Configuring Control Frame Protection - Juniper NETWORK AND SECURITY MANAGER 2010.4 - CONFIGURING SCREENOS DEVICES GUIDE REV 01 Manual

Configuring Control Frame Protection

Copyright © 2010, Juniper Networks, Inc.
the device sends wireless packets in bursts to clients, who can switch to a low-power
sleep state between bursts. The default value is 3 frames; acceptable range is 2 to 255
frames.
Fragmentation Threshold—The fragmentation threshold defines the maximum size
of a packet that can be transmitted without fragmentation. If the packet size exceeds
the specified threshold, the sender (client or WAP) must fragment the packet before
transmitting.
Using a high fragmentation threshold reduces the number of fragments on the wireless
network, which can increase efficiency. However, large, unfragmented packets can be
corrupted during transmission, requiring resend attempts that can decrease efficiency.
The default value is 2346; acceptable range is even numbers between 256 and 2346.
Control frame protection is designed to help avoid collisions on the wireless network.
Transmission collision usually occurs when two wireless devices are within range of the
same WAP, but are not within range of each other (they are hidden nodes). If two wireless
transmissions collide at the WAP, the data in each transmission is lost.
To avoid collisions, you can require wireless clients to first request permission to send
data (clients must send a request-to-send (RTS) frame) and/or receive approval of that
request (client must receive a clear-to-send (CTS) frame) before transmitting data.
Because 802.11b stations cannot hear 802.11g stations using orthogonal frequency-division
multiplexing (OFDM), a method for wireless transmission that divides a signal and
transmits the pieces at different frequencies simultaneously, traffic from these stations
can collide on the network, reducing network efficiency. We recommend you enable
protection to avoid collisions when supporting 802.11b and 802.11g operation modes.
NOTE: CTS protection is not supported when using 802.11b only.
To configure the control frame protection settings:
In the NSM navigation tree, select Device Manager > Devices. Double-click the device
1.
object to open the device configuration.
In the device navigation tree, select Wireless Settings > Advanced, and then edit the
2.
default values for the following settings:
Threshold for RTS to Transmit—The request-to-send (RTS) threshold defines the
maximum size of a packet that a wireless client can send without obtaining permission
from the WAP. If a packet exceeds this threshold, the client must send an RTS message
to the WAP requesting permission to send the packet. You might want to adjust this
setting to control traffic flow through an access point that services a large number of
clients. The default is 2346; accepted range is 256 to 2346.
CTS Protection Mode—Enables clear-to-send (CTS) control frame protection, which
requires wireless client to first receive a CTS frame from the WAP before sending data.
Select one of the following protection modes:
Chapter 14: WAN, ADSL, Dial, and Wireless
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