Re: Sync PPP layer

Alan Cox (
Fri, 27 Jun 1997 23:26:48 +0100 (BST)

> Alan Cox once recommended WANPIPE devices, but then started developing
> synchronous extensions to standard character devices. There also exist 2-4
> other possible models some of them only suitable for one type of protocol.

The synchronous extensions for standard character devices are solely because
I need to be able to flip tty lines into sync modes on the many systems
that support them. To have a sane way to handle them really needs that
to be a line discipline. Where the packets go then is open to debate but
a WANPIPE interface is perfectly viable - basically you'd get

tty-driver dumb-sync-board smart-sync-board
| | |
sync line discipline | |
|___________________| |
| |
Sync support libraries |

The problems we then have that I know of are

a) The existing ISDN layer and glue. Thats a fine example of why we
shouldn't have the system we do now
b) PPP is in the wrong place, PPP really is a sync support library
with some kind of async framing layer able to front it as a line discipline
not two copies of the code (one for ISDN)
c) The other frame relay code and cleanly handling multipoint devices