http://electronics.howstuffworks.com/telephone.htm For other information concerning history, components and internal workings of a small business telephone systems check this Wikipedia entry: http://en.wikipedia.org/wiki/Private_branch_exchange
A carrier in the form of a very low frequency RF signal is placed on the phone line at the exchange that is then audio modulated in the phone instement, it is then detected (converted back to audio) in the instrement on the other side.
2.5.1 Structure of the Telephone System
Soon after Alexander Graham Bell patented the telephone in 1876 (just a few hours ahead of his rival, Elisha
Gray), there was an enormous demand for his new invention. The initial market was for the sale of telephones,
which came in pairs. It was up to the customer to string a single wire between them. The electrons returned
through the earth. If a telephone owner wanted to talk to n other telephone owners, separate wires had to be
strung to all n houses. Within a year, the cities were covered with wires passing over houses and trees in a wild
jumble. It became immediately obvious that the model of connecting every telephone to every other telephone,
as shown in Fig. 2-20(a), was not going to work.
Figure 2-20. (a) Fully-interconnected network. (b) Centralized switch. (c) Two-level hierarchy.
To his credit, Bell saw this and formed the Bell Telephone Company, which opened its first switching office (in
New Haven, Connecticut) in 1878. The company ran a wire to each customer's house or office. To make a call,
the customer would crank the phone to make a ringing sound in the telephone company office to attract the
attention of an operator, who would then manually connect the caller to the callee by using a jumper cable. The
model of a single switching office is illustrated in Fig. 2-20(b).
Pretty soon, Bell System switching offices were springing up everywhere and people wanted to make long-
distance calls between cities, so the Bell system began to connect the switching offices. The original problem
soon returned: to connect every switching office to every other switching office by means of a wire between them
quickly became unmanageable, so second-level switching offices were invented. After a while, multiple second-
level offices were needed, as illustrated in Fig. 2-20(c). Eventually, the hierarchy grew to five levels.
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By 1890, the three major parts of the telephone system were in place: the switching offices, the wires between
the customers and the switching offices (by now balanced, insulated, twisted pairs instead of open wires with an
earth return), and the long-distance connections between the switching offices. While there have been
improvements in all three areas since then, the basic Bell System model has remained essentially intact for over
100 years. For a short technical history of the telephone system, see (Hawley, 1991).
Prior to the 1984 breakup of AT&T, the telephone system was organized as a highly-redundant, multilevel
hierarchy. The following description is highly simplified but gives the essential flavor nevertheless. Each
telephone has two copper wires coming out of it that go directly to the telephone company's nearest end office
(also called a local central office). The distance is typically 1 to 10 km, being shorter in cities than in rural areas.
In the United States alone there are about 22,000 end offices. The two-wire connections between each
subscriber's telephone and the end office are known in the trade as the local loop. If the world's local loops were
stretched out end to end, they would extend to the moon and back 1000 times.
At one time, 80 percent of AT&T's capital value was the copper in the local loops. AT&T was then, in effect, the
world's largest copper mine. Fortunately, this fact was not widely known in the investment community. Had it
been known, some corporate raider might have bought AT&T, terminated all telephone service in the United
States, ripped out all the wire, and sold the wire to a copper refiner to get a quick payback.
If a subscriber attached to a given end office calls another subscriber attached to the same end office, the
switching mechanism within the office sets up a direct electrical connection between the two local loops. This
connection remains intact for the duration of the call.
If the called telephone is attached to another end office, a different procedure has to be used. Each end office
has a number of outgoing lines to one or more nearby switching centers, called toll offices (or if they are within
the same local area, tandem offices). These lines are called toll connecting trunks. If both the caller's and
callee's end offices happen to have a toll connecting trunk to the same toll office (a likely occurrence if they are
relatively close by), the connection may be established within the toll office. A telephone network consisting only
of telephones (the small dots), end offices (the large dots), and toll offices (the squares) is shown in Fig. 2-20(c).
If the caller and callee do not have a toll office in common, the path will have to be established somewhere
higher up in the hierarchy. Primary, sectional, and regional offices form a network by which the toll offices are
connected. The toll, primary, sectional, and regional exchanges communicate with each other via high-
bandwidth intertoll trunks (also called interoffice trunks). The number of different kinds of switching centers and
their topology (e.g., can two sectional offices have a direct connection or must they go through a regional
office?) varies from country to country depending on the country's telephone density. Figure 2-21 shows how a
medium-distance connection might be routed.
Figure 2-21. A typical circuit route for a medium-distance call.
A variety of transmission media are used for telecommunication. Local loops consist of category 3 twisted pairs
nowadays, although in the early days of telephony, uninsulated wires spaced 25 cm apart on telephone poles
were common. Between switching offices, coaxial cables, microwaves, and especially fiber optics are widely
used.
In the past, transmission throughout the telephone system was analog, with the actual voice signal being
transmitted as an electrical voltage from source to destination. With the advent of fiber optics, digital electronics,
and computers, all the trunks and switches are now digital, leaving the local loop as the last piece of analog
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The telephone network works using three technologies. They include a wireless network, a private network and a fixed line network.
erna hoover invented the first computerized switching system for telephone call traffic.
The crystal frquency in an 8085 system is twice the desired clock frequency, so a crystal of 2.2 MHz is required to operate at 1.1 MHz.Note: Clock frequency is not the same as instructions per second, because the instructions in an 8085 take a variable number of clock cycles, between 4 and 18, to execute.
PBX stands for Private Branch Exchange. The system is used in interconnecting telephone lines and extensions within a company or office. The system then link this network the PSTN.
Noise immunity is the ability of a system to perform even when there is noise present. The higher the level of noise a system can still operate under, the higher the noise immunity.
administrator customer and user also invoice all these intities must be prosess
For a small business telephone system and service I would suggest checking what ATT or Cox communications would have to offer as they are relatively inexpensive to operate.
by saying the number and it will dial its self in
No. Because EasyJet do not operate to the USA
A manual system is one you have to operate by hand.
Some people have a telephone system with more than one phone connected to the system. The extension number from the telephone system to that extension of the telephone system then become useful
A telephone system is a key component in any office. An office telephone system is typically located centrally for the best use and convenience for everyone.
Any individual who who knows how to operate telephone are allowed to use it. Most businesses, offices and homes have it too. Telephone is mainly use to get connected to people or establishments in far distances. With the rise of the modern phone system such as the virtual PBX, communication has become more easy due to the functions and features brought by the service.
To operate a Bose av321 system a media center must be used.
system of banking by telephone: a system of transacting business with a bank by telephone is known as Telebanking.
money
how to draw a telephone billing system in huge and sparse datacubes in datamining
Hormons