CS 447 Network and Data Communication

CS 447 Network and Data Communication Final Exam - Summer, 2003

9:00-10:40 A.M. August4, 2003

This question is a closed book and closed note exam. There are eight questions in this exam. You have 100 minutes to finish the eight questions. Please write your answers on separate pieces of papers. To avoid grading problems, please staple your papers in the ascending order in the question number. Questions are printed on total of four pages.

Name: ______Student ID (optional): ______

Question #1 (15 minutes)

(1) We discussed that end user application programs usually will NOT directly exchange (send and receive) data (as shown by a figure below). Instead, a network protocol stack (such as TCP/IP) is responsible for transmitting user data on behalf of user application programs. What is the primary motivation in doing this? Give two most important (you think) reasons. Your solutions should be short (one line of sentence for each) (3 minutes).

(2) What is the primary motivation in transmitting data using "packet"? Mention what would be the problems (mention two problems) if we do not transmit data using packets. Your solutions should be very brief (as long as the ideas are correct, you will get credit) (2 minutes).

(3) What are the five key words that describe "what is socket" (you do NOT have to describe them, just name the five key words)? (2 minutes)

1 (4) Describe what is "port"? How you can choose available port? (2 minutes)

(5) Describe (define) repeater, hub, bridge and router. Make sure to include the keywords – actually you can answer to this question by giving the keywords (2 minutes).

2 (6) Fill out (A), (A'), (B), (B'), (C) and (C') in the PPT slide below (2 minutes):

CS 447 Network and Data Communication

Operation at a router Simplest Most Complex

Multirate Circuit Switching Cell Relay Circuit Frame Relay Packet Switching (ATM) Switching (IP Network)

______(A) ______(A’)

______(B) ______(B’)

______(C) ______(C’)

Frame-Relay/006

(7) What is the probability of non-detectable error for parity error detection using even parity, bit error rate = 10-6, and frame size = 8 bytes (please give the formula - you do not have to complete calculation)? Assume that the start and stop bits are never in error (2 minutes).

(1) Given an IP address of “127.151.3.8” and there are 19 sub-networks in this network domain, give the sub-network address and host address in this IP address. (5 minutes)

(2) What is the minimum requirement (for transmission rate) for the shared link for a statistical TDM (to be non-blocking) shown below – show the required minimum transmission rate using S and n. Assumptions are given below (5 minutes):

Assumptions are:  Assuming there are n inputs (the number of the input lines is assumed to be powers

3 of 2 for simplicity, such as 2, 4, 8, 16, …2k).  All the input lines have the same transmission rate of 17 Mbps.  The slot payload size for each input line is S bits

(3) For the following small network, calculate the shortest path from node A to other nodes in the network using Bellman-Ford's shortest path algorithm. Show all the intermediate work (5 minutes).

5 D B 3 5 2 9 1 F A 1 9 2

Although slow start with congestion avoidance is an effective technique for coping with congestion, it can result in long recovery times in high-speed networks.

(a) Assume a round-trip delay of 85ms (42.5ms for one way), and a link with available bandwidth of 1Gbps, and a segment size (i.e., a packet size) of 750 octets (1 octet = 1 byte). Determine how long will it take the window size becomes large enough to achieve the link utilization = 100% using the sliding window flow control after the window size is reset to 1 due to a network congestion. Assume that all packets are the same size (this is not real, but to simplify your work).

(b) What will happen to the recovery time you calculated for question (a) above if the packet size is increased to 1,215 bytes?

4 Question #4 (7.5 minutes)

An asynchronous transmission scheme uses one-bit start bit, 7 data bits, an even parity bit, and one-bit stop bit. What percentage of clock inaccuracy can be tolerated at the receiver with respect to the framing error? Assume that if a bit sample is taken at after (or before) a bit boundary, then signal of wrong bit will be read. Assume that the sender and receiver clocks are synchronized (both adjusted to be at the middle of the bit at the start bit). Since this is one of the sample midterm questions, you do not have to describe your solution. Just give me your final solution.

Question #5 (17.5 minutes)

(1) For a token-ring network with the following parameters, what is the packet size to reach utilization = 60%? Ignore time to transmit the token and the delay the token propagate to the next neighbor host.

 Transmission Rate = 10Mbps  There are 400 hosts in the ring network  There is 2-bit repeater delay at every tapping-repeater  The link distance is 16Km/link (same distance for every link)  Signal propagation speed = 200m/s

(2) In the following network, host A and B are transmitting data to host D through host (actually a router) C. The sliding window flow control is used for all links. Transmission rate is 10Mbps for all links, too. If the window size is represented by k, what is "k" for link A-C to avoid packet overflow at host C? Packet size is 600 bytes for all links. Assume that there is not any other traffic in the network (no error either). Signal propagation speed = 200m/s.

B 1,000Km k = 25

5 Question #6 (10 minutes)

(1) What are the four major components in ISA to provide QoS data transmission?

(2) What are the four different traffic types defined in ISA (give the names of the four different traffic types and define them)?

(3) Describe the major differences between IP packet transfer and Frame-Relay packet (actually “frame”) transfer.

Describe how the retransmission time out (RTO) interval is calculated in actual TCP. You need to start your description from the beginning (i.e., you need to start from how the round trip time is predicted).

For the following assumptions, find the solution for the following two questions:

Question #1: What is the utilization in the first second after the transmission starts? Question #2: How many bits are enough for the sequence number?

Assumptions:  The round trip time is 50ms (i.e., 25ms for one-way)  Signal transmission rate = 1Mbps  Packet size = 120 bytes (not bits)  Packet life time is 50ms after a packet is transmitted (it is usually much longer, but just for this question, assume that the packet life time is 50ms, which is round trip time for this connection).  Five bits for the packet sequence number  Use sliding widows flow control  Use TCP slow-start  Assume no error and no extra overhead

6  The round trip time is always 50ms for every packet transmission (this is to simplify your work).

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CS 447-Network and Data Communication, Final Exam, August 4, 2003