The wireless edge of the network has become ubiquitous, and so have been the expectations of a reliable and secure connection. Users have become used to the convenience of connecting wherever and however they want. They tolerate the flaws in a typical Wi-Fi connection – pauses in downloads, occasional drop-outs where we must re-connect, and lengthy waits as we try to join a public Wi-Fi network. For personal browsing, we make a conscious compromise between convenience and reliability because apart from being frustrating at times, no real harm is done. But in a business environment, reliable wireless connectivity can’t be a compromise for critical operations, especially where it can be the difference between life and death.
Why multi-channel is not always the best choice
Most Wi-Fi networks operate on a multi-channel architecture (aka micro-cell), where each wireless access point (AP) connects to a mobile client using one of several radio channels. To achieve optimal throughput to each client, it’s important to have good signal strength but minimal radio interference by ensuring that the APs are not too close, and the same radio channels do not overlap (called ‘co-channel interference’). However, this can be difficult when there may be physical layout constraints, and there are only a few channels to choose from, and even harder in a multi-tenancy building when your neighbour chooses the same channels as you. To assist with this, tools are used to survey the physical site to plan the channel map for the optimal experience, but these tools can be expensive and time consuming to use effectively. This is how typical Wi-Fi networks are designed, and why they occasionally exhibit reliability glitches.
Some years ago, an alternative architecture was proposed that utilised the same radio channel for all APs in the network. In this model, placement of the APs was no longer critical because they all used the same channel, so interference was not an issue. If coverage was poor in one location, then additional APs could be easily deployed without worrying about introducing bandwidth-destroying interference. Although the single-channel architecture solved one of the biggest challenges of Wi-Fi network design, it too had some limitations, the main one being that its total network throughput was usually lower than multi-channel.
Since then, multi-channel Wi-Fi has become the predominant architecture and most of the time, it does a great job. However, there are some situations where multi-channel is not the best choice, and alternative solutions can provide a better experience. Applications of this type usually fall into three categories:
- Dynamic physical environments, like warehouses, where radio coverage is continuously being changed as objects are moved and removed. This makes multi-channel planning almost impossible, so the workaround is to deploy more APs. Unfortunately, this not only increases cost, but it introduces more radio interference, which reduces data throughput.
- Environments that must have reliable connectivity to mobile devices, like hospitals, where even a momentary loss of data connectivity can have a serious effect. As a wireless client moves, its connection will ‘roam’ to another AP when it perceives a significantly more attractive signal. Unfortunately, this roaming process can sometimes be slow and disruptive as security credentials must be established or re-negotiated. Often this can manifest as an annoying lag on a VoIP call, or random artefacts in video. One solution is to use only wireless clients that support ‘fast-roaming’ protocols, or intelligent bridging devices that handle the roaming on behalf of the client. Both these solutions add complexity and cost.
- Environments where there are many roaming wireless users, like schools, hospitals, public venues etc. Multichannel struggles to cope in these situations because only one client can talk to an AP at a time. So, having more clients associated with an AP means there is less time for each client to talk, so the effective bandwidth to each client is reduced. Adding more APs doesn’t always help because co-channel interference increases, which also reduces bandwidth.
The answer to these challenges is a cost-effective Wi-Fi solution that combines the best features of both architectures – multi-channel’s throughput with single-channel’s easy deployment, and reliable, seamless roaming connectivity. Previously, users had to choose one architecture or another, and where it was desirable to run both multi-channel and singlechannel systems on premises, they had to manage two different networks with different tools. Administration efforts were increased because firmware updates had to be applied twice, and engineers had two different systems to learn and maintain. Today there is a solution that allows the user to select multi-channel, single channel or both, for the optimal Wi-Fi experience.
By Scott Penno – Regional Marketing Manager, APAC, Allied Telesis