Latency of copper vs latency of fibre?

Jun 18, 2006 2 Replies
Latency of copper vs latency of fibre? open original image

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.

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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

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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