CHAPTER
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Site Survey Guide for Deploying Cisco 7920 IP Phones
OL-6315-01
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Overview
This document begins by identifying the specific radio environmental values that are needed for a
successful voice deployment.
Note Cisco offers a Cisco Aironet Wireless Site Survey class for technical individuals who will be performing
site surveys for wireless LAN solutions. This white paper does not replace the information in the site
survey class. Cisco recommends that wireless LAN survey technicians take the Aironet Wireless Site
Survey class as a requisite. Cisco also recommends that technicians study the Cisco Wireless IP Phone
7920 Deployment Recommendations before studying this white paper.
There are two types of wireless LAN VoIP surveys:
• A survey performed with Wireless IP Telephony (WIPT) handsets
• A survey that simulates WIPT operation
Cisco recommends that, if possible, you install the VoIP network following AVVID design guidelines
before surveying for a WIPT network.
Tip Click this link to browse to a library of AVVID design guides:
http://www.cisco.com/warp/public/779/largeent/it/ese/srnd.html
Recommendations for Successful VoIP Surveys
The most effective surveys are performed using Cisco access points and Cisco WIPT handsets on active
calls through Cisco’s Call Manager. In the site survey, it is important that you test performance from the
source to the end point and also from the end point to the source. For example, your WIPT site survey
should use a wired VoIP phone (such as a Cisco 7960) in the core of the network to a WIPT (such as a
Cisco 7920) handset with a live conversation going in both directions. The Cisco 7920 WIPT handset
enables you to audibly monitor the quality of the call. Cisco also recommends that you use the
customer’s actual handset configuration when performing the survey.
Cisco considers it necessary to re-survey for voice at a site that has a trouble-free WLAN data network.
Voice traffic is isochronous—to be usable, it must be transmitted without delay. Voice traffic has strict
resource requirements for guaranteed bandwidth, low latency, low jitter, and low packet loss. The 7920
G.711 codec voice packets require a guaranteed bandwidth of 80 kbps. The G.711 packets have a
160-byte payload plus a 40-byte RTP/UDP/IP protocol overhead. Typically, voice packets are sent every
20 milliseconds (ms), and a corresponding service rate is expected from the network by the voice
application. A delay or loss of two or more contiguous voice packets is generally noticeable as quality
