The physical telephone line

In spite of all the hype about fiber-optic phone lines, most businesses and residences still connect to the public-switched network using copper wires. Carriers are beefing up their networks by using high-capacity fiber-optic lines, but most of this is between central offices, which are commonly referred to as the “backbone” of the network. It is far too costly to run fiberoptic lines across the “last mile” to the end user. The copper wires are already in place, and it is just too expensive to replace the wiring. No matter how advanced the phone network, a user is still hindered by the limitations of the last mile. The last mile is almost always low-capacity copper wire. This trend is not likely to change any time soon, as the average cost for a “fiber drop” replacing the copper wires into a residence with fiber-optic lines costs approximately $2,000 to $3,000 at the time of this writing. Phone companies are too busy concentrating on competition and profits to make large investments upgrading the last mile from copper to fiber. Therefore, most of us have telephone service via traditional copper wires, rather than high-tech fiber-optic lines.

Circuit is a generic term referring to the physical connection, or path, between two given points, such as your phone and the central office. A common type of circuit, used in residences and businesses, is called “four-wire.” One wire is used to transmit data, and one wire is used to receive data. The other pair of wires is a spare set. That is why the phone company technician only works inside the house if a person orders a second phone line to his or her house. The technician does not need to string a whole new pair of wires all the way to the house from the telephone pole.

The wires connecting to the central office may be identical, but they are called different names according to the type of connection and its purpose. Local service is provided three ways: POTS lines, trunks, and Centrex.

POTS
Regular phone lines are called “POTS lines,” which stands for plain old telephone service. POTS lines are used with single-line termination points, such as a telephone, fax machine, alarm, or modem. For each phone or device, one phone line is required. Residential customers use POTS. Key systems also use POTS lines. Figure below shows how POTS lines work.



POTS lines typically cost around $40 per month for a business, while residential lines cost $15 to $25 per month. Although residential lines are more expensive for the phone companies to maintain, the end user pays less because residential service is subsidized by the phone companies through the higher rates that businesses pay for phone service.

Trunks
A trunk is a circuit that connects two switching devices. The lines connecting two telephone company central offices are called trunks, but for the end user, the term trunk is used to describe the line that connects a customer’s private branch exchange (PBX) to the telephone company’s central office. A PBX is a computer-driven phone system.

A PBX is a highly sophisticated telephone switch located at the customer’s premise with an attendant console. The PBX connects to a group of trunks that are accessed by the caller first dialing “9” to make an outside call. Inside calling from one internal extension to another does not tie up a central office trunk, because the PBX switches the call; only inside wiring is used. Figure 5.2 shows how trunks work with a PBX.



Trunk lines connect internal calls to the telephone company’s central office.

If a business has a PBX, it must purchase trunk lines from the phone company. The physical circuits are still the same copper wires it would have had with POTS service, but with trunks, a business can expect to pay $60 per month, per trunk. The cost is higher than POTS lines, but multiple internal extensions can use one trunk, just not at the same time. Therefore, a business need only purchase a number of trunks equal to the number of calls it expects to have during its busiest time.

Centrex service
Centrex was originally designed for large customers, such as hospitals or college campuses, whose facilities were almost big enough to warrant their own central office or central exchange. The first Centrex system was implemented in 1965 at Prudential’s office in Newark, New Jersey, but today, Centrex can be a cost-effective way to have sophisticated phone service even for a small business.

Centrex is a business service offered by local exchange carriers. These lines are normal telephone circuits with lots of features included in a package, such as call forwarding, call park, call transfer, speed dialing, and off-premise extensions. The local carrier’s central office provides the features.

Like PBX service, Centrex service usually requires the caller to dial “9” to make an outside call (see Figure 5.3). This can be very cumbersome for the customer, especially when equipment may have to be programmed to dial the “9” such as alarm systems, computer modems, and fax machines. Some local carriers “assume the 9” so customers do not have to reprogram their equipment and retrain their employees.



Centrex service.

Centrex pricing varies widely. Sometimes it costs less than POTS lines; sometimes it costs more. Centrex generally costs less than POTS lines with GTE, U S West, Ameritech, and BellSouth. Centrex almost always costs more than POTS lines with Southwestern Bell. Centrex pricing with the other Bell companies varies.