Sniffing with Wireshark I can see that an inbound INVITE from our PSTN sip trunk contains a history-info header, but this header is not forwarded to our endpoint application server where I want to pick it up.
The sip logs on the mediation server does not show the history-info header, so it seems that the Lync 2015 mediation server is tampering with the INVITE requests from the PSTN trunk even before it is logging inbound sip messages.
I have read that Lync 2013 does not support inbound history-info headers, Reference: History-info Inbound is not supported, but am hoping that this does not hold true for 2015.
Is it possible to configure Lync 2015 to forward the history-info header from inbound invites or are they not supported at all?
It seems that the history-info header is only supported in one direction, outbound to PSTN. This is documented here Lync Server 2013: Headers for SIP Trunking.
On page 6 we read • History-info Inbound is not supported. The Mediation Server will not forward any received History-Info headers