[Asterisk-Dev] 487 message in response to CANCEL

[Michael Procter]

> However, asterisk does not send a 487 message to the
> calling party.  I wanted to get others' opinions on whether this last
> issue, where no 487 message is sent to the calling party, is 
> consistent with 3261.  Here is the call flow of what is occurring.  

RFC3261 requires a 487 to be sent.  However, it notes that equipment
compliant with the earlier SIP spec (RFC2543) will not issue the 487,
and so RFC3261-compliant equipment should be compatible with both
approaches.

Therefore, Asterisk MUST send the 487, but SHOULD NOT require it of
party B in your diagram.  See RFC3261 section 9.1 (last para) and
section 28.1 (bullet 5).

Regards,

Michael Procter