D-Link DIR-808L User Manual page 86

Section 3 - Configuration
IPSec (VPN): Allows multiple VPN clients to connect to their corporate network using IPSec. Some VPN clients support traversal of IPSec through
NAT. This ALG may interfere with the operation of such VPN clients. If you are having trouble connecting with your corporate network,
try turning this ALG off. Check with the system administrator of your corporate network whether your VPN client supports
NAT traversal.
RTSP: Allows application that uses Real Time Streaming Protocol to receive streaming media from the Internet. QuickTime and Real Player
are some of the common applications using this protocol.
SIP:
Allows devices and applications using VoIP (Voice over IP) to communicate across NAT. Some VoIP applications and devices have
the ability to discover NAT devices and work around them. This function may interfere with the operation of such devices. If you
are having trouble making VoIP calls, try turning this option off.
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