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Data and computer communication exam i
- 1. Data and ComputerExam 1 Question 1 If computer B is connected to computer A and C by two point-to-point links, then it is possible to send messages from A to C by sending them first from A to B, then from B to C. This is called store-and-forward transmission. A store-and-forward transmission from A to C via B is more efficient if the transmission from B to C can start before that from A to B is completed. Use this concept to answer the following questions: a. Suppose A wants to send a long message to C and that the transmission of that message on a direct link takes one minute. How long would it take for the message to be fully transmitted from A to C? b. Now suppose that the long message in (a) is decomposed into 60 packets that take one second each to be transmitted on a direct link. How long would it take for the message to be fully transmitted (as packets) from A to C? Answer for blank # 1: 2 minutes Answer for blank # 2: 61 seconds Question 2 A 5-story office building has the floor plan of the following figure for each floor. A local network is to be installed that will allow attachment of a device from each office on each floor. Attachment is to take place along the outside wall at the baseboard. Cable or wire can be run vertically through the indicated closet and horizontally along the baseboards. The height of each story is 8 feet. What is the minimum total length of cable or wire required for star topology? Which floor’s closet should house the center of star? Please use the floor plan given at homework 3 except the height of each story is 8 feet now. a. Length on each floor ______ feet b. Total length of cable _______ feet for the star topology? c. Which floor’s closet should house the center of star? _____ Answer for blank # 1: 1330 feet Answer for blank # 2: 7332 feet Answer for blank # 3: 3 Question 3 Define the following parameters for a switching network:
- 2. N = numberof hops between two given end systems L = message length, in bits B = data rate, in bits per second (bps), on all links P = packet size H = overhead (header) bits per packet S = call setup time (circuit switching or virtual circuit), in seconds D = propagation delay per hop, in seconds For N = 5, L = 4800, B = 9600, P = 1024, H = 24, S = 0.1, D = 0.01, compute the end-to-end delay for circuit switching? Assume that there are no acknowledgments Answer: Circuit Switching: = N X D + L/B = 5 X 0.01 + 4800/9600 =0.55 T= C1 + C2 = 0.1 + 0.55= 0.65seconds Question 4 Define the following parameters for a switching network: N = number of hops between two given end systems L = message length, in bits B = data rate, in bits per second (bps), on all links P = packet size H = overhead (header) bits per packet S = call setup time (circuit switching or virtual circuit), in seconds D = propagation delay per hop, in seconds For N = 5, L = 4800, B = 9600, P = 1024, H = 24, S = 0.1, D = 0.01, compute the end-to-end delay for datagram packet switching. Assume that there are no acknowledgments. Answer: 1.011 seconds Question 5 The ...............layer is the layer closest to the transmission medium. Physical data link network transport Question 6 As the data packet moves from the lower to the upper layers (OSI Model), headers are ……….. Added Removed Rearranged
- 3. Modified Question 7 Mail servicesand directory services are available to network users through the ………… layer. Data link Session Transport Application Question 8 Ten out of fourteen stations on a LAN accept the same transmission. The destination address is probably a …………… address. ……………..refers to the way a network is laid out. Topology Access method Addressing Formatting Question 10 The medium interface on a …………….topology is a passive device that is either internal or external to the station. Bus Ring Star 2 and 3 Unicast Multicast Broadcast None of the above Question 9
- 4. Question 11 In aring topology data is transmitted in……………direction(s). one two three four Question 12 Briefly comment on the following ethical question raised by communications networks: Should unauthorized access to a computer account be considered illegal or does the responsibility lie with the owner of the account? It should be considered illegal for unauthorized access to a computer account. Question 13 Light travels between point A and point B in 0.01 seconds. What is the distance between A and B? 3 km 30 km 300 km 3,000 km
- 5. Question 14 A bitrate of 10 Kbps means that ..............bits are sent in 10 seconds. 100,000 20,000 10,000 1000 Question 15 Differential Manchester encoding has...........signal levels. 1 2 3 4