Voice Qos In Wireless Networks - Cisco 7925G Administration Manual

VoIP Wireless Network
Received Signal Strength Indicator (RSSI)
Traffic Specification (TSpec)
The wireless IP phone associates with the AP with the highest RSSI and lowest channel usage values (QBSS)
that have matching SSID and encryption types. To ensure that voice traffic is handled properly, you must
configure the correct QoS in the AP. For configuration information, see Cisco Unified Wireless IP Phone
7925 and 7926 Series Deployment Guide.
Related Topics
Voice Communication Security in WLANs, on page 39
Site Survey Verification, on page 44
Voice QoS in Wireless Networks, on page 35

Voice QoS in Wireless Networks

Voice 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 have serious implications for a voice call. To ensure that voice traffic
receives timely and reliable treatment with low delay and low jitter, you must use Quality of Service (QoS),
and use separate virtual LANs (VLANs) for voice and data. By isolating the voice traffic onto a separate
VLAN, you can use QoS to provide priority treatment for voice packets when traveling across the network.
Also, use a separate VLAN for data traffic, not the default native VLAN that is typically used for all network
devices.
You typically need at least three VLANs on the network switches and the APs that support voice connections
on the WLAN. These VLANs are:
Voice VLAN
Data VLAN
Native VLAN
Assign an SSID to the voice VLAN and a different SSID to the data VLAN. If you configure a separate
management VLAN in the WLAN, do not associate an SSID with the management VLAN.
By separating the phones into a voice VLAN and marking voice packets with higher QoS, you can ensure
that voice traffic gets priority treatment over data traffic, resulting in lower packet delay and fewer lost packets.
Signal strength of available APs within the RF coverage area. The phone attempts to associate with the
AP with the highest RSSI value.
Calculation of call limits and WLAN load balancing. The TSpec value of each voice stream allows the
system to allocate bandwidth to voice devices on a first-come, first-served basis.
Voice traffic to and from the wireless IP phone
Data traffic to and from the wireless PC
Data traffic to and from other wireless infrastructure devices
Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G Administration Guide
Voice QoS in Wireless Networks
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