Check Point UTM-1 Edge - Page 318

Troubleshooting Wireless Connectivity
304 Check Point UTM-1 Edge User Guide
There are excessive collisions between wireless stations. What should I do?
If you have many concurrently active wireless stations, there may be collisions between
them. Such collisions may be the result of a "hidden node" problem: not all of the stations
are within range of each other, and therefore are "hidden" from one another. For example,
if station A and station C do not detect each other, but both stations detect and are detected
by station B, then both station A and C may attempt to send packets to station B
simultaneously. In this case, the packets will collide, and Station B will receive corrupted
data.
The solution to this problem lies in the use of the RTS protocol. Before sending a certain
size IP packet, a station sends an RTS (Request To Send) packet. If the recipient is not
currently receiving packets from another source, it sends back a CTS (Clear To Send)
packet, indicating that the station can send the IP packet. Try setting the RTS Threshold
parameter in the wireless network's advanced settings to a lower value. This will cause
stations to use RTS for smaller IP packets, thus decreasing the likeliness of collisions.
In addition, try setting the Fragmentation Threshold parameter in the wireless network's
advanced settings to a lower value. This will cause stations to fragment IP packets of a
certain size into smaller packets, thereby reducing the likeliness of collisions and
increasing network speed.
Note: Reducing the RTS Threshold and the Fragmentation Threshold too much can
have a negative impact on performance.
Note: Setting an RTS Threshold value equal to the Fragmentation Threshold value
effectively disables RTS.
I am not getting the full speed. What should I do?
• The actual speed is always less then the theoretical speed, and degrades with
distance.
• Read the section about reception problems. Better reception means better speed.
• Check that all your wireless stations support the wireless standard you are using
(802.11g or 802.11g Super), and that this standard is enabled in the station
software. Transmission speed is determined by the slowest station associated
with the access point. For a list of wireless stations that support 802.11g Super,
see www.super-ag.com.