Motorola WS5100 Series Reference Manual page 24

1-14 WS5100 Series Switch System Reference Guide
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 credentials and perform a four-way handshake. This speeds up the roaming process. In
addition to reusing PMKs on previously visited APs, Opportunistic Key Caching allows multiple APs to share
PMKs amongst themselves. This allows an MU to roam to an AP it has not previously visited and reuse a
PMK from another AP to skip the 802.1x authentication.
Interswitch Layer 2 Roaming
An associated MU (connected to a switch) can roam to another access port connected to a different switch.
Both switches must be on the same L2 domain. Authentication information is not shared between the
switches, nor are buffered packets on one switch transferred to the other. Pre-authentication between the
switch and MU allows faster roaming.
International Roaming
The wireless switch supports international roaming 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. The move command permits an MU to roam between ports connected to the
same 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.
When multiple BSSID's are enabled, you cannot tell by snooping the air whether any pair of beacons is sent
out by the same physical AP or different physical AP. Hence the term "virtual AP's"- each virtual AP behaves
exactly like a single-BSSID AP.
Each BSSID supports 1 Extended Service Set Identifier (ESSID). Sixteen ESSIDs per switch are supported.
1.2.2.12 Power Save Polling
An MU uses Power Save Polling (PSP) to reduce power consumption. When an MU is in PSP mode, the switch
buffers its packets and delivers them using the DTIM interval. The PSP-Poll packet polls the AP for buffered
packets. The PSP null data frame is used by the MU to signal the current PSP state to the AP.
1.2.2.13 QoS
QoS provides a data traffic prioritization scheme. QoS reduces congestion from excessive traffic.
If there is enough bandwidth for all users and applications (unlikely because excessive bandwidth comes at
a very high cost), then applying QoS has very little value. QoS provides policy enforcement for mission-critical
applications and/or users that have critical bandwidth requirements when the switch's bandwidth is shared
by different users and applications.
QoS helps ensure each WLAN on the switch receives a fair share of the overall bandwidth, either equally or
as per the proportion configured. Packets directed towards MUs are classified into categories such as