Access Point Association; Qos In A Wireless Network - Cisco 8821 Administration Manual

VoIP Networks
Packet loss occurs during roaming; however, the security mode and the presence of fast roaming determines
Note
how many packets are lost during transmission. Cisco recommends implementation of Cisco Centralized
Key Management (CCKM) to enable fast roaming.
For more information about Voice QoS in a wireless network, see the Cisco Wireless IP Phone 8821 Series
Deployment Guide.

Access Point Association

At startup, the phone scans for APs with SSIDs and encryption types that it recognizes. The phone builds and
maintains a list of eligible APs and selects the best AP, based on the current configuration.

QoS in a Wireless Network

Voice and video traffic on the wireless LAN, like data traffic, is susceptible to delay, jitter, and packet loss.
These issues do not impact the data end user, but can seriously impact a voice or video call. To ensure that
voice and video traffic receives timely and reliable treatment with low delay and low jitter, you must use
Quality of Service (QoS).
By separating the devices into a voice VLAN and marking voice packets with higher QoS, you can ensure
that voice traffic gets priority treatment over data traffic, which results in lower packet delay and fewer lost
packets.
Unlike wired networks with dedicated bandwidths, wireless LANs consider traffic direction when implementing
QoS. Traffic is classified as upstream or downstream relative to the AP as shown in the following figure.
The Enhanced Distributed Coordination Function (EDCF) type of QoS has up to eight queues for downstream
(toward the 802.11b/g clients) QoS. You can allocate the queues based on these options:
• QoS or Differentiated Services Code Point (DSCP) settings for the packets
• Layer 2 or Layer 3 access lists
• VLANs for specific traffic
• Dynamic registration of devices
Although up to eight queues on the AP can be set up, you should use only three queues for voice, video, and
signaling traffic to ensure the best possible QoS. Place voice in the Voice queue (UP6), video in the Video
queue (UP5), signaling (SIP) traffic in the Video queue (UP4), and place data traffic in a best-effort queue
(UP0). Although 802.11b/g EDCF does not guarantee that voice traffic is protected from data traffic, you
should get the best statistical results by using this queuing model.
The queues are:
Cisco Wireless IP Phone 8821 and 8821-EX Administration Guide for Cisco Unified Communications Manager
Access Point Association
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