modem v isdn digital !!!

[jma2@erinet.com (Jim Armstrong)]

  >> Nonetheless, I gather there is agreement that 28.8 Kbps modems
  >> are as "digital" as ISDN "modems."
  >Errr not at all...
  >
  
  >> the "digital network", this distinction, apparently, does not hold.
  >THAT is true. Virtually all inter-office traffic is digital & in DS0
  >format. 
  
  You guys are making it too hard!
  
  1) Both the modem and the BRI TA/TE use a carrier signal to transport the
  digital data.
  
    a) The modem's carrier, being foreign to the telephonic equipment, is
  digitized at the CO switch and is transported throughout the system as if IT
  ( the carrier) was the desired product.
  
   b) The BRI carrier, however, is "known to", and an active element of, the
  CO switch, thus any data riding it is recovered and carrier is stripped...
  only real data in a digital format is forwarded through the connection.
   This will ultimately allow "dynamic compression" of data over trunking
  backbones, that is; only active data transmissions cause a full "cell" to be
  forwarded toward the destination.
  OTOH, because the telco switch equipment can't discriminate modem carrier
  from data, transport layer cells are constantly forwarding the modem's
  carrier signal across the CO-CO connection whether or not that carrier
  conveys intelligence.
  
  2) At the destination end, the ISDN data stream is mounted on a totally new
  and independent carrier for the "last mile", whereas the original modem
  carrier must be faithfully reproduced, either at the switch's  STE or the
  Terminal adapter's POTS port.
  
  Bottom Line:  Because the modem's carrier must be treated as data and
  transported intact between the origination and destination switches,
  transporting it is less efficient than any system (guess why leased line
  terminal equipment is no longer called _modem_) that allows a direct
  transmission of data alone.
  
  THAT is the real operational difference between analog and digital.
  Jim Armstrong
  - Office Information Technologies, Inc -
  513.864.5385
  PO Box 2025
  Fairborn, OH 45324