[SR-Users] Handling Cancel with rewritten To: and From: headers

Hi, I have a kamailio 3.1.0 system. I am using mostly the kamailio.cfg script that came with that release but I've made a couple of changes - The pstn.gw_ip bit doesn't work - syntax error - so I've substituted fixed text for now - I've expanded the PSTN section to IN_PSTN and OUT_PSTN to handle outgoing PSTN calls and route PSTN incoming calls to the correct phones. - As (strange) requirement of my SIP trunk provider I've had to rewrite the To: and From: headers on new outgoing PSTN calls The issue I have is with CANCEL. I'm using the default CANCEL handling stanza in kamailio.cfg # CANCEL processing if ( is_method ( "CANCEL" ) ) { if ( t_check_trans() ) t_relay(); exit; } What I see in wireshark is that the From: header is the same as my rewritten version, but the To: header is as provided by the UA This doesn't cause any real problems but I'd like to know what the rules are for kamailio rewriting a CANCEL message - and if required - whether I can rewrite a header in the CANCEL section and not have it 'adjusted' by the internal t_check_trans and t_relay logic? Thanks Jeremy