Radio-QoS Policy

This chapter summarizes the radio QoS policy in the CLI command structure. Configuring and implementing a radio QoS policy is essential for WLANs with heavy traffic and less bandwidth. The policy enables you to provide preferential service to selected network traffic by controlling bandwidth allocation. The radio QoS policy can be applied to VLANs configured on an access point. In case no VLANs are configured, the radio QoS policy can be applied to an access point‘s Ethernet and radio ports.

Without a dedicated QoS policy, a network operates on a best-effort delivery basis, meaning all traffic has equal priority and an equal chance of being delivered in a timely manner. When congestion occurs, all traffic has an equal chance of being dropped!

When configuring a Radio QoS policy, select specific network traffic, prioritize it, and use congestion-management and congestion-avoidance techniques to provide deployment customizations best suited to each QoS policy‘s intended wireless client base.

A well designed QoS policy should:
  • Classify and mark data traffic to accurately prioritize and segregate it (by access category) throughout the network.
  • Minimize network delay and jitter for latency sensitive traffic.
  • Ensure higher priority traffic has a better likelihood of delivery in the event of network congestion.
  • Prevent ineffective utilization of access points degrading session quality by configuring admission control mechanisms within each radio QoS policy.

Within a managed wireless network, wireless clients supporting low and high priority traffic contend with one another for access and data resources. The IEEE 802.11e amendment has defined EDCA (Enhanced Distributed Channel Access) mechanisms stating high priority traffic can access the network sooner then lower priority traffic. The EDCA defines four traffic classes (or access categories); voice (highest), video (next highest), best effort, and background (lowest). The EDCA has defined a time interval for each traffic class, known as the TXOP (Transmit Opportunity). The TXOP prevents traffic of a higher priority from completely dominating the wireless medium, thus ensuring lower priority traffic is still supported.

IEEE 802.11e includes an advanced power saving technique called U-APSD (Unscheduled Automatic Power Save Delivery) that provides a mechanism for wireless clients to retrieve packets buffered by an access point. U-APSD reduces the amount of signaling frames sent from a client to retrieve buffered data from an access point. U-APSD also allows access points to deliver buffered data frames as bursts, without backing-off between data frames. These improvements are useful for voice clients, as they provide improved battery life and call quality.

The Wi-Fi alliance has created WMM (Wireless Multimedia) and WMM-PS (WMM Power Save) certification programs to ensure interoperability between 802.11e WLAN infrastructure implementations and wireless clients. A wireless network supports both WMM and WMM-Power Save techniques. WMM and WMM-PS (U-APSD) are enabled by default in each WLAN profile.

Enabling WMM support on a WLAN just advertises the WLAN‘s WMM capability and radio configuration to wireless clients. The wireless clients must also support WMM and use the values correctly while accessing the WLAN to benefit.

WMM includes advanced parameters (CWMin, CWMax, AIFSN and TXOP) specifying back-off duration and inter-frame spacing when accessing the network. These parameters are relevant to both connected access point radios and their wireless clients. Parameters impacting access point transmissions to their clients are controlled using per radio WMM settings, while parameters used by wireless clients are controlled by a WLAN‘s WMM settings.

Wireless network controllers (access points, controllers, and service platforms) include a SIP (Session Initiation Protocol), SCCP (Skinny Call Control Protocol) and ALG (Application Layer Gateway) enabling devices to identify voice streams and dynamically set voice call bandwidth.

Wireless network controllers also support static QoS mechanisms per WLAN to provide prioritization of WLAN traffic when legacy (non WMM) clients are deployed. When enabled on a WLAN, traffic forwarded to a client is prioritized and forwarded based on the WLAN‘s WMM access control setting.



Statically setting a WLAN WMM access category value only prioritizes traffic to the client.

Wireless network administrators can also assign weights to each WLAN in relation to user priority levels. The lower the weight, the lower the priority. Use a weighted technique to achieve different QoS levels across WLANs.

All devices rate-limit bandwidth for WLAN sessions. This form of per-user rate limiting enables administrators to define uplink and downlink bandwidth limits for users and clients. This sets the level of traffic a user or client can forward and receive over the WLAN. If the user or client exceeds the limit, excessive traffic is dropped.

Rate limits can be applied to WLANs using groups defined locally or externally from a RADIUS server using VSAs (Vendor Specific Attributes). Rate limits can be applied to users authenticating using 802.1X, captive portal authentication, and devices using MAC authentication.

Use the (config) instance to configure radios QoS policy related configuration commands. To navigate to the radio QoS policy instance, use the following commands:

<DEVICE>(config)#radio-qos-policy <POLICY-NAME>
nx9500-6C8809(config)#radio-qos-policy test
Radio QoS Mode commands:
  accelerated-multicast  Configure multicast streams for acceleration
  admission-control      Configure admission-control on this radio for one or
                         more access categories
  no                     Negate a command or set its defaults
  smart-aggregation      Configure smart aggregation parameters
  wmm                    Configure 802.11e/Wireless MultiMedia parameters

  clrscr                 Clears the display screen
  commit                 Commit all changes made in this session
  do                     Run commands from Exec mode
  end                    End current mode and change to EXEC mode
  exit                   End current mode and down to previous mode
  help                   Description of the interactive help system
  revert                 Revert changes
  service                Service Commands
  show                   Show running system information
  write                  Write running configuration to memory or terminal