Clarification on "Allow legacy 802.11b rates" in advance setting


disabling this would reduce overhead by 40%. so this should be disabled to have better performance. right?

BUT it would also reduce coverage area. so this is not just about wifi B devices it will also affect wifi N or AC devices?
so if i disable this option, devices that are at the limit of the wifi signal will now be unable to connect? right? regardless if their devices are fully wifi N or AC capable.


Regarding your linkt it reduces overhead "up to 40%", not per se 40% and:

"When legacy data rates are disabled, the coverage area will be slightly reduced (distant clients won't be able to fall back to slower but more reliable data rates)" applies to N and AC.

Will they connect at all?.....try yourself ;- )

Why does enabling legacy rates consumes more overhead?
And what overhead?
Cpu resources?

At least airtime. The beacons will be transmitted in the lowest supported protocol, and so will take more time.

This thread should be merged with the other one because it's very applicable to @narmenia's original question of setting up a public hotspot.

You say that like it's a bad thing. It's actually good to limit the coverage area of a public AP. Trying to serve even one or two clients who have located themselves in fringe coverage where low rates must be used is really bad for the use experience of everyone on the AP. If a large space must be covered, more than one AP should be installed.

That isn't exactly right. The legacy rate setting only affects what the AP will transmit. The receiver will always receive and normally process packets at 802.11b rates even with the box unchecked. This is necessary since clients assume that a packet sent at 1 Mb has the best chance to get through. They will start there for the initial connection and data transfer before trying to step up to higher rates.

Though the IEEE has (for good reasons) been wanting to deprecate 802.11b signals all the way off the air for years, the standard still doesn't have a way for an AP to tell a client not to transmit 802.11b to it. The AP can't simply ignore 802.11b signals, because if those initial packets do not get through, the connection will fail even with a strong signal. Clients don't know to try a higher rate.


Even with airtime fairness built in it?
Legacy rates still would have a huge effect?

But why do people say just leave it at default? Enable.
If turning it off will be better overall?

Another problem with supporting 802.11b is not just about the low base speeds used for beacons, but also having to support DSSS on 22 MHz channels, which really messes up the situation for everyone around.

1 Like

will this still apply with wireless n/ac devices that are on the edge of the network?

No, only if genuine 802.11b devices (or at least forced to run in 802.11b mode) are connected to you AP.

1 Like

but will wifi n/ac devices that are running 802.11b mode (because they are on the very edge of the network) trigger it?

n/ac devices will never[0] run in "802.11b mode" because of degraded signal strength, they will turn down the link rate (down to 802.11b speeds and below), but they will never actually switch to 22 MHz channel bandwidth which was the base for IEEE 802.11b and later (802.11g and newer) abandoned in favour of 20/40/80/160 MHz channels.

[0] unless you explicitly set them up for 802.11b, which I don't really expect to be working in contemporary devices anyways.



So basically this just allows N devices to user 802.11b "rates"?
This does not allow "b" devices because im setting mode to "N". Right?

And people at the edge of the wifi singal that previously was connected at "b" rates because of weak signal will now be unable to connect (if uncheck allow legacy 802.11b rates) and they must find a way to improve signal for their devices to have a connection to my ap. Right?

No, This prevents the use of 802.11b rates. It won't effect your 802.11g/n devices connecting, but it will prevent devices that are ONLY 802.11b from working. Unless you KNOW you have a 802.11b/g device, leave it on N.

1 Like

Let's review.

Checking the "Allow b rates" affects what the AP will transmit. In particular it will send most overhead packets including beacons, probe responses, and authentication / authorization as the slow, noisy, 1 Mb DSSS signal. That is bad for you and your neighbors. Do not check that box. The default really should be unchecked.

The AP cannot control what a client will transmit. Clients at the edge of coverage will likely drop down to 1 or 2 Mb and continue to communicate by sending a slow, noisy, DSSS signal. In general the AP has a stronger transmitter than the client, so those clients can continue to receive the AP even though (with the box unchecked) its minimum rate is 6 Mb. DSSS on the air from any source remains bad for you and your neighbors, but since OpenWrt still doesn't have RSSI-based dropping of stations, there isn't much you can do about it...

other than raise the minimum AP rate even higher than 6 Mb. This will make the AP unusable to distant clients, which again is a good thing for public wifi in general. Consider that especially if it is a coffee shop or other small place where legitimate users will be rather close but you don't want moochers from across the street.

Selecting N only instead of Legacy will prevent devices that do not advertise themselves as N capable from connecting at all. It does not affect the rates that may be used after connection is made.


So the box should be unchecked. Got it.

But by default the box is checked. Openwrt should fix this.

Btw i have a older device that is only supported up to 17. And there is no "allow b rates option" can this option be inserted in the configuration?

The reason is it defaulted to be checked is to allow OpenWrt to have the LARGEST compatibility out of the box.

I would assume they do this approach to allow those who don't have the knowledge base to still be able to use it, even if it is sub-optimal. Imagine the situation where someone is asking why their device can't connect to OpenWrt and without the knowledge to know WHAT to ask other than "it doesn't work".

but by default the mode is set to "N" on the 2.4 band.
would that defeat the purpose of broad compatibility?

Well, "legacy" would ALSO include 802.11g (which I've not seen mentioned), but not 802.11b unless the box is checked. So, if you default to 802.11n (WiFi 4 now), maybe the check-box to allow 802.11b over-rides that (due to the fact you have to accept legacy to accept 802.11b)?

I'm not sure how the internal logic would work on that. But, yes, ideally, WiFi 4 (802.11n) would be the lowest you'd want to retro unless you specifically know you need it.

This topic was automatically closed 10 days after the last reply. New replies are no longer allowed.