As a rule of thumb, a single access point can cope with about 10 simultaneous VoIP calls says Warhurst. That would be easy to manage if people didn’t move around, but once people get into huddles it’s easy to overload an access point. Wireless switching takes care of this by dynamically reducing the power output of a busy access point so that some of the handsets automatically associate with a nearby alternative, thus balancing
the load.
According to David Humphries, country manager at Aruba, his company’s wireless switch provides superior performance by not only reserving bandwidth for each phone on the access point it is currently associated with, but also on neighbouring access points to ensure smooth roaming. These switches have other desirable functions, such as the ability to detect “rogue” access points (those installed by users without authorisation from the network manager).
Adam Kleemeyer marketing representative for wireless LAN at Nortel, says another benefit is the application of consistent policies and security settings across the WLAN, and even between multiple WLANs on the same corporate network.
Humphries notes that this can be extended to access points at the remote end of virtual private network (VPN) connections. “I do it at home [or] when I go to a hotel room,” he says. As far as his phone and notebook are concerned, it’s as if he was back in the office.”
Aruba customers in Singapore are planning to use this disaster recovery technology in the event that an outbreak of bird flu keeps their workers at home. “True virtual WLAN is key to successfully implementing wireless voice [alongside data traffic],” says Symbol’s Stock.
The Voice Quality Manager software embedded in the company’s multifunction devices helps this process by throttling back data traffic from the device when voice packets must take priority.
“Depending on usage it is always better to have dedicated access points for VoIP usage. That way your WiFi VoIP handsets can communicate without having to compete with browser and other network traffic,” says Maurice Famularo, D-Link ANZ marketing director.
While most organisations think of WiFi as essentially an indoor technology with the possibility of spilling outside the walls, Kleemeyer points out that a wireless mesh can be used to cover outside areas without a wired network connecting the access points. This is linked using wireless standard 802.11a and talks to user devices over 802.11b/g. This arrangement leaves more bandwidth for users than would be the case with a wireless distribution system (WDS), where the access points and the devices communicate on the same channels. But even if you’ve got the wireless side sorted, you’re not out of the woods.
“The backbone is most important, and in most cases it is necessary that your switching fabric has the capability to handle quality of service for prioritising VoIP packets on the network,” says Symbol’s Famularo.
Stock notes the importance of doing due diligence on the existing network before overlaying it with wireless, warning that a failure to do so has led to project failure when “guesstimates” of sufficient spare capacity proved over-optimistic.
Securing all bases
“The companies that address security [and other aspects] don’t seem to have issues [with VoIP over WiFi],” according to Warhurst. For example, any WLANs that are open to visitors should be isolated from those used for VoIP.
“A lot of the previous security concerns have been resolved,” says Nortel’s Kleemeyer, so a properly implemented WLAN is as secure as its wired equivalent.
Little says the three most important steps towards a secure WLAN are:
1) to use the best encryption method that is supported by all your devices—WiFi protected access (WPA) rather than wireless equivalency privacy (WEP), WEP rather than nothing—and change the key whenever you think it might have been compromised);
2) to disable remote administration of the wireless router and;
3) to make your network harder to find by turning off SSID Broadcasting.
“Once you’ve setup your network there is no need to advertise your presence to every wireless device in range,” Little says.
“If your network is small and you can find the media access control (MAC) addresses of the devices using the network you can turn on MAC address filtering. This will restrict which devices can access the network, though it can be painful to administer.” He adds that as previously noted, wireless switching considerably simplifies WLAN security.
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