Jaypee Institute of Information Technology (JIIT) 2007 B.Tech computer networks - Question Paper

TEST-1


1. Differentiate ranging from 802.3 and 802.11 with respect to layer and various functions used for the layer
2. Define the Physical Layer for 802.11 and discuss any 2 modulation techniques used in WLAN
3. Define the 802.11 services.
4. Explain DCF and PCF. Where they are used and also discuss their mechanism
5. For this problem, use a formula from this chapter, but 1st state the formula. Frames arrive randomly at a 100-Mbps channel for transmission. If the channel is busy when a frame arrives, it waits its turn in a queue. Frame length is exponentially distributed with a mean of 10,000 bits/frame. For every of the subsequent frame arrival rates, provide the delay experienced by the avg. frame, including both queueing time and transmission time.
a. 90 frames/sec.
b. 900 frames/sec.
c. 9000 frames/sec.
6. A group of N stations share a 56-kbps pure ALOHA channel. every station outputs a 1000-bit frame on an avg. of once every 100 sec, even if the previous 1 has not yet been sent (e.g., the stations can buffer outgoing frames). What is the maximum value of N?
7. Consider the delay of pure ALOHA versus slotted ALOHA at low load. Which 1 is less? discuss your ans.
8. Ten thousand airline reservation stations are competing for the use of a single slotted ALOHA channel. The avg. station makes 18 requests/hour. A slot is 125 µsec. What is the approximate total channel load?
9. A large population of ALOHA users manages to generate 50 requests/sec, including both originals and retransmissions. Time is slotted in units of 40 msec.
a. What is the chance of success on the 1st attempt?
b. What is the probability of exactly k collisions and then a success?
c. What is the expected number of transmission attempts needed?
10. Measurements of a slotted ALOHA channel with an infinite number of users show that 10 percent of the slots are idle.
a. What is the channel load, G?
b. What is the throughput?
c. Is the channel underloaded or overloaded?

Earning:   Approval pending.