## Homework 4 - CMSC 417, Spring 2000, Section 0101

All problems except the third one are worth 10 points. The third problem is worth 15 points.

Homework 4 Problems
1. Kurose and Ross, Chapter 5, Problem #3.

2. Kurose and Ross, Chapter 5, Problem #4.

3. A large population of ALOHA users manages to generate 50 requests/sec, including both originals and retransmission. Time is slotted in units of 40 msec.
(a) What is the chance of success on the first attempt?
(b) What is the probability of exactly k collisions and then a success?
(c) What is the expected number of transmission attempts needed?

4. Sketch Manchester encoding for the bit stream: 0001110101.

5. Sketch the differential Manchester encoding for the bit stream of the previous problem. Assume the line is initially in the low state.

6. Consider building a CSMA/CD network running at 1 Gbps over a 1-km cable with no repeaters. The signal speed in the cable is 200,000 km/sec. What is the minimum frame size?

7. Two CSMA/CD stations are each trying to transmit long (multiframe) flies. After each frame is sent, they contend for the channel using the binary exponential backoff algorithm. What is the probability that the contention ends on round k, and what is the mean number of rounds per contention period?