t0 + 2Δ, and so on. Once the client begins playout, each block should be played out Δ time units after the previous block.

    a. Suppose that the client begins playout asa soon as the first block arrives at t1. In the figure above, how many blocks of video (including the first block) will have arrived at the client in time for their playout? Explain how you arrived at your answer.

    b. Suppose that the client begins playout now at t1 + Δ. How many blocks of video (including the first block) will have arrived at the client in time for their playout? Explain how you arrived at your answer.

    c. In the same scenario at (b) above, what is the largest number of blocks that is ever stored in the client buffer, awaiting playout? Explain how you arrived at your answer.

    d. What is the smallest playout delay at the client, such that every video block has arrived in time for its playout? Explain how you arrived at your answer.

  2. Kurose & Ross, Chapter 9, Problem P13.

    Recall the two FEC schemes for VoIP described in Section 9.3. Suppose the first scheme generates a redundant chunk for every four original chunks. Suppose the second scheme uses a low-bit rate encoding whose transmission rate is 25 percent of the transmission rate of the nominal stream.

    a. How much additional bandwidth does each scheme require? How much playback delay does each scheme add?

    b. How do the two schemes perform if the first packet is lost in every group of five packets? Which scheme will have better audio quality?

    c. How do the two schemes perform if the first packet is lost in every group of two packets? Which scheme will have better audio quality?

  3. Kurose & Ross, Chapter 9, Problem P17.

    Consider the figure below, which shows a leaky bucket policer being fed by a stream of packets.

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    The token buffer can hold at most two tokens, and is initially full at t = 0. New tokens arrive at a rate of one token per slot. The output link speed is such that if two packets obtain tokens at the beginning of a time slot, they can both go to the output link in the same slot. The timing details of the system are as follows:

    1. Packets (if any) arrive at the beginning of the slot. Thus in the figure, packets 1, 2, and 3 arrive in slot 0. If there are already packets in the queue, then the arriving packets join the end of the queue. Packets proceed towards the front of the queue in a FIFO manner.

    2. After the arrivals have been added to the queue, if there are any queued packets, one or two of those packets (depending on the number of available tokens) will each remove a token from the token buffer and go to the output link during that slot. Thus, packets 1 and 2 each remove a token from the buffer (since there are initially two tokens) and go to the output link during slot 0.

    3. A new token is added to the token buffer if it is not full, since the token generation rate is r = 1 token/slot.

    4. Time then advances to the next time slot, and these steps repeat.

    Answer the following questions:

    a. For each time slot, identify the packets that are in the queue and the number of tokens in the bucket, immediately after the arrivals have been processed (step 1 above) but before any of the packets have passed through the queue and removed a token. Thus, for the t = 0 time slot in the example above, packets 1, 2, and 3 are in the queue, and there are two tokens in the buffer.

    b. For each time slot indicate which packets appear on the output after the token(s) have been removed from the queue. THus, for the t = 0 time slot in the example above, packets 1 and 2 appear on the output link from the leaky buffer during slot 0.

  4. Kurose & Ross, Chapter 9, Problem P18.

    Repeat P17 but assume that r = 2. Assume again that the bucket is initially full.