Telephony Tdm u4g1r

INSTRUCTION Answer ALL Question, and submit by 21/08/2011 1. Define TDM. 2. Describe the process of TDM. 3. Draw a block diagram of TDM using Pulse Code Modulation (PCM) according to European E-Line(30 channels) 4. Explain the function of sampling, quantizing and encoding. 5. Describe TDM hierarchy: a. European E-line (30 channels) b. North American T-line (24 channels)

1. Time-division multiplexing (TDM) is a type of digital (or rarely analog) multiplexing in which two or more bit streams or signals are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel. The time domain is divided into several recurrent timeslots of fixed length, one for each sub-channel. A sample byte or data block of sub-channel 1 is transmitted during timeslot 1, sub-channel 2 during timeslot 2, etc. One TDM frame consists of one timeslot per sub-channel plus a synchronization channel and sometimes error correction channel before the synchronization. After the last sub-channel, error correction, and synchronization, the cycle starts all over again with a new frame, starting with the second sample, byte or data block from subchannel 1

2. Time Division Multiplexing Time Division Multiplexing is the process of dividing up one communication time slot into smaller time slots. We will use the example of a T1 which is time-division multiplexed at the DS1 rate. A T1 consists of 24 channels which are read 8,000 times per second. Each time a channel is read, a value is obtained. Thus, a time slot for a T1 is 1/8,000th of a second. Timedivision multiplexing combines the values from all 24 channels on the T1 into the same 1/8,000th of a second. In the diagram below you can see the 24 channels (CH 1 through CH 24) of a standard T1. At a given point in time (t), every channel provides an input value (not really, but that's a more complicated subject for later). These input values are represented in this diagram by the letters of the alphabet next to each channel in the diagram. The data es through the multiplexing device and emerges from the other side as a timedivision multiplexed signal that contains the inputs from all the other channels (t+1). Note that all 24 pieces of information are still being transmitted, but are being transmitted together in the same ammount of time as when they were part of their original channels.

CH 1 CH 2 CH 3 CH 4 CH 5 CH 6 CH 7 CH 8 CH 9 CH 10 CH 11 CH 12 CH 13 CH 14 CH 15 CH 16 CH 17 CH 18 CH 19 CH 20 CH 21 CH 22 CH 23

timeslot A B C D E F G H I J K L M N O P Q R S T U V W

next timeslot

M u l t i p l ABCDEFGHIJKLMNOPQRSTUVWX e x e r

CH 24

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