Is 802.11 Ready for VOIP?
There are numerous benefits to using wireless LAN as a conduit for packetized voice data: 802.11 equipment is cheap, easy to install, and, unlike wired voice-over-IP (VOIP) phones, WLAN phone users can wander around a building taking their handsets with them. So it's no surprise that Cisco, NEC Corp. (Nasdaq: NIPNY), Symbol Technologies Inc. (NYSE: SBL), and many others are working to implement the technology. (see Symbol Talks Up Voice Over 802.11 and Airespace Takes Off)
However, before these benefits can be fully appreciated, some issues need to be dealt with to enable VOIP to run smoothly over a wireless LAN infrastructure.
The most notable of these is the fact that all of these companies are working on 802.11 VOIP technology before a WLAN specification that can support voice has been approved by the Institute of Electrical and Electronics Engineers Inc. (IEEE) The IEEE is working on the 802.11e standard, which adds a quality of service (QOS) mechanism to enable voice services (see IEEE Plots Speedier WLAN). A QOS upgrade is required because wireless is inherently a shared medium and without some method of prioritizing packets -- so that packetized voice data is sent down the pipe in a smooth stream before the other bits and bytes are delivered -- VOIP won't work over 802.11 networks. However, there is no word on when exactly the e upgrade will be ratified.
So, in the meantime, Cisco is using software from SpectraLink Corp. to implement software-based QOS mechanisms on its access points. The software, which creates a separate queue for voice traffic, wil be supported on all but the earliest of Cisco's Aironet access point range, according to Ben Guderian, director of marketing at SpectraLink.
Guderian freely admits that his company's software is a pre-standards play. "It’s a mechanism designed specifically for voice -- it's not designed to replace 802.11e but to get to market quickly."
This could lead to interoperability problems down the road. Customers and vendors have already seen how 802.11g (54-Mbit/s over 2.4GHz) products using draft IEEE specifications have trouble working together (see Interop Woes Smite 802.11g).
If a company already has a lot of data users on its WLAN network, there could also be capacity issues when adding VOIP phones. Ten or twelve users per access point is generally considered acceptable for enterprise data usage. However, Guderian says that 802.11b access points using his firm's software can support up to 12 simultaneous calls, presuming that all the users are close to the access point and communicating at 11 Mbit/s. Mobile VOIP phone users are much more likely to move around than laptop users, and once they start to get farther away from the access point and connect at 5.5 Mbit/s and 2 Mbit/s, more bandwidth is required. This, Guderian concedes, drops the number of simultaneous calls that can be supported to seven.
Guderian contends that some of the 4,000 customers that SpectraLink has won since it started to work on voice-over-WLAN use the systems exclusively for voice. "Hospitals in particular," he notes. SpectraLink sells into numerous vertical markets -- including industrial, retail, and healthcare -- as well as corporate accounts.
SpectraLink also recommends that users not run heavy-duty encryption programs with wireless LAN voice services, because the extra processing involved with security alogorithms seriously increases the perceived jitter and delay when making calls. Instead the company recommends that administrators use the standard 802.11b security, the wired equivalency protocol (WEP), which is percieved by many to be too insecure for enterprise usage.
This means that if an administrator is running voice and data services over the same network, the voice services must be fenced off so that a different level of security can be applied to pure data transfers. "We recommmend that they use a separate VLAN," says Guderian. (A virtual LAN could map the users with VOIP phones.)
Guderian says that not offering the full palate of encryption options for WLAN voice services is not a security issue that users should be worried about. "Most hackers aren't interested in real-time phone calls. They want to get into the servers."
However, as has been shown numerous times, wireless LAN security is the number one issue for corporate users (see WLAN: The Four S's and Gartner Eyes WLAN Security). So administrators and users are likely to worry about VOIP security even if it isn't really a big problem .
— Dan Jones, Senior Editor, Unstrung