Network element registration method and system, and network function repository function

A network element registration system, comprising a Network Function Repository Function (NRF), a NRF extra-domain service provider network element, and a NRF intra-domain service provider network element;

• wherein
• the NRF is configured to receive a registration request of the NRF extra-domain service provider network element, the registration request comprising service identification information of the NRF extra-domain service provider network element;
• and
• the NRF is configured to allocate, in response to the registration request, a first network element instance ID for the NRF extra-domain service provider network element,
• the first network element instance ID being different from a second network element instance ID allocated by the NRF for the NRF intra-domain service provider network element;
• wherein the NRF extra-domain service provider network element does not support a registration interface of the NRF, the NRF intra-domain service provider network element supports the registration interface and heartbeat/keep-alive interface of the NRF, the NRF is configured to set the NRF extra-domain service provider network element, identified by the first network element instance ID, to be in a permanent online state;
• and
• the NRF is configured to automatically register and subject to heartbeat/keep-alive detection the NRF intra-domain service provider network element, identified by the second network element instance ID.