layer 5 in internet model, the software that enables the users to perform useful work  ex) instant messaging, videoconference, file transfer, email, web, wordprocessing
uses protocols relating to application being used to transmit data. e.g if using browser, may select high level protocol http or pop3
upper layer data: for network necessary applications. this is what the user uses to interact with the os. i.e chrome, firefox, outlook, etc.