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To transmit audio from the Client's microphone behind NAT to the Server's or camera's loudspeaker, do the following:

1. On the Client, specify a unique port range and an external router's public IP address. Follow the steps below:
   1. Add an NGP_CLIENT_PORT_BASE environmental variable and set its value to the first port number in the range (see Appendix 9. Creating system variable).

   2. Add an NGP_CLIENT_PORT_SPAN environmental variable and set its value to the number of ports in the range.

      Note
      title Attention!
      We recommend you to use no less than 100 ports.

      
      

      Note
      title Attention!
      If you have multiple Clients within your network, their port ranges must not overlap.

      
      

   3. Add an NGP_ALT_ADDR environmental variable and set its value to the public IP address of the externa router.
2. Configure forwarding of the specified ports on both external and internal router.

Example:

To transmit audio from microphones connected to Client 1 and Client 2 to the Server's or camera's loudspeaker, do the following:

1. On Client 1, set port range to 20555-21554, and the public IP address of your Internet provider's router.
2. On Client 2, set port range to 21555-22554, and the public IP address of your Internet provider's router.
3. Configure port forwarding on the internal router:
   1. ports 20555-21554 to the internal IP address of Client 1 and ports 20555-21554;
   2. ports 21555-22554 to the internal IP address of Client 2 and ports 21555-22554.
4. Configure port forwarding on the provider's router:
   1. router ports 20555-21554 to the IP address of the internal router and ports 20555-21554;
   2. router ports 21555-22554 to the IP address of the internal router and ports 21555-22554.