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New Member

WLC settings for high performance cells

I want to tune my cells to gain higher performance. we have a dense AP environment and want to switch off the lower data rates. However, there is much confusion what are the best settings on a WLC. (find questions further down 1 - 3)

I found this in the newest update on the WLAN mobility design guide 7.3:

Mandatory Mode

Mandatory mode allows transmission for all packets, both unicast         and multicast. The data rate on at least one of the APs must be         set to Mandatory, and all clients that associate to the AP must         be able to physically support this data rate on their radio to         use the network. Additionally, for the wireless clients to         associate to the AP they must be able to currently receive         packets at the lowest mandatory rate and their radios must         physically support the highest mandatory data rate. If more than one data rate is set to           mandatory, multicast and broadcast frames are sent at the           highest common mandatory transmission rate of all associated           clients (the lowest mandatory receive rate of all of the           clients). This allows all clients to receive broadcast         packets. The lowest mandatory rate is normally set at 1 Mbps.

Supported Mode

Supported mode allows transmission for unicast packets only. The         AP transmits only unicast packets at this rate; multicast and         broadcast packets are transmitted at one of the data rates set         to Mandatory. The wireless clients always attempt to transmit         and receive at the highest possible data rate. They negotiate         with the AP for the highest data rate set to supported or         mandatory to transmit and receive unicast packets. The wireless         client devices are able to receive broadcast or multicast         packets at any mandatory rate at or below the negotiated rate.

but also this in  a white paper:

http://www.cisco.com/en/US/prod/collateral/wireless/ps5678/ps10981/design_guide_c07-693245_ps11686_Products_White_Paper.html#wp9001240

Wireless=>802.11a/802.11b=>Network

Network - Data Rates

• Mandatory = Client must support in order to associate

• Supported = Optional: client may rate shift to this rate if desired

• Disabled = Not supported on the radio

Recommendations: Set the minimum acceptable data rate for the cell as supported. Choose a higher data rate as the target client speed and set as mandatory. The first or lowest mandatory rate is the speed at which beacons will be sent. The highest mandatory rate is the speed at which multicast will be broadcast. The design for a high-density WLAN should use a minimum mandatory data rate of 18 or 24 Mbps.

1) According to above you should configure something like this:

6m disabled

9m disabled

12m supported

18m mandatory

24m and higher = supported

Does anybody know the reason why you would use 12m=supported and not as mandatory? It does not make sense to me as only clients at 18m can associate, so the 12m is useless anyway.

2) Furthermore, referring to the first stated document, broadcast and multicast can be sent flexible if more than one mandatory rate is defined. the highest mandatory rate is chosen that still is able to serve the client with currently the lowest data rate.

So I would logically choose this setting for a cell with min. data rate of 18m:

6m - 12m = disabled

18m - 54m = mandatory

In this case the broadcast/multicast rate can fluctuate depending on the slowest client and does not need to stick at 18m all the time. Is there anything that speaks against using my settings? Drawbacks of using several mandatory rates?

3) How does this work with 11n-rates? There is no distinction between supported and mandatory. Is it possible at all to disable all 11a-rates i.e.? What rates would the broadcasts and beacons be sent if there were only 11n-rates enabled?

4) and last question: is there a protection mechanism used in mixed client environment with 11a/g and 11n as it is used with 11b and 11g? And the same question applies for 11n 20MHz clients in a 40MHz cell. And how would that be even with 11n and 11ac?

Regards,

Fredy

  • Wireless IP Voice and Video
8 REPLIES

Re: WLC settings for high performance cells

Ok so

1) never use two mandatory rates, you would only set one mandatory rate and multicast is sent at that rate.

2) see above

3) currently with .11n it's either supported or disabled.

4) yes there is still a protection mechanism for backwards comparability

Steve

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HTH, Steve ------------------------------------------------------------------------------------------------ Please remember to rate useful posts, and mark questions as answered
New Member

Re: WLC settings for high performance cells

thanks Stephen for your answers.

I still need some clarification though:

1) do you know why the white paper recommends to set the lowest acceptable rate as 'supported' and not 'mandatory'?

2) can you explain what the drawback is when you enable more than one mandatory rate? for 11b the default settings were all b-rates = mandatory. Even when you have an autonomous AP and use the "speed throughput"-command all rates b/g and a are set to mandatory.

3) does that mean you need at least one mandatory rate for g or a? even if you want to use 11n in Greenfield mode?

Fredy

Re: WLC settings for high performance cells

Honestly it depends. Unusually set the lowest rate I want to allow as mandatory and that's it.

No real drawback, I just don't see the point to it. WLC is going to send multicast at the highest configured rate, aIOS at the lowest.

Yes, currently you can't do a pure n deployment you have to have one legacy rate enabled, though you can just enable 54

Steve

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HTH, Steve ------------------------------------------------------------------------------------------------ Please remember to rate useful posts, and mark questions as answered
New Member

Re: WLC settings for high performance cells

  • No real drawback, I just don't see the point to it. WLC is going to send  multicast at the highest configured rate, aIOS at the lowest.

That's strange... Cisco could fix that and make the simillar configuration.

Cisco Employee

Re: WLC settings for high performance cells

The reason to have rates enabled below the lowest basic rate enabled would be to allow a client to downshift to this rate while beacons and ACKs come out at the lowest basic rate still. Multicast should come out at the highest basic rate enabled.

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Hall of Fame Super Gold

WLC settings for high performance cells

1) do you know why the white paper recommends to set the lowest acceptable rate as 'supported' and not 'mandatory'?

There is no "whitepaper" in this subject matter because different wireless chip maker and/or wireless client manufacturer don't follow the standard.    They'll just say that they are "compatible".

Cisco Employee

Re: WLC settings for high performance cells

To get max # of bi-directional voice streams, enable 24 Mbps and above only (36-54 can optionally be enabled but provide no benefit for an audio only application).
Would need to ensure that there is increased AP density if wanting to baseline on 24 Mbps vs 12 or 6 Mbps.

6 Mbps = 13 streams
12 Mbps = 20 streams
24 Mbps = 27 streams

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New Member

Re: WLC settings for high performance cells

Thanks very much to all of your replies! It clarifies a lot. Just too bad that stuff is not written in the configuration manual.

Sorry for my late reply. I did not check my post as I did not get automated emails when someone replied.

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