Motorola Series Switch WS5100 - Manual (Page 23)

Overview 1-13
L3 Roaming
L3 roaming works with switches in the mobility domain to exchange mobility related control information. This
includes IP addresses, Media Access Control (MAC) address information and the HS-VLAN-id of all MUs in
the mobility-domain. A consistent peer configuration results in full-mesh sessions required for L3 roaming to
work correctly. Peering sessions use Transmission Control Protocol (TCP) as the transport layer protocol to
carry mobility update messages. TCP provides the following advantages:
• TCP retransmits 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.
In a layer 3 environment, the access port adoption process is somewhat unique, for more information, see
Configuring Layer 3 Access Port Adoption on page 4-88.
Fast Roaming
MUs roam from AP to AP as an MU moves throughout a WLAN coverage area. To improve roaming
performance, various fast roaming features are implemented:
• Pairwise Master Key (PMK) — Caching credentials are in the AP, so the MU does not need to re-
authenticate.
• PMK Opportunistic Caching — The MU starts transmitting on another AP in order for both AP's to connect
to a common wireless switch.
• Switch to Switch Hand-Off — When an MU roams from a wireless switch in one subnet to a wireless
switch in another subnet, the transport layer connections will be preserved as far as possible.
• PMK Pre-Authentication —The MU authenticates itself with the AP before roaming to it.
Interswitch Layer 2 Roaming
An associated MU (connected to a particular wireless switch) can roam to another access port connected to
a different wireless switch. Both switches must be on the same L2 domain. Authentication information is not
shared between the switches, nor is buffered packets on one switch transferred to the other switch. Pre-
authentication between the switch and MU allows faster roaming.
International Roaming
The wireless switch supports international roaming as per the 802.11d specification.
MU Move Command
As a value added proprietary feature between Motorola infrastructure products and Motorola MUs, a move
command has been introduced. This command permits an MU to roam between ports connected to the same
wireless switch without the need to perform the full association and authentication defined by the 802.11
standard. The move command is a simple packet up/packet back exchange with the access port. Verification
of this feature is dependent on its implementation in one or more mobile units.
Virtual AP
The switch supports multiple Basic Service Set Identifiers (BSSIDs). An access port capable of supporting
multiple BSSID's generates multiple beacons, one per BSSID. Hence, an AP that supports 4 BSSID's can send
4 beacons. The basic requirement for supporting multiple BSSID's is multiple MAC addresses, since each
BSSID is defined by its MAC address.