Brocade Communications Systems Mobility 7131 Series Service Manual download pdf (Page 39)

Brocade Mobility 7131 Access Point Product Reference Guide 27

53-1002517-01

Media Types

The access point Mobility 7131 Access Point radio interface conforms to IEEE 802.11

specifications. The Mobility 7131 Access Point access point supports multiple-cell operations with

fast roaming between cells. Within a direct-sequence system, each cell can operates

independently. Adding cells to the network provides an increased coverage area and total system

capacity.

The serial port provides a Command Line Interface (CLI) connection. The serial link supports a

direct serial connection. The Mobility 7131 Access Point access point is a Data Terminal Equipment

(DTE) device with male pin connectors for the RS-232 port. Connecting the Mobility 7131 Access

Point access point to a PC requires a null modem serial cable.

Direct-Sequence Spread Spectrum

Spread spectrum (broadband) uses a narrowband signal to spread the transmission over a

segment of the radio frequency band or spectrum. Direct-sequence is a spread spectrum

technique where the transmitted signal is spread over a particular frequency range. The access

point uses Direct-Sequence Spread Spectrum (DSSS) for radio communication.

Direct-sequence systems communicate by continuously transmitting a redundant pattern of bits

called a chipping sequence. Each bit of transmitted data is mapped into chips by the access point

Mobility 7131 Access Point and rearranged into a pseudorandom spreading code to form the

chipping sequence. The chipping sequence is combined with a transmitted data stream to produce

the output signal.

MUs receiving a direct-sequence transmission use the spreading code to map the chips within the

chipping sequence back into bits to recreate the original data transmitted by the access point

Mobility 7131 Access Point. Intercepting and decoding a direct-sequence transmission requires a

predefined algorithm to associate the spreading code used by the transmitting access point

Mobility 7131 Access Point to the receiving MU. This algorithm is established by IEEE 802.11b

specifications. The bit redundancy within the chipping sequence enables the receiving MU to

recreate the original data pattern, even if bits in the chipping sequence are corrupted by

interference.

The ratio of chips per bit is called the spreading ratio. A high spreading ratio increases the

resistance of the signal to interference. A low spreading ratio increases the bandwidth available to

the user. The access point Mobility 7131 Access Point uses different modulation schemes to

encode more bits per chip at higher data rates.

MU Association Process

An Mobility 7131 Access Pointaccess point recognizes MUs as they begin the association process.

An Mobility 7131 Access Point access point keeps a list of the MUs it services. MUs associate with

an access point Mobility 7131 Access Point based on the following conditions:

• Signal strength between the Mobility 7131 Access Point and MU

• Number of MUs currently associated with the Mobility 7131 Access Point access point

• MUs encryption and authentication capabilities

• MUs supported data rate

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Brocade Communications Systems Mobility 7131 Series Service Manual Page 39