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Date:      Sun,  2 Feb 97 17:14:47 +0000
From:      Andrew.Gordon@net-tel.co.uk
To:        hackers@freebsd.org
Subject:   Re(2): bisdn
Message-ID:  <"7527-970202171433-7459*/G=Andrew/S=Gordon/O=NET-TEL Computer Systems Ltd/PRMD=NET-TEL/ADMD=Gold 400/C=GB/"@MHS>
In-Reply-To: <199702020005.RAA06968@phaeton.artisoft.com>

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> > > At least I don't know of any ISP's that offer other ways for
> > > TCP/IP connection.
> > 
> > There aren't too many in the USA.  That doesn't mean that there
> > shouldn't be.  I believe most ISDN routers can be set up to run
> > without PPP.  Certainly the ISPs over here, nearly all of who offer
> > transparent HDLC, use the same routers as are used in the USA.
> 
> The default hardware in the US doesn't do the HDLC for you.  Think
> about what hardware the phone company provides for an ISDN user
> over there, but doesn't provide for an ISDN user over here...

Nor does the hardware provided for you in Europe; the HDLC in question
is done by the TA.  In the case of the Teles/Creatix/AVM cards
supported by BISDN, there are two chips of consequence on the card:
one (PEB2085) does clock generation etc. to demultiplex the 3
channels, and also does HDLC decoding for the D channel; the other
(82525) is a two-channel HDLC controller used to run the B channels
(it can also be put in a byte-clocked mode for doing voice calls,
which are one of the few things that aren't HDLC).

If you do Sync PPP, those PPP packets are themselves encapsulated
in HDLC frames.

Even if you insist on treating the TAs like modems and running
async PPP transparently over V.120 (or SLIP likewise), V.120
itself encapsulates your async data in HDLC frames (so you would
have been better off doing sync PPP as you have now got double
the framing overhead and increased latency).



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