Advanced Settings - Proxim Harmony 8569 User Manual

Configuration 25

Advanced Settings

Supported Rates
The IEEE 802.11a specification supports eight data rates: 54 Mbps, 48 Mbps,
36 Mbps, 24 Mbps, 18 Mbps, 12 Mbps, 9 Mbps, and 6 Mbps. Harmony's 2X mode
supports eight data rates: 108 Mbps, 96 Mbps, 72 Mbps, 48 Mbps, 36 Mbps,
24 Mbps, 18 Mbps, and 12 Mbps.
As a mobile client moves away from an 802.11a Access Point, the data rate
automatically decreases in order to maintain a usable radio connection. Therefore, a
mobile client that is close to an Access Point may operate at 54 Mbps, but a client that
is far away from the Access Point may operate at 6 Mbps. Operation at 6 Mbps or 12
Mbps provides greater range than operation at 54 Mbps or 108 Mbps.
By default, the Harmony 802.11a Access Point dynamically switches between all data
rates for the specified radio mode (802.11a or 2X mode). However, you can also
manually configure a specific data rate that the Access Point will use. Note that the
802.11a and 2X rates are paired and the value used by the Access Point depends upon
whether or not 2X mode is enabled. For example, if you select the "36 / 72 Mbps"
option, the 802.11a Access Point will operate at only 36 Mbps if it is in 802.11a mode
and at only 72 Mbps if it is in 2X mode.
RTS/CTS
The 802.11a standard supports optional RTS/CTS communication.
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.
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 radio.
The RTS and CTS packets contain a reservation time to notify other radios that the
medium is in use for a specified period of time. This helps to minimize collisions.
While RTS/CTS adds overhead to the radio network, it is particularly useful for large
packets that take longer to resend after a collision occurs.
You can configure a Harmony 802.11a Access Point to always use RTS/CTS, never use
RTS/CTS, or use RTS/CTS for packets over a certain size (RTS/CTS Threshold). By
default, RTS/CTS is always off.
The RTS/CTS Threshold supports a range between 256 and 2346 Bytes. If set to 256,
then a sending radio will use RTS/CTS before sending any packet that is 256 Bytes or
larger. If set to 2346, then a sending radio will not use RTS/CTS for any packets except
those that are 2346 Bytes or larger.