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Perfect for businesses that want a more powerful voice service than traditional local and long distance POTS lines. The appeal of ISDN is that it is available anywhere that there are phone lines and it’s cost effective.


What is a PRI?


In the Integrated Services Digital Network (ISDN), there are two levels of service: the Basic Rate Interface (BRI), intended for the home and small enterprise, and the Primary Rate Interface (PRI), for larger users. Both rates include a number of B-channels and a D-channel. Each B-channel carries data, voice, and other services. The D-channel carries control and signaling information.


The Basic Rate Interface consists of two 64 Kbps B-channels and one 16 Kbps D-channel. Thus, a Basic Rate Interface user can have up to 128 Kbps service. The Primary Rate Interface consists of 23 B-channels and one 64 Kpbs D-channel using a T-1 line or 30 B-channels and 1 D-channel using an E1 line. Thus, a Primary Rate Interface user on a T-1 line can have up to 1.544 Mbps service or up to 2.048 Mbps service on an E1 line. PRI uses the Q.931 protocol over the D-channel.


Primary Rate Interface channels are carried on a T-carrier system line (in the U.S., Canada, and Japan) or an E-carrier line (in other countries) and are typically used by medium to large enterprises. The 23 (or 30) B-channels can be used flexibly and reassigned when necessary to meet special needs such as videoconferences. The Primary Rate user is hooked up directly to the telephone company central office.


When Would You Use ISDN PRI?


PRI is typically used by medium to large enterprises with digital PBXs to provide them with digital access over copper wire. The 23 (or 30) B-channels can be used flexibly and are reassigned when necessary for multimedia such as video conferences. The PRI user is hooked up directly to the telecommunications company central office. The appeal of ISDN is that it is available anywhere that there are phone lines. It is a cost effective option for business using very limited video conferencing.

Benefits of PRI


  • Direct Inward Dialing: Providers offer hundreds of numbers which can be used by outsiders to call extensions directly instead of using a PBX auto-attendant.


  • Call Hunting: This occurs when there is a busy channel. Calls are automatically routed to a free channel. This is beneficial when multiple calls are occurring at the same time.


  • Reliability: Since they are digital trunks, PRI lines are more reliable and easier to trouble shoot than analog lines.


  • Flexibility: PRI lines can be used for voice, data, video conferencing, and faxing. All of the above can be done simultaneously on different channels.


  • Quality: Call clarity and quality is better than analog due since they are end-to-end digital lines. Call take lesser time to establish than analog trunk lines.


  • Cost Savings: PRI lines are relatively inexpensive for small and medium sized businesses. PRI lines can send and receive 30 calls simultaneously.


Netari is an IT and Telecom consulting firm that offers a diverse and comprehensive  portfolio of technology products, solutions, and services to businesses, municipalities, and non-profits in the US and internationally.  

Netari helps executives and senior-level leaders manage technology projects with a proven process that begins with discovery, planning & strategy, and evolves into a successful implementation and ongoing lifecycle support.

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