[OpenSIPS-Users] Is NATHELPER module enough in my case? Help please.

Rodrigo Pimenta Carvalho pimenta at inatel.br
Wed Jan 6 13:02:56 CET 2016


Dear OpenSIPS-users,


First of all, happy new year.

I'm still reading about NATs, SIP proxies and SIP, to understand how to solve a question in my project. I'm not expert in TCP, IP, routers, NATs and networks. That is why I would like to get some help here.  I guess I'm almost getting the point to solve it.


In my current network topology case I have:



                                                                                                 Mobile Phone 1 on Internet

                                                                                                               / \                 |

                                                                                                                |                  |

                                                                                                                |      SIP     |

                                                                                                                |                  \/                 Real IP  (Internet)

                                                                                 NAT  ------------------------------------------------

                                                                                                                /\                 |                  'Nated' IP (Wan)

                                                                                                                |                  |

                                                                                                                |     SIP       |

                                                                                                                |                  |

                                                                                                                |                  |

                                                                                                                |                  \/

                                                                       ROUTER   ------------------------------------------------

                                                                                                                /\                 |                  (Lan)

                                                                                                                |       SIP     |

                                                                                                                |                  |

                                                                                                      SIP Proxy OPENSIPS

                                                                                                                |                  |

                                                                                                                |       SIP    |

                                                                                                                |                  |

                                                                                                Mobile Phone 2 on local network



When Phone 2 calls Phone 1, everything is ok. Phone 1 is registered on OpenSIPS with 'Nated' IP, by someway. So, Phone 2 sends INVITE to such IP. When Phone 1 answers with SIP OK, the Contact header filed has the same 'Nated' IP. Then, Phone 2 can send the ACK to the correct path.


However, when Phone 1 calls Phone 2 and Phone 2 answer with SIP OK, Phone 1 can't send the ACK, because  the Contact header field from SIP OK has the local IP for Phone 2.

It is true because when Phone 2 registers itself on OpenSIPS, the local IP is recorded in the local database table.


So I have the following questions:


1 - Can this problem be solved without using the Nat Traversal Module?


2 - Can NATHELPER module fix the Contact header field (as a I saw this module has functions related with it), when Phone 2 sends SIP OK to Phone 1?  If yes, how can such module determine a 'good' IP to put in this header field?


3 - If Phone 2 uses a stun server, will such phone be registered on OpenSIP with a real IP, won't be? Could it be a solution too?


Any hint will be very helpful!


Thanks a lot!







RODRIGO PIMENTA CARVALHO
Inatel Competence Center
Software
Ph: +55 35 3471 9200 RAMAL 979
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