[SR-Users] MetaSwitch ignores Contact: header

[Markus]

Dear list,

I'm running kamailio-4.2.3-3.1.x86_64 in a very simple setup: one 
Asterisk server behind kamailio. But I'm using dispatcher, the other 
servers are just down currently. :)

Different vendors route DIDs to kamailio's IP and kamailio handles the 
communication towards Asterisk.

Now I have a new vendor who uses MetaSwitch, and there is a problem. All 
calls get dropped with a BYE from the Asterisk side after 32 seconds 
because Asterisk never receives the ACK, because kamailio doesn't 
forward it, because MetaSwitch sends it as

ACK sip:number at KAMAILIO-IP

instead of

ACK sip:number at ASTERISK-IP

That means MetaSwitch ignores what we tell it in the Contact: header.

Is this MetaSwitch'es "fault" or kamailio's? All other vendors work fine 
without problems. Therefore I have compared an "old" vendor and the new 
one. Here is the result that shows the difference:

Old vendor - works:

OLDVENDOR-IP.5060 > KAMAILIO-IP.5060: INVITE sip:number at KAMAILIO-IP
KAMAILIO-IP.5060 > OLDVENDOR-IP.5060: SIP/2.0 100 trying

  KAMAILIO-IP.5060 > ASTERISK-IP.5060: INVITE sip:number at KAMAILIO-IP
  ASTERISK-IP.5060 > KAMAILIO-IP.5060: SIP/2.0 100 Trying

  ASTERISK-IP.5060 > KAMAILIO-IP.5060: SIP/2.0 200 OK
KAMAILIO-IP.5060 > OLDVENDOR-IP.5060: SIP/2.0 200 OK

OLDVENDOR-IP.5060 > KAMAILIO-IP.5060: ACK sip:number at ASTERISK-IP:5060
  KAMAILIO-IP.5060 > ASTERISK-IP.5060: ACK sip:number at ASTERISK-IP:5060


New vendor with MetaSwitch - doesn't work:

NEWVENDOR-IP.5060 > KAMAILIO-IP.5060: INVITE sip:number at KAMAILIO-IP:5060
KAMAILIO-IP.5060 > NEWVENDOR-IP.5060: SIP/2.0 100 trying

  KAMAILIO-IP.5060 > ASTERISK-IP.5060: INVITE sip:number at KAMAILIO-IP:5060
  ASTERISK-IP.5060 > KAMAILIO-IP.5060: SIP/2.0 100 Trying

  ASTERISK-IP.5060 > KAMAILIO-IP.5060: SIP/2.0 200 OK
KAMAILIO-IP.5060 > NEWVENDOR-IP.5060: SIP/2.0 200 OK

NEWVENDOR-IP.5060 > KAMAILIO-IP.5060: ACK sip:number at KAMAILIO-IP:5060
  ASTERISK-IP.5060 > KAMAILIO-IP.5060: SIP/2.0 200 OK
KAMAILIO-IP.5060 > NEWVENDOR-IP.5060: SIP/2.0 200 OK

NEWVENDOR-IP.5060 > KAMAILIO-IP.5060: ACK sip:number at KAMAILIO-IP:5060
  ASTERISK-IP.5060 > KAMAILIO-IP.5060: SIP/2.0 200 OK
KAMAILIO-IP.5060 > NEWVENDOR-IP.5060: SIP/2.0 200 OK

NEWVENDOR-IP.5060 > KAMAILIO-IP.5060: ACK sip:number at KAMAILIO-IP:5060
... and so on ...

Can I do something about this or is a change on MetaSwitch'es side in order?

Thank you!
Markus