What is a channel collision in XMS-Cloud and how do I resolve it?

Summary: This article describes XMS-Cloud’s channel collision alert functionality and the steps you can take to resolve the alert.

A channel collision occurs when a radio on one of your APs shares a channel with a radio on another AP, Cambium or otherwise. Devices like legacy APs, personal WiFi hotspots, and printers can cause a channel collision. Detecting channel collisions requires Intrusion Detection (IDS), which is enabled by default for all Cambium APs. This can also be classed as co-channel contention as each device is contending for airtime on particular channel.

How does XMS-Cloud’s channel collision Alert work?

In XMS-Cloud, a channel collision alert appears when one of your APs has detected a collision. Like other alerts, it will auto-close once the collision is resolved.

Example 1: Collision caused by a personal hotspot
Lets say you have a number of APs online in a cafe. On one AP, its radios are configured for channels 1 and 36. A patron brings in a personal WiFi hostpot that broadcasts on channel 1, and sits down within range of the AP. The AP detects the hotspot on channel 1, and XMS-Cloud produces the collision alert. The customer later leaves, and the AP sees that the hotspot is no longer active. XMS-Cloud then automatically closes the collision alert.

Example 2: Collision caused by a neighbors AP
Lets say youre at the cafe from the previous example. A new business opens next door that installs its own WiFi APs, and one of them uses channel 1 within range of the AP from the previous example. Your Cambium AP detects the neighbors AP on channel 1, and XMS-Cloud produces the collision alert. The collision alert will remain until the neighbor changes his APs channel, or you change your APs channel.

Example 3: Collision caused by one of your adjacent Cambium APs.
Lets say youre at a larger venue, such as a football stadium, and have installed several hundred Cambium APs. On one AP, its radios are configured for channels 1 and 36. Another AP within range is also using one of these channels. The APs detect the collision on that channel, and XMS-Cloud produces the collision alert. The collision alert will remain until you change your APs channel.

What do I need to know about channel collisions?

As a general rule, it’s a good idea to avoid channel collisions. However, channel collisions are only an issue when they affect the customer experience. Channel collisions with nearby APs or hotspots that are not passing heavy traffic may not cause any noticeable issues for your users, so you should align your efforts with the extent of the impact to the customer experience.

How can I reduce or eliminate channel collisions?

Since WiFi is a shared medium, its not always possible to prevent channel collisions. Legally speaking, someone can always bring in a personal WiFi hotspot that uses one of the channels youre using, or install her own AP next door that uses one of the channels youre using. But there are a few ways you can reduce the frequency of channel collisions:

  • Optimize channels, which chooses the quietest channels available to the AP by measuring the ambient RF.

  • Optimize power, which generally reduces the coverage overlap between radios.

  • Switch some or all of your 2.4 GHz radios to 5 GHz, which would avoid the most common collisions, which occur on channels 1/6/11. This also reduces 2.4 GHz coverage, so keep that in mind if you must service legacy 2.4 GHz devices.

As always, keep in mind that the collision itself is not necessarily evidence of an issue. Always work with your users to understand whether or not there is an impact to performance.