V1

Question 1

Any circuit provided by a telecommunication service provider is made up of three components:

Answer 1

access, network connection and billing agreement.

Question 2

The commercial organizations that offer services of access, network connection and billing agreement are often called…

Answer 2

carriers or common carriers because they carry many users’ traffic over a common facility.

Question 3

Access circuits are…

Answer 3

physical lines with circuit terminating equipment at each end. These circuits run from a user’s site to the nearest physical attachment point into the common carrier’s network.

Question 4

The location containing this physical attachment point is usually called…

Answer 4

a Central Office (CO). It might be pulled through the CO to another company’s Point of Presence (POP) to get access to that other company’s network.

Question 5

The access network is…

Answer 5

the totality of the physical equipment used to link the user to a Central Office (CO). This is often also called the outside plant.

Question 6

Switches are…

Answer 6

devices that connect one circuit to another for the duration of a communication session.

Question 7

Switching centers are…

Answer 7

the buildings that contain switches.

Question 8

Transmission network is…

Answer 8

the term used to generally refer to the systems that connect the COs.

Question 9

POTS

Answer 9

Plain Ordinary Telephone Service

Question 10

A CO switch connects a user’s loop to a particular inter-office circuit to make an end-to-end communication path for the duration of a phone call, and then releases it so someone else can use that inter-office circuit. This technique of establishing end-to-end communications across a network is called…

Answer 10

circuit-switching. It is sometimes also referred to as dial-up.

Question 11

The transmission network…

Answer 11

connects switches, multiplexers and routers in a Central Office to similar equipment in other switching centers. This includes direct connections between COs within a city and connections for long-distance communications.

Question 12

Connections between switches are called…

Answer 12

runks; a trunk carries one telephone call. For the most part, trunks are not individual circuits, but instead are carried on fiber-optic based trunk carrier systems.

Question 13

Since everything is carried together, redundant connections must be made between COs and other switching centers to protect against cut lines. The most cost-effective way of doing this is to connect switching centers together neighbour-to-neighbour to form…

Answer 13

rings.

Question 14

SONET

Answer 14

Synchronous optical networking

Question 15

When, where and by whom was a telephone invented?

Answer 15

Alexander Graham Bell in Brantford, near Toronto, Canada in 1874

Question 16

Historical pattern of telephone system development

Answer 16

Development of a monopoly on providing telephone service, either owned by the government or regulated by the government; then break-up of this monopoly and introduction of competition in connecting the pieces; and finally competition within the pieces.

Question 17

PSTN

Answer 17

Public Switched Telephone Network

Question 18

The telephone is located in a building called…

and the telephone switch is located in a building called…

Answer 18

a Customer Premise (CP)

a Central Office (CO).

Question 19

The telephone is connected to the telephone switch with…

Answer 19

two copper wires, often called a local loop or a subscriber loop, or simply a loop. This a dedicated access circuit from the customer premise into the network.

Question 20

Copper is a good conductor of electricity - but not perfect:

Answer 20

it has some resistance to the flow of electricity through it. Because of this, the signals on the loop diminish in intensity or attenuate with distance.

Question 21

The maximum resistance allowed is usually

Answer 21

1300 ohms, which works out to about 18,000 feet or 18 kft, which is 3 miles or 5 km on standard-thickness 26-gauge cable but could be as long as 14 miles or 22 km on thicker 19 gauge cable.

Question 22

Thus, COs traditionally had a serving area of about three miles radius around them, about…

Answer 22

27 square miles or 75 km2.

Question 23

With suburban sprawl, we cannot build COs every five miles, so in practice, new subdivisions are served from…

Answer 23

remote switches, which are low-capacity switches in small huts or underground controlled environment vaults. The remote provides telephone service locally on the loops in the subdivision. The remote and the loops are connected back to the nearest CO via a loop carrier system that uses fiber or radio.

Question 24

Telephone switches are connected with…

Answer 24

trunks.

Question 25

While subscriber loops are dedicated access circuits, trunks are…

Answer 25

shared connections between COs.

Question 26

What is known as circuit switching?

Answer 26

To establish a connection between one customer premise and another, the desired network address (telephone number) is signaled to the network over the loop, then the network selects an unused trunk circuit going in that direction and the switch connects the loop to that trunk - for the duration of the call. When one end or the other hangs up, the trunk is released for someone else to connect between those two COs.

Question 27

The technique for representing information on an ordinary loop is called…

Answer 27

analog.

Question 28

Explain the term analog

Answer 28

The term analog comes from the design of the telephone. A microphone in the handset is placed in the path of the sound pressure waves coming out of the speaker’s throat. As the sound pressure waves hit the microphone, they change its electrical characteristics. We use the fact that the electrical characteristics of the microphone change as the sound pressure waves hit it to make a voltage on the telephone wires change.
This voltage is a representation or analog of the sound. This is all we mean by analog: representation. The voltage is an analog of the sound pressure waves coming out of the speaker’s throat.

Question 29

Speech is a form of sound. Sound pressure waves coming out of the speaker’s throat vibrate. If the vibration occurs between 20 and 20,000 times per second, the sound pressure waves are said to be

Answer 29

audible.

Question 30

The two choices in designing the telephone system are then to either:

Answer 30

a) Reproduce sound pressure waves coming out of the receiver exactly as they entered the microphone in the other telephone; or
b) Reproduce the sensations in the listener’s brain the same as they would experience were they speaking directly to the other person.

Question 31

Which choice did Alexander Graham Bell make?

Answer 31

Answer (b). Based on testing human beings’ ears and throats and brains, and some technical limitations at the time, A. G. Bell decided to transmit all of the information in the frequency range between 300 and 3300 Hz. Hertz (Hz) is the unit for frequency, or changes per second.

Question 32

This range or band of frequencies is called…

Answer 32

the voiceband and is chosen based on examining how people’s throats and ears work.