job screening question

William Herrin bill at
Fri Jul 6 03:05:21 UTC 2012

On Thu, Jul 5, 2012 at 10:25 PM, Owen DeLong <owen at> wrote:
> On Jul 5, 2012, at 5:50 PM, Scott Weeks wrote:
>> --- bill at wrote:
>> From: William Herrin <bill at>
>>> 5.      What is the reason for the 100m distance limit within an ethernet collision domain?
>> What's an ethernet collision domain? Seriously, when was the last time
>> you dealt with a half duplex ethernet?
>> -----------------------------------------
>> Now if someone answered it that way, I'd definitely be
>> interested while the HR person would just hang up...
> +1 -- That would be a perfectly valid answer and one of the list of answers I would actually give to HR.

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
signal caused by receiving the first bit of the overlapping packet had
to get back to the sender before the sender finished the 64-byte
minimum-size packet. Allow for the speed of light and variances in the
electronics and that was the width of the collision domain.

Carrier sensing multiple access with collision detection. CSMA/CD. I
haven't thought about that in a long time.


William D. Herrin ................ herrin at  bill at
3005 Crane Dr. ...................... Web: <>
Falls Church, VA 22042-3004

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