A Probe into Basic Telephony and Telecommunications

Jon F. JohnsonExtension Area Specialist

Virginia Cooperative Extension

Telephony?

• The making and operation of telephones – Webster’s New World Dictionary

Telecommunications• More advanced products, services, and

applications of traditional telephone services that not only carry voice traffic but data as well

Talking Beyond the Teleset…• Cable media – copper, fiber optics, microwave• The POTS line - Plain Old Telephone Service• Analogue and Digital Telephone Signals• Circuit Switched Operations • The C.O. – The Central Office• PSTN – The Public Switched Telephone

Network• Traditional and enhanced TELCO (Telephone

Company) services

Analog Telephone Signals…• Analog transmissions began with invention of

the telephone in 1876• Analog signals move along a telephone line as

an electromagnetic wave• Analog signal strength is measured by

frequency and requires amplification as it travels

• Analog signals can easily pick-up electrical interference or noise

Digital Telephone Signals…• Digital signals are transmitted as binary

bits (binary means two values for bits: on and off)

• Digital “on” bits carried by copper medium represent positive voltage while “off” bits represent no voltage

• Bits make Bytes and the amount of transferred Bytes determines Bandwidth

Bandwidth• The measure of the capacity of a

communications channel (path). • Digital channels are measured in bits per

second.• Analog telephone lines are measured by

hertz (cycle of a wave from crest to trough)

Digital versus Analog…• Digital signals are easily recreated as they

travel along a telephone line by digital regenerators or repeaters

• Unlike analog amplification, noise (static from electrical interference) is discarded

• Digital service is more reliable and requires less equipment to boost signals strength

Switching defined…• The establishment on demand, of an

individual connection from a caller to a desired receiver … as long as is required for the transfer of information.

- International Telecommunications Union (ITU)

The Public Switched Telephone Network (PSTN)

• The Central Office (CO)• The Tandem Office• The Toll Office • Interexchange Carrier’s (IEXs) Point of

Presence (POP)

The CO defined…• A telephone company facility that houses

the local switching equipment and serves as the place of termination for the wires from all telephones (the local loop) in a specified geographical area served by that telephone company.

• The Exchange!

Who’s in the CO?• The Local Exchange Carrier or LEC • CLEC or Competitive Local Exchange

Carriers - Maybe?• Interexchange Carriers or IEX (Long

distance services providers)• Local ISPs - Internet Service Providers

The POP• Physical location for Interexchange

carriers (MCI, Sprint, AT&T, etc.) or IEXs to have their Point of Presence or POP

• The POP is the connection between the incumbent network and the carrier’s network.

An ISP is…• Internet Service Provider connects end-

users to the Internet via telephone lines, cable media, or other media.

ISP Services• ISPs often supply services such as voice

mail, web hosting, and domain name registration for websites

• POTS• ISDN – Integrated Services Digital

Network (protocol) via twisted pair

Some Telco Services• POTS• Value added services (voice mail, call waiting,

conference calling, etc.)• DSL (Digital Subscriber Line)• ISDN (BRI and PRI)• ATM (Asynchronous Transmission Mode)• Frame Relay• T1, T3, DS1, DS3• Intrastate and interstate connections• Long-distance service

Transmission Media• T1 uses 2 copper pairs• DS1 uses fiber optics with the same bandwidth

as a 2 copper pairs• Fiber-optics cable is made from glass that

transfers light and not electricity and is used for higher-speed transmissions

• Coaxial cable is capable of delivering up to 10Mbps or more (voice, data, & video)

• Ethernet cabling typically uses 2 of 4 pairs of Category 5 or 6 cable to deliver 10 or 100Mbps of bandwidth

Important Protocols for Most Consumers

• DSL – Digital Subscriber Line (a glorified twisted pair with broadband capabilities 128kps to 6 Mbps with distance limitations)

Residential or Business?• POTS basic service - $20/mth• Dial-up internet access - $15 to $30/mth with

56kps max. capability• DSL basic service - $50/mth with 6Mbps to

128kps (download and upload) with distance limitations Note: DSL carries voice and data

• Broadband cable internet service - $70/mth with 10Mbps, add $18/mth for basic voice and more for TV signal Note: broadband is a shared network

Government, Business, Educational Uses

• T1 lines are most commonly used by larger business and government agencies with greater bandwidth needs

• T1 and DS1 lines can range from $700 to $1000+/mth, depending on competition, and offer up to 1.54Mbps (64kps/channel)

• T3 and DS3 offer 44.7 Mps or the equivalent of 28 T1 (that’s is a lot of money)

Special Notes and Recommended Resources:

• Pricing is relevant to September 2002 and is based on the Richmond Metro Area

• The Essential Guide to Telecom by Annabel Dodd

• Verizon Communications at www.verizon.com