How does my EPOS communicate with the IPC and the PED?
Your EPOS application will not communicate directly with the PED, the EPOS app only communicates with IPC which handles all communication with the PED and Worldpay servers for payment processing.
EPOS and IPC can communicate in two modes: File or Socket. The communication for either method, is in the form of a request for transaction (input) and the transaction result (output).
If you want to read the messages directly from the PED and not use the IPC GUI, you can use the IPC in the Hosted IPC mode. Your EPOS application needs to be listening on the appropriate port (default 8000) to read messages coming from the IPC through the PED.