Date: Sun, 8 Apr 2001 13:01:16 +0200 (MEST) From: Martin Husemann <martin@duskware.de> To: martin@night-porter.duskware.de Cc: Brian Somers <brian@Awfulhak.org>, Martin Husemann <martin@duskware.de>, freebsd-isdn@FreeBSD.org, joerg@FreeBSD.org Subject: Re: PPP encapsulation Message-ID: <200104081101.f38B1GT00379@night-porter.duskware.de> In-Reply-To: "from (env: martin) at Apr 7, 2001 02:25:16 pm"
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Ok, tried it: did not work. 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.) So it only prepends one byte adress (0xff for PPP = all stations), and a controll byte (unnumbered HDLC information element, 0x03). Not doing this makes the PPP conversation not work. Anyone know where this "sync PPP header" (see struct ppp_header in if_spppsubr.c) is specified? While there I noted that some comments and the statisitcs (bytes output, bytes received) always add 3 bytes, from comments indicating exactly the missing parts of RFC 1662 framing (one byte "flag", two byte FCS). IMHO both the comments and the +3 calculation are wrong. Maybe if in CISCO encapsulation mode, the sync hardware does add these, which means we should not add 3 bytes when in PPP mode. Probably best solution would be to add an element in strupt sppp giving the constant byte number added by hardware and always using that (which would be 0 in the PPP over ISDN case, 3 in the sync hardware case and yet something else in the application I'm currently working on). Anyone care to sanity check this? Martin To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-isdn" in the body of the message
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