Wireless coverage – Brocade Mobility 5181 Access Point Product Reference Guide (Supporting software release 4.4.0.0) User Manual
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Brocade Mobility 5181 Access Point Product Reference Guide
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Theory of operations
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The Mobility 5181 Access Point uses DSSS (direct sequence spread spectrum) to transmit digital
data from one device to another. A radio signal begins with a carrier signal that provides the base
or center frequency. The digital data signal is encoded onto the carriers using a DSSS chipping
algorithm. The Mobility 5181 Access Point radio signal propagates into the air as electromagnetic
waves. A receiving antenna (on the Client) in the path of the waves absorbs the waves as electrical
signals. The receiving Client interprets (demodulates) the signal by reapplying the direct sequence
chipping code. This demodulation results in the original digital data.
The Mobility 5181 Access Point uses its environment (the air and certain objects) as the
transmission medium.The Mobility 5181 Access Point can either transmit in the 2.4 to 2.5-GHz
frequency range (802.11b/g radio) or the 5 GHz frequency range (802.11a radio), the actual range
is country-dependent. Brocade devices, like other Ethernet devices, have unique, hardware
encoded Media Access Control (MAC) or IEEE addresses. MAC addresses determine the device
sending or receiving data. A MAC address is a 48-bit number written as six hexadecimal bytes
separated by colons. For example: 00:A0:F8:24:9A:C8
Also see the following sections:
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Direct-sequence spread spectrum
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Mobility 5181 Access Point MAC address assignment
Wireless coverage
An Mobility 5181 Access Point establishes an average communication range with Clients called a
Basic Service Set (BSS) or cell. When in a particular cell, the Client associates and communicates
with the Mobility 5181 Access Point supporting the radio coverage area of that cell. Adding Mobility
5181 Access Points to a single LAN establishes more cells to extend the range of the network.
Configuring the same ESSID (Extended Service Set Identifier) on all Mobility 5181 Access Points
makes them part of the same Wireless LAN.
Mobility 5181 Access Points with the same ESSID define a coverage area. A valid ESSID is an
alphanumeric, case-sensitive identifier up to 32 characters. An Client searches for an Mobility
5181 Access Point with a matching ESSID and synchronizes (associates) to establish
communications. This device association allows Clients within the coverage area to move about or
roam. As the Client roams from cell to cell, it associates with a different Mobility 5181 Access Point.
The roam occurs when the Client analyzes the reception quality at a location and determines a
different Mobility 5181 Access Point provides better signal strength and lower Client load
distribution.
If the Client does not find an Mobility 5181 Access Point with a workable signal, it can perform a
scan to find any AP. As Clients switch APs, the AP updates its association statistics.