The way I see it Drew is that every switched port 'contains' a collision
domain, which means the collisions are not propogated to other switched
ports.
I'll try to explain by commenting below:
>Marc,
>
>I'm not sure I understand this.
>
>Let's say I have a hubbed network with 20 hosts. Lots of collisions.
>
>I bring a 4 port switch into it, and sub-divide it into 4 hubbed segments
>of
>5 hosts each. No collisions? Or just extremely low likelihood of collisions
>on a given segment?
Collisions will still occur within each switch port, because there are hubs
attached. In other words, each port will still receive collisions from the 5
hosts. But the key is that each switched port 'contains' that collision
domain, so that the collisions are not propogated onto the other swithed
ports.
>
>Extend the scenario - those 4 hubbed segments grow into 4 hubbed segments
>of
>approximately 20 hosts each. Lots of collisions on each segment but no
>collisions across segments? Or no collisions on any segment because it's
>switched?
No collisions extended across the switched ports.
>
>I *thought* [don't know] the idea behind subdividing networks with switches
>was to reduce the likelihood of collisions by introducing more and more
>smaller network segments, and that as the number of hosts grows on a
>particular segment, one needs to continuously subdivide to minimize the
>likelihood of collisions.
The ideal network is a completely switched network, no hubs. No collisions
in full-duplex mode.
>
>You and others in this thread seem to be saying that incorporating switches
>into a network is to completely eliminate collisions. True? False?
True, but only when eliminating the hubs.
>
>Please clear this up for me....thanks.
I think you've got it all right Drew. But maybe I was unclear with my
response. If you have a totally switched environment, no hubs, running
full-duplex, no collisions will occur.
>
>
>Drew M. Mooney
>Invisix -- Motorola and Cisco Together
>1334-394 The Alameda // San Jose, CA 95126
>408-525-0873 [office] 408-287-3188 [home]
>817-937-7880 [mobile] 888-809-9678 [SkyTel Pager]
>+44-(0)7715-055-944 UK Mobile
>
>
>-----Original Message-----
>From: Marc Quibell [mailto:[EMAIL PROTECTED]]
>Sent: Thursday, July 27, 2000 4:49 PM
>To: Drew Mooney-DMOONEY1
>Subject: RE: CCDA question-512 bit times
>
>
>I agree. Once you get out of the switched environmet, collisions will
>occur...
>
>Marc
>
>
> >From: Mooney Drew-DMOONEY1 <[EMAIL PROTECTED]>
> >To: "'Marc Quibell'" <[EMAIL PROTECTED]>
> >Subject: RE: CCDA question-512 bit times
> >Date: Thu, 27 Jul 2000 11:25:51 -0500
> >MIME-Version: 1.0
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> >From [EMAIL PROTECTED] Thu Jul 27 09:29:40 2000
> >Message-ID:
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> >
> >Ahhh - but suppose the switched segment is not to a single PC - but to a
> >hubbed group of PC's. The switch in that case, minimizes the likelihood
>of
> >collision, but won't entirely eliminate it.
> >
> >Two stations in the same segment are still able to attempt transmission
> >simultaneously.
> >
> >Drew M. Mooney
> >Invisix -- Motorola and Cisco Together
> >1334-394 The Alameda // San Jose, CA 95126
> >408-525-0873 [office] 408-287-3188 [home]
> >817-937-7880 [mobile] 888-809-9678 [SkyTel Pager]
> >+44-(0)7715-055-944 UK Mobile
> >
> >
> >-----Original Message-----
> >From: Marc Quibell [mailto:[EMAIL PROTECTED]]
> >Sent: Thursday, July 27, 2000 8:51 AM
> >To: [EMAIL PROTECTED]
> >Subject: Re: CCDA question-512 bit times
> >
> >
> >I think she answers in her book, in a roundabout way, that in FULL-DUPLEX
> >mode, collisions are non-existant, since two stations can transmit at the
> >same time on the wire (a switch and the PC or device on it's port,
> >transmitting and receiving at the same time)
> >
> >Marc
> >
> >
> >"Steve Brokaw" <[EMAIL PROTECTED]> wrote in message
> >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > > Well, I have a different question that kinda goes along here. If you
> >are
> >in a switched environment, i.e. dedicated bandwidth per port, how can you
> >have a collision at all? To me it seems (and Radia Perlmann touches on
> >this
> >in her book but doesn't give any explanation) that if there is no chance
> >for
> >a collision (switched environment) then why a distance limitation? I'm
> >sure
> >there are some other physics factors that would limit distance but would
> >they be the same as the distance required to detect a collision?
> > >
> > >
> > > Steve
> > >
> > >
> > > ------Original Message------
> > > From: "Randy Witt" <[EMAIL PROTECTED]>
> > > To: [EMAIL PROTECTED]
> > > Sent: July 27, 2000 1:53:55 PM GMT
> > > Subject: CCDA question-512 bit times
> > >
> > >
> > > I have a question regarding the round-trip propagation delay on an
> >Ethernet network.
> > >
> > > Page 123 of the Cisco Press "Designing Cisco Networks" book states:
> > >
> > > "The most significant design rule for Ethernet is that the round-trip
> >propagation delay in one collision domain must not exceed 512 bit times,
> >which is a requirement for collision detection to work correctly."
> > >
> > > With 100Mbps Ethernet, the maximum round-trip delay would be 5.12
> >seconds,
> >resulting in a distance limitation of 205 meters.
> > >
> > > I currently oversee a large flat network covering several miles in
> >diameter. All of the links between buildings are single-mode fiber
>links.
> >No routing is involved, everything is switched - one large broadcast
> >domain.
> > >
> > > How does the 512 bit time rule apply to fiber optic cabling? I see on
> >page 127 of the same book that the Round trip delay in bit times per
>meter
> >for Cat5 cable is 1.112, whereas Fiber-optic cable it's 1.0.
> > >
> > > I guess I'm having difficulty understanding how fiber can overcome the
> >512
> >bit-time rule and can have a much longer distance.
> > >
> > > I do realize that this is not exactly a Cisco question, though covered
> >on
> >the DCN/CCDA material. If someone could kindly refer me to any material
> >that covers this topic, I'd appreciate it.
> > >
> > > ___________________________________
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> > > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
> > > Steve Brokaw, MCSE CCNA
> > > Sprint Enterprise Network Services
> > > [EMAIL PROTECTED]
> > > [EMAIL PROTECTED] (pager)
> > >
> > >
> > >
> >***************************************************************************
>*
> >***
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> > > Never mistake motion for action.
> > >
> > > -- Ernest Hemingway
> > >
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