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

[Roger Kouchi <Roger@WUTC.WA.GOV>]

  Jaime - Here is some additional info ...
  In answer to Jamie's question, residential trunk ratios are typically 10 to 
  1 or 12 to 1 while business users are more likely to see 8 to 1 ratios. 
    Whether ISP traffic creates network problems or not is more dependent on 
  network dynamics than the actual ratios themselves.  A large number of ISP 
  or even a single ISP with many lines in relation to the size of the network 
  may create problems, but this will be a function of individual situations. 
   If ISPs have different busy hours than the rest of the network, chances are 
  good that they will not be a problem.  If the two (network and ISP) have 
  concurrent busy hours, then there may be blockage, again depending on total 
  ISP usage.
   ----------
  From: isdn
  To: Multiple recipients of list
  Subject: Re: ISP phone ratio's and Interoffice trunkage for voice
  Date: Friday, July 12, 1996 5:20PM
  
  thanks, i understood some of this.  Now I take this comment to say that
  company's measure calling by smaller units, something called 36 CCS's to
  an hour, and that they assume a particular  distribution of calling
  (Poisson distribution??)..   I'm not an engineer, so bear with me.
  Now, if an Online caller makes call which are longer in duration than
  phone calls (say one hour rather than 6 minutes), what does this mean?
  Does this make the online calls more or less expensive (on a per minute
  basis, holding total calling constant), than modem calls?
  
    Also, what does it mean when you say switch bandwith is cheaper than
  trnnkage bandwidth?  Doesn't everything have to go over a switch at some
  point?  jamie
  
  On Fri, 12 Jul 1996, Fred R. Goldstein wrote:
  
  > At 02:38 PM 7/12/96 -0400, James Love wrote:
  > >I am informed that ISP's need one incoming line for each 8 to 20
  > >subscribers, depending upon how high the level of service is.
  > >
  > >I am curious.  What is the buildout for interoffice trunkage for voice
  > >calls, for residents?    If lower than 8 to 1, then it would seem that
  > >calls to ISP's do not cause any congession problems, that don't exist
  > >with voice calls.  Is there a hitch somewhere?
  >
  > It's not quite that simple.  The magic number used in this function is the
  > number of Erlangs of busy-hour traffic capacity, where an Erlang is one 
  hour
  > of call time (or 36 CCS, if you prefer to read traffic tables that way).
  >
  > The "typical" resi voice telephone line might generate around 3 CCS, or 
  1/12
  > Erlang, distributed bewteen intra-switch and the various inter-switch
  > destinations.  Thus a thousand resi subscribers might generate 3000 CCS, 
  or
  > around 83 Erlangs.  If all of this were carried over one trunk group, it
  > would need 106 channels in order to achieve 1% blockage, or 99 channels 
  with
  > around 5% blockage.  (This from the "Poisson" tables.)
  >
  > Of course the real world isn't like that.  Calls go every which way.  So
  > each trunk group is simply engineered to handle the demand it sees, and 
  the
  > switch fabric is engineered for aggregate demand.  Switch bandwidth is
  > somewhat cheaper than trunk bandwidth, especially with recent-generation
  > digital COs. We're talking small fractional cents/minute.
  >
  > Now an ISP will get different usage/subscriber depending upon, among other
  > things, the way it prices.  If it doesn't offer unlimited usage, then I'd
  > guess that typical peak usage will be under 3-4% of the subscriber base. 
   If
  > they offer unlimited usage options, some folks will be slow to hang up and
  > the number will be higher.
  >
  > All it takes is a small percentage doing "7x24" to throw the averages off,
  > though!
  >
  > Does this data usage affect telco?  Sure, but so do teenagers who, as is
  > well known, often grow telephone handsets as bodily appendages.  I doubt 
  the
  > average web surfer is on more than they are.  But again that ignores the
  > 7x24 crowd; at least teenagers stop to eat, sleep, go to the mall, etc.
  > ___
  > Fred R. Goldstein      fgoldstein@bbn.com
  > BBN Corp.              Cambridge MA  USA    +1 617 873 3850
  >
  >
  
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