Ascend Archive
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Re: (ASCEND) Software compression ?? (fwd)
On Thu, Apr 16, 1998 at 09:38:52AM +0000, Claire Bradford wrote:
> Andre Beck wrote:
> >
> > On Wed, Apr 15, 1998 at 12:55:43PM +0300, Vesa Halkka wrote:
> > >
> > > > Seriously, the Ascends are doing LZS in hardware using the appropriate
> > > > Hi/Fn (Stac) chips. The Win95 DUN implementation is pure software, so
> > > > they call it "software compression".
>
> (Slightly different discussion) The Win NT implementation of MS-Stac is
> different to that of Win 95. I have customer unable to negotiate MS-Stac
> compression through NT to the Ascend Max (with MS-Stac set in the
> customers RADIUS profile). I guess either Microsoft change the NT
> implementation or Ascend *could* implement an NT version ;-).
To my current knowledge it is more complicated: Win95 uses LZS check mode
4 (so called extended mode), also known as coherency compression. This is
just a slightly different variant of LZS, it uses a 12 bit coherency
counter to ensure packet sequence and communicates compressor resets and
uncompressed data inband (all other checkmodes communicate resets expli-
citely as a Reset-Ack and uncompressible data "outband" by just sending
normal PPP frames). The default LZS checkmode is a 8 bit sequence number.
You will find all that in RFC1974.
The bad thing with M$ NT is that AFAIK it will _not_ use LZS checkmode 4
but use MPPC (M$ Point-to-point-compression). This one has a similar
framing logic to LZS checkmode 4 but a remarkably different compression
engine (histories are 8K and so on). It has an RFC of its own (don't re-
member, just search the index, may be 2118). But it is likely not compa-
tible with LZS aka MS-Stac.
I dunno which HiFn chips Ascend plugs into the Maxes, but only somewhat
newer chips can talk MPPC at all. This gives to think about upgradability
of existing Max4k base to MPPC.
BTW, I'm pretty sure that this is actually just another nasty move of M$.
The NAS market has severe impact on sales of NT RAS servers and M$ found
another way to suck. It's pretty obvious that the RAS server _can_ talk
LZS checkmode 4, Win95 clients dialing in use this.
Corrections ?
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