Gallery

Voice over IP

Posted on 28 Jun 2005 at 12:38

However, passing voice traffic over a network is a far from trivial feat. It is now well known that the Internet works by splitting data into separate packets, which are then sent across the network using whichever route is the most efficient. This route can change by the second, so there is no guarantee each packet will immediately follow the one that went before it. Once they reach their destination, they must therefore be put back together in the right order and translated into a form we can use. Doing this with a constant two-way voice stream is a highly complex operation, and can result in slight latency.

VoIP protocols employ a number of techniques to minimise this effect, the most effective of which is to transmit just the audible part of each conversation. For much of any call, at least one of the participants will be silent, and so only the incoming stream will be transmitted. A poorly configured microphone without noise cancellation, however, will continue to transmit background noise even when a participant is not talking, making the data exchange more complex.

You should also consider security, particularly with proprietary systems such as Skype. Despite being one of the most popular VoIP services, the company is protective of its code: although it has released a development API, few people really know what is going on under the hood. This makes the security difficult to verify. Some are worried that it would be technically possible for less scrupulous developers to produce a Skype-specific virus, either exploiting the fact that it acts as both a server and a client, or by dialling premium-rate landlines. Skype itself claims to rigorously check all its code and that security remains a top priority.

The road ahead

IDC said 124.3 million homes worldwide had broadband access at the end of 2004. This was up 47 per cent on the year before and opened up a vast market for Internet telephony. The potential for global point-to-point PC calling is growing on a daily basis, giving the nomadic VoIP user more opportunities to hook up their personal number wherever they stop for the night.

That's not to say VoIP will replace conventional setups any time soon. For a start, there are just too many problems inherent in using an entirely packet-based medium for voice. Beyond the issue of emergency calls, there is availability to consider. The public phone network does not power VoIP hardware the way it does with conventional handsets, so will be out of action if your power blacks out, which could be when you need it most. Most VoIP services cannot host a fax machine (although this is included in the Vonage business option), and you can rarely connect a set-top TV box to download updated schedules either.

Each of these factors counts against VoIP, which will remain a complementary service for most users, with corporates retaining at least a handful of conventional lines as entry points to the legacy network for fax machines and monitored alarms. Home users too will be given the choice of reliable, conventional calling and cost-saving, innovative VoIP. Even the providers accept this, with Skype's Sarah Myers explaining that: '[in the same way] email is free but people still pay for and use the fax, we feel that voice calls using Skype could be a free alternative to other telephony for anyone using the Internet.'

This is something we have heard before, with BT last year reminding analysts that mobiles would never have taken off if cheap calls were all that mattered.