System Programming and Computer Control
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Multiplexing SECTION A
Review Questions 1.
What are the three major multiplexing techniques?
2.
How does FDM combine multiple signals into one?
3.
What is the purpose of a guard band?
4.
How is one FDM signal separated into its original components? components?
5.
Describe the analog hierarchy in which groups of signals are successively multiplexed onto higher-bandwidth lines.
6.
How is WDM similar to FDM? How are they different?
7.
How does TDM combine multiple signals into one?
8.
How is one TDM signal separated into its original components? components?
9.
Discuss the duration of a data unit before and after the TDM process.
10.
Describe the DS hierarchy.
11.
How are T lines related to DS service?
12.
How can T lines be used for analog transmission?
13.
What is the relationship between the number of slots in a frame and the number of input lines for TDM?
14.
Is bit padding a technique for FDM or TDM? Is the framing bit used in FDM or TDM?
15.
What is inverse multiplexing?
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SECTION B
Multiple Choice Questions 16.
The sharing of a medium and its link by two or more devices is called a) Modulation b) Encoding c) Line discipline d) Multiplexing
17.
Which multiplexing technique transmits analog signals? a) FDM b) TDM c) WDM d) and (c)
18.
Which multiplexing technique transmits digital signals? a) FDM b) TDM c) WDM d) None of the above
19.
Which multiplexing technique shifts each signal to a different carrier frequency? a) FDM b) TDM c) Both (a) and (b) d) None of the above
20.
In TDM, for n signal sources of the same data rate, each frame contains __________ slots. a) n b) n+l c) n — I d) 0 to n
21.
In TDM, the transmission rate of the multiplexed path is usually _________ the sum of the transmission rates of the signal sources. a) Greater than b) Less than c) Equal to d) 1 less than
22.
In AT&T's FDM hierarchy, the bandwidth of each group type can be found by multiplying __________ and adding extra bandwidth for guard bands. a) The number of voice channels by 4000 Hz b) The sampling rate by 4000 Hz c) The number of voice channels by 8 bits/sample d) The sampling rate by 8 bits/sample
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23.
DS-1 through DS-4 are ___________ while T-l through T-4 are __________.. a) Services; multiplexers b) Services; signals c) Services; lines d) Multiplexers; signals
24.
In a T-l line, _________ interleaving occurs. a) Bit b) Byte c) DS-0 d) Switch
25.
Guard bands increase the bandwidth for ____________ a) FDM b) TDM c) Both (a) and (b) d) None of the above
26.
Which multiplexing technique involves signals composed of light beams? a) FDM b) TDM c) WDM d) None of the above
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SECTION C Exercises
27.
Given the following information, find the minimum bandwidth for the path. a) FDM multiplexing b) Five lines, each requiring 4000 Hz c) 200-Hz guard separating each band
28.
Given the following information, find the maximum bandwidth for each signal source. a) FDM multiplexing b) Total available bandwidth = 7900 Hz c) Three signal sources d) A 200-Hz guard band between each signal source
29.
Five signal sources are multiplexed using TDM. Each source produces 100 characters per second. Assume that there is byte interleaving and that each frame requires 1 bit for synchronization. What is the frame r ate? What is the bit rate on the path? 100 frames/second, each frame contains 5 characters (40 bits) and one extra frame bit, for the total of 41 bits per frame. Bit rate is 100 x 41 = 4100 bps or 4.1 Kbps
30.
Draw the TDM frames showing the character data, given the following information: a) Four signal sources b) Source 1 message: TEG c) Source 2 message: A d) Source 3 message: e) Source 4 message: E FIL
31.
What is the time duration for a T-l frame? 125 s
32.
The T-2 line offers a 6.312-Mbps service. Why is this number not 4 x 1.544 Mbps?
33.
In Figure 6.19 the sampling rate is 8000 samples/s. Why? Nyquist theorem dictates that the sampling rate must be twice the highest frequency; 2 4000 Hz or 8000 Hz.
34.
If a single-mode optical fiber can transmit at 2 Gbps, how many telephone channels can one cable carry?
35.
Calculate the overhead (in bits) per voice channel for each T line. What is the per centage of overhead per voice channel? T1 line (1,544,000 – 24 64000) /24 = 333 bits /channel (6,312,00 – 96 64000) /96 = 1750 bits /channel 2.7%
0.5% T2 line
T3 line (44,736,000 – 672 64000) /672 = 2571 bits /channel 4.0% T4 line (274,176,000 – 4032 64000) /4032 = 4000 bits /channel 6.2% 36.
Level 2
Three voice-grade lines, each using 4 KHz, are frequency multiplexed together by using AM and canceling the lower modulated band. Draw the frequency-domain
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representation of the resulting signal if the carrier frequencies are at 4, 10, and 16 KHz, respectively. What is the bandwidth of the resulting signal? 37.
Show the frequency-domain representation of the resulting signals in each stage in Figure.22. Assume no guard band. Choose appropriate carrier frequencies.
38.
We have multiplexed 100 computers using synchronous TDM. If each computer sends data at the rate of 14.4 Kbps, what is the minimum bit rate of the line? Can a T1 line handle this situation?
39.
What is the minimum bit rate of each line in Figure 23 if we are using synchronous TDM? Ignore framing (synchronization) bits. 2 × 566 Kbps = 1.132 Mbps
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40.
Figure 24 shows a multiplexer. If the slot is only 10 bits long (3 bits taken from each input plus 1 framing bit), what is the output bit stream? What is the output bit rate? What is the duration of each bit in the output line? How many slots are sent per second? What is the duration of each slot?
41.
Figure 25 shows a demulitplexer. If the input slot is 12 bits long (igonore framing bits), what is the bit stream in each output> What is the bit rate for each output line?
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42.
Figure 26 shows an inverse multiplexer. If the input data rate is 15 Mbps, what is the rate for each line? Can we use the service of T-1 lines for this purpose? Ignore the framing bits.
43.
What is the overhead (number of extra bits per second) in a T-1 line? 8 Kbps
44.
If we want to connect two Ethernet LANs with 10-Mbps data rates, how many T-1 lines do we need? Do we need multiplexers or inverse multiplexers? Show the configuration.
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