Within Limits As impressed as I was with Polycoms HD Voice sound quality at the time I saw it demonstrated and during eWeek Labs tests, I was struck by the overwhelming limitations of the technology. The reliance on wideband codecs means that HD Voice is a boutique affair. The endpoint devices must support the proper codecs for full benefit, but Polycom offers HD Voice only in its pricier and fully featured models. Lower-end models designed for cubicle workers are on Polycoms HD Voice road map.While SIP (Session Initiation Protocol) trunking provides some promise of relief for this problem, high-definition VOIP support will most likely extend to the carriers own customers because U.S.-based service providers typically fall back to PSTN connectionsrather than to IPfor peering between carriers. HD VOIP requires new measurement criteria. Click here to read more. Polycom officials admit that their greatest traction with HD Voice comes from the largest companiesthose with more than 10,000 seats and often with international offices. These companies will reap the greatest benefits from HD Voice calls placed within their own network and between branches (or countries), relying on corporate connectivity to place calls while avoiding the PSTN. Companies PBXes will need to support the codecs needed for HD Voice. Polycom officials informed me that HD Voice has been shown to work with the open-source Asterisk project, BroadSoft, Cilantro and Interactive Intelligence systems. However, as Ive seen in tests, mileage will vary. I was able to enable HD Voice with Asterisk with a few simple modifications, but, as is the case with the main fork of the Asterisk 1.4 distribution, such a step hindered the ability for HD phones to connect with legacy non-HD devices. As I later learned from Kevin Fleming, director of software development at Digium, in Huntsville, Ala., "Asterisks code negotiations currently treat the call legs independently, and thus never renegotiate the initial call leg based on the requirements of the secondary call legs." However, Fleming continued, "In the Asterisk SVN trunk, we have a G.722 code module, so this problem would not occur, and well be putting that module into Asterisk Business Edition as well." Page 3: Should You Heed the Call for HD Voice?
More disconcerting is high-definition VOIPs lack of extensibility in general: Under no circumstances will high-definition VOIPs full audio quality be maintained if a call touches the PSTN. Any time a call gets routed through the PSTN, whether through a corporate gateway or when peering between service providers, the call will immediately be down-sampled to toll quality, thereby losing all the additional information carried by the wideband stream.