Wi-Fi Network Components; Ap Channel And Domain Relationships; Ap Interactions - Cisco 8821 Administration Manual

Wi-Fi Network Components

The AP uses the connection to the wired network to transmit data and voice packets to and from the switches
and routers. Voice signaling is transmitted to the call control server for call processing and routing.
APs are critical components in a WLAN because they provide the wireless links or hot spots to the network.
In some WLANs, each AP has a wired connection to an Ethernet switch, such as a Cisco Catalyst 3750, that
is configured on a LAN. The switch provides access to gateways and the call control server to support wireless
IP telephony.
Some networks contain wired components that support wireless components. The wired components can
comprise switches, routers, and bridges with special modules to enable wireless capability.
For more information about Cisco Unified Wireless Networks, see
wireless/index.html.

Wi-Fi Network Components

The phone must interact with several network components in the WLAN to successfully place and receive
calls.

AP Channel and Domain Relationships

Access points (APs) transmit and receive RF signals over channels within the 2.4 GHz or 5 GHz frequency
band. To provide a stable wireless environment and reduce channel interference, you must specify
nonoverlapping channels for each AP.
For more information about AP channel and domain relationships, see the "Designing the Wireless LAN for
Voice" section in the Cisco Wireless IP Phone 8821 Series Deployment Guide.

AP Interactions

Wireless phones use the same APs as wireless data devices. However, voice traffic over a WLAN requires
different equipment configurations and layouts than a WLAN that is used exclusively for data traffic. Data
transmission can tolerate a higher level of RF noise, packet loss, and channel contention than voice transmission.
Packet loss during voice transmission can cause choppy or broken audio and can make the call inaudible.
Packet errors can also cause blocky or frozen video.
Wireless phones users are mobile and often roam across a campus or between floors in a building while
connected to a call. In contrast, data users remain in one place or occasionally move to another location. The
ability to roam while maintaining a call is one of the advantages of wireless voice, so RF coverage needs to
include stairwells, elevators, quiet corners outside conference rooms, and passageways.
To ensure good voice quality and optimal RF signal coverage, you must perform a site survey. The site survey
determines settings that are suitable to wireless voice and assists in the design and layout of the WLAN; for
example AP placement, power levels, and channel assignments.
After deploying and using wireless voice, you should continue to perform postinstallation site surveys. When
you add a group of new users, install more equipment, or stack large amounts of inventory, you are changing
the wireless environment. A postinstallation survey verifies that the AP coverage is still adequate for optimal
voice communications.
Cisco Wireless IP Phone 8821 and 8821-EX Administration Guide for Cisco Unified Communications Manager
20
VoIP Networks
http://www.cisco.com/c/en/us/products/