VoIP makes life a lot more convenient for telephone users. It lets them do all sorts of things over the phone that they couldn't with traditional telephony, from managing their e-mail and address books online, to clicking to call. But it also makes life a lot more complicated for those in charge of making it work. IP wasn't designed to carry voice, so forcing it to do so takes real effort. Making VoIP work with TDM networks, which it usually has to at one point or another, adds further complication.
Here's a brief look at potential problem areas. Some mainly involve the IP part of the equation, while others are traditional telephony issues that have become problematic again in the age of VoIP. The categories aren't exclusive -- some of them overlap significantly. Either way, they're going to be with us for awhile, so we'd better start making them part of our vocabulary.
When you pick up a phone, you want to get a dial tone right away. You also want near-instantaneous connection (technically known as call set-up) once you dial. That's called availability. But while it's rarely a problem with the PSTN these days, that's not always true with VoIP, notes Arun Bhardwaj, senior product manager at network test and measurement firm Keynote Systems. As a result, if you're using a hosted provider, you might want to get some guarantees written into your service contract.
Same with reliability. With a traditional phone call, once you've established a clear connection, you can expect it to remain clear until you hang up. With a VoIP call, it could deteriorate as soon as the rest of the crew comes back from lunch and starts checking their e-mail. You'd better make sure the bandwidth you have available can accommodate surges.
Your IP telephony system, whether in-house or outsourced, may at some point be converting a lot of analog voice to digital, and vice versa. It might also be sending a lot of voice packets over a congested or erratic network. Both can cause delays. When they do, notes Bhardwaj, some packets -- or words -- you are expecting might not arrive when you are expecting them to. Naturally, they'll show up just after you've started speaking again to fill the silence. That means you and the person at the other end will talking over each other, doing that awkward conversational dance known as double talk.
Packet problems might cause you to hear noise or gaps in the conversation. You might also hear words stretched out far longer than they should be. So when you hear someone telling you something was baaaaad, they might not joke making a sheep joke. What they are telling you, without knowing anything about technology, is that it's time to do something about your network's inconsistency.
This is one of those oldies but goodies from the olden days of traditional telephony. Echo was almost a trademark signature of calls over satellite and pre-fiber cables. For a brief interval, it seemed to have disappeared. Now VoIP systems are great places for it to make a comeback. Notes Mike Hollier, CTO of voice and video quality measurement company Psytechnics, IP network edge devices are increasingly using echo cancellers to deal with the problem. If they don't, or if the ones they or your desk phones use aren't good enough, you could feel like you're talking to Central Asia when you're just making a call across town.
Here's another relic of staticky copper cables that remains with us in the VoIP age. Psytechnics' Hollier describes an IP phone system in a top London financial firm that suffered from noisy, hissy voice quality. It turned out that the signals coming into the media gateway were too low-powered. The gain control automatically boosted it, and the result was a superbly digitized reproduction of a hissy-sounding call. The more disparate types of equipment a voice call has to traverse, the greater the likelihood of such problems.
A modern mixed network offers all kinds of places to get the speech levels wrong. The hissy sound in the previous example ironically occurred because the financial firm had outstanding headsets, according to Hollier. They used noise cancellers to get rid of background sound, which was why they could put out a low-powered signal. And that in turn was why the encoder ended up distorting the wave form as it turned it into digital signals. Finding such subtle causes can take considerable technological detective work.
Ultimately, speech distortion involves acoustic wave forms that aren't the shape they should be. And however your sound gets distorted, packetizing it preserves the distortion. In fact, the better your IP network, the more faithfully and efficiently it delivers the packets containing the distorted speech. So it takes a lot more than analyzing the performance of your data network to figure out why your expensive new IP telephony system sounds so bad.
Though there are as many solutions as there are problems, quality-monitoring companies have some suggestions on how to at least figure out what the problems are. Keynote emphasizes, for example, that it's necessary to monitor and test the quality of calls from end to end, rather than just in the IP part of the network. For Psytechnics, it's crucially important to monitor and measure performance every step of the way, in order to learn where distortion is actually happening. And by odd coincidence, the two companies have products that do just those things.
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