CS 558 - Computer Networking
Homework 5

Due: See class webpage.

The following questions are related to the paper:

Question 1

• What is the goal of the control method proposed in Kanakia's paper ?

• What feedback signals is used in the feedback control scheme by Kanakia ?

• How are each feedback signal determined by the bottlebeck router ?

Question 2

A steady state is a state where there are no changes made to the system parameters for some period of time. For a system to be in a steady state, the data consumption rate must be equal to the data production rate.

A video source is transmitting using Kanakia's scheme and has reached a steady state and in this steady state, the video source is sending 10 frames per second and each frame is compressed to 50,000 bytes. (So the source will be transmitting at this rate for some prolong period of time).

• While the system is in the steady state, what is the average data drain rate mu that is being reported by the bottleneck node ?

While in the steady state, a feedback is received from the receiver that was generated at the moment that frame 10 arrives at the congested router. At the moment that the sender receives this feedback information, the sender was about to transmit frame 16.

• What is the end-to-end delay between the sender and the congested router when the system is in this steady state ?

• What was the ideal threshold x* used by the system ?

The following questions are related to the paper:

• "Scalable Feedback Control for Multicast Video Distribution in the Internet", ( click here)

Question 3

• What is the implosion problem ?

• Describe three existing solutions to handle the implosion problem presented in the paper.

• Describe Bolot's algorithm to discover the state of the weakest receiver.

• How does Bolot's algorithm estimate the current number of receivers ?

Question 4

• Bolot's solution is not perfect, because it is still possible for the sender to receive replies from a large number receivers.

Describe a scenario when this will occur.

The following questions are related to the paper:

• "A rate control mechanism for packet video in the Internet", Bolot ( click here)

NOTE: This paper was NOT discussed in class. Read it carefully and then answer the questions below

Question 5 (20 pts)

• Cable television system divide the transmission medium (the coaxial cable) into a number of logical channels. Each channel has a fixed bandwidth (approximately 6 Mbps). Each channel will carry one video stream and the video data rate must therefore not exceed the channel data rate.

Describe the feedback mechanism that is used by a video encoder for cable TV to make sure that compressed video output does not exceed the channel capacity.

• According to this paper, what was the major drawback of the rate control scheme proposed by Kanakia et. al. ?

Explain why this is such a major drawback.

• What feedback signal does the IVS video conferencing tool send back to the video source if there are 100 receivers ?

How often does IVS take action on adjusting the video output data rate ?

• What protocol did IVS use to determine the number of receivers ?