Multimedia Networking – Homework 2
(Due October 14)
1. Suppose that a sender sends a silence suppressed RTP stream of G.711 audio to a
receiver. During a talk spurt 20 msecs chunks of quantized audio samples are
encapsulated into RTP packets and sent to the receiver (every 20 msecs). Justify your
answers for the following:
a. How many samples are included in each packet?
b. If the RTP time stamp is initialized to zero, and if the first talk spurt consists
of three or more packets, what are the RTP time stamps of the first three
packets in the first talk spurt?
c. Consider the last packet in a talk spurt and the first packet in the immediately
following talk spurt. Does the difference of the RTP timestamps of these
packets depend on the length of the silence period between the two talk
spurts?
d. If the last two packets received at the receiver have a timestamps of 0 and 480
and corresponding sequence numbers of 1 and 3 (i.e. packet 2 is lost), are
these last two packets in the same talk spurt or in different talk spurts?
e. Outline an algorithm that uses sequence numbers and time stamps of RTP
packets to determine the beginning of a new talk spurt?
2. Consider the adaptive playout delay algorithm. Illustrate through a simple example
that adjusting the playout delay at beginning of each talk spurt results in compressing
and elongating the silence period between talk spurts.
3. Consider an RTP session consisting of four users, all of which are sending and
receiving packets to the same multicast address. Each user sends video at 100 kbps.
a. RTCP will limit its traffic to what rate?
b. How much RTCP bandwidth will each sender be allocated?
c. How much RTCP bandwidth will each receiver be allocated?
4. Consider N users participating in an audio/video conference using IP multicasting.
Each user is equipped with a microphone, a camera, and speakers. Justify your
answers for the following. Assuming no RTP mixers are used:
a. How many distinct SSRCs are needed?
b. How many distinct canonical names are needed? How will canonical names
be used?