[SR-Users] Question about relaying

[Henning Westerholt]

Am Freitag, 3. Mai 2013, 16:13:36 schrieb Leo Brown:
> [..]
>   MVNO Carrier  -->  Our Edge Switch  -->  Our PSTN Switch  -->  Our
> carrier's switch
>                                                  |--->  Our internal routing
>                                                  |switch
> 
> The issue is with our PSTN switch and the fact that it is not staying in the
> SIP signalling path, so when the call ultimately between our MVNO carrier
> and outbound Carrier is established (200 OK) the MVNO carrier and PSTN
> carrier begin talking to each other.
> 
> When the MVNO carrier issues a BYE to the outbound carrier, the outbound
> carrier does not then receive this packet as they are firewalled (and
> always will be).
> 
> What is the correct method of relaying calls through Kamailio but not
> passing on the Contact: header info? I have read that forcing a change of
> Contact is not the right way.

Hello,

if you want to ensure that your kamailio stays on the path of the dialog for 
following requests you probably want to use record-route headers for this. 
This is usally done with the rr module, record_route() function.

To quote from iptel.org:

"[A] Mechanism by which a proxy can inform user agents that it wishes to stay 
on the path of all further messages is called record routing. Such a proxy 
would insert Record-Route header field into SIP messages which contain address 
of the proxy. Messages sent within a dialog will then traverse all SIP proxies 
that put a Record-Route header field into the message.

The recipient of the request receives a set of Record-Route header fields in 
the message. It must mirror all the Record-Route header fields into responses 
because the originator of the request also needs to know the set of proxies."

Best regards,

Henning Westerholt