Chapter 16: The Telephone System Key
1. Prior to the introduction of the telephone in 1876, the primary methods of communicating over long distances
were the postal service and telegraph.
2. Early telephones had the same primary components of today’s telephones: a switch acting as a mechanism to
connect a caller to the telephone network, a speaker to hear the other caller’s voice, and a microphone to detect
human speech and convert these sound waves into electrical current.
3. Early telephone microphones consisted of small argon granules that would compress and decompress in
response to the sound waves they detected.
4. In 1950, Bell founded the Bell Telephone Company, which would become the largest company in the world.
5. The Telecommunications acts of 1996 was the antitrust settlement agreement between the Department of
Justice and AT&T.
6. AT&T’s local phone service was divested into seven independent regional companies called regional Bell
operating companies (RBOCs) as a result of the Modified Final Judgement.
7. The MFJ resulted in competition for long-distance telephone services and in equipment manufacturing, and it
regulated monopolies in regional phone services.
8. Under the terms of the MFJ, the United States was divided into regions called Local Access and Transport
Areas (LATAs).
9. The geographical areas called LATAs were regulatory designations of regions within which each RBOC
could provide services.
10. Any communications originating in one LATA and terminating in another was considered inter-LATA
traffic and was handled under law by an IXC.
11. The objective of the 1996 Telecommunications Act was to promote greater competition, allowing any
service provider to compete in any sector of the telecommunications market.
12. The telegraph was invented in Bell labs.
13. The transistor was invented in Bell labs.
14. The integrated circuit was invented in Bell labs.
15. The PSTN is short for Publicly Switched Telegraph Network.
16. The transmission facilities that connect homes, businesses, and institutions to a switching center called a
central office are known as the local loop.
17. The demarcation point and the central office are usually also connected by twisted pair cable, but they are
sometimes connected by parallel wire, known as parallel wire to the premises (PWTTP).
18. The telephone network is primarily analog with the exception, in some cases, of the local loop.
19. In the telecommunications industry, the term “outside plant” refers to telephone system facilities that are
outdoors.
20. Transmission between two microwave antennas in the telephone network is point to point.
21. An omindirectional antenna such as a microwave system radiates energy in a single direction, while a
directional antenna can transmit or receive energy from all directions.
22. International calls that use satellite communications present a small but perceptible delay; the signal must
reach a transponder on an orbiting satellite, regenerate, and be transmitted back to Earth, traversing a path of
tens of thousands of miles.
23. The telephone system uses a combination of digital and analog transmission facilities, but is mostly analog.
24. If the timing between pulses is not precisely reproduced, the quality of the signal becomes distorted. The
telecommunications industry refers to this problem as latency.
25. Another problem within the telephone system is jitter, a form of electrical interference between adjacent
communication channels.
26. Crosstalk can be a problem when multiple pairs of twisted pair cable are distributed together over a single
cable.
27. Providing a transmission line between every two devices that might communicate with each other is clearly
untenable, so switching is used within the telephone network.
28. The automatic switching that connects a telephone subscriber to its destination takes place through a large,
versatile, computer-controlled switch called an electronic switching system (ESS).
29. The switching centers that traditionally connect central offices to each other are called long distance
switching centers.
30. A PBX is similar to a central office switch, except that it is leased and managed by the telephone service
provider.
31. Most modern PBX systems also integrate multimedia Internet services and VoIP.
32. Centrex are large offices that accommodate high volumes of incoming and outgoing telephone calls.
33. In the telecommunications industry, the technique for converting an analog audio signal into a digital bit
stream is called pulse code modulation (PCM).
34. Because voice signals are sampled at a rate of 64000 samples per second, and because a 1-bit code
represents the value of each sample, each voice transmission that uses PCM techniques to convert an analog
voice signal into a digital binary stream requires a 64-Kbps transmission channel.
35. FDM served as the primary multiplexing technique when the telephone network predominantly used analog
transmission.
36. FDM divides signals based on time, allocating different time slots for each signal.
37. Stat muxes allow for dynamic allocation of time slots based on the activity of incoming signals to be
multiplexed
38. Synchronous Optical Network (SONET), serves as the transmission specification for multiplexing over
coaxial cable in the United States and Canada.
39. SS7 defines how signals are exchanged for establishing, managing, and terminating a call over a digital
network.
40. A dedicated, end-to-end path is not established using circuit switching until SS7 determines the availability
of the device.
41. Within carbon microphones, which property of the carbon granules changes with pressure variations caused
by the voice signal?
42. Which regulatory decision resulted in AT&T’s local phone service being divested into seven independent
regional companies called regional Bell operating companies (RBOCs)?
43. Which of the following are examples of RBOCs?
44. Which of the following is an important regulatory milestone in the telecommunications industry?
45. How many RBOCs were formed as a result of the MFJ?
46. The United states was split into geographical areas called _____________ as a result of the MFJ.
47. Which of the following are inventions attributed to Bell Labs?
48. Which of the following are physical components of the PSTN?
49. PSTN is short for:
50. The transmission facilities that connect homes, businesses, and institutions to a switching center called a
central office are known as:
51. Which of the following terms refers to telephone system facilities that are outdoors?
52. Transmission facilities that connect switching centers to each other are called:
53. Which of the following equipment can receive weakened signals, amplify and regenerate them?
54. Which of the following are problems associated with signals as they travel through the telephone network?
55. How many distinct transmission lines would be required in total to connect 50 telephones to each other
without a switch?
56. How many distinct transmission lines would be required in total to connect 100 telephones to each other
without a switch?
57. The types of switches used within switching centers today are:
58. An ESS within the telephone network is also referred to as a:
59. Which of the following are examples of CPE?
60. What is the standard sampling rate for digitizing analog audio signals within the PSTN?
61. What is the standard number of bits assigned per sample for digitizing analog audio signals within the
PSTN?
62. Which multiplexing technique assigns a unique time slot to each channel?
63. Which multiplexing technique assigns a unique frequency to each channel?
64. Which multiplexing technique assigns a unique time slot to each channel based on need/priority?
65. Which WDM technique has the highest multiplexing capacity?
66. Which WDM technique has the lowest multiplexing capacity?
67. What is the reason that the data rate of a T-1 line is 1.544 Mbps and not 1.536 Mbps?
68. Which of the following is the global standard for exchanging control, routing, and call setup information
within the PSTN?
69. Using a telegraph key and a receiver, ____________________ used a combination of dots (short electrical
pulses) and dashes (long electrical pulses) to transmit a simple message.
70. On March 6, 1876, Alexander Graham Bell successfully called his assistant, ____________________ in
another room.
71. Early telephone microphones consisted of small ____________________ granules that would compress and
decompress in response to the sound waves they detected.
72. For a century, the ____________________ Company—also called the Bell System or “Ma Bell,” and later
AT&T—served as a telecommunications monopoly in the United States.
73. The _________________________was the antitrust settlement agreement between the Department of
Justice and AT&T.
74. AT&T’s local phone service was divested into ____________________ independent regional companies
called regional Bell operating companies (RBOCs) as a result of the MFJ.
75. The RBOCs were effectively regulated regional monopolies, while long-distance services were open to
competition. In addition to AT&T, long-distance service providers called ____________________ included
companies such as Sprint and MCI.
76. The objective of the 1996 _________________________ was to promote greater competition, allowing any
service provider to compete in any sector of the telecommunications market.
77. The history of the telephone system in the United States includes Bell Labs, the Bell System’s research arm,
which was founded in 1925, and its manufacturing arm, ____________________.
78. Bell Labs, now part of ____________________, was responsible for many of the technologies and
techniques related to the telecommunications industry.
79. Traditional phone service has historically been referred to as POTS, which is short for
______________________________.
80. The transmission facilities that connect homes, businesses, and institutions to a switching center called a
central office are known as the ____________________.
81. The ____________________ point is where the customer’s own telephone line ends and the local loop of
the carrier begins.
82. The demarcation point and the central office are usually also connected by twisted pair cable, but they are
sometimes connected by fiber-optic cable, referred to as ______________________________.
83. Longer-distance transmission facilities, such as those between switching centers of the PSTN, are called
____________________.
84. Antennas typically are divided into two general classes: ____________________ and
____________________.
85. Microwave transmission requires a ____________________path, meaning that obstructions such as
buildings or mountains between antennas disrupt transmissions.
86. ____________________ are special fiber-optic or coaxial cables that span the ocean floor to enable
intercontinental communications.
87. The telephone system uses a combination of digital and analog transmission facilities, but is mostly
____________________.
88. Digital transmission systems work better than analog systems because they can reconstruct a degenerated or
weakened signal after it has passed through a transmission medium and has been subjected to
____________________.
89. A signaling method wherein a signal pulse fluctuates from a negative to a positive value to represent 1s and
0s is called ____________________ signaling and is traditionally employed within telephone systems.
90. A repeater’s first task is to ____________________ the signal to a level at which it can determine the
signal’s state at various intervals.
91. ____________________ can be a problem when multiple pairs of twisted pair cable are distributed together
over a single cable.
92. ____________________ located throughout the telephone network play a critical role in establishing
connections between two devices connected to the PSTN.
93. Originally, switching was provided through a ____________________ where an operator would manually
connect two telephone subscribers.
94. A ____________________ is a privately owned CPE that allows a sizable percentage of telephone calls to
remain within the confines of a campus, building, or office complex.
95. By paying a monthly fee, Centrex customers can avoid the ____________________ costs and
____________________ fees that are associated with a PBX.
96. ____________________ are large offices that accommodate high volumes of incoming and outgoing
97. One important example of call center CPE is the ____________________, equipment that receives
incoming calls and makes decisions about how to allocate these calls to available agents.
98. For outbound services such as telemarketing, call center software often provides “____________________
dialing,” in which the software begins dialing other potential customers before the call center agent has finished
a call.
99. Because personnel (i.e., the agents) costs are a call center’s primary operating expense, these offices have
been part of the historical trend of ____________________labor, especially to other countries.
100. In the telecommunications industry, the technique for converting an analog audio signal into a digital bit
stream is called ____________________.
101. ________________________________________ enables the simultaneous transmission of multiple
signals over a single medium by assigning a different frequency to each channel.
102. In WDM, if the number of channels is small, the technique is called ____________________. If the
number of channels is large, the technique is referred to as ____________________.
103. The 64-Kbps channel is known as ____________________ within the telephone system multiplexing
hierarchy.
104. ANSI standardized ____________________, which was also adapted into the SDH standard established by
105. The global standard for exchanging control, routing, and call setup information is called
____________________.
106. The PSTN provides “____________________” of reliability, meaning that the network works properly
99.999% of the time.
107. Explain how carbon granules may be used with a microphone.
108. Discuss the impact of the MFJ on the telephone industry.
109. List some innovations which Bell Labs contributed to.
110. List the main physical components of the PSTN.
111. What is the formula used for calculating the number of transmission lines that would be needed for
connecting n telephones with each other without a switch.
112. What is an alternative to PBX that is not privately owned but rather leased from the telephone service
provider?
113. List the various multiplexing techniques employed within the PSTN.
FDM (frequency-division multiplexing)
114. Discuss the difference between TDM and STDM.
115. What is the difference between CWDM and DWDM?
116. If a T1 line carries 24 channels multiplexed together, with each signal sampled 8000 times per second and
8 bits used to encode the value of each sample, calculate the data rate of the T1 line.