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DataCom exam1 - STUDENT ID NO MULT'MED'A a UNNERS'TY Ml...

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Unformatted text preview: STUDENT ID NO MULT'MED'A a UNNERS'TY Ml MULTIMEDIA UNIVERSITY THIRD TRIMESTER EXAMINATION, SESSION 2003/04 SUPPLEMENTARY ECP2056 —- DATA COMMUNICATIONS AND COMPUTER NETWORKING (BE, CE, ME, TE, MCE, BMM) 10 May 2004 2:30pm — 4:30pm ( 2 Hours ) INSTRUCTION TO STUDENT 1. This question paper consists of 7 pages including cover page with 6 questions only. 2. Attempt TWO out of THREE questions from SECTION A and any TWO out of three questions from SECTION B. All questions carry equal marks and the distribution ofthe marks for each question is given. 3. Please print all your answers in the answer Booklet provided. ECP2056 DATA COMMUNICATIONS & COMPUTER NETWORKING MAY 2004 SECTION A Question 1 (a) (b) (C) Identify the key elements of a basic communication system connecting two parties by sketching the system block diagram and explaining the function of each element. [5 marks] Given a data bit stream of l 100000000110000010. Sketch the wave forms when the data bit stream is encoded with the following clock encoding schemes: (i) NRZ—I [2.5 marks] (ii) AMI [2.5 marks] (iii) Manchester [2.5 marks] (iv) High Density Bipolar 3 (H033) [2.5 marks] Assume that the signal level for the preceding bit for all the above codes is low. Messages comprising seven different characters, ‘A’ through ‘G’, are to be transmitted over a data link. Analysis has shown that the relative frequency of occurrence of each character is given as follows: A 0.10, B 0.25, C 0.05, D 032,152 0.01, F 0.07, G 0.2 (i) Derive the Huffman code tree. [6 marks] (ii) Derive the average number of bits per character. [4 marks] Continued... ZiKSI’Wl-l'l'r'HAGfHTCfA ’ " ' ' " ' 2/7 ECPZOSG DATA COMMUNICATIONS & COMPUTER NETWORKING MAY 2004 Question 2 (a) Briefly describe three types of transmission impairment. [6 marks] (b) Name three types of noise. [3 marks] (c) Name three types of digital modulation. [3 marks] ((1) How is QAM related to ASK and PSK? What is the advantage of QAM over ASK or PSK? [5 marks] (6) A line has a signal—to-noise ratio of 1000 and a bandwidth of 4000KHZ. What is the maximum data rate supported by this line? [4 marks] (f) State four important characteristics of RS-232 standard? [4 marks] DEW—HE (a) Sketch the TCP/IP protocol suite and the 081 model. [4 marks] (b) A sender transmits a TCP segment of 2000-bytes data with sequence number 2004 to a receiver. The receiving TCP has defined a 2k byte buffer, and the receiving application consumes only 500 bytes of data before an ACK is returned to the sender. (i) What are the sequence number and the maximum data bytes that can be sent in the next TCP segment? [3 marks] (ii) Determine the efficiency of the transmission in (i) at the TCP level if the binary value in the header length (HLEN) field is 1010. [2 marks] (c) Explain how flow control and congestion control can be achieved with TC]? in relation to the roles played by a sender and receiver. [6 marks] (d) In a network employing TCP with congestion control, the original slow start threshold (ssthresh) is 32 segments and the initial sender window is 1 segment. After the congestion window being increased to 16, a packet lost is detected. If subsequently there is no congestion and packet lost, determine the total time needed for the congestion window to increase to 20 segments from the beginning of the transmission if the round—trip time is constant at 5ms. [5 marks] Continued... H ztkstwurmActHrCtA ’ ' 3/7 DATA COMMUNICATIONS & COMPUTER NETWORKING MAY 2004 ECP2056 1, frames are generated at node A and sent to e A can only send the subsequent frame once it t frame from node D. Determine the link owing conditions: [5 marks] (e) In the network shown in Figure 3. node D through nodes P and Q. Nod receives the acknowledge for the curren utilization between nodes A and P based on the foil I The data rate between A and P is 128kbps I The data rate between P and Q is 64kbps I The date rate between Q and D is 256kbps I The propagation delay in all links is 2><108 ms'] I All links are full duplex I All data frames are 512 bytes long I ACK frames are negligible in size and the processing instantaneous Idle-RQ flow control scheme is used between all connected nodes at the nodes is - Assume that there is no error Given that: T Link efficiency. U = % l on for the transmitter to transmit a frame where Tm is the durati t before it can send the next T, is the time the transmitter has to wai segment Continued... / zrksrwnrrrmG/HTCM 4/4 ECP2056 DATA COMMUNICATIONS & COMPUTER NI’E'I‘WO RKING MAY 2004 M. SECTION B Question 4 (21) Briefly highlight the different types of fiber and sketch the propagation of light beams through these fibers. [9 marks] [8 marks] (b) Describe the mechanism of CSMAI’ CD. (0) A 1.5Mbps token ring network has 20 equally spaced stations. Assume that the packet size is 256 bit and the propagation speed on medium is 2.5):108 ms". (i) Determine the ratio of propagation delay to frame transmission time (a) and the utilization factor (U), if the length of the ring is 80km. [4 marks] (ii) What is the answer for part (i) ifthe length of the ring is 40km? [4 marks] The efficiency of the network is given by l 1 a S l + (I U = 1 N _____ a > 1 a(l + m) where a is the ratio of propagation delay to frame transmission time N is the number of stations on the network Continued... Z/KS/WHTH’IAG/HTCIA i - 5/7 ECPZOSb DATA COMMUNICATIONS 84 COMPUTER NETWORKING MAY 2004 M H ut'n (a) Referring to Figure 5.1, describe in details the three phases involved in circuit switching assuming a connection is to be se tup and torn down between station A and E. [10 marks] (b) State two disadvantages of circuit switching? [2 marks] (c) A message with size 1000bits is to be sent from station A to station F (3 hops). Calculate the total time needed to send the whole message (including the setup success acknowledgement). The following parameters should be considered: Distance between switching nodes, Lnode = 1km Signal Propagation speed, V = 2 xlO8 rns'l Call Request Signal processing delay per node, Tamas: : 10us Network data rate (on all links), B = IOMbps *Assume the distance between the edge switching nodes and workstations are negligible. (d) If this is a datagram network with a maximum allowable packet size of lSOObits and a packet processing time per node, Tpkt of 15us, what is the time required to send this message over assuming the header size is negligible? Comment on the result in comparison to the result obtained in (c) focusing on the message size. [5 marks] \iniain'nnu- Prr‘iunnl rnmpllli-r I'vnmml I‘Hlllllllll‘l‘ l___fi F31 I't-Hunul [that Continued... / ZIKSIWH'wimornrcm , - . 6/7 ECPZOSG DATA COMMUNECATIONS & COMPUTER NETWORKING MAY 2004 uin (a) A router with 3 Ethernet interfaces is shown in Figure 6.1. Specify the network addresses and their classes for LAN A, B and C. [3 marks] Also, determine the IP addresses for Hostl and Host6 that have hostid of 01 1 13 and 10012, respectively. [2 marks] Router interface C Router Interface A 1P: 223.255.2554 1]". 126.255.2551 LAN A 1P: 191.255.2552 Figure 6.1 (b) The initial routing table for the routers in Figure 6.2 is given below. Derive the [16 marks] final routing tables using distance vector algorithm. Initial routing table: R1 : R2 : R3 : R4= :3 use D: distance Figure 6.2 (c) Explain briefly the function of ARP. [4 marks] End of page zmsxwm/HAo/Hrcm ~ , ~ , 7/7 ...
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