Wednesday, February 10, 2010

Color coded QoS chart from the Voice over Wireless LAN 4.1 Design Guide

I like the QoS  charts that are in this chapter of the design guide, but the chart runs of the page and isn't color coded like the nice QoS charts from Cisco Live BRKRST-2500 Campus QoS Design.




The LWAPP AP and WLC perform QoS baseline conversion, so that WMM values as shown below are mapped to the appropriate QoS baseline DSCP values, rather than the IEEE values.
From ccie(w)

In cases where the AP is translating CoS values, autonomous APs for example, the translation shown is below:

From ccie(w)


WMM uses the 802.1p classification scheme developed by the IEEE (which is now a part of the 802.1Q-2005 specification).  This classification scheme has eight priorities, which WMM maps to four access categories: AC_BK, AC_BE, AC_VI, and AC_VO. These access categories map to the four queues required by a WMM device.
 
From ccie(w)


... It is generally recommended that the Per-User Bandwidth Contracts settings be left at their default values, and that the IEEE 802.11 WMM features be used to provide differentiated services. For WLANs using a given profile, the IEEE 802.1P classification in that profile controls two important behaviors:
  • Determines what class of service (CoS) value is used for packets initiated from the WLC.  The CoS value set in the profile is used to mark the CoS of all LWAPP packets for WLAN using that profile. So a WLAN with a platinum QoS profile, and the IEEE 802.1P mark of 6, will have its LWAPP packets from the ap-manager interface of the controller marked with CoS of 5. The controller adjusts the CoS to be compliant with Cisco QoS baseline recommendations. The reason why it is important to maintain the IEEE CoS marking in the configuration is covered in the next point. If the network is set to trust CoS rather a DSCP at the network connection to the WLC, the CoS value determines the DSCP of the LWAPP packets received by the AP, and eventually the WMM classification and queuing for WLAN traffic, because the WLAN WMM classification of a frame is derived from the DSCP value of the LWAPP packet carrying that frame.
  • Determines the maximum CoS value that can be used by clients connected to that WLAN.
    The IEEE 802.1P classification sets the maximum CoS value that is admitted on a WLAN with that profile. WMM voice traffic arrives with a CoS of 6 at the AP, and the AP automatically performs a CoS-to-DSCP mapping for this traffic based on a CoS of 6. If the CoS value in the WLC configuration is set to a value less than 6, this changed value is used by the WLAN QoS profile at the AP to set the maximum CoS marking used and therefore which WMM AC to use. The key point is that with the Unified Wireless Network, you should always think in terms of IEEE 802.11e classifications, and allow the Unified Wireless Network Solution to take responsibility for converting between IEEE classification and the Cisco QoS baseline.
This is the chart from the QoS class at Cisco Live 2009 [QoS on Cisco switches]:

From ccie(w)



There was also a nice colorized chart explaining the packet tagging translation that occurs to and from the client device at the controller.  This image is from BRKAGG-2013 Design and Deployment of Voice over Wireless LAN.

From ccie(w)

4 comments:

  1. I dig those. Adding to my bookmarks to study for my ONT test! Thanks, Jennifer!

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  2. This is good stuff. :) 802.1p (has a little p) and it's actually part of 802.1Q-2005 now. Very nice post.

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  3. Thanks Devin - I fixed the naming & updated the info that it is part of 802.1Q.

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