Thanks John,
There is an article where explain the difference. But for still very confusing for me.
IP Camera Protocols: PSIA ONVIF CGI ISAPI
->ISAPI is an N-tier API of Internet Information Services (IIS) runs on Windows OS. The ISAPI is the abbreviation of Internet Server Application Programming Interface.
So meaning that if the camera if Linux based cannot support ISAPI? Also, there is no documentation available to implement this protocol. Like ONVIF, for example, there is an available document for integration.
So seems that is not an open protocol to be implemented in camera firmware.