Wireless High Latency

[ciscoscott2012]

Hi All,

I have just setup a new WLAN using 5508 controllers (located in our HQ) and 3602I APs located in the branches configured in Flexconnect mode.

I created a basic WLAN with WPA2/AES/802.1X and wireless clients are seeing high latecny of 200ms and packet loss, this happens on both 2.4 and 5 with and without wireless N enabled. No significant interferance being reported on the APs or by cleanair. This happens on a range of wireless client devices and wireless adapters.

After lots of testing I noticed that disabling WMM on the WLAN dramatically reduces latency down to 2-3ms. Has anyone seen this behaviour before with 3602I clean air aps?                

[andrie prabudhi]

hi Scott,

thanks for your advice,

I already  setting what you said, but the connection still slow,

I have upgrade IOS too (from 7.3 to 7.4)

I have cisco PRIME NCS that reporting Channel utilization every AP on :

1. RF 2,4Ghz (channel 1,6,11) is high (>60%),

2. but on RF 5 Ghz the CU is low (<50%),

when the CU on AP low, we have good performance

my Tshoot :

1. I change and using channel 3,8,13.. suddenly the CU AP is low (<50%), and we have good performance.

2. there is no issue on this RF

my question is :

1. why we get high CU on AP on radio 2,4Ghz?

2. is there any setting on WLC that make CU still low without using non-standart channel ?

Thanks in Advance Scott,

--

Andrie

[Luc Paulin]

Hi Scott, What is the difference beetween mandatory and supported. When / Why would I want to use mandatory instead of supporte ? As an exeample in the 5 band you select everything that is 18 and over to supported except 24 and 54 whihc you set to mandatory, Why ?   I havent' been able to find clear explanation about this

Thanx

[Scott Fella]

You first need to know your RF coverage before tweaking anything.

Mandatory means the client has to be able to meet the lowest mandatory rate in order to associate to the AP. now if the client associates and drops down to a supported rate that is fine. Supported is just what it say. It will support these rates. The mandatory rate I also have at 54 is for my multicast which is sent at the highest mandatory rate. So setting the mandatory rate is shrinking your cell size because only clients that can meet the lowest mandatory rate will be allowed to associate.

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[Scott Fella]

Well you really should stick with the standard channels since maybe some clients aren't connecting:)

The reason for high CU is interference and other RF using the 2.4ghz frequency. If you are around other companies or home, you might see high CU because of that. This is one reason the 5ghz is there. There is not 3 channels like the 2.4ghz but you have 12 available in the US. Now it seems like the CU that high might not be caused by other 2.4ghz wireless AP but might also be caused by interference on those channels. If you have high density of users, then that can also cause high CU because everyone want to send traffic on this half duplex network.

So as long as you make sure it's not the client drivers, etc maybe it's time to tweak your configuration on the WLC.

Do you have high density of APs and it clients, do you have to support 802.11b devices, do you have 802.11a compatible APs, are the APs connected to 10/100 or gigabit. What applications do these WLC use in the wireless? Things like these help decide how to setup your WLC.

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[Richard Marot]

I set WMM to required and upgrading to 7.4.100 and afterwards all of my IOS devices started working perfectly. very little latency and proper speedtests and download speeds were acheived.

-R

[Saravanan Lakshmanan]

N rates are not achieved if wmm is disabled, are you getting good throughput on non N 2.4 & 5ghz bands.

If N AP is performing poor try this:

WLC>config ap tcp-adjust-mss enable all 1363  --- All AP

WLC>config ap tcp-adjust-mss enable ap-name 1363 -- Specific AP

[Richard Marot]

Saravanan, We are achieving very good thoughput. See attached screen grab.

Thank,

R

[Saravanan Lakshmanan]

Thanks for Sharing it.

[George Stefanick]

Great post by scott. I would only add be very aware of these settings. If you make 5.5 as your lowest and you wifi can't support that rate in all areas you will create a hole.

Same is true on the highest. If you set 54 as mandatory and your client goes into a room and connects at 48 phy, that client will not get the multicast packet ..

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[Scott Fella]

This works fine for ofdm devices, but if you have any 802.11b clients, your highest mandatory needs to be 11mbps or else if you have another mandatory rate set like 24mbps, the 802.11b client will not associate.

Thanks,

Scott

Help out other by using the rating system and marking answered questions as "Answered"

[George Stefanick]

Correct ..

who still has 802.11b devices anyway ?

__________________________________________________________________________________________
"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."

[Scott Fella]

You never know George. I typically disable all the b rates but then all if a sudden.... Someone complains:)

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[Luc Paulin]

Great, thanx Scott and George, This clarify much better my understand of the data rate. So to resume setting data rate will reduce the the cell coverage and therefore force client to roam to roam to another AP.  However have to be carefull in changing data rate to be sure that we're not create a coverage hole depending on the placement of the AP. 

[Abhishek Abhishek]

Hello,

As per your query i can suggest you-

Please specify the radio-bands the users are on. Also check the maximum number of users supported per access-point to avoid high latency and packet loss.

Hope this would work

[zahidhamdani01]

Thanx dear it solved my issue. I disabled the WMM and my issue is solved. now i am able to go to 15MB on -65dbm while before on the same dbm i could hardly achive 1MB.