D-Link DWL-6600AP Users Manual - Page 62

Unified Access Point Administrator's Guide Modifying Radio Settings Field Protection Beacon Interval DTIM Period Fragmentation Threshold Table 19: Radio Settings (Cont.) Description 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. D-Link November 2011 Unified Access Point Administrator's Guide Page 62