Wireless Roaming - Motorola RFS7000 Series System Reference Manual

1-16 Overview
MU Balancing Across Multiple APs
As per the 802.11 standard, AP and MU association is a process conducted independently of the switch. 802.11
provides message elements used by the MU firmware to influence the roaming decision. The switch
implements the following MU load balancing techniques:
• 802.11e admission control — 1 byte: channel utilization % and 1 byte: MU count is sent in QBSS Load
Element in beacons to MU.
• Load balancing element (proprietary) — 2 byte: Kbps, 2 byte: Kbps and 2 byte: MU Count are sent in
beacon to MU.
AP Balancing Across Multiple Switches
At adoption, the AP solicits and receives multiple adoption responses from switches on the network. These
adoption responses contain preference and loading information the AP uses to select the optimum switch to
be adopted by. Use this mechanism to define which APs are adopted by which switches. By default, the
adoption algorithm generally distributes AP adoption evenly among the switches available.
NOTE Each switch can support a maximum of 256 access ports. However, port adoption
per switch is determined by the number of licenses acquired.

1.2.2.10 Wireless Roaming

The following forms of wireless roaming are supported:
• L3 Roaming
• Fast Roaming
• Interswitch Layer 2 Roaming
• International Roaming
• MU Move Command
• Virtual AP
L3 Roaming
L3 Roaming works across a set of switches configured to exchange mobility related information for all MUs
associated with "mobility-enabled" WLANs. The switches have to be explicitly configured as mobility peers.
A full mesh of peering sessions is required for L3 Roaming to work correctly. Peering sessions use TCP to carry
mobility update messages that include the MAC address, IP address, home switch, current switch and home-
switch VLAN ID of the all MUs. Data packets to and from MUs are tunneled between mobility peers using GRE
(Generic Routing Encapsulation) tunnels. TCP provides the following advantages:
• TCP re-transmits lost messages thereby providing reliable connectivity
• TCP ensures ordered message delivery using sequenced numbers.
• TCP has a built-in "keep-alive" mechanism which helps detect loss of connectivity to the peer or peer
failure.
Fast Roaming
Using 802.11i can speed up the roaming process from one AP to another. Instead of doing a complete 802.1x
authentication each time a MU roams between APs, 802.11i allows a MU to re-use previous PMK
authentication and perform only a four-way handshake. This process greatly speeds up the roaming process.
In addition to reusing PMKs on previously visited APs, Opportunistic Key Caching allows multiple APs to share