[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Comparisons

  >In a study we are finishing we note that there are no industry
  >wide standards for ISDN for compression.
  True and we need them!
  >This means, unless you have identical equipment employing the same
  >compression scheme at both ends of your ISDN line, you will get
  >only raw 128K.
  >Now take any v.34 28.8 modem, this does have a compression standardd
  >and at a compression of 3:1, the through put is 86 kbps.  This
  >is very close to 128.
  >So, I suggest for the push for ISDN to be meaningful, someone
  >better pay attention to standardizing compression.
  While I agree 100% with Curtiss about the need for BRI Terminal Adapter
  compression standards, I take issue with his simplistic presentation of
  these facts and I'm quite surprised considering this is an MIT study we're
  talking about!
  Assumption: the application is connection to an ISP.
  1.  Compression to 86kbps is not at all a given (even statistically) with
  v.34.  It depends, of course, on the binary makeup of the data; Text
  compresses to the max, downloaded .zip files run at about 1:1 - on a _clear_
  day. Web graphics also run closer to 1:1 than they do to 3:1. 
  Granted, PPP efficiencies (or lack of;) muddy this but let's take that as a
  common factor.
  In fact, given my experiences, I'm not sure there's even much compression
  benefit at all - connecting to PPP through v.34.
  2. Seems to me that 86kbps is much closer to 64 than to 128; given the
  above, I'll take a clear channel 64kbps over 28.8 with compression anyday!
  In addition, v.34 only addresses async format.  Non ISP applications such as
  synchronous gateways (Virtual network links) e.g. LAN - LAN connections
  would not benefit; so vanilla bandwidth  offered by BRI, along with the very
  fast call setup time, still beats the heck out of modem technology.
  Correct me if I'm wrong, of course.
  Jim Armstrong
  - Office Information Technologies, Inc -
  PO Box 2025
  Fairborn, OH 45324