Dear Jens,
>>>>> "Jens" == Jens Axboe <axboe@suse.de> writes:
Jens> On Sun, Apr 16 2000, jamal wrote:
>> Michal and I are working on cleaning up things. The code that
>> michal posted is important for any one trying to do "PPP over
>> X" -- the pppoe code is being used as an example. Hopefully,
>> folks doing L2TP, PPPoATM,
Jens> I didn't think any code had been posted for PPP over X yet,
Jens> could you point me in that direction and I'll be more than
Jens> happy to convert my PPPoATM stuff.
The PPPOX code certainly seems to be a good framework for PPPoE and
similar, where some new and somewhat complex ppp-specific encapsulation
methods for ppp frames are needed. But for tunneling ppp over existing
protocols, where the additional ppp-related encapsulation is simple,
maybe another approach might be more appropriate.
I've started to implement ppp over the AF_X25 socket layer. Here,
ppp frames are carried directly inside the X.25 payload, without
any additional encapsulation headers. The RFCs for ppp over other
protocols are frequently similar (no additional ppp frame encapsulations
or just some pad bytes). For such protocols, the encapsulation of the
ppp frames is trivial and the PPPOX framework (which makes the task
of implementing complex ppp encapsulations schemes more easy), does
not give any advantage. Instead, the hard problems faced when interfacing
such a protocol to ppp are the interactions with the protocol internals.
Existing network protocol stacks differ in various areas (e.g. which
parts of the protocol processing need process context, how can
ppp_channel flow control be interfaced to the carrier protocol's flow control
mechanism).
Thus, the design chosen is a library approach, providing services which
make interfacing of existing socket code to the ppp_generic code as well as
to generic tunnel network interfaces (e.g raw-IP on top of X.25 payload)
easy. It aims beeing re-usable for other protocol stacks.
Currently, I've just finished the design and some of the prototype coding,
but totally untested until now. Thus, I did not upload it yet. But If you
(or soembody else) is interested to have a look at the prototype code
(I don't know whether this or the PPPOX approach will be more appropriate
for your PPPoATM), please drop me a mail.
Henner
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