[pjsip] choosing an IP address -regarding

Benny Prijono bennylp at pjsip.org
Fri May 9 06:48:52 EDT 2008


I think probably you have been going on the wrong route there. In both
SIP and media transports, there are two IP address settings:
  - IP address used as the transport name (to be published in SIP
messages or SDP)
  - the bound IP address

You have been addressing the former setting, while I think the
appropriate one is the later. If you change the bound IP address, then
the transport name will automatically use that address. No need to
change source code at all. While if you only change the former (that's
what you did), then the transport will still be bound to INADDR_ANY,
so the OS will chose whatever interface it sees appropriate to send
the packet.


On Fri, May 9, 2008 at 1:03 AM, Knight Tiger <caugar at gmail.com> wrote:
> Hi,
> I am using PJSIP on a Windows Mobile device. (I am using version 0.5.3) .
> This device has Wi-Fi and a 3G connection. When I connect through only one
> network (either 3G or Wifi), I am able to register with my SIP server. (a
> vanilla Asterisk box on the public network).
> I want to be able to configure such that, for SIP messages it must go
> through 3G and for RTP/media it must go through Wifi (when both interfaces
> are available). I am experimenting with a media stack that is not PJMEDIA.I
> am able to assign the WiFi interface IP address for RTP traffic. But for
> SIP, I see the following call in many places in the code.
> status = pj_gethostip(pj_in_addr in_addr);
> This function gets the IP address on the default interface (it checks for
> and if nothing comes up, it returns . As kludgy as it
> sounds, I went and modified everywhere this function is called and checked
> to see if I had a 3G connection, use that IP instead.
> in_addr.s_addr = inet_addr(char *cellular_ip_string);
> My Wifi has a public IP address ( and the 3G provider assigns
> a private IP (10.something)
> I tried to register with the Asterisk server (with both interfaces active on
> my device). The phone registers but it uses the WiFi interface IP address. I
> inspected the packet and I shall reproduce the REGISTER message observed on
> the Asterisk server.
> Internet Protocol, Src: (, Dst:
> (
>  User Datagram Protocol, Src Port: 5060 (5060), Dst Port: 5060 (5060)
> Session Initiation Protocol
>     Request-Line: REGISTER sip:myvoipserver:5060 SIP/2.0
>     Message Header
>         Via: SIP/2.0/UDP
>          Max-Forwards: 70
>         From: <sip:1001 at myvoipserver>;tag=42710002ec722c6d1d79
>         To: <sip:1001 at myvoipserver>
>         Call-ID: 42710001ec722c6d1d79
>         CSeq: 38210 REGISTER
>             Sequence Number: 38210
>              Method: REGISTER
>         User-Agent: pjsua/1.0
>         Contact: <sip:;transport=UDP>
>         Expires: 600
>         Content-Length: 0
> As you can observe, my 3G IP address is seen in the Via and contact headers
> while my Wifi IP address is seen on the IP header. I dont understand where
> did the SIP stack get this IP address from ? The entire SIP message uses the
> 3G connection IP address. In fact, I checked within the code and I find that
> wherever in_addr is used, it uses the 3G IP address.
> Can anyone shed some light as to why this happens ? Is there a place where I
> had neglected to change the IP address setting ?
> Thanks in advance,
> Regards
> Knight

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