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.

Do You Need A Special Phone For VoIP?

I’ve been getting inquiries from people who are wondering if you need to buy a special phone to use VoIP as a replacement for regular telephone service. So, do you?

Answer: It depends.

Here’s why. You have probably figured out that you can’t just take a regular telephone and plug it into your router or broadband modem. The connectors aren’t the same size. That’s good, because you might just cause some equipment damage by plugging these incompatible devices together. What you need is a special phone designed to work on a data network or an adaptor for the phone you have now.

Most VoIP services designed for residential and home business (SOHO) take the adaptor approach. A good example is PhonePower’s VoIP service. You can get residential and small business plans with unlimited calling to the U.S. and Canada for $14.95 a month. Your order the service online and they send you a free adaptor for your phone. In this case it’s the Grandstream HandyTone 502 ATA or Analog Telephone Adaptor. You plug your phone in the phone jack that’s exactly the same size as the phone jack on your wall. You connect the ATA to your broadband modem or router using a standard Ethernet cable. Voila! You now have a regular telephone that works on VoIP.

But what’s going on in that ATA box to work the magic? There is circuitry that makes the phone connection look like it is coming right from your telephone company. That means generating the standard line voltage and ringing voltage that your phone is designed for. Those are analog signals because the phone is analog. The ATA also has to take care of converting between analog voice signals for the phone handset and digital packets for the Internet data network. This is done with CODECS or Coder/Decoders. In summary, the telephone needs to see its standardized analog signals and the Internet needs to see something that looks like a piece of computer equipment.

There’s a little more to it. Signaling for VOIP uses a standard called SIP or Session Initiation Protocol. SIP handles things like dialing and knowing when the phone is off-hook. SIP data is sent through the network just like other packets so it works just fine on the Internet or a private data network.

Because VoIP has become so popular for business, there are phones you can buy called SIP phones. These phones have the analog to digital circuitry of the ATA built-in. You can tell you have a SIP phone because it has a standard RJ-45 Ethernet jack on the back instead of the RJ-11 telephone jack. A SIP phone will connect directly to a LAN, a router or a broadband modem. It will need to be programmed for the VoIP service you are using. Some providers will give you instructions for how to do this. Others insist that you use their adaptor and an analog phone.

If you take your home phone into the corporate office, you may be shocked to find that there’s no place to plug it in. The company has installed an Enterprise VoIP system so that all desk phones plug into the corporate computer network. There is no separate phone network. All the phones are SIP phones. If for some reason you absolutely have to use your phone in that office, you’ll need to get an ATA and have it programmed to look like a SIP phone.

The bottom line is that regular telephones are analog. VoIP is digital. The way to make everything work is to use a phone that is matched to the network it is running on or use an adaptor to connect them.