8.6 Explain in terms of data link control and physical layer concepts how error and flow control are accomplished in synchronous time division multiplexing.

8.12 Find the number of the following devices that could be accommodated by a T1-type TDM line if 1% of the T1 line capacity is reserved for synchronization purposes.

a. 110-bps teleprinter terminals

b. 300-bps computer terminals

c. 1200-bps computer terminals

d. 9600-bps computer output ports

e. 64-kbps PCM voice-frequency lines

How would these numbers change if each of the sources were transmitting an average

of 10% of the time and a statistical multiplexer was used?

8.13 Ten 9600-bps lines are to be multiplexed using TDM. Ignoring overhead bits in the TDM frame, what is the total capacity required for synchronous TDM? Assuming

that we wish to limit average TDM link utilization to 0.8, and assuming that each TDM link is busy 50% of the time, what is the capacity required for statistical TDM?

8.14 A synchronous nonstatistical TDM is to be used to combine four 4.8-kbps and one 9.6-kbps signals for transmission over a single leased line. For framing, a block of

7 bits (pattern 1011101) is inserted for each 48 data bits. The reframing algorithm (at the receiving demultiplex) is as follows:

1. Arbitrarily select a bit position.

2. Consider the block of 7 contiguous bits starting with that position.

3. Observe that block of 7 bits each frame for 12 consecutive frames.

4. If 10 of the 12 blocks match the framing pattern the system is “in-frame”; if not

advance one bit position and return to step 2.

a. Draw the multiplexed bit stream (note that the 9.6kbps input may be treated as

two 4.8-kbps inputs).

b. What is the % overhead in the multiplexed bit stream?

c. What is the multiplexed output bit rate?

d. What is the minimum reframe time? What is the maximum reframe time?

What is the Average reframe time?

8.15 A company has two locations: a headquarters and a factory about 25 km away. The factory has four 300-bps terminals that communicate with the central computer facilities over leased voice-grade lines. The company is considering installing TDM equipment so that only one line will be needed. What cost factors should be considered in the decision?

8.16 In synchronous TDM, the I/O lines serviced by the two multiplexers may be either synchronous or asynchronous although the channel between the two multiplexers

must be synchronous. Is there any inconsistency in this? Why or why not?

8.18 For a statistical time division multiplexer, define the following parameters:

OH = 40 C = 9.6 kbps

C = 9.6 kbps OH = 40,

C = capacity of link, bps

L = load of data in the frame, bps

OH = overhead in a frame, bits

F = frame length, bits

a. Express F as a function of the other parameters. Explain why F can be viewed as a variable rather than a constant.

b. Plot F versus L for and values of 80, 120. Comment on the results and compare to Figure 8.14.

c. Plot F versus L for and values of and 8.2 kbps. Comment on the results and compare to Figure 8.14.

8.19 In statistical TDM, there may be a length field. What alternative could there be to the inclusion of a length field? What problem might this solution cause and how could it

be solved?