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Wireless Router
RNX-G40
User Manual
4.10 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.
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 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).
4.13 What is Preamble Type?
There are two preamble types defined in IEEE 802.11 specification. A long preamble basically gives the
decoder more time to process the preamble. All 802.11 devices support a long preamble. The short
preamble is designed to improve efficiency (for example, for VoIP systems). The difference between the two
is in the Synchronization field. The long preamble is 128 bits, and the short is 56 bits.
4.14 What is SSID Broadcast?
Broadcast of SSID is done in access points by the beacon. This announces your access point (including
various bits of information about it) to the wireless world around it. By disabling that feature, the SSID
configured in the client must match the SSID of the access point.
Some wireless devices don't work properly if SSID isn't broadcast (for example the D-link DWL-120 USB
802.11b adapter). Generally if your client hardware supports operation with SSID disabled, it's not a bad idea
to run that way to enhance network security. However it's no replacement for WEP, MAC filtering or other
protections.
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