[Asterisk-Users] Cisco IOS SIP mime 1.0

[Emilio Panighetti]

I ran into the same problem until I found the answer:

http://lists.digium.com/pipermail/asterisk-users/2004-March/040488.html

Either you have 'signaling forward unconditional' inside voice service 
voip or in a dial-peer.

IPTel SEMS, Asterisk and many other SIP Implementations (including IP 
Phones from Zyxel and Grandstream among others) don't understand SIP 
Messages with MIME encapsulation. Cisco does this when it has too much 
information to send (i.e., additional signaling info, specially if your 
gateway is ISDN or SS7), and most SIP stacks don't implement that.

Regards,
E.