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Re: ISP phone ratio's and Interoffice trunkage for voice

          To provide some more information about the ISP phone ratio dialog,
  the University of Texas at Austin provides a dial service for its students
  that might be considered a UT ISP.  This service is called Telesys and is
  limited to all students faculty and staff at the University of Texas at
  Austin for a FLAT fee with no USAGE or TIME charges.  The service is
  provided via lines to the local exchange carrier (in this case Southwestern
  Bell) and lines from the local campus telephone switch.
          The reason there are lines on the local campus telephone switch is
  because the on campus users started to overload the number of trunks between
  the campus switch and the local serving Bell central office (which is where
  the service was obtained from).  The standard Erlang distribution
  implementation that was serving the campus proved to extremely inadequate
  for the new service because users in dorms and campus offices were dialing
  the Telesys service for network access.  The result was long periods where
  calls were blocked between the Bell office and the campus.  The initial
  offering was a text based offering and revealed the problem.  When the
  offering was changed to provide PPP and SLIP service (meaning the user was
  not an Internet site instead of being a terminal attached to a campus
  computer) the problem exploded and the service was changed to include a
  connection to the local campus telephone switch.  This connection has the
  same telephone number as the Bell provided service which is done by trapping
  that number when dialed from on campus and directing it to the local
  connection to the modems.  If a campus phone dials in and all campus
  connections to modems are busy then the call is allowed to overflow to the
  trunks to the Bell office where it comes back to campus on the Bell lines.
          While this service is not provided by ISDN it is a case study where
  Internet access has produced some tangible results for number of lines and
  call duration that are very different from the standard Erlang calculated
  results.  It should also be noted Telesys is being REQUIRED by some
  professors as the submission method for classwork, there is no time limit on
  the length of use by the students, the University of Texas provides a free
  mail box and mail address for all who register, and the service provides the
  students a complete set of software for PCs and MACs to utilize all Internet
  services like FTP, WEB, Telnet, etc.  This might not mirror the world
  outside the irovy tower, but it does give data about the increase in use of
  the telephone system for Internet access.  The system has grown to 1800
  modems serving about 40,000 students, faculty and staff.  This ratio still
  produces a few times where the users get a busy modem when they call.  Until
  this ratio, the system was 100% busy for several hours from mid afternoon
  until past midnight.  This usage pattern might be more indicative of
  students than the general population but it was constant as the number of
  users went up and the number of modems provided went up.
          Telesys was designed to be a single modem pool on a single rotary,
  but calcualting the cost of the additional trunks to the Bell CO for campus
  calls to reach Telesys, the cost of additional Bell lines to the modem
  service to maintain the level of service and the knowledge the University
  was embarking on a University wide LAN connection to every dorm room and
  campus office led to the decision to provide two modem pools.  One was the
  local campus accessible system that would overflow to the Bell system.  The
  second was the original Bell line accessible system that will not overflow
  to the campus modems.  This decision alters the actual modem utilization
  somewhat but is a driven by the cost of the service of trunks and lines from
  the LEC.
          This data clearly shows the impact on a telephone system designed to
  support voice traffic of data service.  This data will become more the norm
  as the competition between ISPs drives down the cost of usage.  I will add
  that I am accessing the net over an ISDN line and I was very pleased by the
  quicker response of 128K.  The system in Austin was implemented on a
  separate telephone switch that was NOT adequately trunked to the 'analog
  voice switch" in the same CO.  Many times I would get a fast busy dialing a
  voice call to a destination served by the the same CO but on the voice
  switch.  This was the case many times when I would revert to the analog
  modem call to Telesys because of an outage in the ISDN equipment at the
  University, which is an expermental system now.
  So, if ISPs provide both ISDN digital service and ISDN delivered analog
  service there can be an impact on the analog users trying to obtain a trunk
  between "switches" in the same CO, as was the case in Austin, Texas.
          For those of you interested in more information on Telesys from a
  user's perspective you can go to:
  or for a user guide to:
          I think it is clear to say the community of users would jump at an
  ISDN digital service and that ISDN would produce slightly different usage
  data given the same parameters.  There might be some testing of this
  delivery system as the local campus telephone switch has been upgraded to
  support ISDN BRI and PRI connections.  That decision has yet to be made.
  Thank you,
  Wayne Wedemeyer