Title: Wireline Infrastructure
Course: 2016FA-MCO-115-401 > Section: Module 5: Communications

Click here for a downloadable version of this document: Wireline Infrastructure

Wireline Infrastructure

The telephone plays a large role in the life of an American citizen. The communications technology of wired, or landline, telephones is referred to by DHS as Wireline Infrastructure. Landline telephones are an example of how communications got their start before growing into many more communications technologies and applications.

Plain Old Telephone Service in the United States

To get an idea of how wireline/landline communications work we will take a look at the Public Switched Telephone System (PSTN), also known as the Plain Old Telephone Service (POTS). PSTN is the system used to carry telephone calls in the United States. PSTN uses circuit switching to connect telephones together. A call may go through many switches before it is connected with the proper phone. Today’s modern switches are large scale computers used to route calls. These switches can be owned by local telephone companies or carriers, but also could be regional, national, or even international. A connected call completes a circuit and is sometimes called a circuit. This circuit must stay open for the entire length of a phone call. Getting calls to the right place, called routing, is done by using multiple switching offices [7].

Our telephone numbers serve as an address when switching phone calls, similar to writing an address on an envelope to mail a letter. To facilitate routing, the United States uses a ten digit telephone number system. The first three digits of a phone number are the area code, this area code helps to direct calls to the proper region (or area’s) switching station. The next three digits represent the exchange. All phone numbers on the same exchange can be on the same switch. So, in theory, people in the same community, with the same exchange, could call each other without having to be routed onto a different switch. The last four digits of a phone number are called the subscriber number. The subscriber number helps to associate where your phone is located [8].

The United States’ PSTN is a part of the world’s circuit-switched telephone networks that are operated by national, regional, or local telecommunication operators around the globe [7].

The modern PSTN is composed of telephone lines, fiber optic cable, microwave transmission links, and submarine (under ocean) telephone lines. These all connect using switching centers. Technological advances have replaced much of the copper wire that was formerly used in the US telephone system and have replaced much analog equipment with digital. Two wire analog connections are still maintained in the local loop (also called the last mile), the segment of the system that resides at the end user’s location [7]. The wireline telephone could likely endure for many years regardless of the popularity of wireless communications because of its reliability and availability in power outages.

The ability to call for the help of emergency services is a central reason that wireline communications is critical infrastructure.