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Cisco Unified Wireless IP Phone 7921G Series Deployment Guide 6

Requirements for the Cisco Unified Wireless IP Phone 7921G

The Cisco Unified Wireless IP Phone 7921G is an IEEE 802.11a/b/g wireless IP phone that provides voice communications.

The wireless LAN must be validated to ensure it meets the requirements to deploy the Cisco Unified Wireless IP Phone 7921G.

Site Survey

Before deploying the Cisco Unified Wireless IP Phone 7921G into a production environment, a site survey must be completed

by a Cisco certified partner with the advanced wireless LAN specialization. During the site survey the RF spectrum can be

analyzed to determine which channels are usable in the desired band (2.4 GHz or 5 GHz). Typically there is less interference in

the 5 GHz band as well as more non-overlapping channels, so 5 GHz is the preferred band for operation and even more highly

recommended when the Cisco Unified Wireless IP Phone 7921G is to be used in a mission critical environment. The site

survey will include heatmaps showing the intended coverage plan for the location. The site survey will also determine which

access point platform type, antenna type, access point configuration (channel and transmit power) to use at the location. See the

“Designing the Wireless LAN for Voice” section for more information.

Refer to the Steps to Success website for additional information.

http://www.cisco.com/go/stepstosuccess

RF Validation

In order to determine if VoWLAN can be deployed, the environment must be evaluated to ensure the following items meet

Cisco guidelines.

Signal

The cell edge should be designed to -67 dBm where there is a 20-30% overlap of adjacent access points at that signal level.

This ensures the 7921G phone always has adequate signal and can hold a signal for at least 5 seconds in order to roam seamlessly.

Channel Utilization

Channel Utilization levels should be kept under 50%.

If using the 7921G phone, this is provided via the QoS Basic Service Set (QBSS), which equates to around 105.

Noise

Noise levels should not exceed -92 dBm, which allows for a Signal to Noise Ratio (SNR) of 25 dB where a -67 dBm signal should be

maintained.

Packet Loss / Delay

Per voice guidelines, packet loss should not exceed 1% packet loss, otherwise voice quality can be degraded significantly.

Jitter should be kept at a minimal (< 100 ms)

Retries

802.11 retransmissions should be less than 20%.

Multipath

Multipath should be kept to a minimal as this can create nulls and reduce signal levels.

Many different tools and applications can be used to evaluate these items in order to certify the deployment.

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Cisco 7921 Spécifications Page 6