802.11e makes wireless universal

The IEEE's 802.11e draft specification creates the industry's first true universal wireless standard - one that offers seamless interoperability between business, home and public environments (such as airports and hotels), yet still offers features that meet the unique needs of each.

Unlike other wireless initiatives, this is the first wireless standard that spans home and business environments. And it adds quality-of-service (QoS) features and multimedia support to the existing 802.11b and 802.11a wireless standards, while maintaining full backward compatibility with these standards.

QoS and multimedia support are critical to wireless home networks where voice, video and audio will be delivered. Broadband service providers view QoS and multimedia-capable home networks as an essential ingredient to offering residential customers video on demand, audio on demand, voice over IP and high-speed Internet access.

---

Subscribe to the Tech Update newsletter
  Here is a weekly newsletter to help you stay abreast of new networking standards and technologies by providing down-to-earth explanations of how they work.

---

---

QoS is also a critical element for consumer electronic companies looking to offer home wireless networking devices.

The QoS Baseline Document, approved in November, forms the core of what will eventually become an approved draft specification in late 2001.

The QoS Baseline proposes a better way to handle time-sensitive traffic for multimedia applications. The Baseline accommodates time-scheduled and polled communications during the periods when no signal is being sent - contention-free periods (CFP). It also offers improvements in the efficiency of polling.

The QoS Baseline also proposes improvements in channel robustness, which is achieved through forward error correction (FEC) and selective retransmission. It also covers adaptable stream-service interfaces for admission control in higher layers and mechanisms for dealing with adjacent subnets operating on the same wireless channel.

Improved channel access during CFP, and the ability to retain polling for backward compatibility, result in more efficient polling. The ability to schedule transmissions and chain a sequence of polls in a single command is included.

These mechanisms provide for maximum efficiency for high-bandwidth streams, power-management friendly implementations, and polled-style access for variable bit rate and bursty streams.

Channel-access methods can be used in any combination by point coordinators to enable devices to access the channel during CFP.

The centralized scheduler used in the QoS Baseline guarantees collision avoidance and, therefore, improved ability to deliver time-critical payloads. The ability to honor critical QoS contracts such as latency, jitter and bandwidth is much improved. Channel access is tied to the allocations made by subnet bandwidth manager-like higher-layer protocols and mechanisms so system reliability is achieved.

Channel robustness in wireless systems is an important consideration because noise, interference and multipath effects lead to degraded channel throughput in the 2.4-GHz and 5.x-GHz bands, adversely affecting the ability to reliably transmit latency-sensitive or high-bandwidth traffic such as voice and video.

Special attention was paid to improving channel robustness. The proposed schemes include FEC and selective retransmission. These mechanisms include the ability to specify the correction, acknowledgement and retransmission policy on a per-stream basis, thereby accommodating a range of traffic types with policies designed specifically for each.

Channel throughput is improved through FEC, delayed acknowledgements with selective retransmissions and dynamic channel change.

The Baseline enhancements support QoS even when wireless subnets are deployed densely, as in enterprise environments. In such environments, multiple 802.11e subnets could be located within radio range of each other, which would cause interference and/or collisions during the communications by devices in different subnets.

The QoS Baseline has not been approved yet. The next steps in the process are the approval of a draft specification, followed by the approval of the final specification.

Parks is director of strategic alliances for ShareWave. He is a voting member of the IEEE 802.11 and 802.15 committees.