Is PRI the Right Choice for Your Company?

Written by: Dennis Green - Jan 7, 2009

PRI (Primary Rate Interface) is an ISDN connection designed to be provided over T1 lines. In the United States, a PRI line consists of 24 (64 kbps each) DS0 channels. PRI T1 lines are commonly configured so that 23 channels serve as B (Bearer) channels and one as a D (delta) channel. Each B channel serves as a voice (telephone) channel. The D channel provides control and signaling information for the B channels. B channels can be used as independent channels to simultaneously provide a variety of services such as internet, voice, or imaging. They also have the flexibility to be bonded, as needed, to provide higher bandwidth for special needs such as video conferencing. A significant difference between PRI T1 and traditional integrated T1 is that T1s which are not PRI require a portion of each channel to be allocated for signaling functions. This results in a reduction in effectiveness, efficiency, potential and bandwidth for most functions of each channel of non-PRI T1. With T1 PRI, all signaling functions are provided by the 24th channel. This leaves each of the other 23 channels with a full 64 kbps, which can be fully dedicated to bearer functions. One D channel can provide signaling functions for several other PRI lines. It is not uncommon for two D channels (one as primary, one for backup) to provide the signaling functions for a span of as many as 20 PRI T1 lines. This frees the 24th channel of each of the other PRI lines so that they can be used as additional bearer channels. Because PRI lines serve as a direct connection to the telephone company’s central office, PRI is often the preferred choice of PBX customers. PRI T1 provides many advantages over traditional voice T1. These include: call by call service selection, more PBX users can be supported, caller ID, DID (direct inward dial) numbers, messaging, and video conferencing. Because of increased efficiency provided by PRI, companies which switch to PRI from traditional voice T1 often find that they not only receive a much greater variety of services but often do not need to pay for as many trunks as they needed prior to the change. PRI T1 is available in most major metropolitan areas, but is not available in most isolated rural areas. To assess availability and pricing for your location, use the tool at the top of this page or on our home page. This tool will provide real-time answers, it’s free, easy to use, and there is no obligation. (Click here to return to top of page)