Brocade Mobility 5181 Access Point Product Reference Guide (Supporting software release 4.4.0.0) - Manual (Page 32)

18 Brocade Mobility 5181 Access Point Product Reference Guide
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Theory of operations
1
The user can configure the ESSID to correspond to up to 16 WLANs on each 802.11a or 802.11b/g
radio. A Wireless Local Area Network (WLAN) is a data-communications system that flexibly
extends the functionalities of a wired LAN. A WLAN does not require lining up devices for
line-of-sight transmission, and are thus, desirable. Within the WLAN, roaming users can be handed
off from one Mobility 5181 Access Point to another like a cellular phone system. WLANs can
therefore be configured around the needs of specific groups of users, even when they are not in
physical proximity.
MAC layer bridging
The Mobility 5181 Access Point provides MAC layer bridging between its interfaces. The Mobility
5181 Access Point monitors traffic from its interfaces and, based on frame address, forwards the
frames to the proper destination. The access point tracks source and destination addresses to
provide intelligent bridging as Clients roam or network topologies change. The Mobility 5181
Access Point also handles broadcast and multicast messages and responds to Client association
requests.
The Mobility 5181 Access Point listens to all packets on its LAN and WAN interfaces and builds an
address database using MAC addresses. An address in the database includes the interface media
that the device uses to associate with the Mobility 5181 Access Point. The Mobility 5181 Access
Point uses the database to forward packets from one interface to another. The bridge forwards
packets addressed to unknown systems to the Default Interface (Ethernet).
The Mobility 5181 Access Point internal stack interface handles all messages directed to the
Mobility 5181 Access Point. Each Mobility 5181 Access Point stores information on destinations
and their interfaces to facilitate forwarding. When a user sends an ARP (Address Resolution
Protocol) request packet, the Mobility 5181 Access Point forwards it over all enabled interfaces
except over the interface the ARP request packet was received.
On receiving the ARP response packet, the Mobility 5181 Access Point database keeps a record of
the destination address along with the receiving interface. With this information, the Mobility 5181
Access Point forwards any directed packet to the correct destination. Transmitted ARP request
packets echo back to other Clients. The access point removes from its database the destination or
interface information that is not used for a specified time. The AP refreshes its database when it
transmits or receives data from these destinations and interfaces.
Media types
The Mobility 5181 Access Point radio interface conforms to IEEE 802.11a/b/g specifications. The
interface operates at a maximum 54Mbps (802.11a radio) using direct-sequence radio technology.
The Mobility 5181 Access Point supports multiple-cell operations with fast roaming between cells.
Within a direct-sequence system, each cell can operate independently. Adding cells to the network
provides an increased coverage area and total system capacity.
The RS-232 serial port provides a Command Line Interface (CLI) connection. The serial link
supports a direct serial connection (assuming a DB9 connector is used). The Mobility 5181 Access
Point is a Data Terminal Equipment (DTE) device with male pin connectors for the RS-232 port.
Connecting the Mobility 5181 Access Point to a PC requires a null modem serial cable.