A Probe into Basic Telephony and Telecommunications Jon F. Johnson Extension 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