job screening question

Fri Jul 6 03:26:49 UTC 2012

In a message written on Thu, Jul 05, 2012 at 11:05:21PM -0400, William Herrin wrote:
> Incidentally, 100m was the segment limit. IIRC the collision domain
> comprising the longest wire distance between any two hosts was larger,
> something around 200m for fast ethernet. Essentially, the collision

Actually it can be much longer, having worked on a longer such ethernet
many, many moons ago.

The longest spec-complaint, repeated only network looks like:

   |
   | Host Segment
   | 
   + Copper to Fiber Repeater
   |
   | 2km fiber, no hosts
   |
   + Copper to Fiber Repeater
   |
   | Host Segment, with or without hosts
   |
   + Copper to Fiber Repeater
   |
   | 2km fiber, no hosts
   |
   + Copper to Fiber Repeater
   |
   | Host Segment
   | 

With 10base5, a copper segment can be 500m, so 500+2000+500+2000+500, or
5.5km.

With 10base2, a copper segment can be 185m, so 185+2000+185+2000+185, or 
4.5km.

WIth 10baseT, a copper segment can be 100m, so 100+2000+100+2000+100, or
4.4km.

The introduction of fiber repeaters is why folks started to use the
broken term "half repeater".  This was so folks who learned the
rules as "2 repeaters in the path" could deal with the fact that
it's actually the 5-4-3 rule, so they called the 4 repeaters two
half repeaters.

Of course, each repeater could be a multi-port repeater (or a hub in
10baseT speak) and thus have a star configuration off of it in the
diagram.

Add in a couple of 2 port bridges to reframe things, and it's quite
possible to run a layer 2 ethernet that is 10's of km long, and has
thousands of hosts on it.  There was a day when 3000-4000 hosts on
a single layer 2 network at 10Mbps was living large.

Thankfully, not anymore.

-- 
       Leo Bicknell - bicknell at ufp.org - CCIE 3440
        PGP keys at http://www.ufp.org/~bicknell/
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