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From: woody@ucscb.UCSC.EDU (Bill Woodcock)
Newsgroups: comp.protocols.appletalk
Subject: Re: Farallon StarController restictions
Summary: <long>
Message-ID: <11024@darkstar.ucsc.edu>
Date: 14 Jan 91 08:15:32 GMT
References: <10299@pogo.WV.TEK.COM>
Sender: usenet@darkstar.ucsc.edu
Distribution: na
Organization: University of California, Santa Cruz
Lines: 70


       > We are in the process of planning the installation of some
       > Farallon PhoneNET StarControllers to relieve some overloaded
       > net problems.  For each of the 12 ports on a single
       > controller, there are 4 "branches" each of which can have up
       > to 750 feet of cabling.  Farralon technical support says
       > that they recommend and support only one device (Mac,
       > printer, whatever) per branch. Given that each port is
       > electrically isolated from the others, this seems extremely
       > conservative.
       > 
       > Hence my question:  Have any of you installed this
       > controller and what do you find are the *practical* limits
       > on devices per branch?
   
   To summarize the _Farallon Party Line_...  StarControllers have
   twelve ports, each of which can best support one device at the end of
   <3000' of 24ga. solid core twisted pair IC phone cable.  The
   _maximum_ rated spec for a StarController is 48 devices.  Dividing 48
   by 12 yields 4 devices per port.  Dividing 3000' by 4 devices yields
   750'.  Thus the maximum allowable within spec is four devices per
   port, each at the end of <750' of cable.
   
   As you've correctly surmised, the electrical isolation of each port
   makes each one a separate physical (if not logical) network.  It's
   relatively easy to address your question from this standpoint.  What
   Farallon is saying is exactly what they'd tell you if you were
   building twelve separate extrememly small networks without a
   StarController. You can use up to a grand total of 3000' of cable in
   your network, and if you're going to make a passive star topology
   with it, you'd better not try to use more than four branches, since
   signal strength on a passive star is divided by the number of
   branches.  The little networks you're planning on attaching to each
   of the ports of your StarController can be treated as individual
   passive stars (evil, evil, evil...) and should follow the same rules.
   
   In addittion, there's the problem of traffic.  48 Macs and gateways
   and LaserWriters generate a heck of a lot of traffic on a baseband
   network, and if you actually did put that many nodes in one zone,
   odds are you wouldn't be a happy person for the experience.  Farallon
   has always recommended about 45 nodes per zone, traffic-wise, and
   Apple has always said 32.  The figure is going to actually depend on
   the amount of traffic your particular users generate.  Kurt
   Vandersluis published a formula for roughing it out in MacAbuser
   around last August sometime.
   
   In answer to your final question, I'd say from my own experience that
   you would do well to stick to either one or two nodes per port, but
   that you might be able to get up to 4000' of cable, if you're careful
   laying it, and avoid intermediary punchdown blocks as much as
   possible.  It's also possible to use 22ga. cable, to increase the
   possible length of your cable segments.
   
                            
                           -Bill Woodcock
                            BMUG NetAdmin
   
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