WLAN hurdles 1: QoS
Prioritisation and garantees are on their way.
By Galen Gruman, InfoWorld | InfoWorld | Published: 01:00, 30 November 2004
LAN managers and CIOs can breathe a little easier, now that solid security standards are available for WLANs. This summer, the IEEE released - and many vendors have already implemented - the 802.11i authentication and encryption standard (explained here), bolstered by the WPA2 (Wi-Fi Protected Access 2) interoperability certification from the Wi-Fi Alliance industry group
Yet, as they deploy broader WLANs as part of the overall corporate network, IT managers will face other issues - for which standards are still in development or have not yet even been started, notes Warren Wilson, an analyst at Summit Strategies. "Now the top problem is making it work robustly and reliably," says Paul Congdon, chief architect of ProCurve networking products at Hewlett-Packard.
These issues fall into four categories: quality of service, WLAN management, roaming, and interoperability with other wireless technologies. Today, we'll look at quality of service, and follow up with the other aspects.
Quality of service
As WLANs are more broadly deployed, traffic management will become an issue. APs can typically handle a dozen or so connections at a time, and the burst-traffic nature of data traffic means that most enterprises will find this adequate, especially if their APs can offload traffic to one another during peak demand. "Most users aren't saturating the bandwidth," says Harry Simpson, vice president of sales and marketing at wireless management tools provider Roving Planet.
Bob O'Hara, vice president of systems engineering at wireless hardware provider Airespace, also sees increasing uptake in the warehousing and hospitality industries leading to potential saturation. "Health care is the exception because they have lots of other applications in use," he says.
Bandwidth saturation could be problematic for all enterprises in two areas. One is in high-traffic zones, such as hotspots, where throngs of users might suddenly appear, requiring both prioritisation and handoff to other APs. The other is in organisations that deploy VoIP on the WLAN for mobile workers, such as within a corporate campus or to allow follow-me-anywhere IP-based telephony systems that permit both wired and wireless access.
Contention causes drop-outs
Because 802.11 wireless networks are contention-based, the first packets to arrive get the AP's attention. For streamed data such as voice, this contention causes dropouts. Fortunately, "wireless VoIP handsets haven't gotten there yet," Summit Strategies' Wilson notes. Roving Planet's Simpson concurs, adding that voice over wireless is not high on the list of most enterprises' needs [We agree. See Voice on Wi-Fi? Just say No].
Because there has been no QoS standard, VoIP provider SpectraLink has made its own prioritisation protocols available to other vendors; among those using it are Chantry, Cisco, and Meru. The IEEE expects to finalise its 802.11e QoS standard in spring 2005 (read more). The standard will set four priority levels each for users and applications so that network administrators can prioritise both user classes and application types, such as data, voice, and streaming media. It will also standardise power settings and traffic scheduling to help APs optimise radio range and bandwidth usage based on traffic patterns.
Usually, prioritisation is enough
For most data applications, "the prioritisation of 802.11e running on 802.11b networks is sufficient," Airespace's O'Hara says. For voice traffic, however, 802.11e is a minimum requirement, so O'Hara recommends enterprises use an 802.11a network for voice because it provides four times as many channels for carrying traffic than 802.11b does. If the US FCC succeeds in its efforts to allocate 12 more channels to 802.11a, that would make 802.11a even more compelling for voice traffic.
No matter the transport used, voice quality could still be compromised because 802.11e can't change the contention-based approach of 802.11 networks, notes Phil Belanger, vice president of marketing at hotspot deployer BelAir Networks. "But it will be better," he says, adding that "a lot of vendors are ready to go with the draft versions" because several of 802.11e's proposals are all but officially agreed on.
So the Wi-Fi Alliance has developed the WME (Wireless Media Extension) interim certification for the prioritisation aspects of 802.11e, and is developing the WSM (Wi-Fi Scheduling Media) certification for the scheduling aspects. "We felt it was best to work on a shared implementation for a part of the standard that was very stable," notes Frank Hanzlik, managing director of the alliance (read our recent interview with Hanzlik).
Tomorrow: the next wireless hurdle is management.