X-Micro Tech. WL-1502 - Manual (Page 39)

USER’S MANUAL OF X-MICRO WLAN 11b BROADBAND ROUTER Version: 1.2
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.
4.11 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.
4.12 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
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