PAP model

The PAP model is a recommendation of the German Federal Office for Information Security( BSI) for a firewall system. The term PAP model stands for packet filter, application level gateway( ALG).

A model in which an application level gateway is protected on the user side and on the network side by a packet filter. Because of the three components, it is also called a three-tier firewall system.

Depending on the concept, the external packet filters can be static or dynamic packet filters. The application level gateway acts as a proxy server with a virus scanner and examines the e-mail, HTTP, etc. protocols operating at the application layer.