Interconnecting with - The Basics

This is a set of basic networking requirements and terminologies for connecting to


SIP.TRUNK has two SIP Gateways which you may connect to:

  • Both gateways will only accept SIP traffic on UDP port 5060


Audio related to SIP calls is delivered via RTP over UDP. Since our SIP gateways are just a proxy, the audio can be delivered from various IP addresses and many different ports. 


NAT stands for Network Address Translation. Most customers are behind some form of NAT, and many do not have a static IP address. Try to connect your PBX or softphone through our service without any special NAT configuration. If it becomes apparent that you may be having a NAT issue, there are three possible solutions:

STUN: if your PBX or softphone supports it, you may connect to our STUN server at on port 3478

ALG: If your router or firewall is capable of properly implementing ALG, enabling it may alleviate your issue

STATIC IP: your internet service provider (ISP) may provide a static IP at an additional cost


Network security can be a consideration when implementing a VoIP solution. Here are some basic tips:

1. You should allow incoming SIP traffic from:

  • Individual IPs and and Subnets and 
  • If you cannot allow subnets, then allow individual IPs,, and

2. You should forward all RTP ports used by your device to the private IP address of your device if it is behind NAT

3. Your SIP device should only accept RTP traffic for a SIP call which is active, so the forwarding in tip 2, above, should not be accompanied with blocking traffic from certain IP addresses (see here for an extended explanation).

4. If your device is accessible from the internet, choose a strong password, or preferably, consider disallowing anyone from logging in through the internet

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  • Avatar
    Clayton McKinney

    are those IP addresses correct?  we show gw1 resolving differently

  • Avatar
    David Dickson

    is there, (
    this keeps popping up in the firewall log

  • Avatar
    hh h

    caul es el numero asignado?

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