Identifi Radio Bandwidth Logic

[Ian_Broadway]

Hi All,

I'm trying to understand the logic behind radio bandwidth.

Our clients seem to get quite poor bandwidth when it comes to WiFi.

We have a mixture of 3825 and 3935 APs within our estates. for the sake of this argument, I'm going to refer to 5ghz radio only.

Max bandwidth on 5ghz for 3825i, 1.3Ghz
Max bandwidth on 5ghz for 3935i, 1.7Ghz

So firstly, based on some behaviour we have noticed, I am right in thinking that radio bandwidth is shared across SSIDs and then clients?

For example, I have tested with a single client connected to 5ghz to which the AP is only broadcasting the relevant SSID and my client is the only client connected to it.

I get excellent data rates and bandwidth, but as soon as i enable an additional SSID on 5ghz (no clients on it) my bandwidth suffers.

at this stage, the AP has two SSIDs on the 5ghz radio, with a single client on one of the SSIDs

It appears then that with multiple SSIDs broadcast on the 5ghz radio, the identifi software allocates/divides half the bandwidth even before clients?
Is this right? I guess then it allows clients access to this allocated bandwidth?

I know having minimum data rates set low will affect the radio etc but right now I have everything tailored to a single client and testing with 1 and 2 SSIDs enabled.

I'm finding it hard to find knowledge around the settings and best practices for the Identifi suite, anyone with knowledge on the above I would be most grateful

Thanks
Ian

[ckelly]

Our clients seem to get quite poor bandwidth when it comes to WiFi.
We would need more details to determine if what the clients are seeing is considered normal or abnormal bandwidth degradation.

We have a mixture of 3825 and 3935 APs within our estates. for the sake of this argument, I'm going to refer to 5ghz radio only.
Max bandwidth on 5ghz for 3825i, 1.3Ghz
Max bandwidth on 5ghz for 3935i, 1.7Ghz
So firstly, based on some behaviour we have noticed, I am right in thinking that radio bandwidth is shared across SSIDs and then clients?
Yes, but the actual bandwidth available is shared not only by all client devices associated to that radio, but also all APs and clients that happen to be utilizing that same channel...even if those other APs and client devices are not yours. Wifi devices listen to the airwaves first before transmitting. So even if they hear another client or AP that doesn't belong to you that is currently transmitting, they will wait for them.

I get excellent data rates and bandwidth, but as soon as i enable an additional SSID on 5ghz (no clients on it) my bandwidth suffers.
at this stage, the AP has two SSIDs on the 5ghz radio, with a single client on one of the SSIDs
It appears then that with multiple SSIDs broadcast on the 5ghz radio, the identifi software allocates/divides half the bandwidth even before clients?
Is this right? I guess then it allows clients access to this allocated bandwidth?
With multiple SSIDs, the radio continues to share the SAME total bandwidth between all clients using any of those SSIDs. The AP software does NOT perform any sort of bandwidth allocation process whereby it segments off a percentage of bandwidth for each SSID.
Can you provide actual test numbers for when you have a single SSID and run a test and then when you have two SSIDs and run the same test? Also, are the test results repeatable?

I know having minimum data rates set low will affect the radio etc but right now I have everything tailored to a single client and testing with 1 and 2 SSIDs enabled.
I'm finding it hard to find knowledge around the settings and best practices for the Identifi suite, anyone with knowledge on the above I would be most grateful
If you are referring to wifi configuration settings, then this is definitely where things get more involved and lengthy. I'll look to see if there's possibly any documentation that might cover this. It's possible that there is something but that it's not specific to any single wireless management platform.

[Gareth_Mitchell]

Ian

This is a complex wifi subject.  Can I suggest you have a read of this article and then any questions that remain, please let me know and I'll get answers for you.  https://extremeportal.force.com/ExtrArticleDetail?an=000079922

-Gareth

[Ian_Broadway]

Hi Gareth,

So this does help understand more thank you.

It almost seems though that anymore than one SSID per radio and your penalised for it? is that an industry standard thing or is that how the extreme identifi architecture works?

Surely clients should be able to access the bandwidth available on a AP radio regardless of how many SSIDs are broadcast from it.

and anymore than perhaps single digit amount of clients on an AP per radio and again almost seems not worth having WiFi in the first place?

Ian

[Gareth_Mitchell]

Hi Ian

It almost seems though that anymore than one SSID per radio and your penalised for it? is that an industry standard thing or is that how the extreme identifi architecture works?
GM> Each SSID you add increases 802.11 management traffic, for examples beacons are sent approx 10 per sec per SSID you advertise.  This is the way WIFI works not specifically Extreme.  General industry guidelines is to keep the number of SSID's to <=4 per radio.  If you search for wifi overhead calculator in google you will find a tool that helps visualise this.

"Surely clients should be able to access the bandwidth available on a AP radio regardless of how many SSIDs are broadcast from it."
GM> Unlike ethernet which uses CSMA/CD, 802.11 uses CSMA/CA, CA being collision avoidance.  Once a station obtains a TXOP (TXOP is the opportunity to transmit) it does have all of the bandwidth for that time, other stations will sense the medium is busy and must wait to transmit any data they might have. AP or client must gain access to the medium in the same way.

"and anymore than perhaps single digit amount of clients on an AP per radio and again almost seems not worth having WiFi in the first place?"
GM> Wireless technology is very robust, despite all the complexities involved it works very well.  Having high data-rates, good SNR etc help to get data transmitted very rapidly and the medium cleared for the next transmission, never technologies such as wifi-6 bring big efficiency improvements.  Understanding user counts and applications used play a huge part in successful deployment, for example 10 clients doing 4k video streaming is a different proposition to 10 clients doing email and web surfing.

-Gareth