Re: Sync PPP layer

Tomasz Motylewski (
Fri, 27 Jun 1997 23:00:13 +0200 (MET DST)

On Fri, 27 Jun 1997, Jan Kasprzak wrote:

> I am writing a driver for a synchronous serial card. I wonder if
> Linux kernel has any kind of generic sync PPP layer (and if it has,
> where I can read more about its interface). I have found some sync PPP stuff
> in ISDN tree, but it seems to work on ISDN devices only. There is
> a generic HDLC/LAPB layer. I think there should be something similar
> for sync PPP. How can I run Sync PPP on top of a generic character device?

I support this question. I was also developing a driver for a synchronous
serial card, and I was able to get 2 channels running 256 kbps on 486DX66/2
The chip used has 16 byte FIFOS. I wanted to use Frame Relay with that. But
what had stopped me was lack of a generic synchronous device type on Linux.
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.

I have been archiving discussion on that topic and I have put it on

Problem is the following: if we have M synchronous device drivers in the
kernel tree and N synchronous protocols we are going to write MxN device
drivers, because each of the protocols like syncPPP, X.25, FR, HDLC uses
different interface to communicate with the hardware driver. This is a
nonsence! There is a need for a common synchronous interface and 2 example
drivers using that interface - one "smart" and one "dumb". And than a little
modules feeding data from that interface to PPP, X.25, FR encapsulation
modules. Once it is demonstrated to work, and some configuration utilities
are written (not a very exiting job for a kernel hacker) it will run by

Tomasz Motylewski

P.S. Anyone knows some better discussion forum for that problem? Is linux-net or linux-serial or linux-x25 more suitable for that discussion?