D-Link DWL-2600AP Administrator's Manual page 42

Unified Access Point Administrator's Guide
Field
Short Guard Interval
Supported
STBC Mode
Protection
Beacon Interval
DTIM Period
Fragmentation
Threshold
January 2015
Description
This field is available only if the selected radio mode includes 802.11n.
The guard interval is the dead time, in nanoseconds, between OFDM symbols. The guard
interval prevents Inter-Symbol and Inter-Carrier Interference (ISI, ICI). The 802.11n mode
allows for a reduction in this guard interval from the a and g definition of 800 nanoseconds
to 400 nanoseconds. Reducing the guard interval can yield a 10% improvement in data
throughput.
Select one of the following options:
•) Yes — The AP transmits data using a 400ns guard Interval when communicating with
clients that also support the short guard interval.
•) No — The AP transmits data using an 800ns guard interval.
This field is available only if the selected radio mode includes 802.11n.
Space Time Block Coding (STBC) is an 802.11n technique intended to improve the reliability
of data transmissions. The data stream is transmitted on multiple antennas so the receiving
system has a better chance of detecting at least one of the data streams.
Select one of the following options:
•) On — The AP transmits the same data stream on multiple antennas at the same time.
•) Off — The AP does not transmits the same data on multiple antennas.
The protection feature contains rules to guarantee that 802.11n transmissions do not cause
interference with legacy stations or APs. By default, these protection mechanisms are
enabled (Auto). With protection enabled, protection mechanisms will be invoked if legacy
devices are within range of the AP. This causes more overhead on every transmission,
which will impact performance. However, there is no impact on performance if there are no
legacy devices within range of the AP.
You can disable (Off) these protection mechanisms; however, when 802.11n protection is
off, legacy clients or APs within range can be affected by 802.11n transmissions. The 802.11
protection feature is also available when the mode is 802.11b/g. When protection is enabled
in this mode, it protects 802.11b clients and APs from 802.11g transmissions.
Note: This setting does not affect the ability of the client to associate with the AP.
Beacon frames are transmitted by an AP at regular intervals to announce the existence
of the wireless network. The default behavior is to send a beacon frame once every 100
milliseconds (or 10 per second).
Enter a value from 20 to 2000 milliseconds.
Specify a DTIM period from 1 to 255 beacons.
The Delivery Traffic Information Map (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 AP awaiting pick-up.
The DTIM period you specify indicates how often the clients served by this AP should check
for buffered data still on the AP awaiting pickup.
The measurement is in beacons. For example, if you set this field to 1, clients will check
for buffered data on the AP at every beacon. If you set this field to 10, clients will check on
every 10th beacon.
Specify a number between 256 and 2,346 to set the frame size threshold in bytes.
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) effectively disables fragmentation.
Fragmentation plays no role when Aggregation is enabled.
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.
Section 4 - Managing the Access Point
Unified Access Point Administrator's Guide
Page 42