Hello,

On 30.05.17 20:02, Phil Lavin wrote:

Hi all,

Theoretical question about the role of a Kamailio proxy which is also a registration server for UAs.

Assuming a B2BUA on IP 1.2.3.4 behind the Kamailio proxy. Kamailio receives an INVITE from this B2BUA with From and Contact as something like sip:4321@1.2.3.4

When Kamailio routes the INVITE to that UA, is it Kamailio’s responsibility to change the domain part of the From and/or Contact to itself (e.g. sip:4321@proxy.mytld.com)?

The question has arisen from Polycom missed call “call back” behaviour. When issuing a call back from a Polycom, following a missed call, it sends the call directly to the full URI in the INVITE’s From (or maybe Contact… I’ve not fully tested yet). As such the call is sent to the B2BUA, which UAs do not have access to, and thus times out.

I suspect here the answer is “no”, and the Polycom must be configured to force all outbound calls through the proxy… but thoughts welcome.

iirc, by specs, the proxy should not change the contact, many devices complain if they receive a R-URI with an address that was not set by them as contact in an earlier request.

In you case, very likely it is the From header that is used to dial back, being a common behaviour of SIP endpoints.

From header should not be changed either, but without doing it a lot of things don't work as expected by users. That's why we have uac_replace_from() exported by uac module.

Usually, all the nodes (proxy, b2bua, media servers, a.s.o.) in the core platform should use a domain instead of their IP address when constructing From/To headers, the domain pointing at the edge proxy, so any call back will end up there.

Cheers,
Daniel

-- 
Daniel-Constantin Mierla
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