# Packet assembler/disassembler > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Packet_assembler%2Fdisassembler > Markdown URL: https://mediated.wiki/source/Packet_assembler%2Fdisassembler.md > Source: https://en.wikipedia.org/wiki/Packet_assembler%2Fdisassembler > Source revision: 1245981799 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Redirect|X.29|similarly named topics|X29 (disambiguation){{!}}X29}} {{refimprove|date=September 2016}} A '''packet assembler/disassembler''', abbreviated '''PAD''' is a communications device which provides multiple [asynchronous](/source/asynchronous_serial_communication) terminal connectivity to an [X.25](/source/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 [Frame Relay assembler/disassembler](/source/Frame_Relay_assembler%2Fdisassembler) (FRAD) is a similar device for accessing [Frame Relay](/source/Frame_Relay) networks. == ITU-T (Triple-X PAD) == The structure of a PAD is defined by the [ITU-T](/source/ITU-T) in recommendations [X.3](/source/X.3), [X.28](/source/X.28), and X.29. Sometimes, this is referred to as a Triple-X PAD, due to the three X-series recommendations which define it: * '''X.3''' specifies the parameters for terminal-handling functions such as line speed, [flow control](/source/flow_control_(data)), character echo, et al. for a connection to an X.25 host. The X.3 parameters are similar in function to present-day [Telnet](/source/Telnet) options. * '''X.28''' defines the DTE-C (asynchronous character mode) interface to a PAD, including the commands for making and clearing down connections, and manipulating the X.3 parameters. The commands were very crude, a bit like (but not at all compatible with) the [Hayes command set](/source/Hayes_command_set). Many commercial PAD products provided completely different enhanced user interfaces. * '''X.29''' defines the DTE-P (packet mode) interface to a PAD, i.e., how the PAD encapsulates characters and control information in X.25 packets.{{cite web |title=X.29 : Procedures for the exchange of control information and user data between a Packet Assembly/Disassembly (PAD) facility and a packet mode DTE or another PAD |url=http://www.itu.int/rec/T-REC-X.29/en |website=www.itu.int}} Connections are established using [X.121](/source/X.121) 14-digit X.25 addresses. == Green Book PAD == One of the UK [Coloured Book protocols](/source/Coloured_Book_protocols), '''Green Book''', also defines two PAD protocols. Green Book was developed by (UK) [Post Office Telecommunications](/source/Post_Office_Telecommunications) in the 1970s. Although not identical to Triple-X, Green Book is sufficiently similar to X.3 and X.29 that generally the two will interwork. Green Book also specifies '''TS29''', a very similar protocol which ran over the Yellow Book Transport Service, which is another of the Coloured Book protocols. == ITP == '''ITP''' (Interactive Terminal Protocol) was an early PAD protocol for use over X.25 developed in the 1970s for use with [UK GPO's](/source/Post_Office_Telecommunications) EPSS (Experimental Packet Switching System, the predecessor of [PSS](/source/Packet_Switch_Stream)). ITP predated Triple-X, and is a completely different protocol. [Science and Engineering Research Council](/source/Science_and_Engineering_Research_Council) (SERC) also used ITP on SERCnet and continued developing ITP after EPSS, although it eventually gave way to Triple-X. == See also == * [Terminal node controller](/source/Terminal_node_controller) ==References== {{reflist}} == External links == *[http://www.chilton-computing.org.uk/ca/technology/networking/p001.htm ITP: Protocols in the SERC/NERC Network"] {{DEFAULTSORT:Packet Assembler Disassembler}} Category:Packets (information technology) Category:X.25 --- Adapted from the Wikipedia article [Packet assembler/disassembler](https://en.wikipedia.org/wiki/Packet_assembler%2Fdisassembler) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Packet_assembler%2Fdisassembler?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.