[Freeswitch-users] Rewriting media address in SDP as well as contact IP/port

Kristian Kielhofner kris at kriskinc.com
Wed Nov 21 07:49:52 MSK 2012

You can rewrite the SDP to anything you want but that doesn't mean
you'll get media.

I suggest you do some research on the two main schools for SIP NAT
traversal (far end and near end).  In a nutshell, far end NAT
traversal is implemented by the server.  This is the FreeSWITCH
default.  The SDPs are rewritten to the address of the FreeSWITCH
server and passed to the remote endpoint.  This causes the media to be
relayed at the server between the endpoints.  This has the advantage
of being universally compatible - regardless of how dumb the
endpoint(s) is/are.  Disadvantages are many - increased sever load,
bandwidth, latency, etc.  However, with many endpoints this is the
only choice.

Near end NAT traversal relies on advances technologies such as STUN,
TURN, and ICE to be supported by the client (and the servers to enable
them configured and available).  TURN actually blurs the lines between
these two strategies, as do various hybrid approaches using local
proxies, etc but that's for another day.

Bypass media is incompatible with NAT unless you're using
STUN/TURN/ICE in your clients and even then I'm not sure FreeSWITCH
will completely and cleanly handle the various ICE/SIP/SDP

On Tue, Nov 20, 2012 at 3:35 PM, PhilQ <philq at qsystemsengineering.com> wrote:
> We're running in bypass media mode with aggressive-nat-detection enabled.  FS
> handles the signaling but passes the internal 10.x.x.x addresses for media
> along unchanged, even between different sites.
> Any recommendations for SIP proxies if FS can't do it automatically?
> Rewriting the SDP from the dialplan might be worth looking into depending
> upon how it's implemented.
> Thanks for the info.
> - Phil
> --
> View this message in context: http://freeswitch-users.2379917.n2.nabble.com/Rewriting-media-address-in-SDP-as-well-as-contact-IP-port-tp7584712p7584773.html
> Sent from the freeswitch-users mailing list archive at Nabble.com.
> _________________________________________________________________________
> Professional FreeSWITCH Consulting Services:
> consulting at freeswitch.org
> http://www.freeswitchsolutions.com
> Official FreeSWITCH Sites
> http://www.freeswitch.org
> http://wiki.freeswitch.org
> http://www.cluecon.com
> FreeSWITCH-users mailing list
> FreeSWITCH-users at lists.freeswitch.org
> http://lists.freeswitch.org/mailman/listinfo/freeswitch-users
> UNSUBSCRIBE:http://lists.freeswitch.org/mailman/options/freeswitch-users
> http://www.freeswitch.org

Kristian Kielhofner

Join us at ClueCon 2011 Aug 9-11, 2011
More information about the FreeSWITCH-users mailing list