D-Link DPH-300S User Manual page 43

Making a Call
7. No audio in call
Port forward the appropriate ports to the phone. The phone needs ports 1720 (TCP) and ports 15328-15333 (TCP and UDP) open to
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function properly. See the section Opening Ports on Routers and Gateways on page 58, or consult your router's documentation or your
network administrator for help on doing this.
D-Link DPH-300S User Manual 43