IV. Voice-over-IP (VoIP)

SIP ALG on DrayTek Routers

Vigor 2620Ln
Vigor 2760
Vigor 2762
Vigor 2763
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Application Layer Gateway
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SIP ALG usage on DrayTek Routers

DrayTek routers have a SIP ALG (Application Layer Gateway) to help SIP route the audio through NAT, this is Disabled by default and can be enabled by following the steps shown in this guide.

The SIP ALG facility is able to modify SIP packets that it identifies and modifies the IP address details in the SIP header information. Without SIP ALG, the SIP header information would contain the private IP address of the VoIP client / phone, which could stop audio from being routed correctly by the remote side of the call. The router modifies the packet to contain the public IP address of the router so that the remote side sends audio to the router's public IP address which is then passed through NAT to the client.

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In the [NAT] > [ALG] menu, the router's SIP and RTSP (not RTP) ALG services can be enabled.

Enabling the SIP Protocol option and clicking OK will enable the router's SIP ALG facility.

Change the Listen Port from the default of 5060 will change the port that the router will monitor for SIP packets to modify, for instance if your SIP provider or hosted PBX uses port 5070 instead, specify it here.

The TCP and UDP options control the protocols that the SIP-ALG will monitor.

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