Pulse-Code-Modulation - Computer Networks - Old Exam Paper, Exams of Computer Networks

Download Pulse-Code-Modulation - Computer Networks - Old Exam Paper and more Exams Computer Networks in PDF only on Docsity! Cork Institute of Technology Bachelor of Science (Honours) in Software Development – Stage 2 (NFQ Level 8) Summer 2007 Computer Networks (Time: 3.0 Hours) Answer 4 questions. Examiners: Mr. R. Miller All questions carry equal marks. Dr. J. Twomey Dr. M. O’Cinneide Mr. M. Donnelly Q1 (a) A PC transmits data at 14Kbps. The data undergoes binary encoding involving (4 marks) 128 states prior to entering a communications channel. Determine the baud rate in the channel? (b) What are the essential features of Pulse-Code-Modulation (PCM). (4 marks) (c) A 6-bit PCM system is employed in a telephone network having an analogue (4 marks) bandwidth of 4000Hz. Determine the sampling rate and the bit rate. (d) Describe with the aid of diagrams the operation of Phase-Shift-Keying (PSK) (5 marks) (e) What is QAM and how is it implemented ? (2 marks) (f) What are the main activities that occur when a MODEM is connected to a (6 marks) dial-up telephone network for the purpose of transferring data? Explain why the data-rate of a 56K MODEM is faster when downloading data from an ISP than when uploading data? Q2 (a) Explain the main features of CDMA (Code-Division-Multiple-Access) (4 marks) Technologies? What are the main advantages and disadvantages of CDMA Technology? (b) Draw a block diagram of a frequency-hopped CDMA system and explain (4 marks) its operation. . (c) A Direct-Sequence Spread Spectrum (DSS-SS) CDMA system requires 36dB of (9 marks) continuous wave (CW) power interference rejection and employs a 10-stage shift register m-sequence pseudo-random generator to transmit 500bps of a data message on a 1.0GHz carrier. Determine the clock rate of the code generator and the first-lobe bandwidth. (d) Compare and briefly describe the following types of multiplexing TDM, FDM and (4 marks) Statistical Multiplexing. (e) A number of 1200bps terminals are connected to a data-line having a bit rate of (4 marks) 16800bps. Estimate the maximum number of terminals that may be connected reliably to the line assuming low utilization. Q3 (a) Deduce the number of additional bits required to transmit data consisting of (12 marks) 600 eight bit characters in each of the following situations:- i) Transmission is asynchronous with one start bit and two stop bits.. ii)Transmission is synchronous with one synchronisation byte and one STX byte at the beginning and one end of text ETX byte at the end of each frame. 50 bytes of data is transferred during each frame. What is the efficiency in each of the above situations ? (b) Explain briefly what error detection is and how it functions. (3 marks) (c) What is the binary representation for the following polynomial:- (3 marks) X11+X3+X (d) Another bit stream 11101010110 has been detected at the receiving end of a (5 marks) network. Has it been received error free ? [Use the polynomial X3+X2+X ] (e) When data is not received correctly what is the next stage in the process? (2 marks)