Media Types; Direct-Sequence Spread Spectrum - Motorola AP-7131 Product Reference Manual

Introduction 1-23
interface to another. The bridge forwards packets addressed to unknown systems to the Default
Interface (Ethernet).
The access point internal stack interface handles all messages directed to the access point. Each
stores information on destinations and their interfaces to facilitate forwarding. When a user sends
an ARP (Address Resolution Protocol) request packet, the 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 access point database keeps a record of the destination
address along with the receiving interface. With this information, the access point forwards any
directed packet to the correct destination. Transmitted ARP request packets echo back to other MUs.
The access point removes from its database the destination or interface information not used for a
specified time. The AP refreshes its database when it transmits or receives data from these
destinations and interfaces.

1.2.3 Media Types

The access point radio interface conforms to IEEE 802.11 specifications. The 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 access point is a Data Terminal Equipment (DTE) device with male pin
connectors for the RS-232 port. Connecting the access point to a PC requires a null modem serial
cable.

1.2.4 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 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.