One demand that the AAA substrate makes of the upper layers is that they must properly identify the endpoints of the communication. It must be possible for the AAA client at the RP to determine where to send each RADIUS or Diameter message. Without this requirement, it would be the RP's responsibility to determine the identity of the client on its own, without the assistance of an IdP. This architecture makes use of the Network Access Identifier (NAI), where the IdP is indicated by the realm component [RFC7542]. The NAI is represented and consumed by the GSS-API layer as GSS_C_NT_USER_NAME, as specified in [RFC2743]. The GSS-API EAP mechanism includes the NAI in the EAP Response/Identity message.