D-Link DI-604 - Manual (Page 24)

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Some applications require multiple connections, such as Internet gaming,
video conferencing, Internet telephony and others. These applications
have difficulties working through NAT (Network Address Translation).
Special Applications makes some of these applications work with the
DI-604. If you need to run applications that require multiple connections,
specify the port normally associated with an application in the "Trigger
Port" field, select the protocol type as TCP or UDP, then enter the public
ports associated with the trigger port to open them for inbound traffic.
The DI-604 provides some predefined applications in the table on the
bottom of the web page. Select the application you want to use and
enable it.
Note! Only one PC can use each Special Application tunnel.
Trigger Name: This is the name referencing the special application.
Trigger Port: This is the port used to trigger the application. It can be
either a single port or a range of ports.
Trigger Type: This is the protocol used to trigger the special application.
Public Port: This is the port number on the WAN side that will be used to
access the application. You may define a single port or a range of ports.
You can use a comma to add multiple ports or a hyphen to add port
ranges.
Public Type: This is the protocol used for the special application.