[Freeswitch-users] New to Freeswitch - some help needed

Alan Chandler alan at chandlerfamily.org.uk
Fri Aug 7 01:18:35 PDT 2009

I apologize, as my first post to this list, that I ask a detailed set of 
questions, but I have spend some time looking at all the docs and can't 
get what I need to do completely sorted in my head.  I am definitely one 
who likes to UNDERSTAND what is happening rather than follow blank 
recipies, so please bear with me as I try understand all the details. I 
do understand about networking, NAT etc - but I am new to SIP/RTP and in 
particular what I think is a double NAT problem

Firstly - what am I trying to achieve:

I am in the UK and have a small home network behind a D-Link DIR-100 
Router/NAT/Firewall one of those machines, running Debian Lenny, acts as 
my main server for everything (and in an earlier incarnation was the 
firewall/router/nat box too - I only say this is because I had all this 
working using Asterisk a year or so ago, but with this important 
difference in configuration).  Many of the ports on the firewall are 
port forwarded to this machine. I have set Freeswitch up on this server 
to act as a small voip pbx for the home - but MORE IMPORTANTLY - to 
enable my daughter from her house to talk to us.  At my house locally I 
have a Linksys PAP2T two phone SIP box - and that is working with 
Freeswitch's default configuration (I set up to be 1000 and 1001 and 
used all the facilities).  I will later add a Linksys SPA 3102 - 
although I DO NOT intend to use its facility to bridge to the normal 
phone network.

My daughter, living in another house, also has a Nat box (unknown - its 
part of her ADSL modem/router/wireless access point) and also has a 
PAP2T which she will connect to the her network.  This will be her phone.

There is a family relation living in Australia who will load up a 
whatever softphone that we tell him to use.  I expect, but don't know, 
that he will behind a NAT box too.

Later, I have some friends in the USA that I might wish to add it too - 
especially so that we can hold some teleconferences.  They will have a 
mixture of Windows and MACs, and I will need to recommend softphone 
clients for them.

I want to set this up as a small private voice network, so anyone can 
ring anyone else.  I will add fancy facilities such as conferencing and 
voicemail later - I just want to get the basics working first.


I installed a stun client on my home machine and ran it against 

It reported:-

Primary: Independent Mapping, Independent Filter, preserves ports, no 

But I have no idea what this means - I can't find any clear statement 
via googling for it - how this set of answers maps to the different 
types of NAT that might be required to get this to all work.  CAN 


I have set up a sip profile called "double nat" from the recipe in the 
wiki.  This defines the SIP port to be 5090.

However, what I DO NOT UNDERSTAND is how the PAP2T box in my daughters 
house will initiate a connection to my server.  Presumably, I have to 
port forward 5090 from the nat box to my server.  IS THAT CORRECT?

I also assume I will have to tell her to use STUN (I believe this is an 
option on the PAP2T)


If I understand SIP correctly, it just initiates the session and the two 
end points then communicate directly via RTP.  What I don't understand 
is how does a session transition from SIP to RTP via the connection set 
up in the the first phase (in terms of passing through the NAT boxes). 
In particular WHICH OF THE TEST RESULTS from my stun client indicate it 
will do the right thing.  (I am going to take a laptop to my daughters 
house with a stun client in to test her network this weekend).

Could someone explain please.


Is there a recommended SIP softphone with all the right facilities (STUN 
support?)  that works on MAC and WINDOWS (I only use linux myself).

Apologies for the length of this.  I am eager to get the answers so I 
can use an opportunity this weekend to get it working.

Alan Chandler

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