Latency of copper vs latency of fibre?

Latency of copper vs latency of fibre?

Post by anon6.. » Tue, 20 Jun 2006 08:26:28



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.

 
 
 

Latency of copper vs latency of fibre?

Post by J » Tue, 20 Jun 2006 09:02:15



> 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/1565926609/sr=8-1/qid=1150674696/ref...

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

 
 
 

Latency of copper vs latency of fibre?

Post by Michael Newber » Tue, 20 Jun 2006 10:09:37




> 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.
 
 
 

1. High latency when idle, low latency when passing traffic

We are using ppp multilink bundle connections throughout out network to
aggregate bandwidth from multiple T1s. One of these connections is
exhibitying bizarre behavior.

At night, when the traffic rate is low, latency on the line increases
to about 300 ms. As soon as data starts coming down the line, latency
drops down to sub-80 ms. There are 7 T1s in the multilink bundle. I
checked the DSU settings on both ends for each of the lines, and they
all look correct. We are using ESF / B8ZS.

We have three other connects using similar routers, IOS versions, and
numbers of T1s in the multilink bundle;they all show what you'd expect:
really low latency at night, with increases under heavy load. It's not
an issue of ARPing adding to the latency.

Could this be a timing issue?

2. "The Message Could Not Be Sent. An Error Has Occurred"

3. copper pair vs coax vs fibre optic

4. best short term speculation??

5. Latency - ATM vs FDDI

6. HELP AD and TSE problem!!!!!

7. Response Time vs. Latency white paper

8. (no subject)

9. Response Time vs. Latency

10. 56K leased line VS V.FAST or has anyone measured latency lately?

11. Response Time vs. Latency

12. ISDN Router vs TA - Latency

13. Latency, Pipeline 25 vs USR Sportster 128