3500, CleanAir & ED-RRM

[eoinwhite]

Hi,

I'm familiar with the benifit of regular RRM especially for an initial installation of wireless. It saves the headache of trying to figure out a channel and power map.

However when it comes to Clean Air's ED-RRM (event driven RRM) I see an issue (probably more of a miss-understanding on my part). Take a building with 3500i everywhere (all clean air AP's). If regular RRM does its job correctly then it will configure the channel and power settings so that cells 1,6, 11 never overlap onto themselves i.e 1 doesnt overlap 1, 6 doesnt overlap 6 e.t.c . We always design based on 2.4Ghz as its the more restrictive band just like in the diagram below:

Now say for example a 2.4Ghz camera or WiFi jammer is operating on channel 6. The clean-air AP sees this and so ED-RRM kicks in and changes the channel to either 1 or 11 in less then 30 secs (which I believe is one of the main advantages over "slow" regular RRM).

Now however we have introduced co-channel interference on the two cells that are operating on the same channel say for example that it was channel 11.

So my question is ... are we saying with clean-air ED-RRM technology that its better to have 2 cells with co-channel interference on the overlap (channel 11 overlap with channel 11) rather then having a channel jammed (channel 6) anywhere in the radius of the 2.4Ghz camera of WiFi jammer? I guess this also applies to regular RRM technology but that doesnt cost more

Hope that all makes sense. Would love to get a Cisco response on this along with other peoples views.

Cheers,

Eoin.

[Stephen Rodriguez]

Keep in mind that all of the AP in that area would potentially hear the interferer.  And as they are all 3500 talking to the WLC the right choice will still be made.

Cheers,
Steve

--

If  this helps you and/or answers  your question please mark the question as "answered" and/or rate it, so  other users can easily find it.

[eoinwhite]

Hey Stephen,

Thats what im talking about a deployment with all CleanAir Ap's and cells 1,6 & 11 evenly distributed. Now lets say its a high density campus deployment as per the diagram above and there is no "room" to select another channel due to common channel overlap.

I havent had the oppertunity to play with CleanAir yet so im not familar with how it reacts to different scenarios. What will CleanAir do in our scenario ...

1. Will it decide that its better to have some common-channel ineterfence and so change the channel using ED-RRM (I'm guessing here that it will not decide to change the channel on every AP to compensate for a small amount of common channel ineterfence as a result of ED-RRM)
   
2. Or will it not make any change and decide to leave the camera or jammer "jam" the channel for any clients in its radius. Lets say for arguments sake that the camera is close to the AP to keep things simple.

Cheers,

Eoin.

[Nicolas Darchis · Accepted solution]

When 2 APs are on the same channel, they can hear each toher. So it's not interference but since they share the same channel, they share the same bandwitdh. Now ok, in real world, it will also increase the hidden node scenario occurences.

Since 6.0 software, the RRM evaluates the impact of channel change on neighboring cells.

Imagine if the WLC was operating like you are describing in the diagram (and which is how humans behave in site surveys). The middle AP sees an interferer on channel 6 and moves to channel 1. Then the APs around would need to change channel to adapt to that. The AP that was on channel 1 would need to go on channel 6 if there's no interferer there. This is a huge cascade effect, because an ap even a bit further away would also need to change its channel accordingly then.

Changing channel disconnect the clients for short period of time (more or less visible depending on smartness of client driver) so we want to avoid it as much as possible.

Especially if you have 3-4 bluetooth devices on the floor with some DECT phone in another place etc ..., the AP channel plan would constantly be changing.

So the WLC thinks it's ok to have 2 APs on same channel if they are not 100% busy and loaded with traffic. If that was the case, then RRM would take a better decision.

Hope it clarifies a bit.

Nicolas

[eoinwhite]

Nicolas,

It does clarify it a bit. So the WLC (RRM & ED-RRM) decides its ok to have them on the same channel as its not really "interference" as I called it ... more reducuced bandwidth for the clients which is obviously better then having a whole channel jammed.

Thanks,

Eoin.