Going Wi-Fi: A Practical Guide to Planning and Building an 802.11 Network

WLAN QoS stands to benefit from another standard proposal, tentatively labeled 802.11k. The proposed new standard would allow the gathering of detailed information about the communications link between stations and clients. It would standardize the way all 802.11 networks report radio and network performance conditions to other parts of the network stack, to applications, and to administrators and operators for the purpose of network management, fault finding, and other diagnostics. For example, if a network administrator had all the qualitative information about a station, including its performance capabilities, he or she could then know how to provision it downstream.

The gist of 802.11k is to strengthen 802.11e (QoS) by overlaying 802.11k technology. The 802.11k Task Group only came into existence in early 2003, so its work has just begun. The vision of the 802.11k Task Group is to let higher applications see information about wireless access points and clients, even if they're on different subnets. This is an important step in making an enterprise wireless LAN a unified, consistent system, instead of a loose collection of individual subnets. The goal is to make low-level measurements from the PHY and MAC layers of the wireless LAN available to higher-level applications, which can then make decisions and take actions based on this data.

To quote an "unapproved draft" document IEEE document entitled "Radio Resource Measurement Vision and Architecture," dated January 2003:

"The 802.11k vision is to make PHY and MAC layer measurements available to upper layers. This means that it is expected that the upper layers can and will make decisions about the radio environment and what can be accomplished in that environment.

"The most important information is that about the Access Points and the PCMCIA cards (STAs in 802.11 jargon). This information includes all the APs and STA radios that can be seen even if they are not on the same subnets."

The Radio Resource Measurement (RRM) standard will define the requirements for measuring the radio environment, such as:

• Data, Voice, and Video. The Internet has changed and continues to evolve to include voice and video in the data environment it has grown from. The bursty nature of the Internet has been somewhat tamed and garnered to include the added benefits of voice and video in making realistic representations of the real world through networking and computing. Therefore the primary requirement is to enable that voice and video to extend to the radio and wireless LAN environment.

• Rogue Access Points. Companies that are delving into wireless LANs on a big scale must have some means of controlling and managing their environments. This includes the unlicensed radio environment that has become prevalent with the use of wireless LANs. One of the primary requirements is to be able to identify who is in your radio environment and what they are transmitting.

• Quantify WLAN radio topology for AFS and TPC. Also inherent in needing to understand and manage your radio environment are the radio measurements that precipitate a change either in frequency or in the power with which you are transmitting.

• Measure BSS overlap to feed mitigation (802.11e) and help balance coverage, capacity, and QoS. Another requirement is to balance the radio environment to its maximum efficiency. The measurements needed to accomplish this purpose are the loads on the access points and the stations themselves. By measuring or asking for the measurements of the other access points and stations in an area, the WLAN acts as a synchronized network and enables maximum use of that network.

• Quantify each station's local performance to assist admissions control (802.11e) and to facilitate roaming and load balancing. By understanding and measuring the performance of the individual pieces of the network, the whole can facilitate roaming and load balancing of the entire mechanism.

• Detect non-802.11 interference and quantify noise to facilitate adjustments in WLAN configuration (radar). Enabling measurements and adjustments to the radio environment is a requirement if the system is to be capable of understanding its environment.

In practice, the protocol elements that will be specified in 802.11k will be MAC and PHY extensions-most likely MLME and PLME services. The standard will also probably deal with protocol, not decision-making or algorithms. For example, a set of measurements may be defined, but there will be no specific rule as to when these measurements should be made, or how the results should be used.

At this moment, the standard is envisioned more as a means for providing a toolkit for RRM. For instance, specific RRM requirements include:

• Capabilities, measurements, and statistics, i.e. to identify an RRM-capable access point or station, and for a management entity to request that an access point make appropriate measurements to determine the radio environment. Stations would have the ability to make and report measurements on the radio environment. A "Network Management Entity" would be able to obtain configuration and statistics information.

• Improved WLAN information. Information would be available to stations to assist in making association decisions that result in good service characteristics for the individual station, without affecting those experienced by other stations in the network, both wired and wireless. This enables efficient usage of the available resources, which is likely to be particularly important if applications with QoS requirements are being supported.

• Information to streamline roaming, i.e. information would be available to stations to assist in streamlining the roaming process.

These are exactly the problems that wireless "switch" makers are trying to solve (see Chapter 18).