Buffering in wireless network

[ASF_SVI_ITE]

Hi guys,

what about this topic? How can I limit the buffering on APs? Reducing packet retry value? Packet retry timeout? RTS retries? What else?

I thanks in advance for any suggestion

A

[Scott Fella]

Eliminate any interference and co channel interference. Other than that, there really isn't much you can do. Wireless is half duplex so only one device can either transmit or receive.

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[ASF_SVI_ITE]

Hi Scott, thanks for the suggestion. but are you sure that the parameters written above don't care to the problem?

A

[Scott Fella]

I really don't understand what you are saying.  All I can say is that since wireless is half duplex, its like a hub network, every device it going wait for its turn to communicate.  Interference is the biggest problem that causes retires along with multipath.  Its a normal thing to see in wireless, but having a good site survey, knowing of the interferers and having a solid configuration, will help, but not eliminate any retries you will see.

Thanks,

Scott

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[George Stefanick]

Scott is there a command you can set the rts size ?



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[Scott Fella]

George.... I don't believe so unless its one of those hidden commands, but I doubt it.  It would be so much work for TAC if this was configurable:)

Thanks,

Scott

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[George Stefanick]

Looks like you can but only for mesh aps ..

https://supportforums.cisco.com/thread/2001107

Never used it personally ..

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[Saravanan Lakshmanan]

Yes.

this enhancement request is still open.

http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCte53425

[ASF_SVI_ITE]

George...in effect I have already seen the configuration note for this option....in the wgb realized by 1242AP  usage, rts retries is set equal to 8, so lower enough.  I' m asking if there is something to tune on the WLC (WiSM cards on 6500 Catalyst)?

Thanks

A

[ASF_SVI_ITE]

Sorry Scott, I have tried to explain the problem but too speedly...losing details for example of the application and the existing wireless infrastructure. I agree with what you said about wifi, interference,etc....goods indications.

Let me add that I' m triyng to understand the behaviour of a mobile application or, in other words, how is the behavior in a metro environment where a WGB onboard has to connect with the wayside while it is moving

a

[Scott Fella]

Well now since your talking about outdoor mobile devices, that explains it.  That is tough to design just depending on what your really trying to accomplish.  I have done outdoor mesh in a truck yard so that these trucks can get information on what to pickup, where to park, etc.  This however is just for a given area.  I have also done ship yards where the boats prior to docking can connect up to the wireless until the ship has docked and they connect up the fiber.  You will always get a lot of reties because of mobile units moving fast, some object blocking the signal, etc.  I know that George has done some with mining companies so he can also put his 2¢.  I don't think there is a way to increse or decres rts on a WLC.

Thanks,

Scott

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[George Stefanick]

Hummm.. That command states its on the WLC, not the bridge. I must not be understanding ..

__________________________________________________________________________________________
"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."

[Saravanan Lakshmanan]

Monitor > Access Points > 802.11b/g/n

check: on WLC check if you're hitting on RTS Failure Count - This counter increments when a CTS is not received in response to an RTS. If you don't see an issue then the issue is something else. i believe WLC has an default retry count but unsure about the value.

802.11 MAC Counters

Tx Fragment Count Multicast Tx Frame Count Tx Failed Count Retry Count Multiple Retry Count Frame Duplicate Count RTS Success Count RTS Failure Count ACK Failure Count Rx Fragment Count Multicast Rx Frame Count FCS Error Count Tx Frame Count WEP Undecryptable Count

[Saravanan Lakshmanan]

From which direction RTS is seen, RTS retry can happen either direction.

currently, only fragment threshold and tcp mss are configurable for each AP, no rts/cts config on unified. you may try to use the ios command to tweak rts/cts per radio however it is not guranteed that it works and certainly this config can't survive reboot.

It is recommended to only enable 802.11g (OFDM) data rates (e.g. > 12 Mbps) to prevent from engaging in CTS for 802.11g protection when using Coexistence.

[Saravanan Lakshmanan]

currently, only fragment threshold and tcp mss are configurable for each AP, no rts/cts config on unified. you may try to use the ios command to tweak rts/cts per radio however it is not guranteed that it works and certainly this config can't survive reboot.

It is recommended to only enable 802.11g (OFDM) data rates (e.g. > 12 Mbps) to prevent from engaging in CTS for 802.11g protection when using Coexistence.