| technology | networking - Christian Scott
3 Ways to Optimize Wireless Networks with Radio Control
Network optimization is one of the most valuable services you can provide as a wireless engineer. New wireless deployments are costly for businesses, and many business owners will appreciate you greatly if you can make the most with what you have. There are a few proprietary features you should be aware of when it comes to wireless network optimization — and when studying for your CWNA certification exam.
The main three wireless optimization features you should be aware of are:
- airtime fairness
- band steering
- dynamic power and channel management.
These three optimization features enable wireless network performance tuning and dynamic management, to ensure that your networks are performing adequately, regardless of changing radio frequency landscape and physical environmental factors.
How to Optimize Wireless Networks
Network optimization features are commonly available in many wireless deployment systems, including Cisco, Aruba, HP Enterprise, and others. The primary purpose of these network optimization features is to enable support for varying wireless clients with differing bandwidth capabilities, intelligently manage radio and band usage, and alter the radio power and frequency settings to account for sources of interference or changing levels of localized radio usage from other sources.
That last point is key. In a radio frequency environment, many things change, which means we should also strive to maintain a low Signal to Noise Ratio (SNR) when designing and planning wireless networks. To achieve adequate wireless connectivity, the SNR is below 30 Dbm in many environments. In high-density deployments, you should set power and channel values statically on your wireless radios to achieve the sub-30 SNR. This is what you should do in high-density deployments, where there are many radios to manage. In smaller deployments, it may be beneficial to allow your wireless controller (WLAN Controller) to alter these values autonomously.
1. Airtime Fairness
Airtime fairness is a feature many wireless vendors include in wireless systems by default. 802.11 wireless networks are competitive. This means that clients must “fight” for time on the radio to transmit their messages. When one client is transmitting a message over the wireless network, the other clients connected to the wireless network must wait for the transmission to complete before they can submit another request to transmit. This fighting amongst wireless devices is known as wireless medium contention overhead, and can be worsened by many factors.
Medium contention creates an interesting problem, as there are many different types of clients connected to wireless networks at any given time, each supporting different technologies and bandwidth capabilities.
For example, an 802.11b-equipped device is competing with an 802.11ac device, which is much faster. If the 802.11b device transmits first, this transmission will take much longer. During the transmission, the 802.11ac and other devices must wait for the slow 802.11b transmission to finish before competing for another time slot for their transmissions. This is a significant waste of time and does not allow wireless clients equal access to the radio network. Airtime fairness is a solution to this problem. Airtime fairness analyzes client bandwidth capabilities and transmissions requests, changing the order in which they occur to ensure that faster bandwidth clients are permitted to transmit first. These transmissions are much shorter, meaning slower clients don’t have to wait as long, and can then transmit their slower messages while the faster clients do not need to transmit.
You should ensure your wireless deployment supports airtime fairness analyses, and that it is enabled in your WLAN controller settings. If you are having a hard time finding the configuration option for this feature, a firmware update to your access points and controller may fix this problem.
2. Band Steering
Another interesting problem caused by medium contention is cross-channel interference (CCI). CCI is caused by many access points using the same overlapping 2.4GHz channels, driving up medium contention overhead. This problem is realized by many wireless device’s default behavior of utilizing the strongest radio signal available for a particular WLAN. For example, many wireless access points transmit on both the 2.4GHz and 5GHz unlicensed bands advertising the same SSID.
In deployments without band steering, newly associating wireless clients would probe for radio signals by sending requests. These wireless clients receive two responses for the WLAN in question; one from the 2.4GHz radio and one from the 5GHz radio. The client then gets to decide which connection to use and will default to the strongest signal. Since 2.4GHz RF signals propagate further than 5GHz signals, clients will naturally decide to connect to the 2.4GHz band. This behavior results in some problems:
- The 2.4GHz band has three non-overlapping channels. Cross Channel Interference (CCI) from other access points increases media contention overhead for clients connected to these bands. This problem is exacerbated in two noisy RF environments.
- In addition to the three-channel issue, the 2.4GHz band is used by many other wireless communication devices besides 802.11 WiFi. This increases the medium contention problem with additional CCI.
- Because this is the default behavior of 802.11 client devices, many will end up connecting to the 2.4GHz band, leaving the 5GHz band wide open.
Not only does the 2.4GHz band have many of these inherent issues, but the problem is contrasted by the 5GHz band, which has many non-overlapping channels. Additionally, even though 5GHz signal strength is often lower, the quality of the connection is almost always higher, due to reduced CCI issues and higher bandwidth potential.
This is the problem that Band steering solves. In a wireless deployment with band steering enabled when clients probe access points for 2.4GHz and 5GHz connection options, the access points will initially respond with 5GHz channels only, so the client is encouraged to connect to the 5GHz band. If the client refuses to connect with the 5GHz band and continues to probe for channels, the access point will eventually allow the connection with the 2.4GHz band. This saves immensely on medium contention overhead and promotes a higher-quality connection for all clients.
Band steering can also be used to spread client load between an access point’s 2.4GHz and 5Ghz radios in high-density deployments.
3. Dynamic Power and Channel Management
Another interesting problem present in radio frequency environments is the changing levels of noise, interference, absorption, scatter, reflections, and many others. These radio anomalies degrade wireless signal strength and quality and are caused by:
- Moving product in a warehouse, especially paper, cardboard boxes, and other absorbent material.
- Interference from outside sources, such as electric motors, microwaves, and radars.
- Inclement weather, which can increase signal absorption.
- New walls or surfaces which can attenuate or reflect radio signals.
The solution to these problems is coordinated dynamic power and channel management for wireless access points, which is sometimes referred to as radio resource management. In WLAN deployments with dynamic RF management, the wireless access points monitor 802.11 and non-802.11 transmissions and report back to the WLAN controller. Based on analyzing this signal data, the WLAN controller can command access points to alter their power and channel settings to correct issues with interference or the RF environment.
WLAN deployments with this feature can be described as self-managing or self-healing and are often more resilient than statically defined channel and power settings. There are slight drawbacks to dynamic RF management in high-density and some smaller deployments. For example, a short-term RF interference event from a nearby radio could cause the WLAN controller to ramp-up transmit power for an access point.
Once this source of interference is gone, the increased transmit power could cause cross-channel interference issues for the other access points in the deployment. Wireless solution vendors have created intelligent software for managing these dynamic systems, but they are sometimes error-prone. You should monitor dynamic WLANs for a time after enabling this feature to ensure stability.
The RF environment and wireless optimizations can be difficult, but you can create great efficiency by using the tools available in your wireless systems. Changing physical environments, unknown device types and random bandwidth requirements are all challenges with corporate wireless deployments. These challenges are compounded with the recent surge in bring your own device (BYOD) trends.
Studying the features available within the 802.11 specifications and vendor wireless implementations will enable you to optimize your new and existing wireless deployments for your customers. Make sure you understand airtime fairness, band steering, and dynamic power and channel management when preparing for your CWNA certification exam, as these are the most commonly used technologies available for WLAN optimization. Enjoy experimenting with these technologies and as always, best of luck with your technology journey.