In this post, we will have a closer look at QoS in Autonomous AP. Primary focus of the QoS in autonomous AP deployment is for radio downstream (arrow B)
I have very basic configuration in AAP1 as shown below.
hostname AAP1 ! dot11 ssid ONE vlan 1 authentication open mbssid guest-mode ! interface Dot11Radio0 ssid ONE mbssid station-role root ! interface Dot11Radio0.1 encapsulation dot1Q 1 bridge-group 10 ! interface Dot11Radio0.999 encapsulation dot1Q 999 native bridge-group 1 ! interface GigabitEthernet0.1 encapsulation dot1Q 1 bridge-group 10 ! interface GigabitEthernet0.999 encapsulation dot1Q 999 native bridge-group 1 ! interface BVI1 ip address 192.168.99.99 255.255.255.0 ip default-gateway 192.168.99.1
C3750 switch port configured as below. (only shown AAP1 & wireshark PC switchport config)
interface Vlan999 ip address 192.168.99.1 255.255.255.0 ! interface FastEthernet1/0/11 switchport trunk encapsulation dot1q switchport trunk native vlan 999 switchport trunk allowed vlan 1,3,6,999 switchport mode trunk ! interface FastEthernet1/0/9 description BACKTRACK ! monitor session 1 source interface Fa1/0/11 monitor session 1 destination interface Fa1/0/9 encapsulation replicate
Let’s have a close look at packet captures in this case. We will analyze traffic between 7921 wireless phone to 7965 wired phone. We will take signalling traffic(SCCP) & voice traffic(RTP) for this analysis.
Here is traffic goes from switch to AP (Ethernet Downstream – Arrow A). SCCP traffic mark with CoS=3 & RTP traffic mark with CoS=5.
Now if you look at Radio Downstream (Arrow B) you will observe the following. As shown below, you would notice AP will not do any mapping AVVID CoS value to 802.11e UP by default. They will pass CoS value as it is onto 802.11UP value.
Here is the wireless traffic coming from 7921 wireless phone to AP (radio upstream – Arrow C). As you can see SCCP traffic comes with 802.11e UP of 4 & RTP traffic comes with 802.11e UP of 6. Note that SCCP traffic coming from 7921 have DSCP of 0, still 802.11e UP of 4. This UP value is the important parameter as it get translated in to CoS value at the AP.
finally if you look at Ethernet Upstream (AP to switch – Arrow D) you will see the following. Note that by default UP value does not convert into appropriate CoS value and all traffic goes as CoS of 0 (Best Effort).
Let’s enable 802.11e to AVVID mapping on AP & see what would be the effect. This would map CoS 5 packet coming from ethernet side on to 802.11e UP of 6 prior to send it to wireless client.
AAP1(config)#dot11 priority-map ? avvid Map priority 5 packets to priority 6 AAP1(config)#dot11 priority-map avvid
Here is the packet capture (arrow B) after this configuration. You can see this time CoS values correctly map to 802.11e UP values (ie CoS 3 -> UP 4, CoS 5 -> UP 6)
Also this time 802.11e values correctly map onto CoS value before sending it ethernet upstream towards the switch.
From switch port perspective it has to trust CoS value set by AP in order to preserve the correct QoS settings. Again remember that management traffic goes to AP is untagged & do not have CoS value. Therefore switch will apply default CoS=0 for those traffic (Best Effort)
interface FastEthernet1/0/11 switchport trunk encapsulation dot1q switchport trunk native vlan 999 switchport trunk allowed vlan 1,3,6,999 switchport mode trunk priority-queue out mls qos trust cos
Here is few guidelines for AAP QoS. You can refer configuration guide for more detail
The QoS implementation for wireless LANs differs from QoS implementations on other Cisco devices. With QoS enabled, access points perform the following:
• They do not classify packets; they prioritize packets based on DSCP value, client type (such as a wireless phone), or the priority value in the 802.1q or 802.1p tag.
• They do not construct internal DSCP values; they only support mapping by assigning IP DSCP, Precedence, or Protocol values to Layer 2 COS values.
• They carry out EDCF like queuing on the radio egress port only.
• They do only FIFO queueing on the Ethernet egress port.
• They support only 802.1Q/P tagged packets. Access points do not support ISL.
• They support only MQC policy-map set cos action.
• They prioritize the traffic from voice clients (such as Symbol phones) over traffic from other clients when the QoS Element for Wireless Phones feature is enabled.
• They support Spectralink phones using the class-map IP protocol clause with the protocol value set to 119.