Asus USB-N66 - Manual (Page 22)

USB-N66 WLAN Adapter User Manual
22 ASUS WLAN adapter
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.