User`s guide

Appendix
User’s Guide 9-36 BreezeNET PRO.11 Series
9.5.7.1 Preventing Access to Network Resources
This is done by the use of an Authentication mechanism where a station needs to
prove knowledge of the current key. This is very similar to Wired LAN privacy, in
the sense that an intruder needs to enter the premises (by using a physical key) in
order to connect his workstation to the wired LAN.
9.5.7.2 Eavesdropping
Eavesdropping is prevented by using the WEP algorithm which is a pseudo-random
number generator initialized by a shared secret key. This PRNG outputs a key
sequence of pseudo-random bits equal in length to the largest possible packet which
is combined with the outgoing/incoming packet producing the packet transmitted in
the air.
The WEP is a simple algorithm based on RSA’s RC4 which has the following
properties:
• Reasonably strong:
Brute-force attack to this algorithm is difficult because every frame is sent
with an Initialization Vector which restarts the PRNG for each frame.
• Self Synchronizing:
The algorithm re-synchronizes for each message. This is necessary in order to
work in a connection-less environment, where packets may get lost (as any
LAN).
9.5.7.3 Power Saving
Wireless LANs are typically related to mobile applications. In this type of
application, battery power is a scare resource. This is the reason why the 802.11
standard directly addresses the issue of Power Saving and defines an entire
mechanism which enables stations to go into sleep mode for long periods of time
without losing information.
The main idea behind the Power Saving Mechanism is that the AP maintains a
continually updated record of the stations currently working in Power Saving mode,
and buffers the packets addressed to these stations until either the stations
specifically request the packets by sending a polling request, or until they change
their operation mode.