Intellinet 525497, User Manual

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5.10 What is Fragment Threshold?
This 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 a size equal to the
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 lead 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 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 smaller 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.
5.11 What is RTS (Request to Send) Threshold?
The RTS threshold is the packet size at which packet transmission is governed by the RTS/CTS
transaction. The IEEE 802.11-1997 standard allows for short packets to be transmitted without RTS/
CTS transactions. Each station can have a different RTS threshold. RTS/CTS is used when the data
packet size exceeds the defined RTS threshold. With the CSMA/CA transmission mechanism, the
transmitting station sends out an RTS packet to the receiving station and waits for the receiving station
to send back a CTS (Clear to Send) packet before sending the actual packet data. This setting is useful
for networks with many clients. With many clients and a high network load, there will be many more
collisions. By lowering the RTS threshold, there may be fewer collisions and performance should
improve. Basically, with a faster RTS threshold, the system can recover from problems faster. RTS
packets consume valuable bandwidth, however, so setting this value too low will limit performance.
5.12 What is Beacon Interval?
In addition to data frames that carry information from higher layers, 802.11 includes management and
control frames that support data transfer. The beacon frame, which is a type of management frame,
provides the "heartbeat" of a wireless LAN, enabling stations to establish and maintain
communications in an orderly fashion. Beacon Interval represents the amount of time between beacon
transmissions. Before a station enters power save mode, the station needs the beacon interval to know
when to wake up to receive the beacon (and learn whether there are buffered frames at the access
point).