What is Public PAD?

PAD is a short form of packet assembler/ diassembler, a device (hardware/ software) used in packet switching to enable data terminal equipment (DTE) to access a packet switched network. PAD is generally associated with an X.25 network where the PAD divides the data stream into individual packets and formats the data packet headers for asynchronous transmission. Public PAD is a  kind of service provided by the Post Telephone and Telegraph (PTT) administration or network provider that you can access through a local call on a public switched network. Once the terminal connected to the public PAD, you are required to enter NUA (it is the X.121 address in X.25 communications, comprising up to 15 binary code digits) of your host DTE, and then the PAD establishes the communication.