3Com WL-550 User Manual page 71

Firewall 69
DMZ If you have a client PC that cannot run an Internet application properly
from behind the firewall, you can open the client up to unrestricted
two-way Internet access. This may be necessary if the NAT feature is
causing problems with an application such as a game or video
conferencing application.
Figure 48 DMZ Screen
Enter the IP address of a DMZ (Demilitarized Zone) host on this screen.
Adding a client to the DMZ may expose your local network to a variety of
security risks, so only use this option as a last resort