The SET protocol is located at the application layer and can provide security services for the application layer of the network.

SET protocol (Secure Electronic Transaction), known as the secure electronic transaction protocol,

is jointly developed by Master

Card and Visa, Netscape, Microsoft and other companies , a new electronic payment model launched on June 1, 1997. The SET protocol is designed based on the credit card payment model on B2C. It ensures the security of online shopping using credit cards on the open network. SET is mainly designed to solve credit card transactions between users, merchants, and banks. It has various advantages such as ensuring the integrity of transaction data, non-repudiation of transactions, etc., so it has become the current Recognized as the international standard for credit card online transactions.

The application layer is also called an application entity (AE), which consists of several specific application service elements (SASE) and one or more common application service elements (CASE). Each SASE provides specific application services, such as File Transport Access and Management (FTAM), Electronic Mail Processing (MHS), Virtual Terminal Protocol (VAP), etc. CASE provides a common set of application services, such as Contact Control Service Element (ACSE), Reliable Transportation Service Element (RTSE), and Remote Operation Service Element (ROSE).