CODECS
There is one area of IP telephony implementation where standards compliance is pretty much a check-box item today. Generally speaking, if two vendors’ phones both implement the same standardized codec—the most commonly chosen are G.711 and G.729—the two phones should be able to communicate without any intervening transcoding function needing to be employed. And, indeed, most vendors do use standard codecs in their phones. With one exception.
That exception is Microsoft, which uses only its own proprietary codec, called the Real-Time Audio codec, in all of its endpoints, whether softphones or hard phones. The reason Microsoft gives for making this choice is that the whole point of moving to IP-based communications is that endpoints should be able to be located anywhere, attached to any network, and still be able to register on their enterprise system and thus appear as if they’re within the corporate network, even if the user is at home or in a hotel on the other side of the world. The implication of this state of affairs is that the end user, and the enterprise IT manager, will not always be able to control the quality of the network across which the real-time traffic is traveling. If it’s a high-quality network, as the internal enterprise is presumed to have, you’re OK; but if it’s the Internet or a low-bandwidth/quality wireless network somewhere, there are lots of impairments that will degrade voice quality.
One way to improve voice quality in the face of network impairments is to use a wideband codec—essentially, to dedicate more bandwidth to each voice stream. The RT Audio codec requires 80 kbps per voice channel for optimal performance, versus 64 kbps for G.711 and 8 kbps for G.729. But the Microsoft codec is proprietary, and the only way for other vendors’ phones to talk to Microsoft endpoints is via Microsoft’s Mediation Server, which transcodes between standard codecs and Microsoft’s RT Audio.
Mark Straton, senior VP at Siemens Communications, has been one of the most persistent critics of Microsoft’s approach to interoperability, and he calls their implementation of the proprietary codec a form of lock-in. “People don’t want a closed model; they really do want an open model,” Straton said. Of big Microsoft customers like Siemens’ own parent company, the German industrial conglomerate, Straton said, “I don’t think they’re going to be forced into a codec that Microsoft demands.”
Microsoft senior director Eric Swift’s response is that this is a non-issue. “Can I make a phone call from OCS to a user who’s not on OCS?” he asks. “The answer is yes, of course. And the Mediation Server does that. Well, why do you use a Mediation Server? The same reason anybody else uses [any sort of] mediation server. It’s to get from one codec and one set of signaling to another. Whether that’s a PRI gateway or whether it’s mediating from different codecs.”
Swift said Microsoft’s implementation of the wideband codec reflects a conscious decision to offer a value proposition that’s different from other players in the market. “One of our primary value propositions is that we don’t expect our endpoints to be stationary. We don’t assign a phone to an office and expect it to sit there. I can pick up this phone and drive it to my house, plug it into my DSL connection at my house, I can make the same phone call that we’re having right now without any involvement from IT.” Of course, all vendors’ IP telephony gives you that portability in terms of call routing--but Swift is arguing that you can’t automatically bring the quality of experience with you wherever you go, because that remote connection might be happening over a poor-quality network that requires you to “fix” the impairments at the endpoint itself, via the wideband (proprietary) Microsoft codec.
Swift plays down the burden that the requirement for Microsoft’s Mediation Server places on adopters. “We don’t charge an extra cost for it; It’s free if you’ve got the [Office Communications Server, OCS] server up and running. We did that because we didn’t want to limit the way people deploy it.
“I think sometimes our competitors put a little false information out there about what a big deal this is,” Swift said. “It’s really a pretty straightforward little piece of software.”
This particular interoperability debate has little to do with technology and everything to do with the company that’s at the center of it. Microsoft is both the booster that rocketed first generation IP telephony into its second-generation orbit as Unified Communications; and it’s also, well, Microsoft: The company that competitors and some customers love to fear, loathe, and, more often than not, whom they eventually must embrace.
But the debate illustrates some things about what various people mean when they talk about “interoperability.” Microsoft points out that the SIP implementation in OCS follows all the RFCs, which in some sense makes them more interoperable than vendors whose original IP-PBXs relied on proprietary call control protocols. But as we’ve seen, even a fully SIP-compliant implementation only gets you so far on the road to interoperability. And then, does the fact that Microsoft used a proprietary codec mean they’re not, in fact, open and interoperable? Or does the fact that they provide a gateway at no cost mean that you really can interoperate?
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