D-Link DIR-822 User Manual page 58

Section 4 - 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 Application Level Gateway (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. Please check
with the system administrator of your corporate network whether
your VPN client supports NAT traversal.
RTSP:
Allows applications that uses Real Time Streaming Protocol (RTSP)
to receive streaming media from the Internet.
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 ALG
may interfere with the operation of such devices. If you are having
trouble making VoIP calls, try turning this ALG off.
Click Save when you are done.
D-Link DIR-822 User Manual 54