Layer 2 Roaming/IAPP
Network designers working with mobile users
in a large area will often find it necessary to deploy more than one access
point. The 802.11 standard does not define how access points track moving users
or how to negotiate a handoff from one access point to the next, a process
referred to as roaming. Several companies have introduced proprietary
Inter-Access Point Protocols (IAPP) to support roaming. IAPP accomplishes
roaming within a subnet. However, it does not address how the wireless system
tracks users moving from one subnet to another when the same session must be
maintained, as in the case of voice calls
.
Layer 3 Roaming/Mobile IP
Where wireless is being deployed across
multiple subnets, there are options to achieve seamless roaming. Wireless
client adapters can contain proprietary client IP stacks that understand
mobility and allow roaming between subnets. All mobile users on the network
must have this software installed
.
Layer
3 Roaming/Proxy Mobile IP
Another option is to have the wireless
infrastructure contain the intelligence to perform the task. Cisco’s Proxy
Mobile IP delivers this functionality. Mobile IP is designed for use in even
the most complex network environments. As the wireless station leaves one area
and enters the next, the new access point queries the station for its home
agent. After it has been located, packet forwarding is established
automatically between the new and old access points to ensure the user can
transparently exchange data.
Standard Mobile IP
Standard
Mobile IP requires IT personnel to install Mobile IP client software on all
clients.
Proxy Mobile IP
Proxy Mobile IP does not require IT
personnel to install client software on every client. However it does require
firmware to be installed and configured on the routers to support the Home
Agent/Forwarding Agent function. The access points will also need to be
configured to support Proxy Mobile IP, as shown in Figures
,
, and
.