Advanced Wireless Settings - Guard Interval, Preamble Length, etc.

[flyoffacliff]

I recently got a Unifi system, thinking they would be customization since it's enterprise, but there is no way to adjust advanced wireless settings such as "Frame aggregation", "Preamble Length", and "Short Guard Interval". There may be a way via the command line, and if anyone knows, please tell me. Thanks.

But don't most consumer wireless routers have these settings available in an advanced menu?

 

[flyoffacliff]

Anyone? Am I the only one that cares about and messes with these settings?

 

[sfx2000]

Anyone? Am I the only one that cares about and messes with these settings?

Defaults generally work well... some of these settings are left over from 802.11g and early 11n draft releases...

The items you mention - Frame Aggro, Preamble Length, Short GI - these days, it's handled automatically by the WiFi chipsets themselves, and behavior here is generally good (Frame Aggro - should never change this, it breaks 11n/11ac as an example) - same with Preamble Length (only needed for 11b stations) and Short GI (default is short, and fallback to long for legacy).

 

[flyoffacliff]

Defaults generally work well... some of these settings are left over from 802.11g and early 11n draft releases...

The items you mention - Frame Aggro, Preamble Length, Short GI - these days, it's handled automatically by the WiFi chipsets themselves, and behavior here is generally good (Frame Aggro - should never change this, it breaks 11n/11ac as an example) - same with Preamble Length (only needed for 11b stations) and Short GI (default is short, and fallback to long for legacy).

Thank you for clarifying. I couldn't find much online. Sometimes my WAP uses long GI, I can tell because the negotiated signal rates are not valid for short, but I don't have any legacy (pre 802.11n) devices on my network. I would like to figure out why if I can't force it to short. I can't even find good ways to verify what settings are being used.

 

[sfx2000]

Thank you for clarifying. I couldn't find much online. Sometimes my WAP uses long GI, I can tell because the negotiated signal rates are not valid for short, but I don't have any legacy (pre 802.11n) devices on my network. I would like to figure out why if I can't force it to short. I can't even find good ways to verify what settings are being used.

There still are some older 802.11n stations that request long Guard Intervals - some broadcom and realtek I have first hand knowledge of... remember though, GI is client/session specific, and not global...

If one forces short GI, then those clients cannot attach.

Preamble Length - I prefer to keep this to auto, and this is 2.4GHz specific anyways, and mostly for 11b (non-ERP stations) - why do we leave that alone on the AP - so that adjacent stations (keeping in mind that all AP's and Clients are STA's, just different roles) can see the primary AP, and as such, won't step on the transmissions...

(Side hint - if you see in Wireless Packet Captures "Barker Preamble" set to true - you've likely got an 11b or early 11g station somewhere near by - doesn't have to be on your WLAN, just nearby - most likely these days are HP printers, lol)

(hint - this is also why I recommend B/G/N mixed mode for 2.4GHz, if one doesn't want 11b stations, just set auth to WPA2-AES, 11b clients don't know this, so they can't associate)

In auto, it really doesn't matter, again, this is client/session dependent.

GI and Preamble Length are negotiated between a client and the AP at association time, and tracked as such.

frame aggro - this is pretty much a requirement for 11n/11ac, along with WPA2 - so always should be enabled...

 

[flyoffacliff]

There still are some older 802.11n stations that request long Guard Intervals - some broadcom and realtek I have first hand knowledge of... remember though, GI is client/session specific, and not global...

If one forces short GI, then those clients cannot attach.

Preamble Length - I prefer to keep this to auto, and this is 2.4GHz specific anyways, and mostly for 11b (non-ERP stations) - why do we leave that alone on the AP - so that adjacent stations (keeping in mind that all AP's and Clients are STA's, just different roles) can see the primary AP, and as such, won't step on the transmissions...

(Side hint - if you see in Wireless Packet Captures "Barker Preamble" set to true - you've likely got an 11b or early 11g station somewhere near by - doesn't have to be on your WLAN, just nearby - most likely these days are HP printers, lol)

(hint - this is also why I recommend B/G/N mixed mode for 2.4GHz, if one doesn't want 11b stations, just set auth to WPA2-AES, 11b clients don't know this, so they can't associate)

In auto, it really doesn't matter, again, this is client/session dependent.

GI and Preamble Length are negotiated between a client and the AP at association time, and tracked as such.

frame aggro - this is pretty much a requirement for 11n/11ac, along with WPA2 - so always should be enabled...

Wow, you really know what you're talking about, very helpful, thank you! May I ask where you learned all this stuff?

I didn't realize preamble length and GI were negotiated between each client, I thought the whole BSSID had to use the same settings. I guess this is the case with all modern clients and APs? So 5Ghz connections are always short GI and short preamble?

Not sure what barker preamble is, never heard of it. I don't understand why you recommend mixed mode, even if no legacy clients need to be supported. What does disabling mixed mode actually do? I was under the impression that disabling A, B, and G would improve performance on N and AC. I don't even know if I can disable G.

Sorry for all the question, just interested in learning more.

 

[sfx2000]

Wow, you really know what you're talking about, very helpful, thank you! May I ask where you learned all this stuff?

I used to participate in 802.11/802.16 within the IEEE...

I didn't realize preamble length and GI were negotiated between each client, I thought the whole BSSID had to use the same settings. I guess this is the case with all modern clients and APs? So 5Ghz connections are always short GI and short preamble?

Back in the 11g/draft11n - many AP chipset applied these globally - but modern chipsets are quite a bit smarter about things - and they do this on the fly for any client/session context.

In any event - short GI is nice, but a client can ask for long GI dependent on range and other considerations to improve overall robustness of the session - 11n/11ac client chipsets are pretty smart about this (goes to beamforming and other items)

Not sure what barker preamble is, never heard of it. I don't understand why you recommend mixed mode, even if no legacy clients need to be supported. What does disabling mixed mode actually do? I was under the impression that disabling A, B, and G would improve performance on N and AC. I don't even know if I can disable G.

I like keeping b/g/n for 2.4GHz, and a/n/ac for 5GHz - if there is a legacy client/AP out there - by keeping things mixed mode, it reduces the risk/impact of that legacy network on 11n/11ac, as management frames and beacons are intended to be backwards compatible to reduce interference between legacy and current.

Broadcom, QC-Atheros, and Marvell 802.11n/11ac chipsets can actually go greenfield on the fly opportunistically in mixed mode if they do not detect any legacy clients/ap's on own or adjacent networks - neat stuff