Cisco WAP551 Administration Manual page 93

Wireless
Radio
Cisco Small Business WAP551 and WAP561 Wireless-N Access Point
The DTIM message is an element included in some Beacon frames. It indicates which
client stations, currently sleeping in low-power mode, have data buffered on the WAP
device awaiting pickup.
The DTIM period that you specify indicates how often the clients served by this WAP
device should check for buffered data still on the WAP device awaiting pickup.
The measurement is in beacons. For example, if you set this field to 1, clients check for
buffered data on the WAP device at every beacon. If you set this field to 10, clients
check on every 10th beacon.
• Fragmentation Threshold—The frame size threshold in bytes. The valid integer must be
even and in the range of 256 to 2346. The default is 2346.
The fragmentation threshold is a way of limiting the size of packets (frames) transmitted
over the network. If a packet exceeds the fragmentation threshold you set, the
fragmentation function is activated and the packet is sent as multiple 802.11 frames.
If the packet being transmitted is equal to or less than the threshold, fragmentation is not
used. Setting the threshold to the largest value (2,346 bytes, which is the default)
effectively disables fragmentation.
Fragmentation involves more overhead both because of the extra work of dividing up
and reassembling of frames it requires, and because it increases message traffic on the
network. However, fragmentation can help improve network performance and
reliability if properly configured.
Sending smaller frames (by using lower fragmentation threshold) might help with some
interference problems; for example, with microwave ovens.
By default, fragmentation is off. We recommend not using fragmentation unless you
suspect radio interference. The additional headers applied to each fragment increase the
overhead on the network and can greatly reduce throughput.
• RTS Threshold—The Request to Send (RTS) Threshold value. The valid integer range
must be from 0 to 2347. The default is 2347 octets.
The RTS threshold indicates the number of octets in an MPDU, below which an RTS/
CTS handshake is not performed.
Changing the RTS threshold can help control traffic flow through the WAP device,
especially one with a lot of clients. If you specify a low threshold value, RTS packets
are sent more frequently, which consumes more bandwidth and reduces the throughput
of the packet. However, sending more RTS packets can help the network recover from
interference or collisions that might occur on a busy network, or on a network
experiencing electromagnetic interference.
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