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I've recently bought some wireless access points from Draytek. I understand what most of the settings do but I'm trying to fine-tune the roaming behaviour and there's one setting which my colleagues and I can't make sense of. In the AP-assisted Client Roaming Parameters section, I've got two fields/options enabled:

Minimum RSSI = -66 dBm (60%) (default value)

with Adjacent AP RSSI over = 5 dB (default value)

Here's a screenshot of the settings page:

Screenshot from web UI on VigorAP 903

The gist seems quite simple to me: only 'hand over' a client to a new AP when the current connection is below signal strength X, and there's another AP available with signal strength over Y.

What I don't understand is why the first field uses dBm (with a negative value) and the second one uses dB (with a positive value). I've read this post from Draytek, but I still don't really understand how the signal strength could ever be -5dB let a lone +5dB. In my tests, my laptop never goes over -30dB even when it's right next to an AP on my desk.

Roaming is working when I move around the building, but I want to understand this properly before I start messing with it.

Peregrino69
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Vilāsamuni
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1 Answers1

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"Roaming is working when I move around the building"

Roaming = client changes connection from one AP to another broadcasting the same SSID. So unless you have multiple APs broadcasting the same SSID, you're not roaming.

What this means is simply that when RSSI (Received Signal Strength Indicator) from the client on AP 1 drops below -66dB and AP 2 detects it with 5dB higher RSSI (-59dB) the AP will force the client to roam; i.e. terminate connection with AP 1 so it connects to AP 2.

Strictly Minimum RSSI isn't enabled. If it is, the AP will terminate connection to the client when the RSSI drops below the named value whether or not another AP is available.

The RSSI is measured with negative dB scale. That means the theoretical max is 0dB; you'll never see a positive value.

Peregrino69
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  • This actually isn’t entirely correct. The Access Point cannot control what the client will do. It can, however, kick the client, and that is what this option will do. “Roaming Assist“ is just a fancy way to say “GTFO”. ;-) The AP is initiating the action here, not the client. Clients can (and will) reconnect immediately, so there’s usually an anti-bounce mechanism. – Daniel B Mar 02 '23 at 16:26
  • Uhh... of course it does, always... got confusioned troubleshooting a client roaming issue at the same time :-D Would be nice if the mfg:s would agree on terminology... on the enterprise side we usually talk about Client Steering. Maybe that's too fancy term for SoHo market :-D Thx for pinging, fixed. – Peregrino69 Mar 02 '23 at 18:23
  • @Peregrino69 My Draytek APs call it 'AP-assisted roaming', which seems like a fair enough name for it, but I agree - more standardisation would be nice. – Vilāsamuni Mar 06 '23 at 16:10
  • @Peregrino69 thanks for your thorough answer. Mostly it's confirming that I already understood, but the critical bit I've learned from this is that the _with adjacent AP RSSI over_ field is the **difference** in signal strength between AP 1 and AP 2 rather than the 'absolute' signal strength of AP 2. – Vilāsamuni Mar 06 '23 at 16:18
  • @Vilāsamuni Yap. Like DanielB pointed out - roaming is _always_ initiated by an AP :-) The client's responsibility is to make and maintain connection, therefore the client will maintain it as long as it can. This leads to [sticky client problem](https://eyenetworks.no/en/sticky-clients/). Two means to combat that are on the infrastructure side Client Steering (AP encourages the client to roam by kicking it off) and Band Steering. They're established industry terms. I bet "AP Assisted Roaming" was some marketing guy's invention to make it more understandable to a layperson :-) – Peregrino69 Mar 06 '23 at 17:45