Pri
The easiest way to think about PRI is to remember that it is merely ISDN deployed over T- or E-carrier facilities. This means that you have to configure the T1 or E1 controller first and then add the ISDN functionality. PRI does not use elements such as SPIDs for connectivity to the switch, and the TEI is always set to 0. PRI is a larger offering of N-ISDN that accommodates more bandwidth and that offers more flexibility. For PBX uses or where SS7 is not readily available, PRI allows for the transmission of voice and data over a single link.
In North America and Japan, PRI is deployed over a T1 facility and comprises twenty-three B channels and a full 64-kbps D channel. In most other international countries, PRI is deployed over E1 facilities using 30 B channels and a 64-kbps D channel. International PRI is also referred to as ISDN-30. Many of the same troubleshooting techniques involved with PRI circuits are standard with T1 and E1 circuits.
Make sure that you check to make sure that your controller is up and that no alarms are being detected. As a refresher, a red alarm is if you are receiving a loss of frame (LOF) or LOS. This means that you are unable to receive the proper information from the service provider's network. Next, look for a yellow or blue alarm, also called and alarm indication signal (AIS). If you are receiving a red alarm, your equipment attempts to send a yellow alarm to the remote end to notify them that you are experiencing a problem.
ISDN PRI requires that ISDN facilities are available at the CO. In recent years, it has become difficult to keep up with the demand. PRI is still a local loop technology, as is BRI, but it can be expensive depending on the tariff of the associated carrier circuit.
PRI is common in enterprise voice applications because it does not require any knowledge of SS7 to provide voice service. In many areas, PRI is preferred to SS7 even though SS7 is less expensive. Typically, enterprise customers deploy PRI circuits from their corporate headquarters to remote locations or over dry copper within the same location to facilitate PBX connectivity between all sites. Dry copper is a portion of the circuit that does not go through the service provider's network but is completely contained within the customer's private system.
Recently, a new application of PRI connectivity is to have ISDN on the local loop and then use a private Voice over Internet Protocol (VoIP) network is a transport system for the long distance haul between sites. At the destination, the call is dumped out of the IP network, back onto PRI facilities, thus saving the customer long distance charges while maintaining the features of ISDN PRI. Basic PRI deployment is the same as with E1 or T1 circuit deployment, with the addition of the ISDN cards at the CO and the ISDN support at the user end. For this reason, you need to have a channel service unit (CSU)/DSU to terminate the E1 or T1 circuit and then be able to add ISDN support on top of that.
