The xApp A1 mediator exposed a generic REST API by which xApps can receive and sent northbound messages, e.g., for receiving policy intents A1 Mediator listens on the northbound interface of the RIC for policy guidance. The caller (e.g., “isolate UEs from cell 5”), for receiving machine learning models, or for sending current application state like a neighbor cell relations table learned from the RAN. The A1 mediator will take the payload from such generic REST messages, in the future, validate them, and then communicate the payload to the xApp via RMR messaging, non RT RIC, SMO, etc.) creates policy types and policy instances through A1, and subsequently A1 exchanges messages with xApps via RMR.
Please see here for the docs: https://docs.o-ran-sc.org/projects/o-ran-sc-ric-plt-a1/en/latest/index.html
This wiki page may be useful for discussion about the A1 Mediator, feel free to post comments here.