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Building Telephony Systems with OpenSIPS - Second Edition by Bogdan-Andrei Iancu, Flavio E. Goncalves

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Building the solution

The solution for NAT is a little complex and requires several steps. We will split the solution into three pieces and a few steps for each segment in order to simplify the understanding:

  1. Installing STUN
  2. Solving the SIP signaling
  3. Using a media relay server
  4. Engaging a media relay server

Installing STUN

Simple traversal of UDP over NAT, or simply STUN, is the most common method for near-end NAT traversal. The IETF standardized STUN in three RFCs: 3489, 5389, and 7350. STUN is a near-end NAT traversal solution. STUN's biggest advantage is to fix addresses in the client side. Clients using STUN appear to the proxy as a client using a valid IP address. You do not require any extra configuration on the server. On the other hand, STUN ...

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