CDA 4527: Computer Communication Networks
Fall 2005
Homework 2
(assigned 09/29; due: 10/06 in class by submitting homework in paper)
1. Chapter 3, problem 1.
2. Chapter 3, problem 3. You don't need to answer "why is that UDP takes the 1s complement of the sum; that is, why not just use sum?".
3. Chapter 3, problem 8. Please draw the new FSM for sender and receiver to show how you modify the protocol (you don't need to explain it by words). You don't need to answer "why your protocol can communicate correctly over this channel".
4. Chapter 3, problem 10 (the alternating-bit protocol is the rdt3.0).
5. Chapter 3, problem 12.
6. Chapter 3, problem 19. Justify your answer even if the answer is true. For 19(a), you should justify it by drawing a protocol running example.
7. Chapter 3, problem 20. For 20(b), assume that the network is perfect and there is no error or retransimssion.
8. Refer to the Figure 3.31 in the textbook, suppose those three packets transmission are successful. In the first packet transferring from A to B, the packet has 10 bytes of data and has Seq=1000 and ACK=100. Suppose the second packet returning from B to A has 25 bytes, the third packet (from A to B) has 40 bytes. Show what sequence number and acknowledge number used in the second and the third packets?
9. Write the simple C code to drive the EstimatedRTT based on the equation given on Page 236 in textbook. Save the results in the EstimateRTT[], the i-th entry is the data at time i.
Suppose the beginning part of the code is:
#define N 1000 // 1000 points in the data.
double SampleRTT[N]={3, 5, 4.6, 9.8, ....};
double EstimateRTT[N];
10. A simple queuing problem: suppose a router has two hosts, A and B, sending packets through it; the router has one output link with bandwidth 1Mbps (with an infinite buffer). Host A sends 250 packets/second, host B sends 400 packets/second through the router. Each packet has exponential distribution length with average packet size of 1.4Kbps.
(a). What is the average delay of packets from A and B, respectively?
(b). How many packets on average staying in the router?
(c). What is the probability that the router holds 4 packets?