R: [Serusers] SER with 2 ethernet + PSTN gateway: RTPPROXY bridge mode conf

Fabio Macchi f.macchi at keeptelecom.com
Thu Jul 13 17:32:32 CEST 2006

Greger, thanks for you answer, it helped to place order in my confused


About the bug you mentionated,  has it been fixed in the cvs stable branch (
rel_0_8_14 , currently I have upgraded to this release ) or I have to
install the main unstable branch ?


I’ve sniffed a call from the SER interface connected to the GW: it appears
that the entire SIP negotiation on this side ( I mean source IP address of
UDP packet ) is between the GW ip ( x.x.x.243 ) and the SER IP assigned to
the other interface ( ) but, if I’m not wrong, I expected a SER UDP
source address x.x.x.246 .  Is this the problem ?  May it depends from the
mentionated bug ?


After successfully SIP negotiation, I see RTP packet from GW -> rtpProxy  (
x.x.x.244 -> x.x.x.246 ) and from client -> rtpproxy ( ->
), but rtpproxy is not bridging packets between the two interfaces.


Another question: is there any documentation about the use of
force_rtp_proxy options more complete then nathelper README ?

That document only mentionate force_rtp_proxy("FI") and
force_rtp_proxy("FE") ( hope this is correct in this case ), but in many
example I see force_rtp_proxy("FII") or force_rtp_proxy("FIE") and I don’t
understand the double option.


Many thanks again





Da: Greger V. Teigre [mailto:greger at teigre.com] 
Inviato: mercoledì 12 luglio 2006 8.46
A: Fabio Macchi
Cc: serusers at iptel.org
Oggetto: Re: [Serusers] SER with 2 ethernet + PSTN gateway: RTPPROXY bridge
mode conf


That's a tricky one :-) A few comments:
- I believe bridge mode is necessary and thus rtpproxy is what you need
(mediaproxy does not have this capability AFAIK)
- rtpproxy just waits for the peers to connect, it does not connect rtp to
anything, so if you see traffic from the wrong pstn interface, I would look
at GW
- Just inspect your INVITE and OK SDP to get the options straight: The one
going to your 10. network should have the 10.address in SDP, the one to your
GW, should have your .246 address
- Please note that 0.9.x has a bug (fixed in cvs head). The problem is
related to signalling on different listen ports/interfaces: If SER is
configured to listen to more than one port, the signalling may not return
with the correct src_ip/port (UDP packet, not SIP message). I'm not sure if
this holds for listening on different interfaces as well, but I would think


Fabio Macchi wrote: 



I’m using SER with nathelper and rtpproxy as a proxy to guard a PSTN gateway
( calls can only be generated by SIP client and terminated to PSTN, no SIP
to SIP or PSTN to SIP calls allowed, REGISTER is not needed ).


PSTN gateway and SER eth0 have pubblic internet IP address ( SER eth0
x.x.x.246,  PSTN gateway with two interfaces, x.x.x.243 for SIP and
x.x.x.244 for RTP ), SER is setted to force rtpproxy for every call and
rtpproxy is started in standard mode: this is running fine, every client
from internet ( behind a NAT box or not ) is able to place calls.


Now the problem is that I need to collect SIP traffic from another non
routable network to the PSTN gateway ( es. )  


I have connected SER interface eth1 to this network ( ip ) and I am
trying to connect to the PSTN from a client in the network SIP
signaling seems to be ok, but I’m unable to setup RTP stream.

With this configuration it appears that RTPproxy try to connect to PSTN
gateway on x.x.x.243 and not x.x.x.244.


I have tryied to set RTP proxy in bridge mode ( rtpproxy -l
x.x.x.246/ ) without succes, but documentation is not very clear
about this case (I think it has been designed for client to client, not
client to PSTNgateway ).




if (dst_ip == x.x.x.246) {         #!! Internet IP address




          } else if (dst_ip == {  #!! Private IP address








Now the question is: what is the correct design to implement this ?


RTPproxy in standard mode ?

RTPproxy in bridge mode ? ( how ??? )

Mediaproxy ?



Any help would be appreciated, many thanks in advance.






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