Download Pulse Stuffing and TDM Systems-Data Communication and Computer Networks-Quiz Solution and more Exercises Data Communication Systems and Computer Networks in PDF only on Docsity! COMSATS INSTITUTE OF INFORMATION TECHNOLOGY Islamabad campus Dept of Electrical Engineering BTE Program, 6th Semester, Spring 2012 Course Title: Data Communication and Computer Networks Task: Quiz #3 Instructor: Dr. Zeeshan Ali Khan Designation: Assistant Professor, Dept. of Electrical Engineering Contact Info: zakhan@comsats.edu.pk, Room # 217 Date: 10th Apr, 2012 @0830 hrs, Duration: 30 minutes Marks: 50 Student Name: ……………………………………. Student #: ……………………………………. Instructions: All examination rules as per COMSATS policies apply. Do not write in this area Q1 Q2 Q3 Q4 Total Q1-Q4 Date Marks in words Total Q1: What is the purpose of pulse stuffing in TDM systems? (10 marks) In synchronous time division, if each source has a separate clock, any variation among clocks could cause loss of synchronization. Also, in some cases, the data rates of the input data streams are not related by a simple rational number. For both these problems, a technique known as pulse stuffing is an effective remedy. With pulse stuffing, the outgoing data rate of the multiplexer, excluding framing bits, is higher than the sum of the maximum instantaneous incoming rates. The extra capacity is used by stuffing extra dummy bits or pulses into each incoming signal until its rate is raised to that of a locally generated clock signal. The stuffed pulses are inserted at fixed locations in the multiplexer frame format so that they may be identified and removed at the demultiplexer. Q2: What is the functionality of Discrete Multitone? (10 marks) Discrete multitone (DMT) uses multiple carrier signals at different frequencies, sending some of the bits on each channel. The available transmission band (upstream or downstream) is divided into a number of 4-kHz subchannels. On initialization, the DMT modem sends out test signals on each subchannel to COMSATS INSTITUTE OF INFORMATION TECHNOLOGY Islamabad campus Dept of Electrical Engineering BTE Program, 6th Semester, Spring 2012 determine the signal-to-noise ratio.The modem then assigns more bits to channels with better signal transmission qualities and less bits to channels with poorer signal transmission qualities. Q3. The binary chip sequence for four stations which are transmitting the data using CDMA is given below: A: 0 0 0 1 1 0 1 1 B: 0 0 1 0 1 1 1 0 C: 0 1 0 1 1 1 0 0 D: 0 1 0 0 0 0 1 0 The six transmissions consisted of the following sequences: S1 = (-1 +1 -1 +1 +1 +1 -1 -1) S2 = (-2 0 0 0 +2 +2 0 -2) S3 = (0 0 -2 +2 0 -2 0 +2) S4 = (-1 +1 -3 +3 +1 -1 -1 +1) S5 = (-4 0 -2 0 +2 0 +2 -2) S6 = (-2 -2 0 -2 0 -2 +4 0) What is the value of the bit stream that is transmitted by the station C? (15 marks)
