Prior to configure QoS for Autonomous AP you need to understand what is the impact of it on a wireless LAN. QoS on WLAN focuses on downstream from the access point (highlighted in the below diagram).
Following are few key points to remember.
1. AP does not classify packets, they prioritize packets based on DSCP value, client type or priority value in 802.1q/802.1p tag.
2. AP does not construct internal DSCP values.
3. AP does EDCF (Enhanced Distributed Coordinated Function) like queuing on the radio egress port only.
4. AP does only FIFO queuing on the Ethernet Egress port.
5. AP only support 802.1q tag packets (no ISL)
6. AP supports only MQC policy-map set CoS action.
7. AP prioritize voice traffic from voice clients when QoS Element for Wireless Phone feature is enabled.
When you enable QoS, the AP queues packets based on layer 2 CoS value for each packet.AP applies QoS policies in this order,
1. Packets already classified (non-zero 802.1q/p value of incoming packet). An existing classification takes precedence over all other policies on the AP.
2. QoS Elements for Wireless Phone Setting – Prioritize certain vendor phones voice packets. Additionally QBSS is enabled to advertise channel load information on its beacon.
3. Policies you create on AP.
4. Default Classification for all packets.
When you enable QoS, AP uses WMM (WiFi Multi Media) mode by default. Now we will look at example of configuring QoS on Autonomous AP. You have to remeber basic MQC rules components namely Class Maps->Policy Map-> & Service Policy. Aslo remember the policy-map only support “set CoS” action only.
So we will configure AP to set all DSCP=46 (ef) packets as CoS=6 & DSCP=24 (CS3) packets as CoS=4 when sending to client (Radio Egress, where normally QoS takes effect). Remember this CoS is convert into WMM priority value in 802.11 headers.
First step to define the class maps & I have named those two class maps “VOICE” & “SIGNALLING”. If you want to match multiple DSCP values remember to use “match-any” keyword as without that it will always assume “match-all” logic.
class-map match-all VOICE match ip dscp ef class-map match-all SIGNALLING match ip dscp cs3
Second step to configure the policy map. Remember that only “Set CoS ” is the action allowed. I have given AAP2-QoS as policy-map name.
policy-map AAP2-QoS class VOICE set cos 6 class SIGNALLING set cos 4
Third step to apply the policy map using “service-policy” commands. since this is really going to affect traffic going out of radio interfaces I have applied it on under radio interface.
interface Dot11Radio1.14 service-policy output AAP2-QoS
That completes QoS policy configuration of a AAP. If you want to do this via GUI you can do this under “Services > QoS” Section which you can see in the below screenshot.
But there are certain Advance features you need to know.
1. QoS Elements for Wireless Phones: When you enable QoS Elements for wireless phones, the AP give top priority to voice packets even if you do not enable QoS. This settings operate independently from the QoS policies that you configure.
** “dot11 phone dot11e” is the command to do this via CLI **
2. IGMP Snooping Helper : When IGMP snooping enabled on a switch and a client roam from one AP to another, client multicast session is dropped. When AP IGMP snooping helper is enabled, the AP sends general Query to WLAN, prompting the client to send in an IGMP membership report. When the network infrastructure receives host IGMP membership report, it ensure delivery of host’s multicast stream.
** If there is no multicast router for processing IGMP query & responses from the host, it is mandatory to “no igmp snooping” configured on AP. If not all multicast traffic for a group is dropped **
3. AVVID Priority Mapping: This maps ethernet packets tagged as CoS 5 to CoS6. This feature enables the AP to apply correct priority to voice packets for compatibility with Cisco AVVID networks. This is disabled by default.
** “dot11 priority-map avvid” is the command to enable this via CLI **
4. WMM (Wifi Multi Media) : You can enable WMM on radio interfaces & then using the Admission Control you can enforce client to complete Admission Control procedure before they allow to use allocated Access Category (Voice, Video, Best Effort, Background).
Following shows the screenshot of these features with its default settings.
Below diagram shows how Admission Control settings can be changed for a given radio interface.
This table shows the default value of those settings.
1. Autonomous AP with WEP Security
2. Autonomous AP with WPA-PSK Security
3. Autonomous AP as Local Radius Server
4. Autonomous AP with LEAP Security
5 Autonomous AP with EAP-FAST Security
6 Autonomous AP with EAP-TLS Security
Thank you for this useful post. Just one question regarding custom QoS policies on for example radio interfaces:
Like you and the Cisco documentation states, the AP does not classify packets based on for example ACLs. In the class maps you have to match a DSCP marking. If the AP is connected to QoS enabled switch trunk (802.1Q), the switch (Cisco) will always add an CoS value, based on the mapping table (default).
So in any case, the custom QoS policy on the AP won’t trigger, because the AP first of all honors already in place layer-2 markings (CoS). Is this correct?
I think so Joe