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List:       freebsd-isdn
Subject:    Re: PPP encapsulation
From:       J Wunsch <j () uriah ! heep ! sax ! de>
Date:       2001-04-08 20:38:59
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As Martin Husemann wrote:

> Actually the framing implemented by if_spppsubr.c is not a complete
> implementation of RFC 1662 framing, it does not add the flag byte (0x7e) nor
> FCS. (The FCS was my main concern.)

I also wondered how this is supposed to happen, yes.  Well, the flag
_byte_ is only for octet stuffing (aka. running over an async line),
while bit stuffing uses a flag bit sequence.  My guess is that this
flag sequence is already handled in hardware anyway (at least that's
how i remember it from the old Z80 SIO which could do hardware HDLC).

I have no idea about the FCS...  The way it's done right now is what i
have inherited from Sergej when i started modifying sppp(4).  Since it
happens to work against a good number of peers, i never thought about
it.

We could dump the raw ISDN data and analyze it...

-- 
cheers, J"org               .-.-.   --... ...--   -.. .  DL8DTL

http://www.sax.de/~joerg/                        NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)

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