INSTRUCTIONS: This Is a Diagnostic Test to Assist You and the Instructor to Evaluate Your

CSE 534 (Fall 2006)

Pre-Test

(30 min, 25 points)

INSTRUCTIONS: This is a diagnostic test to assist you and the instructor to evaluate your preparation for this class. Grade on this test will not be a part of your overall score.

NAME:_____________SAMPLE________ STUDENT ID:______________________

Answer the following questions:

1. What is your computer networking background e.g. courses, work experience, etc.?

2. What are your expectations from this class, i.e. what do you expect to learn in this class?

Multiple Choice Questions (15 points)

_______ 1. Which one of the following services TCP does NOT provide?

(A) Reliable data transport

(B) Connection-oriented service

(D) Minimum bandwidth guarantee

_______ 2. Which of the following techniques is NOT used by reliable data transmission protocols to ensure reliability?

(A) Timeouts

(B) Acknowledgements

(D) Pipelining

_______ 3. If a 16 KB packet is sent over a 1000 m fiber channel whose propagation speed is 2 x 108 m/sec, what is the propagation delay of the channel?

(A) 65 msec

(B) 5 msec

(D) 7.6 msec

_______ 4. Which of the following types of delay will increase as the traffic

intensity increases?

(A) Processing delay

(B) Queueing delay

(D) Transmission delay

(E) All of the above

(F) None of the above

_______ 5. Which of the following factors does NOT affect the window size in a sliding window protocol?

(A) Congestion in the network

(B) Reliability of the links

(C) The available buffer space at the sender

(D) Speed (Bandwidth) of the links

(E) All of the above

_______ 6. Which of the following characteristics make UDP suitable for real-time applications?

(A) UDP does not spend time doing error recovery, so it is very fast.

(B) UDP is connection oriented, so packets do not need to be reordered by the application.

(D) All of the above

(E) A and C only

(F) A and B only

(G) B and C only

_______ 7. If the countdown timer used by the stop-and-wait protocol expires which of the following must be done?

(A) The receiver will send a NAK to the sender.

(B) The sender will resend the most recently sent packet.

(D) The sender will send a packet with the next available sequence number.

_______ 8. Suppose there is a 10 Mbps microwave link between a geostationary satellite and its base station on Earth. Every second the satellite takes a digital photo and sends it to the base station. Assume a propagation speed of 2.4 · 108 meters/sec, an altitude of 36,000 km and no processing delay. If the base station has to receive the photo no later than one second after it is taken, what is the maximum size of the photo?

(A) 15 Mb

(B) 10 Mb

(D) 1.5 Mb

_______ 9. Which of the following is NOT a category for Medium Access Protocols:

(A) Random Access

(B) Channel Partitioning

(D) Statistical Multiplexing

_______ 10. Which of the following is a loss-tolerant application:

(A) Instant Messaging

(B) Interactive games

(D) Web documents

_______ 11. Which of the following applications has elastic bandwidth requirement:

(A) Real-time Audio

(B) Stored Video

(D) E-mail

_______ 12. Which of the following is a Time Insensitive application:

(A) Instant Messaging

(B) Realtime Video

(D) E-mail

_______ 13. Which of the following application-layer protocols does not normally use TCP:

(A) SMTP

(B) Telnet

(D) Net2Phone

_______ 14. The number of bits a sender can transmit to a receiver on a connection with bandwidth R and one-way latency L, before it receives any acknowledgement from the receiver is:

(A) RL

(B) 2RL

(D) 2L/R

_______ 15. Assuming that tprop is the maximum propagation delay between any two adapters in an Ethernet, ttrans is the maximum size of an Ethernet frame, N is the number of adapters connected to the Ethernet, and L is the length of the Ethernet cable, which of the following is NOT true about efficiency of Ethernet:

(A) As tprop approaches 0, efficiency approaches 1.

(B) As ttrans becomes very large, efficiency approaches 1.

(D) As N increases, efficiency approaches 1.

Short Answer Questions (10 points)

1. (2 point) Explain why packet switching is used in the current Internet.

Better sharing of the bandwidth than circuit switching.

Simpler, more efficient and less costly to implementation.

2. (5 points) Answer the following questions for the figure shown below:

a) (1 point) Which host’s/router’s ARP table entries would change if the host with IP address 223.1.3.2 goes down for a long time?

R3 (because of adapter 223.1.3.27) and Host 223.1.3.1

b) (1 point) Suppose we want to add a new host to the LAN at the top (connected to router R1 via interface 223.1.1.3). What is a valid IP address that can be assigned to this new host?

223.1.1.x where x can be 0,2 or any integer between 5 and 255 (inclusive)

c) (1 point) Suppose we want to connect another new LAN to router R3. What is a valid IP address that can be assigned to the fourth interface of R3?

223.1.x.y where x can be 0,4,5,6, or any integer between 10 and 255 (inclusive) and y can be any integer between 0 and 255 (inclusive).

d) (1 point) What is the maximum number of hosts that can be connected to this new LAN?

255 because one is used by the router

e) (1 point) What will be the effects on the traffic in the LANs if routers (R1,R2,R3)

1) are replaced by Switches (Bridges) (S1,S2,S3)?

The traffic increases before the switch tables are established at the switches. After that, the traffic should be similar to the network using routers because both have isolated collision domains.

2) are replaced by Hubs (H1,H2,H3)?

Traffic increases because the network becomes one big collision domain. In other words, each host can be received by any one else in the network.
3. (3 points) Consider a broadcast channel with 10 nodes and a transmission rate of 10 Mbps. Suppose the broadcast channel uses:

a) (2 points) Polling (with an additional poll node) for multiple access: Suppose that the amount of time from when a node completes transmission until subsequent node is permitted to transmit (that is, the polling delay tpoll) is 100 micro sec. Suppose that within a polling round, a given node is allowed to transmit for at most 1 milli sec. What is the maximum throughput of the broadcast channel?

N = 10; R = 10Mbps; Q = 1ms x 10Mbps = 104bits; tpoll = 100x10-6s; the maximum throughput = == 9090909 bps

b) (1 points) TDMA for multiple access: Suppose that the size of each slot is 1 milli sec. long and there is a 1 micro sec. gap between two slots. What is the maximum throughput of the broadcast channel?

N = 10; R = 10Mbps; Q = 1ms x 10Mbps = 104bits; tpoll = 10-6s; the maximum throughput = == 9990009 bps