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38 A111 Wireless Card Adaptor
Chapter 5
Chapter 5 - Glossary
Glossary
DHCP (Dynamic Host Configuration Protocol)
This protocol allows a computer (or many computers on your network) to
be automatically assigned a single IP address from a DHCP server.
DNS Server Address (Domain Name System)
DNS allows Internet host computers to have a domain name and one or
more IP addresses. A DNS server keeps a database of host computers and
their respective domain names and IP addresses, so that when a user
enters a domain name into the Internet browser, the user is sent to the proper
IP address. The DNS server address used by the computers on your home
network is the location of the DNS server your ISP has assigned.
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.