Download Chapter 11: Voice and Data Delivery Networks

Chapter 11: Voice and Data Delivery Networks
TRUE/FALSE
1. The Internet can transfer conventional data and voice data.
ANS: T
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REF: 360
2. It wasn’t until the 1950s that POTS began carrying computer data signals as well as voice signals.
ANS: F
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REF: 360
3. Only two wires are required to complete a telephone circuit.
ANS: T
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REF: 360
4. A trunk has a unique telephone number associated with it.
ANS: F
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REF: 361
5. Subscriber loops usually transmit digital signals, which require amplifiers every few kilometers.
ANS: F
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REF: 362
6. Prior to 1984, AT&T (American Telephone and Telegraph) owned all the long-distance telephone
lines in the United States.
ANS: T
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REF: 362
7. Telephone systems were originally designed to transmit the human voice.
ANS: T
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REF: 364
8. The more information you wish to send over a medium, the lower the frequency of the signal you need
to represent that information.
ANS: F
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REF: 365
9. When they were originally introduced many years ago, dial-up modems were capable of data transfer
speeds of merely 15 to 30 bits per second.
ANS: F
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REF: 365
10. A V.92 modem can place a data connection on hold should someone call the user’s telephone number.
ANS: T
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REF: 368
11. An asymmetric service is useful for an Internet connection in which the bulk of the traffic comes down
from the Internet to the workstation.
ANS: T
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REF: 369
12. Most residential DSL services are symmetric.
ANS: F
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13. There is only one DSL format in use today.
ANS: F
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REF: 370
14. A cable modem is a physical device that separates the computer data from the cable television video
signal.
ANS: T
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REF: 371
15. Cable modem connections are typically symmetric.
ANS: F
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16. The most popular example of a leased line service is the T-1.
ANS: T
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REF: 373
17. Quarter-T-1 and half-T-1 lines are called fractional T-1 services.
ANS: T
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18. The frame relay service can only be a long-distance service.
ANS: F
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REF: 374
19. Frame relay is called a layer 6 protocol.
ANS: F
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REF: 376
20. Typically, frame relay is a replacement for the leased lines that connect a business to other businesses
or connect multiple offices of the same business.
ANS: T
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REF: 376
21. Local high-speed telephone connections are almost always less expensive than long-distance, highspeed telephone connections.
ANS: T
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REF: 376
22. The price of the PVC is inversely proportional to the CIR level.
ANS: F
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REF: 378
23. Frame relay was originally designed and used to transfer packets of data between two sites more cost
effectively than leased lines could.
ANS: T
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24. ATM transfer rates are as fast as 311 Mbps.
REF: 377
ANS: F
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REF: 379
25. A real-time interactive application is one of the most demanding with respect to data transmission rate
and network throughput.
ANS: T
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REF: 380
26. DSL and cable modems are more expensive than frame relay systems at comparable speeds.
ANS: F
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REF: 383
27. Convergence has had a particularly noticeable impact on the telecommunications market.
ANS: T
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REF: 383
28. ATM clearly dominates in the local area network arena.
ANS: F
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29. A company that wishes to have its own in-house telephone system will often buy or lease a PBX.
ANS: T
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30. Frame relay and ATM are losing market share to Internet services such as FTP and Telnet.
ANS: F
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31. MPLS on Internet routers and VPNs (virtual private networks) are gaining in popularity in the data
network market.
ANS: T
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COMPLETION
1. The basic telephone system, or ________________________________________, has been in
existence since the early 1900s.
ANS:
plain old telephone service (POTS)
plain old telephone service
POTS
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REF: 360
2. The ____________________ is the telephone line that leaves your house or business.
ANS: local loop
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REF: 360
3. The ____________________ contains the equipment that generates a dial tone, interprets the
telephone number dialed, checks for special services, and connects the incoming call to the next point.
ANS:
central office (CO)
central office
CO
PTS: 1
REF: 360
4. A(n) ___________________________________ is a geographic area such as a large metropolitan area
or part of a large state and determines whether a telephone call is local or long distance.
ANS:
local access transport area (LATA)
local access transport area
LATA
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REF: 361
5. A(n) ____________________ does not have a telephone number associated with it, because it can
carry hundreds of voice and data channels.
ANS: trunk
PTS: 1
REF: 361
6. Immediately after the breakup of AT&T there were 7 Regional Bell Operating Companies (RBOCs).
As of year-end 2009, there are ____________________ RBOCs.
ANS:
3
three
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7. After the 1984’s Modified Final Judgment, the local telephone companies became known as
______________________________.
ANS:
local exchange carriers (LECs)
local exchange carriers
LECs
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REF: 363
8. A(n) ______________________________ is a large, computerized, self-contained telephone system
that sits in a telephone room on a company’s premises.
ANS:
Private Branch Exchange (PBX)
Private Branch Exchange
PBX
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REF: 363
9. ____________________ lines and tie lines are leased telephone lines that require no dialing.
ANS: Private
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REF: 363
10. The ______________________________ paved the way for anybody to offer a local telephone service
to homes and businesses.
ANS: Telecommunications Act of 1996
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REF: 363
11. After the Telecommunication Act of 1996, new providers of local telephone services were called
_____________________________________________.
ANS:
competitive local exchange carriers (CLECs)
competitive local exchange carriers
CLECs
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REF: 363
12. Shortly after V.90 was introduced, _____________________________________________ introduced
the V.92 modem standard.
ANS:
International Telecommunication Union (ITU)
International Telecommunication Union
ITU
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REF: 368
13. _________________________ is a technology that allows existing twisted pair telephone lines to
transmit multimedia materials and high-speed data.
ANS: Digital subscriber line
PTS: 1
REF: 368
14. ____________________ is a slower format compared to ADSL; also known as Universal DSL,
G.Lite, and splitterless DSL.
ANS: DSL Lite
PTS: 1
REF: 371
15. ______________________________ is also known as very high-speed DSL and very high bit-rate
DSL.
ANS:
Very high data rate DSL (VDSL)
Very high data rate DSL
VDSL
PTS: 1
REF: 371
16. A(n) ____________________ is a high-speed communications service that allows high-speed access
to wide area networks such as the Internet via a cable television connection.
ANS: cable modem
PTS: 1
REF: 371
17. The permanent connection in a frame realy network that is necessary to transfer data between two
endpoints is called a(n) ___________________________________.
ANS:
permanent virtual circuit (PVC)
permanent virtual circuit
PVC
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REF: 375
18. ______________________________ , like frame relay, is a very high-speed, packet-switched service
that is offered by the telephone companies.
ANS: Asynchronous Transfer Mode
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REF: 379
19. When a VCC transmits user-to-network control signaling, the connection is called the
_________________________.
ANS: user-network interface
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REF: 379
20. A(n) ____________________ is a definition of a type of traffic and the underlying technology that
will support that type of traffic.
ANS: class of service
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REF: 380
21. The ATM _________________________ class of service is used for traffic that may experience bursts
of data, and whose bandwidth range is roughly known, such as that of a corporate collection of leased
lines.
ANS:
Available bit rate (ABR)
Available bit rate
ABR
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REF: 381
22. ________________________________________ is a relatively new field that combines more
traditional voice networks with modern computer networks.
ANS:
Computer-telephony integration (CTI)
Computer-telephony integration
CTI
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REF: 384
23. ______________________________ means that when a customer calls your company, his or her
telephone number is used to extract the customer’s records from a corporate database.
ANS: Interactive voice response
PTS: 1
REF: 385
24. _____________________________________________ mean that as a person speaks into a telephone,
the system can digitize the voice and store it on a hard disk drive as computer data.
ANS: Text-to-speech and speech-to-text conversion
PTS: 1
REF: 385
ESSAY
1. What was the reasoning behind the development of CLECs?
ANS:
The reasoning behind the development of CLECs was fairly straightforward and meant to better
accommodate the way phone services were already being delivered. For example, in some areas of the
country, local cable television companies already offered local telephone service. Because a majority
of homes and businesses in the United States are already wired for cable television, allowing cable
companies in other areas to offer local telephone service over those same cable TV lines seemed like a
reasonable idea. Termed cable-telephone or cable telephony, telephone services over cable television
lines are now offered by most of the major cable television companies— including Cox
Communications and Comcast, as well as many smaller cable companies—in most major cities across
the country. In fact, large cable companies in the U.S. are achieving penetration rates of as high as 10
to 20 percent in their particular markets. Of new subscribers, 95 percent are dropping their old local
telephone service in favor of the new cable service, and some reports indicate that the number of cable
telephony subscribers in 2005 exceeded 14 million, with 22 million predicted by the end of 2008. The
medium that delivers cable telephony is a hybrid of fiber and coaxial cable called Hybrid Fiber Coax,
or HFC. This technology can also deliver cable modem service into homes and businesses.
PTS: 1
REF: 363-364
2. How does a 56k dial-up modem work?
ANS:
The new 56k modems are a hybrid design, combining analog signaling and digital signaling. The
upstream connection from modem to remote end still uses conventional analog signaling and
modulation techniques, and thus is limited to a maximum transmission speed of 33,600 bps. The
downstream link, however, is where the 56k modem really stands out. Instead of using analog
signaling, the 56k modem employs digital signaling. The telephone system has actually been using
digital signaling over telephone lines for many years. In fact, the telephone system can send an 8-bit
sample 8000 times per second, which corresponds to 64,000 bits per second, or 64 kbps. If the
telephone company can transmit 64 kbps, does this mean that we users can receive a 64-kbps
downstream signal? Unfortunately, the answer is “No.” When the telephone company transmits a
digital 64-kbps telephone signal, the signal is transmitted digitally from one switching center to
another. But when a telephone signal is transmitted into our homes and small businesses, it must be
adjusted so that it can traverse the local loop. The local loop is the stretch of telephone wire that runs
between a house (or small business) and the telephone company’s central office. This local loop is
analog and can support only analog signaling.
Before the telephone signal is transmitted over the local loop, the central office converts the digital
signal to an analog signal. When the analog signal enters your house, your computer’s 56k modem
converts the analog signal back to digital data, because computers manipulate digital data. When an
analog signal is converted to digital data, quantizing noise is introduced. The presence of this noise is
the reason it is not possible to transmit a 64-kbps data stream into the local loop. But a smaller data
stream, of approximately 56 kbps, is possible.
PTS: 1
REF: 366-367
3. What does a business or home user need to establish a DSL connection?
ANS:
At the present time, four components are required. The local telephone company (LEC) must install a
special router called a DSLAM (digital subscriber line access multiplexer) within the telephone
company’s central office. This device bypasses the central office switching equipment and creates and
decodes the DSL signals that transfer on the telephone local loop. Next, the local telephone company
may also install a DSL splitter on its premises, which combines or splits the DSL circuits (the
upstream and downstream channels) with the standard telephone circuit of POTS. Some DSL systems
transmit over the same telephone line that runs from a central office to a home or business. Because it
is the same telephone line, DSL must share the line with a POTS signal.
On the user end, a DSL modem is required to convert the DSL signals into a form that the user
workstation or network can understand. If the DSL circuit is also carrying a POTS telephone circuit,
the user will also need a splitter to separate the regular telephone line from the DSL data line. Finally,
the DSLAM router at the telephone company’s central office must be connected to an Internet service
provider via a high-speed line. Because this highspeed line will be supporting the Internet service
requests from multiple users, the line needs to be a very fast service, such as ATM.
PTS: 1
REF: 369-370
4. What are the advantages of frame relay?
ANS:
A frame relay service provides many attractive alternatives to leased lines. One of the first noticeable
characteristics of a frame relay network is its very high transfer speeds. The data transfer speeds can be
very fast, up to 45 Mbps and sometimes even higher. Along with the high data transfer rates, there is
high throughput—the network as a whole is also very fast. Using fiber-optic cables, frame relay
switches quickly transfer data so that it travels from one end of the network to the other in a relatively
short period of time. Frame relay networks also provide very good security. Because of the encryption
techniques used to transmit data between frame relay switches, it is extremely difficult to intercept and
decode the transmitted data. In addition, frame relay connections are permanent connections. Because
the connection is fixed, it is always available.
Another advantage associated with frame relay (and other modern high-speed wide area networks) is
that their error rates during transmission are low. In fact, the error rate of frame relay networks is so
low that the network does not have any form of error control. If an error occurs, the frame relay
network simply discards the frame. It is the responsibility of the application, and not the frame relay
network, to perform error control.
Last, frame relay networks are reasonably priced. Fixed monthly pricing is based on three charges: a
port charge for each access line that connects a business into the frame relay network; a charge for
each permanent connection that runs through the frame relay network between two endpoints
(companies using the service); and a charge for the access line, which is the high-speed telephone line
that physically connects the business to the frame relay port. Because a port and access line are capable
of supporting multiple permanent connections, a user may pay one port charge, one access line charge,
and several permanent connection charges.
Recently, frame relay network are starting to lose ground to MPLS over Internet routers and virtual
private networks (VPNs).
PTS: 1
REF: 3743-375
5. What are the advantages and disadvantages of ATM?
ANS:
Due to its range of features, such as high transfer speeds, various classes of service, and ability to
operate over many types of media and network topologies (LANs as well as WANs), ATM has a
number of significant advantages. ATM can support a wide range of applications with varying
bandwidths, at a wide range of transmission speeds. Cell switching, which is performed by ATM’s
high-speed, hardware-based switches that route cells down the appropriate path, is so fast that it
provides short delays and high bandwidths. ATM’s different classes of service allow customers to
choose service type and pricing individually for each data connection (VCC). Finally, ATM is
extremely versatile. It can carry voice, packet data, and video over the same facilities.
As you might expect, ATM also has a number of disadvantages. It is often more expensive than other
data transmission options. The cost of ATM equipment is high. This is because the cell-switching
equipment, to be capable of delivering such a fast connection, is by necessity relatively complex. Due
to the complexity of ATM, there is a high learning curve for setting up and managing the network.
Lastly, compatible hardware and software may not be widely available.
ATM is now being heavily used by the large telecommunications carriers (AT&T, Sprint, and so on)
to provide voice and Internet services. Because of its complexity and cost, smaller businesses have
been reluctant to use ATM. Alternate technologies that can offer reasonably comparable speeds at
much lower costs have, however, attracted much attention from smaller businesses. One attractive
alternative to ATM on a local area network is high-speed Ethernet, which has transfer speeds hitting
100 Mbps to 10 Gbps. Metropolitan area networks are also seeing a growth in high-speed Ethernet, as
it is chosen over ATM.
Recently, ATM network are starting to lose ground to MPLS over Internet routers and virtual private
networks (VPNs).
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REF: 382