Wireless QOS

[Adnan Khan]

Need Help!

I want to test Wireless QOS in enterprise production network, running two Cisco WLCs and 1240 AG LAPs.

Is that possible to test QOS on test SSID and check in production environment without messed up with network or please suggest any better way. secondly I want to apply Voice, video and sepesific IP protocol to prioritize traffic above data but using only 1 SSID for example SSID abc.

Please explain.

[ArunWadhawan]

Hi,

I must say interesting threat.

But after reading all that I must say I am still a bit confused. Did I get that right? Even if you configure a SSID to PLATINUM it is not a guarantee that every traffic from the wireless client will be marked with 46(EF) (DSCP) or Priority 6-7 (Platinum)? Is only the application responsible for traffic marking? I thought that the wireless medium or better the originated SSID will take care of that and every traffic that is sent over the channel will be marked with Priority 7.

But while doing a capture (with wireshark) of standard HTTP Traffic on that SSID it does only report QoS Control- Priority: 0 (Best Effort).

I was not able to test it with a voice application at this moment as I have to reconfigure the wireless access for that purpose to a different network. With that I would have had an application that could set the traffic marking to Priority 7.

Would be great f you could help me out with this confusion! If I am wrong and the originated SSID does not take care of the traffic classification isnt it a bit frustrating? As I would say that only the wired Infrastructure is capable to classify traffic and prioritise on your own policies.

Thanks, Arun

[Nicolas Darchis]

you're missing a critical point.

Over wired, you put a tagging and the switch will treat the packet with priority.

Over wireless, the important part is when you send the info to the AP. And the AP can only read the tags once it received it, so it's a different issue.

This is why the clients have to use a special wireless tagging (wmm/802.11e) that the AP will simply overwrite with a wired-QoS like CoS or dscp.

What is critical is that the client sends the frame towards the AP with priority, with more agressive timers in order to avoid collisions and avoid having to wait for medium access. This is why :

-the client application should be the one tagging and the AP can't do the job for him

-The client driver has to be smart and send that packet with aggressive priority over the medium.

What the AP/WLC really do is simply correlating wireless Qos tagging to wired tagging actually.

However, note that you also have to consider the opposite. Packets from the wired have to be tagged so that the WLC correlates the tag to a WMM wireless tag and sends with priority towards the client.

[ArunWadhawan]

Hi Nicolas,

thanks for the great explanation. Would be great if this clearification would be written down in any QoS chapter that talks about Wireless QoS in the first place. Is there a list or table to find out which application support QoS?

With this information I would guess that as the first step in our environment we should activate QoS on any SSID to support Wireless QoS and give the wireless Infrastructure the opertunity to benefit if any wired or wireless application suports QoS. As AIFS are used instead of DIFS that should improve our wireless infrastructure especially for those applications that support QoS 802.11e and with that the classification of access classes.

But in the end the wireless QoS has two scenarios one getting QoS tagged packets from the wired side and QoS classified packets on the wireless side depending on the Application that runs on the wireless device (e.g.: Voice Client as BRIA).

Therefore enabling QoS is a good way to support QoS and non QoS devices or am I missing anything? Is there a problem for wireless devices that do not support QoS?

I would like to enable QoS but avoid running into any problem in our enterprise environment.

Regards, Arun

[thomas03usmcsf]

All I can say is wow..... great reading!!!

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[Adnan Khan]

In document If we choose Voice and video optimized in EDCA parameters then we should not check the box 7920 AP CAC, I don't understand why.?

[migilles]

7920 AP CAC is to enable/disable the Cisco version of CCA based QBSS.

QBSS is what is used to display the channel utilization info.

7920 AP CAC does control EDCA settings/config.

EDCA is included with WMM config.

The standard CCA based version of QBSS is enabled when WMM is enabled.

See the 7925 Deployment Guide for more info on the QBSS versions.

https://www.cisco.com/en/US/docs/voice_ip_comm/cuipph/7925g/7_0/english/deployment/guide/7925dply.pdf

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[Adnan Khan]

I want to captures wirless traffic and beacon frams to check EDCA parameters for Wireless Qos. Please help!

[migilles]

You will need a WLAN sniffer to view the WMM elements.

Or you can use 792x site survey application to view this info b

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[Adnan Khan]

I tried several sniffers like wireshark, etherreal etc but they require USB capturing device. Is that possible to capture wireless beacons on my Wlan card.

[George Stefanick]

If you do wirelshark for windows you need to purchase AriPcap. Although, if you run wireshark for linux you can capture 802.11 frames with most adapters.

You can download backrack for free, which has wirelshark built in ..

[migilles]

Most sniffers will require you to purchase a USB adapter.

Check the sniffer vendor's website for a list of supported adapters and if they have a driver for your built-in adapter.

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