21. 【Multiple Correct】 [Multiple correct] Which of the following protocols are industry defined application layer protocols? A. FTP B. ONVIF C. ISAPI D. ISUP

The correct answers are:

A. FTP B. ONVIF C. ISAPI

These are all application layer protocols. FTP (File Transfer Protocol) is used for transferring files over the internet. ONVIF (Open Network Video Interface Forum) is a global and open industry forum with the goal to facilitate the development and use of a global open standard for the interface of physical IP-based security products. ISAPI (Internet Server Application Program Interface) is a set of Windows program calls that let you build a Web server application that will run faster than a common gateway interface (CGI) application.

However, ISUP (ISDN User Part) is a part of Signaling System #7 (SS7) used for setting up telephone calls in the public switched telephone network (PSTN). It is not an application layer protocol.