Table of Contents
Advertisement
Chapter 5 - Appendix
DSL Modem (Digital Subscriber Line)
A DSL modem uses your existing phone lines to transmit data at high speeds.
Direct-Sequence Spread Spectrum (for 802.11b)
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.
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 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.
Wireless mobile clients 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 wireless device. Intercepting and
decoding a direct-sequence transmission requires a predefined algorithm to
associate the spreading code used by the transmitting wireless device to the
receiving wireless mobile client.
This algorithm is established by IEEE 802.11b specifications. The bit
redundancy within the chipping sequence enables the receiving wireless mobile
client 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 wireless
device uses a constant chip rate of 11Mchips/s for all data rates, but uses different
modulation schemes to encode more bits per chip at the higher data rates. The
wireless device is capable of an 11 Mbps data transmission rate, but the coverage
area is less than a 1 or 2 Mbps wireless device since coverage area decreases as
bandwidth increases.
Encryption
This provides wireless data transmissions with a level of security.
Extended Service Set (ESS)
A set of one or more interconnected basic service set (BSSs) and integrated
local area networks (LANs) can be configured as an Extended Service Set.
ESSID (Extended Service Set Identifier)
You must have the same ESSID entered into the gateway and each of its wireless
clients. The ESSID is a unique identifier for your wireless network.
56
ASUS 802.11g Access Point
Advertisement
Table of Contents
