DataCom exam8 - STUDENT ID N O {11.3mm MULTIMEDIA m...

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Unformatted text preview: STUDENT ID N O {11.3mm MULTIMEDIA m UNIVERSITY MULTIMEDIA UNIVERSITY THIRD TRIMESTER EXAMINATION, SESSION 2006/07 ECPZflSé —- 3113311311 COMMUNICATIONS AND COMPUTER NETWORKING- (BE. TE, (31;, ME, MCE, OPE, NANO and BMM) 18 MAY 2007 3:00 AM — 11:00 AM (2 HOURS) INSTRUCTION TO STUDEi T 1. This Question paper consists of 6 pages including cover page with 2 Sections and 6 Questions only. Attempt TWO out of THREE questions fiom EACH SECTION. All questions carry equal marks and the distribution of the marks for each question is given. Please print all your answers in the answer Booklet provided. ECP2056 DATA COMMUNICATIONS AND COMPUTER NETWORKING MAY 2007 SECTION A (Attempt any 2 out of 3 questions from this section) Question 1 (a) What is a communication and networking protocol? [1 mark] I (b) Briefly explain three key elements of a communication and networking protocol. [6 marks] (c) State two reasons why standards are needed for communications. [2 marks] (d) State two benefits to layering as seen in the OSI and TCP/IP architectures. [2 marks] (e) The OSI model consists of several layers. Name all layers and state one function of each layer. 4 [10 marks] (f) What is a Protocol Data Unit (PDU)? Briefly explain with the aid of a sketch the PDU of-a transport layer in the OSI model. [4 marks] Question 2 (a) When data is transmitted between two communicating devices, three analogous modes of operation can be used. Name these three modes of communication and give one example for each [6 marks] (b) A poem which consists of 20000 characters (including text, space, and punctuation symbols) is to be transmitted through a communication channel with bandwidth of 3000 Hz. To achieve frame synchronization, these characters are encapsulated between one STX and one ETX control characters. Each character is encoded with 7- bit ASCII data code, plus one odd parity bit. Using asynchronous communication, with one start bit and two stop bits per character, calculate the duration of transmission if the poem is sent: i. at the maximum bit rate through a noisy channel with a signal—to-noise ratio of 34dB. [4 marks] ii. through a noise—free channel, at the maximum bit rate using a transmission scheme with 4 levels per signaling element. ' [4 marks] iii. using a 3600 baud QAM modem that is able to provide 16 signaling states. [4 marks] (c) i. What is the main difference between a Forward Error Control (PEG) and a feedback (backward) error control? [2 marks] ii. Describe two disadvantages of forward error control. [2 marks] iii. Determine the message (including 3-bit CRC) to be sent by the sender to the receiver if the data unit is 110011012 (rightmost bit is least significant bit) and the polynomial divisor is x3 + x + 1. [3 marks] Continued NNA/LSUZMsrrWH/GHA/MHH 2 / 6 ECP2056 DATA COMMUNICATIONS AND COMPUTER NETWORKING MAY 2007 Question 3 (a) Popular P2P applications such as the BitTorrent allow you to share data with a peer Via the Internet. Assuming that your ISP does not perform content filtering, calculate the minimum time (in hour) required to download a compressed digital movie with the size of 1 Giga bytes (1 ><109 bytes) if you are using: 1. ii. iii. iV. V. Vi. V32 modem [2 marks] V.32bis modem [2 marks] V.90 modem [2 marks] DS-l TDM line [2 marks] ISDN BR] [2 marks] Analyze the results from (i) to (iii). Are they realistic? Explain your answer in detail. [3 marks] (b) Carefully describe the attributes that lead to the trade—offs between Go—Back-N and Selective Reject Automatic Repeat Request (ARQ). Your discussion should make it clear when Go-Back—N is best suited and when Selective Reject is best suited. [7 marks] (c) Assume a lOOMbps link of 10,000m in length with 5ns/1n propagation delay. Assume constant length 400—byte data frames, 64-byte ACK frames, IOus of processing delay for each data frame, and 5 us of processing time for each ACK. The sender always has data to send. Solve for the link utilization (U) between a sender and a receiver assuming a stop-and-wait protocol. Show your calculation clearly.[5 marks] Continued NNA/LSL/ZMS/TWH/GHA/MHH 3/6 ECP2056 DATA COMMUNICATIONS AND COMPUTER NETWORKING MAY 2007 SECTION B (Attempt any 2 out of 3 questions from this section) Question 4 (a) Local Area Network (LAN) is a popular mean to interconnect distributed communities of computer-based data terminal equipments (DTEs) located within a single building or localized group of buildings. i. State two characteristics of LAN. [2 marks] ii. Give two advantages of LAN. [2 marks] (b) In the 100Mbps Fast Ethernet network depicted in Figure Q42), the distance between each station and the hub is 100m. The maximum and minimum Ethernet frame lengths (including overhead bits) are 1518 bytes and 64 bytes respectively. Assume Figure Q4b i. What is the maximum allowable delay in the hub if proper collision detection is not compromised? ' [4 marks] ii. If station A transmits a frame of 512 bits at time t = 0s and station B transmits a frame of 1024 bits at time t = 2us, determine the time when the hub detects the collision. Assume that all other stations remain idle and the hub has the maximum delay as calculated in (i). (Hint: Represent the hub as additional medium with a length that causes the same propagation delay as the hub’s delay) [5 marks] (c) An IEEE 802.11 MAC frame may contain up to 4 address fields as shown in Figure Q4c. Determine the contents of each address field for the MAC frame in Figure Q40. [4 marks] 2 bytes 2 bytes 6 bytes 6 bytes 6 bytes 2 bytes 6 bytes 0 to 2312 bytes 4 bytes n Wireless distribution system Station A I, Access point 1 Access point 2 MAC address: MAC address: MAC address: MAC address: OO:BO:D0:86:BB:F7 OO:30:OA:32:52:SD 00:14:BF:D9:84:78 00:04:E2:84:89:20 Figure Q4c or Continued NNA/LSL/ZMSh‘WH/GHA/MHH 4 / 6 ECP2056 DATA COMMUNICATIONS AND COMPUTER NETWORKING MAY 2007 (d) Figure Q4d shows the topology of a local area network (LAN), which is divided into multiple smaller LAN 5 using connecting devices such as hubs, bridges and repeaters. i. State and briefly elaborate two reasons of dividing one LAN into multiple LAN s. [4 marks] ii. Name the layers in the 031 model that are related to the implementation of hubs, bridges and repeaters. [4 marks] Hubs Bridge Repeater Figure Q4d Question 5 (a) A switch is required to connect 15 input channels with 15 output channels. i. If a single stage crossbar switch is used, find the total number of cross-points available. [1 mark] ii. Instead of a one stage crossbar switch, design a three stage crossbar switch that utilized a series of switches with 5X4 cross-points, 3X3 ’cross-points and 4X5 cross-points. [7 marks] iii. Find the efficiency improvement if approach (ii) is used instead of (i). [2 marks] (13) Name two types of packet switching and state three key differences between them. [8 marks] (c) i. Explain why fixed length cell is used in ATM networks. [3 marks] ii. If the data field size is 48 octets, the header size is 5 octets and the transmission efficiency is defined as: number of information octet Total number of octet transmitted Calculate the efficiency if 1,500 bytes of data are to be transmitted. [4 marks] Continued fiA/LSUZMSHWWGHA/MHH 5 / 6 ECP2056 DATA COMB/IUNICATLQJS AND COMPUTER NETWORKING MAY 2007 Question 6 (a) You are the new network engineei for a company. The company has several networks interconnected to each other as shown in Figure Q6a. End hosts Ethernet A ' Ethernet B figure Q60: Network layout of your company “viable Q6a: IP address and Host [1221ng network IP address t 125.255.2531 r_...e.._.___..._ Router interface E3 Router interface E4 191.255.2552 End host E8 223.255.2554 Router interface E6 1000; 5 i. The list containing some of the IP addresses of your network is lost. Based on the information given in the figure and table above, find out the IP addresses of Ethernet A, Ethernet B, end host E1, end host E2 and router interface E6. [10 marks] ii. Specify the netwmk classes of Ethernet A and Ethernet B. Compare them in terms of number of networks and number of hosts supported. -' Calculate the actual number when you do the comparison. [6 marks] iii. Define the name of the process you should carry out if your employer requested you to divide Ethernet A into smaller subnetworks connected together by routers. {1 mark] (b) Briefly explain: i. Address Resolution Protocol (ARP) [2 marks] ii. Time to live (TTL) field in IP datagram [2 marks] iii. Domain Name Server (DNS) ' [2 marks] iv. Round-Trip Time (RTT) [2 marks] End of Paper NNA/LSUZMSFFWH/GHA/MHH o / 6 ...
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DataCom exam8 - STUDENT ID N O {11.3mm MULTIMEDIA m...

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