[mod.computers.vax] Ethernet Questions

pung@ornl-ncc.ARPA.UUCP (03/27/87)

Hi,
	A couple of Ethernet questions for you experts.

	We have a requirement to use a very short segment of an
	Ethernet fiberoptic link for security reasons.  What we are
	looking at is having a short segment of Coaxial cable with
	a tap to which a fiberoptic repeater (1/2 of a DEREP-RA) will
	be connected.

			I have a few questions:

		1. What is the shortest segment of Coaxial Cable that
		   will support Ethernet without transmission errors,
		   collisions, attenuation problems, etc ??

		   If you want to have a short segment, should you
		   cut the cable on the magic black marks (i.e. make it
		   a multiple of 2.5 meters) ??
		   
		   I am aware of the magic cable lengths that Digital sells.


		
		2. What is the shortest segment of Fiberoptic Cable that
		   will work over without the problems mentioned above ??

		   With some of our other fiberoptic gear, we have found
		   that the fiberoptic LED's are designed for long
		   distances and when connected with a short segment of
		   fiber have an overrun/overdriving effect.

		   I noticed that DEC sells fiberoptic cable in lengths as
		   small as about 50 feet.



	Does anyone have any experience with these issues???
	Thanks in advance...

	|------------------------------------------------------------------|
	|          Mike Pung               |	   (615) 574-8082          |
	|     Oak Ridge National Lab       |  Pung%ornl-ncc@ornl-msr.arpa  |
	|  Martin Marietta Energy Systems  |                               |
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