Brocade Mobility RFS Controller System Reference Guide (Supporting software release 5.5.0.0 and later) - Manual (Page 132)

120 Brocade Mobility RFS Controller System Reference Guide
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10. Set or override the following profile WLAN Properties for the selected Access Point radio:
11. Select a mode from the Feed WLAN Packets to Sensor check box in the RadioShare section to
enable this feature. Select either Inline or Promiscuous mode to allow the packets the radio is
switching to also be used by the WIPS analysis module. This feature can be enabled in two
modes: an inline mode where the WIPS sensor receives the packets from the radios with radio
operating in normal mode. A promiscuous mode where the radio is configured to a mode
where it receives all packets on the channel whether the destination address is the radio or
not, and the WIPS module can analyze them.
Beacon Interval Set the interval between radio beacons in milliseconds (either 50, 100 or 200). A beacon is a packet
broadcast by adopted radios to keep the network synchronized. Included in a beacon is the WLAN
service area, radio address, broadcast destination addresses, a time stamp, and indicators about
traffic and delivery (such as a DTIM). Increase the DTIM/beacon settings (lengthening the time) to let
nodes sleep longer and preserve battery life. Decrease these settings (shortening the time) to support
streaming-multicast audio and video applications that are jitter-sensitive. The default value is 100
milliseconds.
DTIM Interval Set a DTIM Interval to specify a period for Delivery Traffic Indication Messages (DTIM). A DTIM is
periodically included in a beacon frame transmitted from adopted radios. The DTIM indicates broadcast
and multicast frames (buffered at the Access Point) are soon to arrive. These are simple data frames
that require no acknowledgement, so nodes sometimes miss them. Increase the DTIM/ beacon
settings (lengthening the time) to let nodes sleep longer and preserve their battery life. Decrease these
settings (shortening the time) to support streaming multicast audio and video applications that are
jitter-sensitive.
RTS Threshold Specify a Request To Send (RTS) threshold (between 1 - 2,347 bytes) for use by the WLAN's adopted
Access Point radios. RTS is a transmitting station's signal that requests a Clear To Send (CTS) response
from a receiving client. This RTS/CTS procedure clears the air where clients are contending for
transmission time. Benefits include fewer data collisions and better communication with nodes that are
hard to find (or hidden) because of other active nodes in the transmission path.
Control RTS/CTS by setting an RTS threshold. This setting initiates an RTS/CTS exchange for data
frames larger than the threshold, and sends (without RTS/CTS) any data frames smaller than the
threshold.
Consider the trade-offs when setting an appropriate RTS threshold for the WLAN's Access Point radios.
A lower RTS threshold causes more frequent RTS/CTS exchanges. This consumes more bandwidth
because of additional latency (RTS/CTS exchanges) before transmissions can commence. A
disadvantage is the reduction in data-frame throughput. An advantage is quicker system recovery from
electromagnetic interference and data collisions. Environments with more wireless traffic and
contention for transmission make the best use of a lower RTS threshold.
A higher RTS threshold minimizes RTS/CTS exchanges, consuming less bandwidth for data
transmissions. A disadvantage is less help to nodes that encounter interference and collisions. An
advantage is faster data-frame throughput. Environments with less wireless traffic and contention for
transmission make the best use of a higher RTS threshold.
Short Preamble If using an 802.11bg radio, select this option to transmit using a short preamble. Short preambles
improve throughput. However, some devices (SpectraLink/Polycomm phones) require long preambles.
The default value is disabled.
Guard Interval Use the drop-down menu to specify a Long or Any guard interval. The guard interval is the space
between characters being transmitted. The guard interval eliminates inter-symbol interference (ISI). ISI
occurs when echoes or reflections from one character interfere with another character. Adding time
between transmissions allows echo's and reflections to settle before the next character is transmitted.
A shorter guard interval results in shorter character times which reduces overhead and increases data
rates by up to 10%. The default value is Long.
Probe Response Rate Use the drop-down menu to specify the data rate used for the transmission of probe responses. Options
include, highest-basic, lowest-basic and follow-probe-request (default setting).
Probe Response Retry Select this option to retry probe responses if they are not acknowledged by the target wireless client.
The default value is enabled.