Midterm review questions/topics: (Nov 21)

• Quality of Service concepts: diffServ, intServ

(Chapter 7: 7.6-7.9)

Problem 1. Suppose that Weighted Fair queuing scheduling policy is applied to a buffer that supports three classes, and suppose the weights are 0.5, 0.25, 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?
(b) Suppose that class 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 achive the WFQ weights?

Problem 2. Describe how RSVP works, explain why it is receiver-oriented, what role soft state plays here.

• Multi-access: Ethernet

(Chapter 5: 5.1-5.5)
Problem 1. Describe how CSMA/CD works.
Problem 2. Suppose nodes A and B are on the same 10Mbps Ethernet segment and the propagation delay between the two nodes is 225 bit times. Suppose A and B send frames at the same time, the frames collide, and then A and B choose different values of K in the CSMA/CD algorithm. Assuming no other nodes are active, can the retransmissions from A and B collide? For our purposes, it suffices to work out the following example. Suppose A and B begin transmission at t=0 bit times. They both detect collisions at t=225 bit times. They finish transmitting a jam signal at t=225+48=273 bit times Suppose K_a=0 and K_b=1. At what time does B schedule its retransmission? At what time does A begin transmission?
• Coding: Shannon, Nyquist

(see lecture notes)
Remember the Shannon and Nyquist algorithms.
• Multimedia Networks: playback buffer

(Chapter 7: 7.1-7.5)
Problem 1. Describe the purpose of Adaptive Playout Delay.
Problem 2. Are the TCP receive buffer and the media player's client buffer the same thing? If not how do they interact?
• Peer to peer networks: Chord, CAN algorithms

(see lecture notes)
Problem 1. Describe the overall structure of DHT and how it can be used to locate a file with a known file name.
Problem 2. how to build a p2p file sharing system on top of DHT in a way that doesn't require "hot" nodes to store shared files.
• Multicast: ALM, IP-multicast

(Lecture Notes)
Describe why native IP multicast did not take off on the global Internet.
Describe the advantages of ALM and metrics to evaluate the efficiency of ALM.