Landline
Landline telephone systems are part of the Plain Old Telephone Service (POTS), the analog service with copper wiring that is the direct descendant of the original telephone system courtesy of Alexander Graham Bell. The advantages of this system include standardized equipment, predictable sound quality, and — due to direct connections to the central office of the company — no need to share the system’s capacity with others. Because switches are in place, creating a private circuit for each phone call, it is also called the Public Switched Telephone Network (PSTN).
Cell Phone
Another system is for cellular phones, with individual companies having their own networks with varying technology. Like POTS systems, cellular telephone systems are full-duplex systems, meaning that both people on the call can talk at the same time, but cell phones use radio frequencies, rather than copper wire. Though cellular networks began as mobile voice networks only, they now carry both voice and data. Some networks are national, while others are international, and new technologies are continually in development. The networks known as 3G support not only cell phones, but also netbook computers, smartphones, and wireless modem aircards.
VoIP
Internet Protocol (IP), also called Voice over Internet Protocol (VoIP), another type of telephone system that is in use in the 21st century. This service piggy-backs on existing Internet connections, either cable service or DSL broadband. A device called an Analog Telephone Adaptor is the go between that connects whatever phone a person happens to have with either the broadband modem or the router.
IP systems can be set up with a single line for both Internet and telephone service, which can save money. With an Integrated T1 line, instead of being set up for voice or data, the T1 line is able to handle both. With Dynamic T1, the line is capable of assigning bandwidth as needed, given the current use.
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