Packet Assembler/Disassembler
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A packet assembler/disassembler, abbreviated PAD is a communications device which provides multiple asynchronous terminal connectivity to an X.25 (packet-switching) network or host computer. It collects data from a group of terminals and places the data into X.25 packets (assembly). A PAD also does the reverse, it takes data packets from packet-switching network or host computer and returns them into a character stream that can be sent to the terminals (disassembly). A FRAD (Frame Relay Assembler/Disassembler} is a similar device for accessing Frame Relay networks.
The structure of a PAD is defined by ITU-T (International Telecommunication Union); recommendations X.3, X.28, and X.29.
X.3 specifies the parameters for terminal-handling functions such as line speed, flow control, character echo, et al for a connection to an X.25 host. The X.3 parameters are similar in function to present day Telnet options.
Recommendations X.28 and X.29 specify the user interface or remote host requirements for controlling a PAD.
A PAD's connectivity to the network/host is defined by the X.121 14-digit addressing format for X.25.
The following is list of X.3 parameters associated with a PAD:
- 1 PAD recall using a character
- 2 Echo
- 3 Selection of data forwarding character
- 4 Selection of idle timer delay
- 5 Ancillary device control
- 6 Control of PAD service signals
- 7 Operation on receipt of break signal
- 8 Discard output
- 9 Padding after carriage return
- 10 Line folding
- 11 DTE speed
- 12 Flow control of the PAD
- 13 Linefeed insertion after carriage return
- 14 Padding after linefeed
- 15 Editing
- 16 Character delete
- 17 Line delete
- 18 Line display
- 19 Editing PAD service signals
- 20 Echo mask
- 21 Parity treatment
- 22 Page wait
