Thread View: comp.dcom.lans.fddi
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Started by SEAH Winston
Sat, 09 Jan 1993 03:39
Signal Propagation Delay in FDDI fibre optic media?
Author: SEAH Winston
Date: Sat, 09 Jan 1993 03:39
Date: Sat, 09 Jan 1993 03:39
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What is the actual signal propagation delay in an FDDI fibre optic cable? Is it equal to the speed of light in free space, or is it a fraction of that? Similarly, what is the signal propagation speed in a coaxial cable that is used by the common LANs, such as, Ethernet and Token Bus? Winston. -- ******************************************************************************* * * * * SEAH Khoon Guan Winston * Email: winston@kuamp.kyoto-u.ac.jp * * Logical Systems (Hasegawa) Laboratory * Tel (Home) : +81-075-712-9325 * * Dept of Applied Mathematics & Physics * Tel (Lab) : +81-075-753-5518 * * Faculty of Engineering * Fax (Lab) : +81-075-761-2437 * * Kyoto University, Kyoto 606 * * * JAPAN * * * * * *******************************************************************************
Re: Signal Propagation Delay in FDDI fibre optic media?
Author: Richard Lawrence
Date: Sat, 09 Jan 1993 16:54
Date: Sat, 09 Jan 1993 16:54
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In article <WINSTON.93Jan9123922@yuka.kuamp.kyoto-u.ac.jp> winston@kuamp.kyoto-u.ac.jp writes:
>
>What is the actual signal propagation delay in an FDDI fibre optic cable?
>Is it equal to the speed of light in free space, or is it a fraction of that?
It's my understanding that the velocity of propagation in any media
besides vacuum is lower than c. I've seen figures of .8+ c for fiber
cabling, but I think it's really up to the cable.
>Similarly, what is the signal propagation speed in a coaxial cable that is
>used by the common LANs, such as, Ethernet and Token Bus?
Typical 10base5 VP is .77c. 10Base2=.66 c, 10BaseT=.58 c. This is the
main reason for different distance limitations, to compensate for
different delay budgets (10BaseT being a special case; you loose the
signal long before you exceed the delay budget in most cases).
Having a higher VP does not mean you have a faster LAN. A 10Mhz or
100Mhz signal rate is the same regardless of how fast it travels from
point A to point B. High VPs do grant you extra distance, though.
--
Rich Lawrence, Synoptics Systems Engineer DOD#9630 rich@grebyn.com
'92 Seca II "Yuri" CI$:71101,2272 GEnie:R.LAWRENCE14
215 years ago my government gave me certain inalienable rights.
Since then, they've been trying to correct their mistake.
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