October 10, 2005
The IEEE has finally approved a Quality Of Service specification for WiFi, reports Techworld. The IEEE's 802.11e task group, has been working on QOS standards for WiFi for about five years.
The Wi-Fi Alliance adopted a subset of the standard, called WMM (Wi-Fi Multimedia), which has already been adopted by several wireless LAN vendors. The 802.11e specification allows packets to gain priority by defining four traffic classes. By default, they are for voice, video, best-effort and background.
SpectraLink provides wireless QoS by specifying a back-off value of zero for voice packets. That gives voice packets priority over normal data packets. The downside is that if multiple SVP VoIP phones attempt to transmit at the same time, you'll get collisions.
The problem with 802.11e is that it puts the power to request priority in the client, says Ben Guderian, VP at SpectraLink.
Airespace, Cisco Systems and Colubris Networks offer proprietary wireless QoS. They link traffic prioritization to users and groups by assigning priority to either the user's authenticated identity or the 802.11 ESSID (Extended Service Set Identifier). A different priority assignment results in higher performance for prioritized users.
Large scale WiFi networks are not only interested in centralized management, now their interested in Voice over IP. That implies some sort of Quality of Service profile. Meanwhile homes are becoming multi-media hubs, requiring multi-megabit video streams.
VoIP (voice over IP) is expected to be the most common application for QoS, at first. Some hospitals deploy multiband 802.11 a/b/g network infrastructures, dedicating the 5-GHz 802.11a system to data applications and the 2.4-GHz 802.11b/g system for voice.
Wireless VoIP phones include;
Pulver's Wisp Phone,
Senao's SI-7800H and SI-800H Wi-Fi sip phones,
SpectraLink's WiFi phones,
Symbol's WiFi phones and
ZyXEL VoIP WiFi Phone.
SpectraLink's phones use proprietary technology to maintain quality of service (QoS) for voice traffic, according to Ben Guderian, director of market strategy and industry relations at SpectraLink. SpectraLink's phones work with PBX or IP call servers provided by companies such as Cisco Systems and Nortel Networks, which are increasing looking toward VoIP solutions, Guderian said.
SpectraLink plans to replace SVP with 802.11e when the standard is ratified. QoS is more complex in the enterprise because applications are more varied and the physical scale of WLANs is greater.
Cisco's Wireless IP Phone 7920, interface with 802.11b access points. Factors hindering large volume of VoIP handsets include the lack of standardized QoS and fast roaming.
WMM (Wi-Fi Multimedia) is modeled after the IETF's DiffServ architecture, which provides four data-access categories that can be assigned different priorities.
The home market is likely to grow fast as $150 WiFi phones become available and wireless distribution of multimedia picks up.
