BLISS stands for Basic Level of Interoperability for SIP Services

And the whole idea of this IETF 'working group' is to examine situations where the interpretation of the SIP RFCs has led to different implementations of the same function and subsequently sip devices that don't interoperate well

BLISS needs you to join their mailing list and get involved in order to 'shape' future recommended ways to implement SIP functionality and you can do this by visiting the BLISS website.
Thank you...