Subject: [NEXTEL-1] RE: Define System Channel Capacity

From: [email-masked]
Date: Wed, 11 Jun 2003 18:42:15 -0400

-------- Original Message --------
   From: "Maples, Dave" <[email-masked]>
Subject: RE:  Define System Channel Capacity

 All: Mark is right on target.  The traffic model has to take into account the
average length of call, length of time after call completes before channel
releases, total number of transmissions in an exchange and whether or not the
system reassigns a new channel for each transmission in the exchange or not, etc.A
really good independent model would really help to properly size infrastructure
for these systems.Dave Maples

     -----Original Message-----
     From: Mark Krotz [mailto:[email-masked]]
     Sent: Wednesday, June 11, 2003 11:30 AM
     Subject: Re:  Define System Channel Capacity

     Bill McLain wrote:
     >       I have been reviewing the PSWN Operational Best Practices report
     on
     > trunked LMR systems.  They recommend to maintain 20% excess system
     channel
     > capacity.  My question is what does this mean?  How do you really
     determine
     > "system capacity"?  By the FCC determinations, you need from 80 or 100

     > terminal units per channel.  Somehow this doesn't really fit properly
     > either.  This seems correct if it were conventional operations as I
     can see
     > 100 users all on a single channel, all of the same organization.  But
     when
     > you bring in 100 units comprised of 15 units of 8 different
     organizations,
     > you have a major communications problem.

     Good question... many use the Erlang formulas.  Then there's real world.

       Perhaps the Erlang formulas are more suited to cellular type systems,
     though many try to apply them to SMR type trunking.

     One of the trunk systems I maintain is for an airline's hub operation.
     It is a 10 channel, with roughly a thousand user radios on it.  The
     airline is a hub-and-spoke operation.. meaning generally, the aircraft
     arrive and depart in banks.  Most of the activity is while a bank of
     aircraft is on the ground.  In between banks.. the system is pretty
     open.. During banks, it's not unusual to have a bit of a busy queue.

     There's never really been any criteria in 'the formulas' for type of
     activity/use.

     M

---

From: Rick Parrish <[email-masked]>
Date: Thu, 12 Jun 2003 05:11:30 -0500

Has anyone had any success with using a Poisson distribution to model 
capacity?
-rick

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