In the following synchronous time-division multiplexer, each TDMA frame consists

Question

In the following synchronous time-division multiplexer, each TDMA frame consists of one bit taken from each input plus one framing bit.

a) Sketch the output frames, clearly showing the frames and its contents. Use ”F” to represent the framing bit and use ”X” to represent an empty slot. You should assume that the input is taken from the right hand side of each bit-stream. The output frame is also formed right-to-left and the framing bit is the left-most bit.

b) What is the output bit rate?

c) If the multiplexer in the gure below performs statistical multiplexing and the data rate of the output ismaintained to be 20 Kbps, sketch the output frames. Ignore any framing or addressing bits,and clearly describe how the output frame is being constructed.

Explanation / Answer

hii thanks for choosing chegg!! here you go with the answer!!

a)Assuming that every frame has one framing bit(F) at the starting of the frame. In TDMA the frame is constructed by placing the frame bit at the starting and then the bit from the first source, then the bit from the second source, a bit from the third source and the bit from the fourth source. If there is no bit from any of these sources then that time slot would be empty which is denoted by 'X' here.

Hence, the multiplexed output would be F1010F0100FX001FXXX1 this one could be represented by putting a frame around from 'F' to the before bit before the next 'F' . That is F1010 F0100 FX001 FXXX1 , the gaps represent each frame.

b) The output bit rate is calculated as follows..

The input bit duration is the inverse of the bit rate:
1/5 Kbps = 200 s.

The output bit duration is one-fourth of the input bit duration, or (1/4)*200 s=50s.

The output bit rate is the inverse of the output bit duration or 1/(50s) =20 Kbps.

This could also be simply devised as the output bit rate would be 4 times the input rate that would give 4*5Kbps=20Kbps.

c) Statistical multiplexing is used for effective usage of bandwidth. In TDM there are fixed time slots for eact source, here when one of the source is not transmitting then the slot is left empty which leads to wastage of bandwidth. And also statistical multiplexing allows to allocate extra bandwidth to a particular source for a particular time. Which makes the statistical multiplexing more dynamic. Here the frames are constructed in a similar fashion as in in TDM but when there is a empty slot because of no information from any of the sources then the frame size changes and instead of having an empty slot the next bit is put in. Hence the sequence of bits would be 1010 0100 001 1.

Thank you!! happy learning!! :)

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.