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From: eckert@immd4.informatik.uni-erlangen.de (Toerless Eckert)
Newsgroups: comp.protocols.iso
Subject: Re: Implementation of start/stop (was: Re: Status of HDLC Standard)
Message-ID: <1991Apr29.214651.23667@informatik.uni-erlangen.de>
Date: 29 Apr 91 21:46:51 GMT
References: <1991Apr5.073800.6984@ugle.unit.no>
Distribution: comp
Organization: CSD., University of Erlangen, Germany
Lines: 41

From article <1991Apr5.073800.6984@ugle.unit.no>, by hta@isolde.er.sintef.no (Harald Tveit Alvestrand):
> Someone who has done work on this stuff should be able to know.
> In for example Sunlink X.25, the X.25 module is done in layers.
> In the configuration file, one typical command is
> 
>         iflayer $X25line $HDLCline $port
> 
> Does anyone want to guesstimate the possibility of changing this to
> (lets say)
> 
>         iflayer $X25line $HDLCstartstopline $ttyline
> 
> and writing an inbetween "HDLC start/stop stream module"?
> Would we then have an async-X25 connection for SUN with compatibility with
> other software, or are other magic tricks required?
> Would this be a man-month or a man-year project?
> Inquiring minds want to know (and to have cheap X.25 this year.....)

The layering done in sunlink products is not a streams module
layering as in SysV. It is really a stacking of ifnet structures,
which originate from berkeley unix. Sun extended those structures
to provide for upper and lower connecting ifnet structures.
This is explained a little bit in the X.25 manual from sun. 

The problem is, that not every bit of the software interfaces between
the layers is explained in the current documentation. Also i fear that
the interface between the X.25 layer and the data link layer will change
in 7.0 given that sunlink X.25 can use X.25/LLC in that version.

Anyway, you might want to take a look into 
inria.inria.fr:/pub/x25_tcp.tar.Z from Francis Dupont (dupont@inria.inria.fr). 
This is a probgram which emulates the X.25 over TCP encapsulation for
remote X.25 switching from cisco. It uses a pseudo LAPB level ifnet 
and a device triver to tunnel out the X.25 packets from the kernel and
put them into a TCP socket at the user level. 
(That software is experimental).
---

             Toerless.Eckert@informatik.uni-erlangen.de
    /C=de/A=dbp/P=uni-erlangen/OU=informatik/S=Eckert/G=Toerless
             bandwidth - the final frontier.