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Why separate SSIDs for 2.4 and 5 GHz is a bad idea

December 8, 2021
Industry Commentary

The question of why the Uplevel System does not support assigning separate Wi-Fi SSIDs to the 2.4 GHz and the 5 GHz bands has come up several times.

Assigning different SSIDs to the 2.4 GHz band and the 5 GHz band is a common practice in home Wi-Fi. It is not unusual to find SSIDs like 'Xfinity-2.4' and 'Xfinity-5' when doing a scan. Since each SSID is associated with a different profile in the client device, the user must select the band to use for each client device. The user could optionally enter both profiles into the client, but this is unlikely to do much good, as clients rarely move away from their currently configured Wi-Fi profile unless it is completely disconnected and seeking a new network.

The ostensible reason for doing something like this is to provide more 'control' over the behavior of the Wi-Fi system. The user can manually 'steer' a client device to a specific band by entering only the profile for that band into the device. More control is good, right?

Wrong.

With two separate Wi-Fi profiles, the clients are unable to switch quickly - or in some cases even at all - from using 5 GHz for capacity, to 2.4 GHz for range. Switching between bands occurs far more often than one would expect, even for stationary devices such as printers.

The Wi-Fi environment is highly dynamic; signal strength and RF propagation are greatly affected by people and things moving about, surrounding devices, interferers, etc. (At one Intel Corp open air test lab I visited several times, people were even prohibited from parking in the lot out front, because a car pulling up would cause dramatic changes in signal strength and throw off their measurements).

A client that initially connects to 5 GHz with a clear channel may find that maintaining good throughput requires moving to 2.4 GHz. However, if it does not have the Wi-Fi profile for 2.4 GHz, it is denied that chance. Even if the profile should be configured, since each profile represents a different virtual interface, switching profiles causes a disconnect and reconnect. Keeping the same profile for both 2.4 and 5 ghz lets the client roam from band to band without the disconnect.

It is interesting that a long time ago (relatively speaking!), band-specific Wi-Fi profiles were frequently used in enterprise Wi-Fi layouts. At that time, many Wi-Fi client devices did a poor job of band selection; to avoid having client devices pick the wrong band and then stay on it through thick and thin, the IT staff determined which devices should be allowed to use 5 GHz and confined the rest to 2.4 GHz. (Manual "band-steering").

However, all classes of Wi-Fi devices have come a long way since then! Virtually all modern client devices do a decent job of selecting the appropriate band and trading capacity for range as required. Enterprise Wi-Fi setups thus have the same SSIDs for both 5 GHz and 2.4 GHz, allowing the clients to do their job properly.

Being designed for business Wi-Fi applications, the Uplevel system follows this practice. Assigning the same SSID to both 2.4 GHz and 5 GHz across the board allows modern dual-band clients to move up to 5 GHz whenever possible, freeing up the congested 2.4 GHz band for clients at extreme ranges that really need the additional 6-10 dB of pathloss advantage (And if the 2.4 GHz band is mostly free of strong clients that have no business being there, then the weak clients have a better chance of getting through on it). This results in an overall better experience for both categories of clients.