Wireless: The new hotspot for VoIP

Just as voice over IP is becoming widely used over wired connections, the technology is also starting to crop up on wireless networks as an cheap alternative to mobile phone service. Ben King looks at the outlook for this space - and the challenges that must be overcome.

Mobiles work pretty well for voice calls. Wi-Fi works pretty well for data. So why on earth would anyone want to run voice calls over Wi-Fi?

Like climbing Mount Everest, the simplest reason for it is: 'Because it's there.'

Once you've found a Wi-Fi hotspot in an airport, your home or office, you have a generous supply of bandwidth, and usually you'll be on an all-you-can-eat tariff. So you might as well run your voice calls over it at no extra cost, and save your mobile bill.

Also, in theory, once you're on an IP-based network, you can get the benefit of all the services which IP-based telephony is meant to deliver - a unified voice mailbox, instant-messenger style presence and a single number which follows you wherever you go.

The simplest way to do run VoIP over a wireless LAN is to go to a wireless hotspot and make a call using a simple VoIP telephone service like Vonage or Skype.

This is possible at the moment, and some people are already doing it, says Vonage CEO Jeffrey Citron. "We are starting to see wireless as an important part of voice over IP."

Voice over IP is likely to become particularly useful for business travellers. Booting up a soft phone on a PC in a coffee shop when you're in your home country won't save a great deal.

Do the same in an overseas airport, avoiding monstrous mobile roaming charges, and it starts to make a lot of financial sense.

Abdel Missa, director of product marketing at Wi-Fi provider GoRemote, expects this trend to take off. "The market is growing. The technology is there and it is reliable," he says. "There are a lot of opportunities."

GoRemote allows users to log on to wireless, dial-up or wired LANs from different providers with a single sign-on and receive a unified bill. They plan to add an IP phone to their offering in the near future, Missa says.

And if booting up a PC seems like too much trouble, Vonage is planning to launch a wireless handset that can make voice calls over Wi-Fi from the home, the office or wireless hotspots.

However, VoWLAN is catching on in some business premises, too. For employees who don't sit at a desk but spend most of their working day moving about within a single large building, VoWLAN can be a cost-effective way of providing portable telephone services, either via software phones on PDAs, or special phone handsets. If the company already has a Wi-Fi network set up for data, the cost savings are even better.

Jason Angelus, product manager at Cisco, says: "We are seeing it take off in vertical markets, like retail, light industrial and healthcare. Anywhere where you have a mobile workforce centred on a specific area. For the moment that is the sweet spot."

The trouble with running VoIP over Wi-Fi is that you'll end up running one somewhat unreliable protocol on top of another. The internet protocol was designed to run data on an as-needed basis across a decentralised network. With simple data traffic like email, it didn't matter overly if it took two milliseconds or two minutes. Voice traffic, however, is much more sensitive.

To overcome this, a network needs to have 'Quality of Service' (QoS), a technology which guarantees bandwidth to time sensitive applications like voice and tells others to wait their turn. This ensures, for example, someone downloading a large presentation file doesn't interrupt everyone else's voice calls.

Another challenge for VoIP over Wi-Fi is a user making a phone call strutting down a hospital corridor needs to be able to switch seamlessly between one access point and another.

There are various standards initiatives on their way which are intended to solve these issues - in these cases, 802.11e for QoS and 802.11r for access point handover. However, these standards are not yet ready and may not appear in products until the end of the year - a factor which is delaying the widespread adoption of VoWLAN.

Equipment with early versions of these technologies is already available. Cisco, for example, makes handsets with its own QoS standard. Manufacturers Spectralink and Symbol use it too, allowing them to interoperate with Cisco kit.

Handsets are still quite expensive - Cisco cites a list price of $595 for a VoWLAN handset. Once standards are set and adoption increases, manufacturing volumes will grow and prices come down - but that's still in the future.

Leif-Olof Wallin, analyst at Meta Group, says: "The cost of these handsets is still way too high. 2006 - that is when we expect to see some initial uptake and 2007 is when we expect to see some significant rollout. That is when it will get some place in the consumer space."

However, for VoWLAN to really become useful, it will have to integrate with other networks, particularly mobile phones. So when you're at home or in a hotspot, it will use the cheap Wi-Fi network and when you're out and about, it will roam onto the mobile network.

Dual-mode VoWLAN/cellular devices are starting to become increasingly widespread. In Japan, NEC has already launched a phone which can roam from Wi-Fi to NTT DoCoMo's FOMA 3G service. PDAs with VoIP and mobile are on the market and Motorola has announced the CN620 VoWLAN-capable phone for countries with GSM mobile networks, including Europe.

With WiMax and other exotic wireless networks on the horizon, the prospect of seamless roaming looks increasingly enticing. However, there's still a thorny question or two to sort out before this becomes a reality.

The mobile and various Wi-Fi operators will have to sort out a way to allow customers to roam from one network to the other and agree on a means of charging each other.

And mobile networks may not be too keen to allow Wi-Fi hotspots to eat away at the voice revenues which are still the core of their business.

Ovum principal analyst Jeremy Green says: "It's possible that this won't have a happy outcome for everyone. But the devices will still be useful without seamless handover. The device manufacturers can still go somewhere else."

Though there are still some technical challenges to sort out, VoWLAN looks set to be big business. Cisco's recent $450m acquisition of voice-capable WLAN provider Airespace proves this area is starting to heat up. The technology should provider cheaper calls for the consumer but could prove quite expensive for some of the established players.