D-Link DPH-150S - Manual (Page 30)

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UPnP Enable or disable universal plug and play. Some NAT supports UPnP so STUN
is not required and must be disabled
Always send keep-alive
packet
Enable or disable to keep the SIP signaling channel alive.
Keep-Alive Time
The time interval that the IP phone always sends the keep-alive packet in order
to ensure that NAT is working properly.
6.12. Network – NAT
NAT mode can be set to ROUTE Mode or Bridge Mode.