So, What Does ISDN Stand For?

If you are involved with business telephone systems, you’ve no doubt heard the term ISDN bandied about. But what is ISDN and what can it do for your company?

As you might suspect, ISDN is an acronym. It stands for Integrated Serviced Digital Network.

I guess that’s not much help in and of itself. ISDN is a digital telephone standard that was originally intended to replace analog telephone lines for both residential and business users. It never really took off on the consumer side because DSL, Cable broadband and VoIP came along with higher bandwidths and lower prices. But ISDN did become a popular trunking service for PBX telephone systems. It also has a specialty niche application.

There are two ISDN standards you should know about. The low bandwidth version is called BRI or Basic Rate Interface. The higher bandwidth version is called PRI or Primary Rate Interface. They are constructed from the same elements. PRI just has more of them than BRI.

The two basic building blocks of ISDN are the B or bearer channel and D or delta channel. B channels have a bandwidth of 64 Kbps each. That’s exactly enough for one digitized telephone call or a low bandwidth digital modem. Remember 56 Kbps dial-up modems? ISDN BRI was supposed to replace them with one B channel for telephone service and a second B channel for modem service. The D channel is 16 Kbps and is used for signaling and control of the two bearer channels.

This arrangement of two bearer channels plus a delta channel is called 2B+D in telephony lingo. You have the option to use both bearer channels for telephone service so that you’ll have two digital phone lines. Or both bearer channels can be assigned to modem data with a bandwidth of 128 Kbps. That was considered fast when ISDN BRI was introduced, but quickly became obsolete with the introduction of broadband Internet service.

While ISDN BRI flopped as a digital home telephone service, it has found a new lease on life with radio stations and audio production. Standard analog telephone lines don’t have the bandwidth to reproduce natural sounding voices. But ISDN lines with the right CODECs (Coders/Decoders) can transport studio quality microphone signals from sports venues and other remote locations. They are also used extensively by voiceover artists and for high fidelity call-in interviews on-air.

ISDN PRI has the same B and D channels that make up BRI service. Only PRI is configured as 23B+D. That’s 23 bearer channels and one delta channel. The delta channel is still used for signaling and call control. Each B channel can support one telephone conversation. So, if you order ISDN PRI service for your PBX telephone system you can have up to 23 outside lines. They can be individually configured as incoming, outgoing, local, long distance, toll free or some combination of these.

Most PBX phone systems come with at least one ISDN PRI interface standard. Some have multiple ISDN ports so that you can add more phone lines if you exceed the capacity of 23 lines on one ISDN PRI trunk. Larger companies and call centers can make good use of the extra ports. The D channel handles call switching much faster than a standard analog phone line and also provides Caller ID for all B channels.

Is ISDN the service that is right for your telephony needs? If you have more than a half-dozen outside lines, you might be able to save money by converting to ISDN PRI. Even if you already have PRI service, prices have plunged in recent years and you may be able to cut your monthly phone expenses significantly with a competitive service provider. Find out right now by checking ISDN PRI prices and availability for your business location.

T1 Telephony Has Many Flavors

T1 telephony was originally invented to transfer hundreds and thousands of phone calls between telephone company central offices. It’s grown far beyond that initial vision to become the digital phone line of choice for thousands upon thousands of businesses. You may already have or be thinking about installing a T1 phone trunk for your business. But are you aware that you have many options to consider?

T1 is a digital line standard that can be used for voice, data, video or all of these. In its original form, it transports 24 separate phone calls on individual channels called DS0. The combination of these is the T1 line or DS1. Each of the DS0 channels is responsible for transmitting digitized voice, plus call control and signaling.

Today’s T1 voice circuit of choice is called a T1 PRI or ISDN PRI. It’s is still organized as 24 channels on a single digital phone trunk, but one of the channels is used exclusively for call control and signaling, leaving the other 23 channels as the equivalent of 23 separate phone lines. The signaling channel is also used to support data services such as Caller ID.

T1 PRI is popular with businesses that have their own PBX telephone systems and with telephone intensive operations, such as customer contact centers and call centers. Nearly all PBX equipment supports this line format. If more than 23 outside lines are needed, then additional T1 PRI lines can be installed.

There’s a T1 telephony solution designed especially for smaller companies that can’t fathom needing 23 phone lines. Integrated T1 lets you have up to a dozen outside phone lines and uses the rest of the T1 line capacity for broadband Internet service. If you get what’s called a dynamic T1, it will automatically assign any bandwidth not currently being used for phone calls into the broadband pool. This is a very efficient use of resources and can be less expensive than having a dozen separate phone lines plus an independent broadband service.

VoIP has become a popular form of telephone service. An Internet connected T1 line can provide the bandwidth and reliability to support VoIP phone services for a dozen or more simultaneous calls.

T1 PRI lines will also interface with IP PBX systems, the VoIP equivalent of the PBX telephone system. T1 PRI is known for its high voice quality, reliability and support of telephony features such as Direct Inward Dialing.

There is also a new form of T1 telephony called SIP trunking. SIP is the signaling standard used in VoIP phone systems. A SIP trunk is often implemented on a T1 data line, but it is not connected to the Internet. It is a direct point to point connection between your business location and your service provider. This avoids the vagaries of Internet performance and helps the service provider ensure high voice quality and service reliability.

Are you ready for T1 telephony or interested in comparing lower cost options for the service you already have? If so, then check T1 telephony prices and options now.