DIDADIT

Motivation

There are quite a lot of file transfer protocols or packet radio, such as YAPP, AutoBIN and 7plus encoding, additionally FTP over TCP/IP. Why another protocol? While TCP/IP gains more and more interest, it is only suitable for access points with sufficient high bitrates. But it is unlikely that the huge amount of 1k2 laps will be upgraded in the forseeable future. YAPP isn't supported by most software used in central Europe (mainly Germany). AutoBIN is widely known bit an ugly hack. So we tried to do it "the right way"™.

Requirements

• Robustness: It has to be able to recognize and correct errors during the transfer and in the case of a link failure. There has to be a mechanism to resynchronize if some bytes get lost.
• It must not depent on the underlying protocol (AX.25).
• It should be easy to monitor transfers of other stations to minimize traffic.
• It should be possible to request missing blocks of a file you have passively monitored.
• It must be easily extendable.
• It should be easy to implement

We have met all of our requirements except for the last one (more or less).

The protocol

View the protocol as a seperate document or as a PDF.

Implementations

To our knowledgem the following programs already support DIDADIT or are preparing DIDADIT support:

• LinKT
• Paxon
• WinSTOP
• WPP
• BayBox
• OpenBCM

Other software authors have expressed interest. If you know about other software using DIDADIT, please tell us so we can update this list.

The sourcecode of BayBox and LinKT is freely available under the GPL, so if you need example code, just go ahead. Note that if you include LinKT or BayBox sourcecode in your program you have to publish your whole work under the GPL too (which we encourage you to do, it is much more fun!). If you just look at the code to understand how the protocol works and the implement your own that's ok.

We explicitely encourage the use of DIDADIT in all flavors of software, even commercial. But please note somewhere in your docs that DIDADIT itself is © by the 1409.org group. This is a kind request, not a requirement (we don't want to violate the GPL ourselves ;).

Extensions

Marco Loos of WinSTOP has specified and implemented a compression-layer for didadit, specification is available in the current spec.

The Paxon team has specified a chat extension which is covered in the current spec.

Publications

An article about DIDADIT was published in the scriptum of the 16^th Packet Radio Convention Darmstadt in April 2000. Download it here (German, postscript)