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New Member

WLC Data Rates behaviour

Hello everyone!

I have some questions about the data rates configuration in WLC. I've been reading Cisco documentation and this forum, but as I've seen some contradictory information I would like you to clarify me some points.

I want to disable 802.11b clients, so for that I'm going to disable 1, 2, 5.5 and 11Mbps data rates (other option could be set these as supported only). Then, I have to assign at least one of the other data rates as mandatory...

I could think in one of these three options

Option 1: all 802.11g data rates as mandatory. In this case, as far as I understand:

Broadcast are sent to the lowest data rate

Multicast are sent to the highest data rate (but if a client is connected to other data rate than the highest, then multicast frames are sent to this data rate supported by the client, is that right??). Basically, you cannot be sure at which data rate multicast frames are sent as it can change depending on the clients.

Clients can connect as soon as they support one of the mandatory data rate

Option 2: one 802.11g data rate as mandatory. This would define better the cell limits.

Broadcast and multicast are sent at the same data rate

Clients can connect if they support the mandatory data rate

Option 3: set two data rates as mandatory (or the OFDM required data rates: 6,12, 24Mbps), and the others as supported

Broadcast are sent at the lowest data rate

Multicast are sent at the highest data rate (shifting back to the lowest if a customer cannot connect to this data rate)

Clients can connect if they support at least one of the mandatory data rates.

Am I right with this assumptions? I have read some other different behaviors, like broadcast and multicast are sent at the same common data rate...

I hope I have explained myself...

Thank you very much for your support.

Carolina

19 REPLIES
Hall of Fame Super Gold

WLC Data Rates behaviour

I want to disable 802.11b clients, so for that I'm going to disable 1, 2, 5.5 and 11Mbps data rates

So you disable data rates 1, 2, 5.5, 9 and 11 Mbps.  You put 12 Mbps to 54 Mbps as Supported and choose one of these data rates as Mandatory.  I've seen people choose 12 and/or 18 as Mandatory and the rest are supported.

Hall of Fame Super Silver

Re: WLC Data Rates behaviour

Just to add. In high density deployments I have disabled everything below 18, made 24 and 54 mandatory and 12, 24, 36, 48 as supported. I have also went higher is some ares to having 36 and 48 as mandatory or even just having 54 as mandatory. It depends in your RF and how big of a cell you want. TX power is the other part of this which helps shrink your cell down.

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-Scott
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New Member

Re: WLC Data Rates behaviour

Hello,

thank you Leo and Scott for your answers!

My main concern is about the data rates for multicast traffic...

Maybe you know where is well explained in Cisco website, and I can take a look.

Thanks!

Carolina

Hall of Fame Super Silver

Re: WLC Data Rates behaviour

Multicast will use the highest mandatory rate and will down shift to the supported rates if needed.

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-Scott
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New Member

Re: WLC Data Rates behaviour

Thanks Scott!

Do you know where I could find this information? In wlc releases notes, configuration, or Cisco book?

If you tell me it is documented in Cisco Website, I will look for this information

Thanks!

Carolina

Hall of Fame Super Silver

Re: WLC Data Rates behaviour

TAC has posted this info in one of the threads on this forum. I have tried to look for it but couldn't find it.

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-Scott
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Hall of Fame Super Silver

Re: WLC Data Rates behaviour

Carolina,

Here is the thread. Hope this helps.

https://supportforums.cisco.com/thread/2006498

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-Scott
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Re: WLC Data Rates behaviour

I need to add. If your RF isnt designed properly to support the respected rates and you change the PHY rates you could cause and an outage. You have a poor coverage area and you trun off 5.5 or 11 you lose clients connected at 1 or 2 phy. Same with multicast.

__________________________________________________________________________________________
"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
__________________________________________________________________________________________
‎"I'm in a serious relationship with my Wi-Fi. You could say we have a connection."
__________________________________________________
"Im like bacon, I make your wireless better"

__________________________________________________________________________________________ "Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin ___________________________________________________________
New Member

Re: WLC Data Rates behaviour

Hello,

thank you Scott and George!

I read the post, and it is ok, and I finally have found some information in Cisco's website:

http://www.cisco.com/c/en/us/td/docs/wireless/controller/7-4/configuration/guides/consolidated/b_cg74_CONSOLIDATED/b_cg74_CONSOLIDATED_chapter_01011.html#ID2482

"Access points running recent Cisco IOS versions transmit multicast frames at the highest configured basic rate and management frames at the lowest basic mandatory rates, can cause reliability problems. Access points running LWAPP or autonomous Cisco IOS should transmit multicast and management frames at the lowest configured basic rate. Such behavior is necessary to provide good coverage at the cell's edge, especially for unacknowledged multicast transmissions where multicast wireless transmissions might fail to be received. Because multicast frames are not retransmitted at the MAC layer, clients at the edge of the cell might fail to receive them successfully. If reliable reception is a goal, multicast frames should be transmitted at a low data rate. If support for high data rate multicast frames is required, it might be useful to shrink the cell size and disable all lower data rates.

Depending on your requirements, you can take the following actions:

  • If you need to transmit multicast data with the greatest reliability and if there is no need for great multicast bandwidth, then configure a single basic rate, that is low enough to reach the edges of the wireless cells.
  • If you need to transmit multicast data at a certain data rate in order to achieve a certain throughput, you can configure that rate as the highest basic rate. You can also set a lower basic rate for coverage of nonmulticast clients."

Based on your experience, does it have any sense to have configured all datarates as mandatory? This is the current configuration I have in our controllers but it wasn't done by me.

Thanks.

Carolina

Hall of Fame Super Gold

WLC Data Rates behaviour

In my experience, ALL DATA RATES?  No way.

This holds true when you are deploying 802.11b/g in an environment where there are neighboring wifi that is not under your control.

New Member

WLC Data Rates behaviour

Hello Leo,

could you explain this a bit more? why?

"This holds true when you are deploying 802.11b/g in an environment where there are neighboring wifi that is not under your control"

We have different types of sites, some of them are isolated, but others are spreaded all over a city...so we can see the ssid from the neighbors, and also you can see our ssid all over the city (we are not containing the SSID to our buildings).

We definitely want to migrate to 802.11a/g/n (disabling 802.11b if possible...) and move to 802.11ac as a second step...

Thanks.

Carolina

Hall of Fame Super Silver

Re: WLC Data Rates behaviour

Carolina,

RF is RF and your not going to control how far this is being seen. As far as configuring data rates.... This is a TWEAK that can improve your wifi or break it. You are reducing the RF footprint for YOUR clients by saying that they have to be able to connect to the AP using the lowest mandatory data rate. If they are too far away and can't meet the lowest mandatory rate, then they will not connect. In high density this works great because you can force devices to only connect to a few access points in a given area.

Lightweight and IOS is different as IOS uses the lowest mandatory rate for multicast. WLC's will use the highest.

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-Scott
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Hall of Fame Super Gold

WLC Data Rates behaviour

could you explain this a bit more? why?

"This holds true when you are deploying 802.11b/g in an environment where there are neighboring wifi that is not under your control"

I'm not going to discuss 802.11a, yet.

If you enable all the data rates in 802.11b/g, this means that your wireless signal goes FURTHER.  The lower the data rates, the further the distance you can cover.  This not only means that wireless clients can hear you from AFAR but so can your wireless network hear the signal from others wifi that you don't control.  

If you disable the lower-end data rates, like 1, 2, 5.5, 9 and 11 Mbps, this means that your signal DOES NOT go that far (about 15 to 20 metres in a single direction) but your AP doesn't get to hear other people's wifi.  It boils down to co-channel interferrence.  The less your AP hear other people's wifi, the less chances of co-channel interferrance.  The benefit means you've got better 802.11b/g stability as well as HIGHER throughput rate.

Now, you mentioned you want to run 802.11ac.  When you do this, you will also need to consider disabling low speed data rates because 802.11ac will only have FOUR (4) non-overlapping channels. 

New Member

WLC Data Rates behaviour

Hello,

thank you so much for all your answers!

Hall of Fame Super Silver

Re: WLC Data Rates behaviour

Well hopefully it helped you understand it better.

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-Scott
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Re: WLC Data Rates behaviour

I have to disagree, simply based on my experience. I've personally seen multicast apps fail because the client was connected below the highest mandatory phy. I have also searched and only find statements that multicast is sent at the highest phy, not a variable phy rate.



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__________________________________________________________________________________________ "Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin ___________________________________________________________
New Member

Re: WLC Data Rates behaviour

Hello George,

I am with you. I cannot find any documentation explaining this statement from

Saravanan Lakshmanan (coming from the discussion posted by Scott: https://supportforums.cisco.com/thread/2006498)

"for unicast data traffic, based on negotiated rssi it selects datrates, when there are data retries then it starts switching to next available supported/mandatory rate downward until it hits lowest mandatory. for multicast data traffic on the ap radio, it starts at highest mandatory, also if there is an edge/slow client that always uses lowest mandatory then that ap radio adapts to that rate for all multicast apps. if required, configure only one mandatory datarate to avoid this situation. we've to remember multicast on wireless is best effort due to no ack and no qos"

Having this statement into account, then you can have all the data rates as mandatory, and all your clients are going to receive the multicast.

I would like to see this explanation in a Cisco document...

Thanks!

Carolina

New Member

Re: WLC Data Rates behaviour

From this link:

https://supportforums.cisco.com/docs/DOC-32337

#AP delievers Multicast packet at mandatory datarate, This can be tweaked using RF profile based on the deployment/requirement.

#Broadcast and multicast (if enabled) are sent at the lowest associated data rate (to ensure that all clients can receive the packets). This reduces the throughput of the WLAN because traffic must wait until frames are processed at the slower 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.

#Use Videostream feature to send Multicast as Unicast to use unicast datarate on wireless at AP.

Hall of Fame Super Silver

Re: WLC Data Rates behaviour

This link is also created by Saravanan who also spoke about multicast rate shifting. Why not ask the question on the link you posted and see if Saravanan will comment back. The only other way is to test it out yourself.

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-Scott
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