What are the Open System and Shared Key authentications?
IEEE 802.11 supports two subtypes of network authentication services: open system and
shared key. Under open system authentication, any wireless station can request authentica-
tion. The station that needs to authenticate with another wireless station sends an authentica-
tion management frame that contains the identity of the sending station. The receiving station
then returns a frame that indicates whether it recognizes the sending station. Under shared
key authentication, each wireless station is assumed to have received a secret shared key
over a secure channel that is independent from the 802.11 wireless network communications
channel.
What is WEP?
An optional IEEE 802.11 function that offers frame transmission privacy similar to a wired
network. The Wired Equivalent Privacy generates secret shared encryption keys that both
source and destination stations can use to alert frame bits to avoid disclosure to eavesdro-
ppers.
WEP relies on a secret key that is shared between a mobile station (e.g. a laptop with a wire-
less Ethernet card) and an access point (i.e. a base station). The secret key is used to encrypt
packets before they are transmitted, and an integrity check is used to ensure that packets are
not modified in transit.
What is Fragment Threshold?
The proposed protocol uses the frame fragmentation mechanism defined in IEEE 802.11 to
achieve parallel transmissions. A large data frame is fragmented into several fragments each
of size equal to fragment threshold. By tuning the fragment threshold value, we can get
varying fragment sizes. The determination of an efficient fragment threshold is an important
issue in this scheme. If the fragment threshold is small, the overlap part of the master and
parallel transmissions is large. This means the spatial reuse ratio of parallel transmissions is
high. In contrast, with a large fragment threshold, the overlap is small and the spatial reuse
ratio is low. However high fragment threshold leads to low fragment overhead. Hence there is
a trade-off between spatial re-use and fragment overhead.
Fragment threshold is the maximum packet size used for fragmentation. Packets larger than
the size programmed in this field will be fragmented.
If you find that your corrupted packets or asymmetric packet reception (all send packets, for
example). You may want to try lowering your fragmentation threshold. This will cause packets
to be broken into smaller fragments. These small fragments, if corrupted, can be resent faster
than a larger fragment. Fragmentation increases overhead, so you'll want to keep this value
as close to the maximum value as possible.
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