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HD Voice: Definitely Worth a Look

High Definition (HD) voice sounds great. You may already own HD voice. HD voice is an IP phone capability existing in many IP phones, but enterprises may not know they can use it.Enterprises deploying newer VoIP telephone systems could be overlooking the HD voice feature. TDM phone systems and cheaper IP phones limit the audio frequencies carried to a range of roughly 300 to 3400 Hz (narrowband). IP phones often offer wideband capability, carrying frequencies from 50 to 7000 Hz.

Wideband phone calls are calls where both ends have wideband equipment and the connection between them supports 64kbps speech. Wideband conference calls are where at least some of the participants are connected in wideband through a wideband-capable bridge. Such calls sound much better than narrowband.

So what are the benefits of HD voice?

* Recognize the speakers more easily * Understand speakers who speak a different native language and whose accents can be difficult to understand * Overcome background noise during the call * Reduce audible mistakes (Mark Straton of Siemens has remarked that HD voice could reduce the listening errors from 40 to 4 per 30-minute conversation) * Less strain/stress occurs with HD voice when there are long calls * Improves the sound quality for conference calls

Enabling wideband calling within the IP-PBX is usually a matter of setting a configuration parameter, as long as both ends of the call have HD voice capable IP phones. But once your call exits the IP PBX HD voice island, then supporting HD voice becomes an issue.

The popular IP PBX systems can support a common wideband codec, ITU standard G.722. This codec operates with the same bandwidth (64kbps) as the standard narrowband codec, G.711. There are numerous other HD codecs (including G.722.1, G.722.2, Speex, iSAC, SILK, iPCM-wb, EVRC-WB). Some are designed for limited-bandwidth situations or high packet loss networks. Most of them are not supported by IP phones.

The challenge is that HD voice calls cannot be routed through the PSTN. The trunk gateways to the PSTN require the use of the G.711 codec standard.

David Frankel is the founder of ZipDX, an HD voice conferencing service. He has worked in computer and networking technology since 1974 and was the founder of Jetstream Communications, Inc. which supplied voice-over-packet technology to telecommunications carriers.

David made these comments in a recent conversation:

The solution is to give the PBX routing instructions so that when possible, it connects calls via IP (not PSTN), either using the public Internet or peering links between PBXs. That means constructing and maintaining routing tables, or subscribing to a directory service for this purpose. Connecting to a wideband conference service is easier: when a PBX extension dials the service's 8XX number; have it route the call directly to the conference bridge in IP, rather than sending it via the PSTN.

In addition to the "soft" benefits of wideband [noted above], there can be direct cost savings as well. Connecting calls via IP avoids PSTN charges. ZipDX, a wideband-capable conference service, charges half price for wideband IP connections.

In addition to the "soft" benefits of wideband [noted above], there can be direct cost savings as well. Connecting calls via IP avoids PSTN charges. ZipDX, a wideband-capable conference service, charges half price for wideband IP connections.

Some users are concerned that VoIP calls will be of lower quality as packets get lost or delayed. Experience has shown that as long as an enterprise has a "right-sized" broadband connection, call quality is consistently good. Right-sized means that there is sufficient bandwidth available for the maximum number of anticipated simultaneous phone calls (at roughly 90Kbps each per call in each direction), plus nominal data traffic, and the router gives priority to voice packets. Once the packets enter the backbone, current infrastructure is such that there's typically zero loss even on the public Internet.

Call security is another issue. Unencrypted calls are relatively secure, as demonstrated by an analysis of potential interception scenarios. Private, secure connections can be established for more secure control and assurance.

David went on to say:

Once the user has HD voice exposure, it will be hard to take it away. The concept of HD voice conferencing extends the HD quality beyond the enterprise for connection to other HD islands.

Gary will be presenting a session on HD Voice at VoiceCon San Francisco; a Discussion Forum on this session can be found here.