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Network cables and impedances that go bump in the night

Hi,

I often need to plug something in to the network temporarily (e.g., to configure something or talk to a NAS box, etc.). I have a switch in the office to serve the dozen or so nodes there. So, there is always a spare port that I can use.

But, it's on the floor amid a tangle of power cords, network cables, etc. I.e., I have to get out of my chair and *kneel* on the floor to make the connection.

My knees don't like it when I do this. They go to great pains to remind me of their displeasure! :)

I have these little "surface mount" (as in "surface of the wall") boxes that are intended as four point drops. I.e., you feed four cables into them "from behind" and have four connectors available on the face of the box. Much like a wall plate but this will mount *on* the wall instead of flush.

I had thought of installing three connectors in the box. Then wiring connector 1 to connector 2 "straight thru" and then chaining on connector 3 "with a twist". After mounting this on the underside of one of the desktops, I could connect connector 1 to the switch "permanently" with a standard patch cord.

Connector 2 would give me a convenient "outlet" to which other devices could be attached, temporarily. And, in those cases where I need to connect "node to node", I could use connector

1 (or 2) with connector 3 (to get the "twist") without the need of a crossover cable. I.e., I can keep one "regular" patch cord handy and use it for all needs.

Neglecting the problems with trying to get two wires on a single punchdown block... am I likely to have other problems from the impedance bump that the "extra" connector will present? Or, will it be insignificant enough (especially since this is just a temporary connection, normally)?

Thx,

--don

Reply to
D Yuniskis
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Don't do this daisy chaining. It will break every rule of XBase-T=20 twisted pair network wiring. Put in little $15 switches instead.

Reply to
JosephKK

On Mon, 25 Jan 2010 03:10:23 -0700, D Yuniskis wibbled:

Netgear 5 port metal cased jobbies have keyhole slots and are happy to be mounted upside down on a couple of roundhead screws...

eg GS105, gig, 40 quid sterling. or if you want to be cheap, FS105 for half the money 100/10. Bear in mind that you might do well selling the former on ebay at end of use and be no worst off than using the FS105.

--
Tim Watts

Managers, politicians and environmentalists: Nature's carbon buffer.
Reply to
Tim Watts

I'm aware that it "breaks the rules". The point of my query was to determine how any problems would manifest themselves. I.e., for what is admittedly a "temporary connection", I can easily life with reduced bandwidth, etc. OTOH, if it simply "didn't work", then it would be a wasted effort.

Adding yet another "small switch" means finding a way to mount that switch someplace convenient (most of the 4 or 5 port switches I've seen are intended as "desktop" devices -- not viable, here -- so I would have to physically modify one in order to fasten it to the underside of the work surface. And, then make room for yet another wall wart to power the damn thing -- despite the fact that 95% of the time the switch will be unused (so, even if I install a power switch

*in* the switch, the wall wart is still wasting power and taking up space).
Reply to
D Yuniskis

Nope. This is done in many commercial Ethernet hubs. One port will be brought out in two jacks, one wired as a crossover, so that hubs can be daisy chained.

Its possible that leaving a longish cord in the unused port might cause reflections (from the open end) that will interfere with the port in use. But I doubt an open stub of only a few inches length will produce much of an effect.

Don't go connecting both jacks to live equipment. That will bugger things up. I can't remember how many times I've been asked to debug a friend's office LAN and found a new PC plugged into the one remaining open jack on the hub. I wish they'd make a little sliding door that would block one or the other jack sharing that port.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Human beings were created by water to transport it uphill.
Reply to
Paul Hovnanian P.E.

Yes, that was the inspiration for attempting this. But, doing it in foil is considerably different than trying to get it right with discrete wires (e.g., it is usually a PITA just to keep the tight twists all the way up to the punchdown blocks -- and I would have to keep them

*beyond* ... to the *next* punchdown block!)

Dunno. I don't know how to gauge what the impedance bump will do to the "legitimate" data signals.

Ah, that's a great idea!! Or, If they had specified *all* cables needed a twist and done away with that "special" connector entirely...

Reply to
D Yuniskis

I haven't had a problem like this in a number of years now -- almost all routers, switches, etc. that you see today implement auto-MDIX on the Ethernet ports, in which case it doesn't matters whether or not your cables perform the crossover.

I do still carry around one of those Ethernet crossover fobs just in case I encounter someone's older network equipment, though. :-)

Reply to
Joel Koltner

Because of the conceptual differences and operational differences=20 between coax networking and twisted pair networking i bet there is a=20 odds on chance of not working. It may be possible with 1:1:1=20 transformers but i would still bet against it. The inevitable=20 impedance change may cause line levels to shift beyond acceptable=20 bounds. The bump from the daisy chain is not so much the issue,=20 unless you want 1GBASE-CX. 10BASE-T will not hardly notice, though=20

100BASE-TX probably will. All 3 of them may die if the parallel=20 connection is tried.

You might try running two cables out of your existing switch. And yes, i understand that pulling the new cable may well be a=20 real pain.

Reply to
JosephKK

One advantage of this approach is I can remove the cable to the switch from the backside of this little box and then I essential have that "crossover fob" sitting there under the desktop. I.e., I could plug two devices directly together (via this "fob") instead of having to dig up a crossover cable.

Reply to
D Yuniskis

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