In order to easily understand what a PRI is just think of it as '24 things'. Those things can be; telephone lines, fax lines, a modem, Internet service, video, a VoIP phone, etc. Technically, A PRI at its basic level is the ISDN (Integrated Services Digital Network) equivalent of a T1 circuit. But that doesn't tell you anything - does it? (Check: wiki.answers.com/What_is_a_PRI)
What is a PRI: (Using your circuit 100% for voice) If you are using all 24 trunks for telephone service; you will receive 23 telephone lines that can all be used simultaneously (called 'B' channels). The 24th line (called a 'D' channel) is used for signaling information (ensuring that when someone hangs up - the line disconnects and is free to be used immediately) and special features, such as; caller ID, DID (Direct Inward Dialing), which allows a telephone number to bypass the Operator, or voice mail system and go directly to a specific person or a department, such as sales or service. What is a PRI: (Using your circuit 100% for data) A PRI circuit that is using all 24 trunks for data has a speed of 1.544 Mbps, or 64 Kbps per individual channel.
What is a PRI: (Using your circuit for both voice and data) The nice thing about a PRI circuit is its flexibility. So, using our initial statement above that a PRI is '24 things', you can configure your circuit in a variety of ways. For example, you could have a PRI that has 12 circuits for voice, giving you 12 simultaneous phone calls, and 12 circuits for data, giving you a speed of approximately 768 Kbps that could be used for Internet service. To see other examples of how your PRI circuit can be configured, just click on; What Is a PRI Line. Buying a PRI can be extremely confusing. Not only that, but you're usually locked into your decision for a minimum of 1 year, some contracts can go as high as 7 years, the most common are 2 to 3 year terms.
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