PowerSchool and PASI must establish a client/server relationship to exchange data electronically. PowerSchool (the client) sends and requests data to/from PASI (the server). This relationship is established using the PASI Direct Connect plugin for PowerSchool. Once the plugin is installed, both PowerSchool and PASI must send digital certificates to authenticate communication. The certificates represent a "digital handshake" indicating that both sides are trusted to communicate data.
Once secure communication is established, PowerSchool can request to send/receive updates to/from PASI. This communication is also known as "calling". In other words, PowerSchool calls PASI to send or request data. PASI answers the call and enables PowerSchool to synchronize data.