The POTS transport

As you already know, POTS is a transport that runs through the  circuit- switched PSTN. All transport lines  in the  PSTN have  a circuit-identification number, which is either all numeric or alphanumeric. For example, a POTS telephone number has  an area  code, a prefix, and  a suffix that correspond to the  physical circuit and  the  lines that make up that circuit.

Although POTS does not  run VoIP directly, POTS is required for the  later digi- tal transport, DSL. Because of the  need for a POTS line to have  a circuit ID, you must have  a POTS line established before you can order broadband DSL.

DSL runs on the  same line as your  POTS telephone service. This raises an interesting question. If you are looking  to get broadband DSL so you can run VoIP, do you need to have  the  added cost of the  POTS service? For now, you do. I expect this  will change as competition heats up and POTS carriers con- tinue to lose  consumers to the  broadband cable carriers. (More about this  dilemma in a moment, in “The DSL transport.”)