The Cisco UWN solution supports seamless client roaming across lightweight access points managed by the same controller, between controllers in the same mobility group on the same subnet, and across controllers in the same mobility group on different subnets. Also, in controller software release 4.1 or later releases, client roaming with multicast packets is supported.
You can adjust the default RF settings (RSSI, hysteresis, scan threshold, and transition time) to fine-tune the operation of client roaming using the controller GUI or CLI.
Multiple-controller deployments support client roaming across access points managed by controllers in the same mobility group and on the same subnet. This roaming is also transparent to the client because the session is sustained and a tunnel between controllers allows the client to continue using the same DHCP- 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 session timeout is exceeded.
Each controller supports same-controller client roaming across access points managed by the same controller. This roaming is transparent to the client as the session is sustained, and the client continues using the same DHCP-assigned or client-assigned IP address. The controller provides DHCP functionality with a relay function. Same-controller roaming is supported in single-controller deployments and in multiple-controller deployments.
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 Wireless 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 Wireless 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.
To see whether a particular client supports E2E, choose Wireless > Clients on the controller GUI, click the Detail link for the desired client, and look at the E2E Version text box in the Client Properties area.
Roam reason report—This feature enables CCXv4 clients to report the reason why they roamed to a new access point. It also allows network administrators to build and monitor a roam history.
Directed roam request—This feature enables the controller to send directed roam requests to the client in situations when the controller can better service the client on an access point different from the one to which it is associated. In this case, the controller sends the client a list of the best access points that it can join. The client can either honor or ignore the directed roam request. Non-CCX clients and clients running CCXv3 or below must not take any action. No configuration is required for this feature.
Restrictions on Client Roaming
Controller software release
4.2 or later releases support CCX versions 1 through 5. CCX support is enabled
automatically for every WLAN on the controller and cannot be disabled. The
controller stores the CCX version of the client in its client database and uses
it to generate and respond to CCX frames appropriately. Clients must support
CCXv4 or v5 (or CCXv2 for access point assisted roaming) in order to utilize
these roaming enhancements.
The roaming enhancements
mentioned above are enabled automatically, with the appropriate CCX support.
FlexConnect access points in
standalone mode do not support CCX Layer 2 roaming.
Client roaming between 600
Series Access points is not supported.
Seamless L2 and L3 roaming is not supported between a Cisco and a
third-party wireless infrastructure, which also includes a Cisco IOS access
Configuring CCX Client Roaming Parameters (GUI)
Wireless > 802.11a/n or 802.11b/g/n > Client
Roaming. The 802.11a (802.11b) > Client Roaming
you want to fine-tune the RF parameters that affect client roaming, choose
Custom from the
Mode drop-down list and go to
Step 3. If
you want to leave the RF parameters at their default values, choose
Default and go to
RSSI text box, enter a value for the minimum received signal
strength indicator (RSSI) required for the client to associate to an access
point. If the client’s average received signal power dips below this threshold,
reliable communication is usually impossible. Therefore, clients must already
have found and roamed to another access point with a stronger signal before the
minimum RSSI value is reached.
The range is –90 to –50 dBm.
The default is –85 dBm.
Hysteresis text box, enter a value to indicate how
much greater the signal strength of a neighboring access point must be in order
for the client to roam to it. This parameter is intended to reduce the amount
of roaming between access points if the client is physically located on or near
the border between two access points.
The range is 3 to 20 dB.
The default is 3 dB.
Threshold text box, enter the minimum RSSI that is allowed before
the client should roam to a better access point. When the RSSI drops below the
specified value, the client must be able to roam to a better access point
within the specified transition time. This parameter also provides a power-save
method to minimize the time that the client spends in active or passive
scanning. For example, the client can scan slowly when the RSSI is above the
threshold and scan more rapidly when the RSSI is below the threshold.
The range is –90 to –50 dBm.
The default is –72 dBm.
Transition Time text box, enter the maximum time
allowed for the client to detect a suitable neighboring access point to roam to
and to complete the roam, whenever the RSSI from the client’s associated access
point is below the scan threshold.
The Scan Threshold and
Transition Time parameters guarantee a minimum level of client roaming
performance. Together with the highest expected client speed and roaming
hysteresis, these parameters make it possible to design a wireless LAN network
that supports roaming simply by ensuring a certain minimum overlap distance
between access points.
The range is 1 to 5 seconds.
The default is 5 seconds.
procedure if you want to configure client roaming for another radio band.
Configuring CCX Client Roaming Parameters (CLI)
Configure CCX Layer 2 client roaming parameters by entering this command: