Wlans And Roaming - Cisco 7925G Administration Manual

WLANs and Roaming

product numbers for the regulatory domains. The Cisco Unified Wireless IP Phone uses the fourth domain
for all other regions in the world. Wireless LANs in the rest of the world use 802.11d to identify band ranges
and channels.
In a non-controller-based wireless network, Cisco recommends that you statically configure channels for
Note
each AP. If your wireless network uses a controller, use the Auto-RF feature with minimal voice disruption.
Some channels may need to be statically configured if there is an intermittent interferer, to avoid disruptions
in that area.
The AP coverage area depends on the type of antenna and transmission power. The AP coverage range is
from 500 to 1000 feet with effective isotropic radiated power (EIRP) output. To provide effective coverage,
APs need a range overlap of approximately 20 percent to allow uninterrupted connections as phone users
roam from one AP to another.
Wireless networks use a service set identifier (SSID). The SSID differentiates one WLAN from another, so
all APs and all devices attempting to connect to a specific WLAN must use the same SSID. The SSID groups
user devices and associates the group with the APs.
For more information about wireless network components and design, see the "Overview: Cisco Unified
Wireless Network" at
genericcontent0900aecd80529a5f.html.
WLANs and Roaming
Wireless IP phones provide communication mobility to users within the WLAN environment. Unlike cellular
phones that have a broad coverage, the coverage area for the wireless IP phone is smaller; therefore, phone
users frequently roam from one AP to another. To understand some of the limitations of roaming with wireless
IP phones, these examples provide information about the WLAN environment.
Pre-call Roaming
Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G Administration Guide
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http://www.cisco.com/en/US/solutions/ns175/networking_solutions_products_
A wireless IP phone user powers up the phone in the office, and the phone associates with the nearby
AP. The user leaves the building, moves to another building, and then places a call. The phone associates
with a different AP in order to place the call from the new location. If the associated AP is within the
same Layer 2 VLAN, the IP address remains the same for the phone. But, if the roaming phone crosses
a Layer 3 boundary with DHCP enabled and Layer 3 mobility is not enabled, the phone recognizes that
it is no longer in the same subnet. The phone must request a new IP address before it can connect to
the network and place the call. If Layer 3 mobility is enabled, the phone does not need to reconnect to
the network.
Note If a user leaves the WLAN coverage area and then comes back into the same
WLAN area, the phone must reconnect to the network. Pressing a key on the
phone causes the phone to perform immediate scans to find and connect to the
network.
VoIP Wireless Network