- The Telephone System: (Ref: Ch-4, Page-113 of your Text book). - The telephone system remains as the backbone of low-cost telecommunications services in North America. - An understanding of the telephone system is necessary when considering its use for data communications.. - Single wire: In the beginning, the market was for telephones only. - Copper: At one time, 80% 0f AT&T's capital was the Copper in the local loops, the largest Copper mine.. - Local loops consist of twisted pairs, although in the early days of telephony, uninsulated wires spaced 25cm apart on telephone poles were common. - In summary, the telephone system consists of three major components:. - The telephone system (commonly called POTS for plain old telephone service) enables voice communication between any two telephones within its network.. - In the local loop the 2 wires are referred to as. - it is not connected to the circuit. - Off-Hook: When the phone is lifted or connected to the local loop, about 5 volts DC is present at the phone and current flows in the local loop. - This current is detected in the "end office". - or local switch by a relay resulting in the presentation of a dial tone on the circuit.. - Switching machines (or "switches") are used to interconnect any pair of subscribers in the public telephone system. - etc.) CLASS 4 Toll Center Sault Ste. - The telephone system was originally designed as an analog system, but today, most trunk lines are digital.. - A continuous tone in the range 1000Hz to 2000Hz, called a sine wave carrier is used. - They reduce costs by reducing the number of connections to the telephone company’s trunk lines. - Using frequencies in the 870 to 890 MHz range. - A FAX machine scans an image and then transmits over the telephone line.
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