Defining Upstream and Downstream Traffic Flow
At this point, it is important to clarify some terms that are used throughout the wireless QoS chapters:
Upstream: Indicates the flow of packets from the mobile wireless device to the wired network infrastructure, including the following:
Radio upstream: Refers to traffic sent by the WLAN clients and traveling to the AP. WMM provides upstream QoS for WLAN clients over the air. Each IP packet also has an internal DSCP marking that is used for prioritization over the IP network.
Network upstream: Refers to traffic leaving the AP, traveling to the WLC. This traffic is encapsulated within CAPWAP. The DSCP value on the CAPWAP tunnel may differ from the inner packet’s DSCP value. Wired campus QoS policies provision upstream QoS.
Downstream: Refers to the flow of packets from the wired network infrastructure to the wireless devices, including the following:
Network downstream: Refers to traffic leaving the WLC traveling to the AP. This traffic is encapsulated within CAPWAP. Wired campus QoS policies provision downstream QoS.
Radio downstream: Refers to traffic leaving the AP and traveling to the WLAN clients. WMM provides downstream QoS for WLAN clients.
reference -End-to-end Qos Network Design – cisco press
QoS for Wireless LANs Compared to QoS on Wired LANs
The QoS implementation for wireless LANs differs from QoS implementations on other Cisco devices. With QoS enabled, access points have the following behavior:
•They do not classify packets; they prioritize packets based on the Dynamic Host Configuration Protocol (DSCP) value, client type (such as a wireless phone), or the priority value in the 802.1q or 802.1p tag.
Precedence of QoS Settings
When you enable QoS, the access point queues packets based on the Layer 2 class of service value for
each packet. The access point applies QoS policies in this order:
1. Packets already classified—When the access point receives packets from a QoS-enabled switch or
router that has already classified the packets with non-zero 802.1Q/P user_priority values, the access
point uses that classification and does not apply other QoS policy rules to the packets. An existing
classification takes precedence over all other policies on the access point.
Note Even if you have not configured a QoS policy, the access point always honors tagged 802.1P
packets that it receives over the radio interface.
2. QoS Element for Wireless Phones setting—If you enable the QoS Element for Wireless Phones
setting, dynamic voice classifiers are created for some of the wireless phone vendor clients, which
allows the wireless phone traffic to be a higher priority than other clients’ traffic. Additionally, the
QoS Basic Service Set (QBSS) is enabled to advertise channel load information in the beacon and
probe response frames. Some IP phones use QBSS elements to determine which access point to
associate to, based on the traffic load.
You can use the Cisco IOS command dot11 phone dot11e command to enable the future upgrade
of the 7920 Wireless Phone firmware to support the standard QBSS Load IE. The new 7920 Wireless
Phone firmware will be announced at a later date.
3. Policies you create on the access point—QoS Policies that you create and apply to VLANs or to the
access point interfaces are third in precedence after previously classified packets and the QoS
Element for Wireless Phones setting.
4. Default classification for all packets on VLAN—If you set a default classification for all packets on
a VLAN, that policy is fourth in the precedence list.