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 anon6111@hotmail.com 06-18-2006 11:26 PM

Latency of copper vs latency of fibre?

Hi all,

I recently had one of my non-technical colleagues ask me an interesting
questing - how fast is ethernet data transmitted over a UTP cable? So
what he was really asking is "what is the average latency of an
electrical signal over copper cabling?". I've done some googling but
can't find a definitive answer to this. I know that as a rule of thumb
the speed of light is reduced to around 0.66c in a fibre, so you could
say that the signal travels through the fibre at 2/3 the speed of
light. What is the equivalent for an electrical signal in copper?

Thanks.

Ash.

....note that I'm only asking about the signal propagation time in the
cable. The processing delay of the equipment at each end of the cable
is a seperate issue.

 J 06-19-2006 12:02 AM

Re: Latency of copper vs latency of fibre?

anon6111@hotmail.com wrote:
> Hi all,
>
> I recently had one of my non-technical colleagues ask me an interesting
> questing - how fast is ethernet data transmitted over a UTP cable? So
> what he was really asking is "what is the average latency of an
> electrical signal over copper cabling?". I've done some googling but
> can't find a definitive answer to this. I know that as a rule of thumb
> the speed of light is reduced to around 0.66c in a fibre, so you could
> say that the signal travels through the fibre at 2/3 the speed of
> light. What is the equivalent for an electrical signal in copper?
>
>
>
> Thanks.
>
>
> Ash.
>
>
> ...note that I'm only asking about the signal propagation time in the
> cable. The processing delay of the equipment at each end of the cable
> is a seperate issue.

I highly recommend getting a copy of "Ethernet: The Definitive Guide"
by O'Reilly.

http://www.amazon.com/gp/product/156...Fencoding=UTF8

The discussion about Ethernet specifications, specifically minimum and
maximum cable lengths explains the round-trip propogation delay in
detail. If memory serves me correctly I want to say that the maximum
time between any two devices in a broadcast domain is something like
26.5 micro-seconds for a maximum round-trip time of 53 micro-seconds.
I think it's something like that but frankly I can't recall with any
degree of certainty. I recommend the book to everyone in networking.
I've found that the concepts it outlines are applicable in everything I
do in networking every day.

J

 Michael Newbery 06-19-2006 01:09 AM

Re: Latency of copper vs latency of fibre?

anon6111@hotmail.com wrote:

> Hi all,
>
> I recently had one of my non-technical colleagues ask me an interesting
> questing - how fast is ethernet data transmitted over a UTP cable? So
> what he was really asking is "what is the average latency of an
> electrical signal over copper cabling?". I've done some googling but
> can't find a definitive answer to this. I know that as a rule of thumb
> the speed of light is reduced to around 0.66c in a fibre, so you could
> say that the signal travels through the fibre at 2/3 the speed of
> light. What is the equivalent for an electrical signal in copper?

About 75%, for UTP. The difference usually only becomes significant for
long distances (km) at which point moving significant bandwidth over UTP
becomes challenging.

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