[Sip] Is REFER within dialog part of INVITE or subscription usage? (was RE: SIP INFO)

[Brett Tate <brett at broadsoft.com>]

> If the REFER is within an existing dialog that has an INVITE 
> dialog usage, it is still (IIUC) technically not within the 
> invite dialog usage. So it shouldn't be used for negotiating 
> INFO packages.

Paul: Thanks for raising the issues.

Everyone: Is REFER within dialog part of INVITE usage, SUBSCRIPTION usage, or neither?

I'm asking mainly because of REFER 481 impacts; however the answer also has potential implications concerning draft-ietf-sip-info-events.  RFC 5057 appears to imply that it is part of the subscription usage; however I'm not positive if my interpretation and/or RFC 5057 is correct.

If REFER isn't considered part of the INVITE usage, how should REFER 481 be interpreted?  More specifically, should receiver of REFER 481 send BYE?

Thanks,
Brett