Specifications

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Cisco Wireless LAN Controller Configuration Guide
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Chapter 4 Configuring Controller Settings
Configuring Client Roaming
Inter-Subnet Roaming
Multiple-controller deployments support client roaming across access points managed by controllers in
the same mobility group on different subnets. This roaming is transparent to the client because the
session is sustained and a tunnel between the controllers allows the client to continue using the same
DHCP-assigned or client-assigned IP address as long as the session remains active. The tunnel is torn
down, and the client must reauthenticate when the client sends a DHCP Discover with a 0.0.0.0 client IP
address or a 169.254.*.* client auto-IP address or when the operator-set user timeout is exceeded.
Voice-over-IP Telephone Roaming
802.11 voice-over-IP (VoIP) telephones actively seek out associations with the strongest RF signal to
ensure the best quality of service (QoS) and the maximum throughput. The minimum VoIP telephone
requirement of 20-millisecond or shorter latency time for the roaming handover is easily met by the
Cisco UWN Solution, which has an average handover latency of 5 or fewer milliseconds when open
authentication is used. This short latency period is controlled by controllers rather than allowing
independent access points to negotiate roaming handovers.
The Cisco UWN Solution supports 802.11 VoIP telephone roaming across lightweight access points
managed by controllers on different subnets, as long as the controllers are in the same mobility group.
This roaming is transparent to the VoIP telephone because the session is sustained and a tunnel between
controllers allows the VoIP telephone to continue using the same DHCP-assigned IP address as long as
the session remains active. The tunnel is torn down, and the VoIP client must reauthenticate when the
VoIP telephone sends a DHCP Discover with a 0.0.0.0 VoIP telephone IP address or a 169.254.*.* VoIP
telephone auto-IP address or when the operator-set user timeout is exceeded.
CCX Layer 2 Client Roaming
The controller supports five CCX Layer 2 client roaming enhancements:
• Access point assisted roaming—This feature helps clients save scanning time. When a CCXv2 client
associates to an access point, it sends an information packet to the new access point listing the
characteristics of its previous access point. Roaming time decreases when the client recognizes and
uses an access point list built by compiling all previous access points to which each client was
associated and sent (unicast) to the client immediately after association. The access point list
contains the channels, BSSIDs of neighbor access points that support the client’s current SSID(s),
and time elapsed since disassociation.
• Enhanced neighbor list—This feature focuses on improving a CCXv4 client’s roam experience and
network edge performance, especially when servicing voice applications. The access point provides
its associated client information about its neighbors using a neighbor-list update unicast message.
• Enhanced neighbor list request (E2E)—The End-2-End specification is a Cisco and Intel joint
program that defines new protocols and interfaces to improve the overall voice and roaming
experience. It applies only to Intel clients in a CCX environment. Specifically, it enables Intel clients
to request a neighbor list at will. When this occurs, the access point forwards the request to the
controller. The controller receives the request and replies with the current CCX roaming sublist of
neighbors for the access point to which the client is associated.