Even though you are in a switched enviroment, if you
are running HALF duplex you will still encounter
collisions.
--- Steve Brokaw <[EMAIL PROTECTED]> wrote:
> 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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> Steve Brokaw, MCSE CCNA
> Sprint Enterprise Network Services
> [EMAIL PROTECTED]
> [EMAIL PROTECTED] (pager)
>
>
>
*******************************************************************************
>
> Never mistake motion for action.
>
> -- Ernest Hemingway
>
*******************************************************************************
>
>
> ___________________________________
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>
=====
William Swedberg CCNP CCDP
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