Refer to the exhibit. 

Which SIP response message should the TGW send if it cannot process the tunneled QSIG messages from the OGW? 

Answer options:

A. 405 Method Not Allowed
B. 406 Not Acceptable
C. 412 Conditional Request Failed
D. 415 Unsupported Media Type
E. 485 Ambiguous

D

Fallback from QSIG Tunneling - In some situations, QSIG tunneling will fail or need to fall back:Remote party does not support multipart MIME body: In this case, the remote side sends a "415 Media Not Supported" response. Upon receiving this response, OGW will fall back to normal mode and send an INVITE request without any tunneled content. This procedure helps ensure that at least the basic call will work normally.Remote party does not understand tunneled content: If the remote side does not support the tunneled content, it should drop the tunneled content and continue as a normal call; because all essential parameters are present in the original INVITE, the call can go through without the need for fallback. References: http://www.cisco.com/c/en/us/solutions/collateral/enterprise-networks/empowered-branch-solution/white_paper_c11_459092.html