P-661HNU Series Support Notes
27
All contents copyright © 2010 ZyXEL Communications Corporation.
Advanced FAQ
1. What is Ad Hoc mode?
A wireless network consists of a number of stations without using an access
point or any connection to a wired network.
2. What is Infrastructure mode?
Infrastructure mode implies connectivity to a wired communications
infrastructure. If such connectivity is required the Access Points must be used
to connect to the wired LAN backbone. Wireless clients have their
configurations set for "infrastructure mode" in order to utilise access points
relaying.
3. How many Access Points are required in a given area?
This depends on the surrounding terrain, the diameter of the client population,
and the number of clients. If an area is large with dispersed pockets of
populations then extension points can be used for extend coverage.
4. What is Direct-Sequence Spread Spectrum Technology
– (DSSS)?
DSSS spreads its signal continuously over a wide frequency band. DSSS
maps the information bearing bit-pattern at the sending station into a higher
data rate bit sequence using a "chipping" code. The chipping code (also known
as processing gain) introduces redundancy which allows data recovery if
certain bit errors occur during transmission. The FCC rules the minimum
processing gain should be 10, typical systems use processing gains of 20.
IEEE 802.11b specifies the use of DSSS.
5. What is Frequency-hopping Spread Spectrum Technology
– (FHSS)?
FHSS uses a narrowband carrier which hops through a predefined sequence
of several frequencies at a specific rate. This avoids problems with fixed
channel narrowband noise and simple jamming. Both transmitter and receiver
must have their hopping sequences synchronized to create the effect of a
single "logical channel". To an unsynchronised receiver an FHSS transmission
appears to be short-duration impulse noise. 802.11 may use FHSS or DSSS.
