Primer: Types of Telephone Lines

There are a variety of types of telephone lines that are offered by providers. Most lines can be divided into either analog or digital.

Analog Lines

The most common telephone line is the Central Office Analog Trunk. This is what most of us refer to as the basic telephone line. Providers offer a variety of features over analog trunks such as caller ID, call forwarding, voice mail, line hunts, call waiting etc. These offerings can be chosen at the time of subscription.

Where does the name Central Office Analog Trunk come from?

The central office is typically the closest provider office that provides telephone line service to your location. The central office has switching equipment that connects your calls to the correct networks so that you can communicate with the correct party. Analog trunk refers to an analog telephone line. Most lines that small to medium size businesses subscribe to are analog as opposed to digital.

Digital Lines

Larger businesses with greater numbers of telephone lines will often subscribe to digital services (i.e. ISDN, T1, PRI, BRI, etc.). Digital lines can provide multiple channels over a single physical line. For example, T1 service provides 24 digital channels over a single physical line. Each channel can accommodate incoming or outgoing calls. Essentially, you can have 24 conversations over a single physical line. It is often less expensive for a provider to manage and maintain a single physical line for a T1 trunk than 24 individual analog trunks. These lower costs are passed on to the consumer who needs larger numbers of lines. Other benefits of digital service include direct inward dial and data services like internet and video conferencing.