[asterisk-users] Proper way to make Asterisk recognize SIP trunk of incoming INVITE when IP is not available

Alex Villací­s Lasso a_villacis at palosanto.com
Fri Apr 25 18:47:44 CDT 2014

El 25/04/14 18:29, Alex Villací­s Lasso escribió:
> I am currently preparing a kamailio-asterisk combination. The asterisk installation uses realtime for SIP. The kamailio configuration was based on the reference at http://kb.asipto.com/asterisk:realtime:kamailio-4.0.x-asterisk-11.3.0-astdb but has been 
> heavily modified. Currently asterisk runs on localhost and only listens on SIP/RTP at . Therefore, all of the SIP traffic appears to come from localhost, from the point of view of asterisk.
> Currently I have a model on which internal SIP phones get identified by the authentication username, and then the contact names at From: and To: get massaged to incorporate the SIP domain, in order to emulate multiple-domain support. The 'sip' table in 
> Asterisk defines all such contacts as SIP accounts of the form name_domain.com, and the SIP phones are configured to use 'name' as authentication username for domain 'domain.com'. However, SIP providers that register on the server with authentication 
> names are left with their original names, since in the model, SIP trunks are available to all domains.
> Now I have to add support for SIP providers which are to be authorized on the basis of IP only. Apparently, the kamailio module permissions.so (WITH_IPAUTH) is made for just this purpose, so I enabled it. After authentication, I need to route the INVITE 
> to asterisk, and asterisk must somehow match the account for the SIP trunk from the available information on the INVITE request.
> A typical INVITE for this scenario looks like this, before being processed by kamailio:
> INVITE sip:6008010 at;transport=udp;user=phone SIP/2.0
> Via: SIP/2.0/UDP;branch=z9hG4bK+676ea13f680e853fd847230512a347561+32e3da76+1
> Call-ID: FBE75B3A at 32e3da76
> From: <sip:042294440 at;user=phone>;tag=32e3da76+1+544c000c+52be771c
> To: <sip:6008010 at;user=phone>
> CSeq: 975469826 INVITE
> Expires: 180
> Organization: SetelGYE
> Min-SE: 90
> Session-Expires: 18000
> Supported: replaces, 100rel, timer
> Contact: <sip:042294440 at;transport=udp;user=phone>
> Content-Length: 149
> Content-Type: application/sdp
> Max-Forwards: 70
> v=0
> o=- 0 0 IN IP4
> s=-
> c=IN IP4
> t=0 0
> m=audio 5388 RTP/AVP 8 101
> a=rtpmap:101 telephone-event/8000
> a=fmtp:101 0-15
> Here, 6008010 is the phone number that was dialed at the provider in order to reach my system, and 042294440 is the provider-supplied Caller-ID, which I want to preserve all the way to Asterisk. In particular, 042294440 appears as the value that ends up 
> as $fU (From: username) while being processed in kamailio. If I pass the SIP packet as-is to asterisk, asterisk first tries to match by the value of $fU, which obviously fails to match the trunk name. It then tries to match by incoming IP, which also 
> fails because asterisk received this packet from . Finally, asterisk sort of matches to the first record in the sip table, which is *not* the SIP account for this trunk, but some other random account.
> I have a partial solution that uses sqlops to make a query to the sip table, using the $si (source IP) and reads the trunk name in order to replace $fU. This works, as now $fU will have the trunk name and asterisk will now recognize the intended SIP 
> account for the trunk. However, this has the unfortunate side effect of throwing out the Caller-ID information.
> What is the standard/proper way to deal with this situation? Is there a well-known way to make Asterisk match the trunk name, without overwriting the Caller-ID information? Before you ask, requesting the provider to modify its INVITEs is not an option. I 
> believe there is a standard way to deal with this, since this scenario should also arise with a kamailio that faces the internet, and relays INVITEs (after authentication) to an asterisk in a local network. As far as I can tell, the fact that in my case 
> the 'local network' is localhost should be irrelevant.
If I manage to coax Kamailio to add a (synthetized) P-Asserted-Identity header to the INVITE request before sending it to Asterisk, will Asterisk be able to use it? Will this information show up on a CDR?
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