Re: Looking for comments on the 15-pin ethernet connector


Roy Smith (phri!roy@nyu.edu)
14 Jun 88 15:28:03 GMT


dmc@videovax.Tek.COM (Donald M. Craig) writes:
> I am looking for feedback on the quality and reliability of
> the slide latch mechanism used on the DB-15 ethernet connectors.

        In a nutshell, they suck! There is no doubt that the single most
common cause of problems in our entire network (19 Suns, a Vax, and maybe a
dozen Macintoshes and PCs) is loose ethernet tranciever cables, particularly
on the backs of Sun-3/50's which provide no mechanical support for the cable
at all. On our rack-mount systems, we support the cables with cable ties to
various convenient supports. On our deskside suns, we've constructed
assorted mechanical strain reliefs. Some of our 3/50's seem to be OK with
just wedging the cable behind a desk but some are a constant cause of
trouble. For the worse ones, we install a support bracked we've designed
which helps a little (it's just a plexiglass bar notched to fit on the card
extractor ears and with cutouts for the various cables and attachment points
for cable ties in the appropriate places).

> "I am the Component Engineer for connectors at Sun. In regards to your
> question concerning the Ethernet DB-15 [...] I am not aware of any
> significant problems with mechanical integrity of the lock, or for that
> matter with the connector in any aspect.

        I'm not given to public flamage, but this guy must have his head
firmly wedged in a dark place. If he's not aware of any problems, it because
he hasn't been listening. I've complained loudly about this on the net
before. I've complained to Sun field service. I've complained to Sun tech
support. Clearly those complaints havn't gotten back to the right people.

        The stupid little stamped sheet metal clips are simply not strong
enough to secure a connector with a big fat, heavy, and fairly stiff
tranciever cable on it. As long as the cable is secured so if can't move if
accidentally moved, it's OK. For example, on the tranciever ends, we lash
the cable to the main ethernet trunk cable with 2 (or sometimes 3) wire ties
a few inches away. But on systems which might move a little (like a deskside
Sun on wheels), or in situations where the cable might be disturbed (like
hanging off the back of a desk) forget it.

        What was wrong with good-old RS-232-style screws? Or, if they really
wanted a tool-less installation, why not Macintosh-style knurled screws, or
maybe even centronics-style wire bails? We recently got a 3-Com 3C503
ethernet card for an IBM-PC. The connector is a bit different, with screw
holes instead of binding posts. Unfortunately, to use the screw holes you
need a special adaptor bracket which I havn't been able to locate yet (OK, we
just got the thing; I havn't had a chance to look very hard). It looks like
it might be a bit more secure. Our Interlan ethernet board for the vax has a
slight variation on the slide connector which looks like it might be
marginally stronger (it has small extra ridges along the sides), but I doubt
it would still be strong enough if we weren't able to lash the cable to
various places in the vax's rack frame.

        I really don't know what the DIX guys had in mind when they designed
this connector. Administering a network is hard enough without having to
worry about which $5 connector is falling out.

--
Roy Smith, System Administrator
Public Health Research Institute
455 First Avenue, New York, NY 10016
{allegra,philabs,cmcl2,rutgers}!phri!roy -or- phri!roy@uunet.uu.net



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