US Patent 9042378 Method and apparatus for interworking with media fallback

An approach is provided for enabling interworking between a first network domain which does not support downgrading of media compositions, and a second network domain which supports downgrading of media compositions. The call with the first media composition is released and a call with a downgraded second media composition is set up by the gateway control function in the first network domain, in response to a rejection of the first call set-up request, by transmitting a second call set-up request for the downgraded second media composition from the gateway control function to the first network domain via the first leg.