How Many Calls Over A WiFi Access Point?

A couple of years ago, a friend of mine wrote an article that answers the question: how many voice over IP calls can you realistically have over a standard WiFi access point? The answer actually depends on a number of factors, and the article can give you an answer depending on the exact deployment. Here are the factors that affect these numbers:

Shared Bandwidth: Unlike an Ethernet switch, WiFi is more like an Ethernet hub. In particular, that means all users of a given WiFi access point share bandwidth. With an older 802.11b WiFi access point, each user is effectively sharing 11mb (really 5.5mb as the 11mb accounts for both directions). 802.11g and 802.11a offer a bit more bandwidth, and the 802.11n specification offers even more.

Codec Choice: How the call is encoded makes a big difference in the amount of bandwidth the call takes. It not only affects how good the sound is, but it affects how much data is transmitted.

Effective Bandwidth: Partially because of the shared bandwidth situation, partially because of the fact that WiFi uses unlicensed spectrum and thus is subject to interference, and because 802.11g and 802.11n offer backward compatibility modes, the bandwidth that is available for all clients can fluctuate radically. It is possible for an older device to effectively reduce the throughput for the entire network by attempting to connect–if the access point is configured to allow it!

Certainly in a home environment, unless you have a bandwidth hog in your midst, or serious interference issues, you’re unlikely to run into any serious problems. The upper-limit even for the old 802.11b WiFi access points is 23 concurrent connections. Certainly one or two WiFi phones–or calls that happen on a WiFi-enabled laptop–aren’t going to break the bank.

Even a small business should not have too many issues with this. These issues generally pertain to larger deployments in enterprise environments where there many more users per square inch. Unfortunately, there are no easy–or cheap–answers to these questions.