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computer networking

Questions and Answers of Computer Networking

If the power at the beginning of a 1 Km 2.6/9.5 mm coaxial cable is 200 mw, what is the power at the end for frequencies 1 KHz, 10 KHz, and 100 KHz? Use the results of Problem P7-4.
A light signal is travelling through a fiber. What is the delay in the signal if the length of the fiber-optic cable is 10 m, 100 m, and 1 Km (assume a propagation speed of 2 × 108 m)?
Consider an n × k crossbar switch with n inputs and k outputs.a. Can we say that the switch acts as a multiplexer if n > k?b. Can we say that the switch acts as a demultiplexer if n < k?
We need a three-stage space-division switch with N = 100. We use 10 crossbars at the first and third stages and 4 crossbars at the middle stage.a. Draw the configuration diagram.b. Calculate the
We want to transmit 1000 characters with each character encoded as 8 bits.a. Find the number of transmitted bits for synchronous transmission.b. Find the number of transmitted bits for asynchronous
Define analog transmission.
Calculate the baud rate for the given bit rate and type of modulation.a. 2000 bps, FSKb. 4000 bps, ASKc. 6000 bps, QPSKd. 36,000 bps, 64-QAM
Define carrier signal and explain its role in analog transmission.
Calculate the bit rate for the given baud rate and type of modulation.a. 1000 baud, FSKb. 1000 baud, ASKc. 1000 baud, BPSKd. 1000 baud, 16-QAM
Define digital-to-analog conversion.
What is the number of bits per baud for the following techniques?a. ASK with four different amplitudesb. FSK with eight different frequenciesc. PSK with four different phasesd. QAM with a
Which characteristics of an analog signal are changed to represent the digital signal in each of the following digital-to-analog conversions?a. ASKb. FSKc. PSKd. QAM
Draw the constellation diagram for the following:a. ASK, with peak amplitude values of 1 and 3b. BPSK, with a peak amplitude value of 2c. QPSK, with a peak amplitude value of 3d. 8-QAM with two
Draw the constellation diagram for the following cases. Find the peak amplitude value for each case and define the type of modulation (ASK, FSK, PSK, or QAM).The numbers in parentheses define the
Define constellation diagram and explain its role in analog transmission.
How many bits per baud can we send in each of the following cases if the signal constellation has one of the following number of points?a. 2b. 4c. 16d. 1024
What are the two components of a signal when the signal is represented on a constellation diagram? Which component is shown on the horizontal axis? Which is shown on the vertical axis?
What is the required bandwidth for the following cases if we need to send 4000 bps? Let d = 1.a. ASKb. FSK with 2Δf = 4 KHzc. QPSKd. 16-QAM
Define analog-to-analog conversion.
The telephone line has 4 KHz bandwidth. What is the maximum number of bits we can send using each of the following techniques? Let d = 0.a. ASKb. QPSKc. 16-QAMd. 64-QAM
Which characteristics of an analog signal are changed to represent the lowpass analog signal in each of the following analog-to-analog conversions?a. AMb. FMc. PM
A corporation has a medium with a 1-MHz bandwidth (lowpass). The corporation needs to create 10 separate independent channels each capable of sending at least 10 Mbps. The company has decided to use
Which of the three analog-to-analog conversion techniques (AM, FM, or PM) is the most susceptible to noise? Defend your answer.
A cable company uses one of the cable TV channels (with a bandwidth of 6 MHz) to provide digital communication for each resident. What is the available data rate for each resident if the company uses
Find the bandwidth for the following situations if we need to modulate a 5-KHz voice.a. AMb. FM (β = 5)c. PM (β = 1)
Find the total number of channels in the corresponding band allocated byFCC.a. AMb. FM
Describe the goals of multiplexing.
Assume that a voice channel occupies a bandwidth of 4 kHz. We need to multiplex 10 voice channels with guard bands of 500 Hz using FDM. Calculate the required bandwidth.
List three main multiplexing techniques mentioned in this chapter.
We need to transmit 100 digitized voice channels using a passband channel of 20 KHz. What should be the ratio of bits/Hz if we use no guard band?
Which of the three multiplexing techniques is (are) used to combine analog signals? Which of the three multiplexing techniques is (are) used to combine digital signals?
In the analog hierarchy of Figure 6.9, find the overhead (extra bandwidth for guard band or control) in each hierarchy level (group, supergroup, master group, and jumbo group).Figure 6.9 48 kHz 12
We need to use synchronous TDM and combine 20 digital sources, each of 100 Kbps. Each output slot carries 1 bit from each digital source, but one extra bit is added to each frame for synchronization.
Define the analog hierarchy used by telephone companies and list different levels of the hierarchy.
Define the digital hierarchy used by telephone companies and list different levels of the hierarchy.
We have 14 sources, each creating 500 8-bit characters per second. Since only some of these sources are active at any moment, we use statistical TDM to combine these sources using character
Which of the three multiplexing techniques is common for fiber-optic links? Explain the reason.
Ten sources, six with a bit rate of 200 kbps and four with a bit rate of 400 kbps, are to be combined using multilevel TDM with no synchronizing bits. Answer the following questions about the final
Distinguish between multilevel TDM, multiple-slot TDM, and pulse-stuffed TDM.
Four channels, two with a bit rate of 200 kbps and two with a bit rate of 150 kbps, are to be multiplexed using multiple-slot TDM with no synchronization bits. Answer the following questions:a. What
Distinguish between synchronous and statistical TDM.
Two channels, one with a bit rate of 190 kbps and another with a bit rate of 180 kbps, are to be multiplexed using pulse-stuffing TDM with no synchronization bits. Answer the following questions:a.
Define spread spectrum and its goal. List the two spread spectrum techniques discussed in this chapter.
Answer the following questions about a T-1 line:a. What is the duration of a frame?b. What is the overhead (number of extra bits per second)?
Define FHSS and explain how it achieves bandwidth spreading.
Define DSSS and explain how it achieves bandwidth spreading.
Figure 6.34 shows a multiplexer in a synchronous TDM system. Each output slot is only 10 bits long (3 bits taken from each input plus 1 framing bit). What is the output stream? The bits arrive at the
Figure 6.35 shows a demultiplexer in a synchronous TDM. If the input slot is 16 bits long (no framing bits), what is the bit stream in each output? The bits arrive at the demultiplexer as shown by
Answer the following questions about the digital hierarchy inFigure 6.23:a. What is the overhead (number of extra bits) in the DS-1 service?b. What is the overhead (number of extra bits) in the DS-2
What is the minimum number of bits in a PN sequence if we use FHSS with a channel bandwidth of B = 4 KHz and Bss = 100 KHz?
An FHSS system uses a 4-bit PN sequence. If the bit rate of the PN is 64 bits per second, answer the following questions:a. What is the total number of possible channels?b. What is the time needed to
A pseudorandom number generator uses the following formula to create a random series:Ni + 1 = (5 + 7Ni) mod 17 - 1In which Ni defines the current random number and Ni+1 defines the next random
We have a digital medium with a data rate of 10 Mbps. How many 64-kbps voice channels can be carried by this medium if we use DSSS with the Barker sequence?
Using Figure 7.6, tabulate the attenuation (in dB) of a 18-gauge UTP for the indicated frequencies and distances.Figure 7.6 26 gauge Gauge Diameter (inches) 0.0403 20 24 gauge 18 18 0.02320 22
Name the two major categories of transmission media.
How do guided media differ from unguided media?
If the power at the beginning of a 1 Km 18-gauge UTP is 200 mw, what is the power at the end for frequencies 1 KHz, 10 KHz, and 100 KHz? Use the results of Problem P7-1.
What are the three major classes of guided media?
Using Figure 7.9, tabulate the attenuation (in dB) of a 2.6/9.5 mm coaxial cable for the indicated frequencies and distances. Table 7.6 Attenuation for 2.6/9.5 mm coaxial cable dB at 1 KHz dB at 100
What is the function of the twisting in twisted-pair cable?
What is refraction? What is reflection?
What is the purpose of cladding in an optical fiber?
Calculate the bandwidth of the light for the following wavelength ranges (assume a propagation speed of 2 × 108 m):a. 1000 to 1200 nmb. 1000 to 1400 nm
Name the advantages of optical fiber over twisted-pair and coaxial cable.
How does sky propagation differ from line-of-sight propagation?
Using Figure 7.16, tabulate the attenuation (in dB) of an optical fiber for the indicated wavelength and distances.Figure 7.16 100 50 10 0.5 0.1 0.05 0.01 800 1000 1200 1400 1600 1800 Wavelength (nm)
What is the difference between omnidirectional waves and unidirectional waves?
A beam of light moves from one medium to another medium with less density. The critical angle is 60°. Do we have refraction or reflection for each of the following incident angles? Show the bending
Describe the need for switching and define a switch.
A path in a digital circuit-switched network has a data rate of 1 Mbps. The exchange of 1000 bits is required for the setup and teardown phases. The distance between two parties is 5000 km. Answer
Transmission of information in any network involves end-to-end addressing and sometimes local addressing (such as VCI). Table 8.2 shows the types of networks and the addressing mechanism used in each
List the three traditional switching methods. Which are the most common today?
What are the two approaches to packet switching?
Compare and contrast a circuit-switched network and a packet-switched network.
What is the role of the address field in a packet traveling through a datagram network?
What is the role of the address field in a packet traveling through a virtualcircuit network?
The minimum number of columns in a datagram network is two; the minimum number of columns in a virtual-circuit network is four. Can you explain the reason? Is the difference related to the type of
Compare space-division and time-division switches.
Figure 8.27shows a switch (router) in a datagram network.Find the output port for packets with the following destination addresses:a. Packet 1: 7176b. Packet 2: 1233 Output Destination address port
What is TSI and what is its role in time-division switching?
Figure 8.28shows a switch in a virtual-circuit network.Find the output port and the output VCI for packets with the following input port and input VCI addresses:a. Packet 1: 3, 78b. Packet 2: 2, 92c.
Compare and contrast the two major categories of circuit switches.
List four major components of a packet switch and their functions.
It is obvious that a router or a switch needs to search to find information in the corresponding table. The searching in a routing table for a datagram network is based on the destination address;
We need to have a space-division switch with 1000 inputs and outputs. What is the total number of crosspoints in each of the following cases?a. Using a single crossbar.b. Using a multi-stage switch
Compare the telephone network and the Internet. What are the similarities? What are the differences?
What is an internet? What is the Internet?
Categorize the four basic topologies in terms of line configuration.
For each of the following four networks, discuss the consequences if a connection fails.a. Five devices arranged in a mesh topologyb. Five devices arranged in a star topology (not counting the hub)c.
What are the two types of line configuration?
What are the advantages of a multipoint connection over a point-to-point one?
A color image uses 16 bits to represent a pixel. What is the maximum number of different colors that can be represented?
What are the three criteria necessary for an effective and efficient network?
What is the maximum number of characters or symbols that can be represented by Unicode?
Identify the five components of a data communications system.
We have two computers connected by an Ethernet hub at home. Is this a LAN or a WAN? Explain the reason.
What is the difference between half-duplex and full-duplex transmission modes?
In the ring topology in Figure 1.7, what happens if one of the stations is unplugged?Figure 1.7 Repeater Repeater Repeater |Repeater Repeater Repeater
Name the four basic network topologies, and cite an advantage of each type.
In the bus topology in Figure 1.6, what happens if one of the stations is unplugged?Figure 1.6 Drop line Drop line Drop line Cable end Cable end Tap Tap Tap

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