| 摘要 |
The present invention relates to a method, network system, gateway device, and computer program product 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. Establishment of a call with a first media composition is started in a first leg of the first network domain, by transmitting a first call set-up request for the first media composition from a gateway control function to the first network domain in response to the receipt of a set-up message at the gateway control function from a second network domain. 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. A session with the first media composition is updated in the second network domain to match the call with the downgraded second media composition being established in the first leg. Thereby, a fallback to the downgraded second media composition is supported even if the first network domain is inherently a non-fallback network, while standard terminals for the second network domain can still be used. |
