The Pacsat Broadcast Protocol (PBP) defines what a Pacsat File Header (PFH) is and how it is used to handle messages aboard a Pacsat File Server. The PFH contains information fields written mostly by the sender of the message. The PFH is used by receiving stations to generate a directory of server files, from which the appropriate files can be downloaded. The contents of the PFH is clearly important in getting a message from its source to its destination Most users of a Pacsat server use the most widespread implementation of the PBP, the program PB, written by G0K8KA. The program allows users to receive a directory from the server showing which files are currently stored, and then to request a file from the directory. The server deals with each user's request in turn, sending the actual file contents. The broadcast nature of sending data in this way means that users will automatically collect messages of general interest (if they wish), but a message must be requested by its intended recipient to ensure its reception The increasing number of files carried by servers and the increasing level of automation of groundstations demands that files should be reliably selected and also requested as efficiently as possible. The select equation mechanism is designed to improve both the efficiency and the automation of message selection and hence transfer
