Dynamic Frequency Selection (Dfs); Rts/Cts Medium Reservation - Proxim Orinoco AP-2500 User Manual

Network Parameters
Figure 4-10 Wireless Interface Configuration Screen (802.11a)
• DTIM Period: The Deferred Traffic Indicator Map (DTIM) is used with clients that have power management
enabled. DTIM should be left at 1, the default value, if any clients have power management enabled. This
parameter supports a range between 1 and 65535.
• RTS/CTS Medium Reservation: This parameter affects message flow control and should not be changed under
normal circumstances. Range is 0 to 2347. When set to a value between 0 and 2347, the Access Point uses the
RTS/CTS mechanism for packets that are the specified size or greater. When set to 2347 (the default setting),
RTS/CTS is disabled. See

Dynamic Frequency Selection (DFS)

802.11a devices sold in Europe use a technique called Dynamic Frequency Selection (DFS) to automatically select an
operating channel. During boot-up, the AP scans the available frequency and selects a channel that is free of
interference. If the AP subsequently detects interference on its channel, it automatically reboots and selects another
channel that is free of interference.
DFS only applies to 802.11a devices used in Europe (i.e., units whose regulatory domain is set to ETSI). The
European Telecommunications Standard Institute (ETSI) requires that 802.11a devices use DFS to prevent
interference with radar systems and other devices that already occupy the 5 GHz band.
If you are using an AP with a 5 GHz upgrade kit in Europe, keep in mind the following:
• DFS is not a configurable parameter. It is always enabled and cannot be disabled.
• You cannot manually select the device's operating channel; you must let DFS select the channel.
• You cannot configure the Auto Channel Select option. Within the Web browser interface, this option always
appears enabled.

RTS/CTS Medium Reservation

The 802.11 standard supports optional RTS/CTS communication based on packet size. Without RTS/CTS, a sending
radio listens to see if another radio is already using the medium before transmitting a data packet. If the medium is
free, the sending radio transmits its packet. However, there is no guarantee that another radio is not transmitting a
packet at the same time, causing a collision. This typically occurs when there are hidden nodes (clients that can
communicate with the Access Point but are out of range of each other) in very large cells.
When RTS/CTS occurs, the sending radio first transmits a Request to Send (RTS) packet to confirm that the medium
is clear. When the receiving radio successfully receives the RTS packet, it transmits back a Clear to Send (CTS)
packet to the sending radio. When the sending radio receives the CTS packet, it sends the data packet to the receiving
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RTS/CTS Medium Reservation for more information.