[SR-Users] Third party registration help

Mon May 9 08:18:25 CEST 2016

Hello,

I haven't analyzed your message too much now -- just wanted to ask if
you looked at uac module for uacreg feature and if that is suiting or
not your needs?

Cheers,
Daniel

On 05/05/16 14:40, Code Developer wrote:
> Hello,
>
> I'm after some help on third-party SIP registration in Kamailio -
> specifically, how to perform registration of user agents that don't
> register themselves, but only send out occasional messages. The
> UAs not registering themselves are devices on a GSM network that try
> to save band-width by not sending REGISTER requests for themselves.
> They only ever send out SIP messages when necessary, to which they
> expect a reply message from our processing server.
>
> (Note, details like external IP addresses have been changed for security.)
>
> The configuration is as follows. We have a SIP server running Kamailio
> (4.3, location db enabled, nathelper enabled) on a static external IP
> address (50.170.158.149), a processing server on an internal network
> registered with the SIP server (let's say with a User agent name of
> '1000'), and a monitoring device in another part of the country
> connected to the internet via a GSM network (let's say User agent name
> of '2000'). The device is effectively NAT'd on the GSM provider's
> private network.
>
> At some point the device (UA 2000) sends a SIP message to the
> processing server via Kamailio (to sip:1000 at 50.170.158.149). The
> processing server is registered, so the SIP server knows where it is
> and forwards the message accordingly. 200/OK replies propagate back
> successfully to the device.
>
> The message flow appear as below. Only relevant header fields are shown:
>
> Message received by the SIP server from remote device:
> ========
> IP Src:60.250.149.198, Dst:50.170.158.149
> UDP Src Port: 59177, Dst Port: 5060
> --
> Request-Line: MESSAGE sip:1000 at 50.170.158.149
> Via: SIP/2.0/UDP 10.92.240.131:5060;branch=z9hG4bK...
> To: <sip:1000 at 50.170.158.149>
> From: <sip:2000 at 10.92.240.131>;tag=7a82c48a
> ========
>
>
> Message forwarded from SIP server, received by processing server as shown:
> ========
> IP Src:50.170.158.149, Dst: 192.168.0.235
> UDP Src Port:5060, Dst Port:5060
> --
> Request-Line: MESSAGE sip:1000 at 50.170.158.146:5060; ob SIP/2.0
> Via: SIP/2.0/UDP 50.170.158.149;branch=z9hG...
> Via: SIP/2.0/UDP
> 10.92.240.131:5060;rport=59177;received=60.250.149.198;branch=z9hG...
> To: <sip:1000 at 50.170.158.149>
> From: <sip:2000 at 10.92.240.131>;tag=7a82c48a
> ========
>
>
> The processing server now needs to send back a reply message to the
> remote, unregistered device which is NATd on the GSM internal network.
> We can do this by sending back a reply to the external IP address and
> rport values found in the second Via header of the message received by
> the processing server (60.250.149.198, port 59177). The reply can only
> be sent from the SIP server or the GSM network's router will ignore it
> - it's only a temporary reply address/port open for a minute or so as
> it's effectively just a NAT route to the internet.
>
> In the first instance, when the processing server attempts to send
> back a message to the remote device via the SIP server, the SIP server
> replies with a 404 as the remote device hasn't registered and the SIP
> server has no idea where to send it.
>
> After looking at RFC3261 my conclusion was that we must get the
> processing server to perform a third-party registration on behalf of
> the remote device before we can send a reply message back to that device.
>
> My understanding is that to perform the third party registration I
> should send a REGISTER request from our processing server to the SIP
> server:
> 1) Set the 'From' field to the AOR of the UA performing the
> registration (which is the processing server, 1000).
> 2) Set the 'To' field to the AOR of the UA being registered (i.e. the
> remote device, 2000).
> 3) Add a 'Contact' header field set to the IP address and port of the
> remote device (from Via = 60.250.149.198 port 59177).
>
>
> The message flow for the register is as follows (only relevant header
> fields shown):
>
> Processing server sends a register request to the SIP Server:
> ========
> Request-Line: REGISTER sip:50.170.158.149 SIP/2.0
> Via: SIP/2.0/UDP 192.168.0.235:5060;rport;branch=z9hG...
> From: <sip:1000 at 50.170.158.149>;tag=e6e2d70...
> To: <sip:2000 at 50.170.158.149>
> Contact: <sip:2000 at 60.250.149.198:59177>
> ========
>
> SIP server responds to the processing server with a 401 unauthorized
> response containing the auth header field (nonce challenge):
> ========
> WWW-Authenticate: Digest realm="50.170.158.149",
> nonce="VytkJ1crIvu4ekGp/M4mnRlYmJRciF3N"
> ========
>
> Processing server sends a revised register request to the SIP Server,
> augmented with the authorisation header for the supplied nonce:
> ========
> Request-Line: REGISTER sip:50.170.158.149 SIP/2.0
> Via: SIP/2.0/UDP 50.170.158.146:1096; rport;branch=z9hG4...
> From: <sip:1000 at 50.170.158.149>;tag=dae68a...
> To: <sip:2000 at 50.170.158.149>
> Contact: <sip:2000 at 60.250.149.198:59177>
> Authorization: Digest username="1000", realm="50.170.158.149",
> nonce="VytkJ1crIvu4ekGp/M4mnRlYmJRciF3N" response="d4d7ffba8..."
> ========
>
> However, the SIP Server again responds with a 401 and won't perform
> the third-party registration. I haven't been able to determine why. I
> *think* the response hash the processing server is sending back is
> correct. I'm using PJSIP on our processing server to perform all SIP
> functionality. The processing server does obviously register
> itself, the difference being that the To and From fields are the same
> (<sip:1000 at 50.170.158.149>) and there is no Contact  header.
>
> I'm at the point now of being unable to find any information or
> examples on how third-party registration requests should be performed
> - apart from RFC3261, which doesn't really describe the process very well.
>
> Can anyone tell me why the third-party registration would fail,
> despite replying with the authorisation header? Does Kamailio first
> need to be configured to allow third-party reg somehow? Alternatively,
> should I be attempting to send back SIP messages to unregistered
> devices in some other fashion?
>
> I hope someone can help or point me in the right direction.
>
> As an aside, when the device (UA2000) is plugged into a network via
> ethernet, it does then perform its own registration and everything
> works - messages go back and forth without issue.
>
>
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-- 
Daniel-Constantin Mierla
http://www.asipto.com
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda
Kamailio World Conference, Berlin, May 18-20, 2016 - http://www.kamailioworld.com

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