TELEPHONES

Telephones

"Hello, hello, baby, you called? I can't hear a thing, I have got no service, in the club, you see, you see Wha-Wha-What did you say, huh? You're breaking up on me Sorry, I cannot hear you, I'm kinda busy....." -Lady GAGA

Basically, that's not what we will be talking about, that's just a part of Lady GAGA song which is related to our topic. Wiki says, "a telephone is a telecommunication device that transmit and receives sound, most commonly the human voice. Telephones are a point to point communication system whose most basic function is to allow two people separated by large distances to talk to one another."

The bandwidth of a telephone line has a theoretical limit(with perfect filters) is therefore 4kHz - but this isn't reality, the maximum frequency is up to 3.4 kHz.


3 Major Components of a Telephone

• Local Loops - analog twisted pairs going to houses and businesses
• Trunks - Digital fiber optics connecting the switching offices
• Switching Offices - where call are moved from one trunk to another

Local Loop

A local loop is the wired connection from a telephone company's central office in a locality to its customers' telephones at homes and businesses. This connection is ussually on a pair of copper wires called twisted pair. The system was originally designed for voice transmission only using analog transmission technology on a single voice channel. Today, your computer's modem makes the conversion between analog signals and digital signals. With Integrated Services Digital Network (ISDN) or Digital Subscriber Line (DSL), the local loop can carry digital signals directly and at a much higher bandwidth than they do for voice only.

Trunk

The main function of the trunk is to provide the path between switches. The switch must route the call to the correct trunk or telephone line. Although many different subscribers share a trunk, only one subscriber uses it at any given time. As telephone calls end, they release trunks and make them available to the switch for subsequent calls.


ILEC vs. CLEC

ILEC is short for incumbent local exchange carrier. Is a telephone company that was providing local service when the Telecommunications Act of 1996 was enacted. Compare with CLEC, a company that competes with the already established local telephone business. CLEC on the other hand is short for competitive local exchange carrier, a telephone company that competes with an incumbent local exhange carrier(ILEC) such as a Regional Bell Operating Company(RBOC), GTE, ALLNET, etc.


LATA (Local Access and Transport Area)

It is a geagraphical and administrative area that is the responsibility of an LEC (Local Exhange Carrier) or any local telephone company that allows to carry not only local calls, but long distance toll calls, as well. Rotary Dialing and Touch-Tone Dialing


900 services and 800 services The difference between the two is that 900 services charge customers for information delivered over the phone. 800 services on the other hand is somehow offers the same service just different rate plus it ha a toll free number.


DSU (Digital Service Unit)

DSU is used to convert the CPE digital data to the phone company's format and vice-versa such as 24 channels of raw data. The DSU sits between the CSU and the CPE, the router,multiplexer, terminal, server, and etc. Here are the two types of DSU:

1. In-Band Signaling - regular old AMI encoded signaling, 56k per channel, which is mostly used for voice, or switched 56. AMI signals usally use D4 framing. AMI signals was originally developed for switched voice circuits - it uses "bit robbing" which requires 8k of overhead for every 64k.
   
2. Out-of-Band Signaling - clearline - Binary 8-zero substitution) - a standard, T1 DSU using B8ZS takes a serial input stream of 24 DSO's at 1.536 Mbps (24 x 64k). The DSU inserts a "framing bit" every 193rd bit.