Cisco 7920 - Unified Wireless IP Phone VoIP, Руководство администратора

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Cisco Wireless IP Phone 7920 Administration Guide for Cisco CallManager Release 4.0 and 4.1
OL-7104-01
Chapter 2 An Overview of the Wireless Network
Components of the VoIP Wireless Network
points are in the same Layer 2 subnet, the Cisco Wireless IP Phone keeps the
same IP address and the call continues. As a Cisco Wireless IP Phone roams
between access points, it must re-authenticate with each new access point.
See the
“Security Mechanisms in the Wireless Network” section on page 2-13
for information about authentication.
If the Cisco Wireless IP Phone user moves from an access point that covers
IP Subnet A to an access point that covers IP Subnet B, the phone no longer
has an IP address or gateway that is valid within the new subnet and the call
can disconnect.
With the release of the Cisco Catalyst 6500 Series Wireless LAN Services
Module (WLSM), the Cisco Wireless IP Phone 7920 now supports Layer 3
roaming. For details about the Cisco WLSM, refer to the product
documentation available at:
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/cfgnotes/wls
m_1_1/index.htm
•
Fast and Secure Roaming—Cisco Centralized Key Management (CCKM)
enables authenticated client devices to roam securely from one access point
to another without any perceptible delay during reassociation. With the
support of CCKM protocol, the Cisco Wireless IP Phone 7920 is able to
negotiate the handoff from one access point to another more easily. During
the roaming process, the phone must scan for the nearby access points,
determine which access point can provide the best service, then reassociate
with the new access point. When implementing stronger authentication
methods, such as WPA and LEAP, the number of information exchanges
increases and causes more delay during roaming. For details about CCKM,
refer to the “Cisco Fast Secure Roaming Application Note” at:
http://www.cisco.com/en/US/products/hw/wireless/ps4570/prod_technical_r
eference09186a00801c5223.html
To solve this issue, CCKM, a centralized key management protocol, provides
a cache of session credentials on the wireless domain server (WDS). As the
phone roams from one access point to the next, CCKM compresses the
number of message exchanges during roaming by providing a master key
stored on the WDS for the access point to use. The reassociation exchange is
reduced to two messages, thereby reducing the roaming time.
Related Topics
•
Voice Quality in a Wireless Network, page 2-12