Last change: 2007-10-15
Three months ago I found a copy of the CCITT Q.931 standard. That was a very interesting piece of literature (written in Winword, but aesthetics was not the important aspect here), it is documenting (part of) the DSS1 protocol, also known as EURO-ISDN.
After reading it (and understanding the standardese ;), I wondered wether it would be possible to transfer some data, without making an connection, and thus, without paying for it. And yes, it's possible, and, of course, it's also illegal.
Then I wrote a usermode program for the protocol. After a little thought, I decided to implement my own tcp-like protocol. Although tcp already has quite advanced recovery/retry features (depending on the implementation.. Windoze95 doesn't exactly show off here), the low - very low bitrates of my medium (30-300 baud) demanded specialised retry/timeout features and a reliable protocol.
As a side effect, it's possible to run almost everything on the connection that can talk to a tty. pppd is only one example of a useful program for this purpose ;)
Apart from that (and some minor problems like other isdn-devices rejecting the data packets (protocol conformance? where?)), it seems that the approach basically works...
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