This isn't an actual answer to your question about BSC and SDLC, which
Howard can do, but for all of you wondering about this issue, I recommend
chapter 3 of Tannenbaum, "Computer Networks."
He goes into lots of interesting details about how to allocate a single
broadcast channel among competing users. The traditional way was
frequency-division multiplexing, he says. However when the number of
stations is large and varies, or traffic is bursty, FDM presents some
problems. New methods, models, and assumptions are needed.
He goes into gory details about assumptions and then finally gets into
protocols used in LANs, including ALOHA, 1-persistent CSMA, non-persistent
CSMA, CSMA/CD, CSMA/CA, basic bit-map methods, BRAP, and a bunch of other
stuff.
But, bottom line (and I am finally getting to that), collisions occur on a
single broadcast channel that is shared among competing users. This doesn't
apply to a typical serial link.
Cisco uses a "template" for the output of show interface commands that does
not remove statistics that are irrelevant to the interface being shown. So
show int s0 does include a collision count but it's always zero. It also
shows a runt count and giants. Lazy programming? Memory constraints on how
many templates that could maintain? Who knows.
As a CCIE (even a CCNA?! ;-) you would be expected to know to ignore the
collision, runt, and giants count on a show int s0. Cisco makes life
difficult for engineers by using esoteric and non-intuitive commands and
output, and then makes lots of money certifying people who understand these
esoteric subtleties. ;-)
Priscilla
At 01:44 PM 8/24/01, John Nenye wrote:
>Howard,
>Does is it really matter if it is BSC or SDLC multidrop network. In an IBM
>SDLC network you are dealing with Master/SLave design so you will never get
>collisions becuase the Master controlls the transmission time
>
>
>
>Most are full duplex, so in those cases, no you shouldn't..
> >
> >Brian "Sonic" Whalen
> >Success = Preparation + Opportunity
> >
> >
> >On Thu, 23 Aug 2001, Wright, Jeremy wrote:
> >
> > > Can you have collisions on a serial link? Thanks again.
> >
>
>
>I'm in general agreement, but be aware that you might run into IBM
>BSC or SDLC networks that use polled multidrop on half-duplex
>facilities. Rare now, but you might see them on things like
>automatic teller machines, point-of-sale terminals, etc. -- those
>being critical business applications that work, so no one wants to
>fiddle with them.
>_________________________________________________________________
>Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp
________________________
Priscilla Oppenheimer
http://www.priscilla.com
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=17174&t=17050
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