Ethernet breaker

Thanks for the replies. Maybe I should describe the actual application.

We have a machine with multiple PC based operator interfaces. During machine servicing it is sometimes necessary to disable control of the machine at all but one interface PC. We are looking for a way to disable control that is a) not software based (we already have numerous s/w interlocks built in to the system and b) doesn't involve removing power to the PC. What we'd like to do is simply disable the data line to the PC.

Two easily implemented methods are currently under consideration.

1) Use a managed ethernet switch at the center of the control system and disable individual switch ports as needed. The problems are that switch silicon (arguably or provably) has a higher failure rate than say a mechanical/electrical switch and to the user/safety inspector it still looks and feels like a software switch.

2) Install a low-density ethernet (branch) switch between each PC and the central (core) ethernet switch with an electrical relay controlling power delivery to those branch switches. The relay states can then be selected with a traditional mechanical knob switch. The problems here are that we just greatly increase the number of potential failure points in the control system and introduced a whole bunch more unused ethernet ports which we are trying to limit for other safety reasons (e.g. factory staff plugging in computers without having to follow procedure).

My imaginary solution is a fairly simple, two port device that would sit inline on the PC ethernet link and when it lost power would break the link. Do you know of such a device?

Thanks again- Rich

PS I'm using the groups.google interface for the first time. Apologies if it does anything rude like top post or full-quote.

Several companies make boxes that can switch 120VAC frm an RS232 connection or TCP/IP via ethernet. You can just cut the power to the switch.

See

ISTM if you lose power to "that device" it obviates the need to turn off the bits. It's no longer listening.

Black Box Corp

specializes in odd gadgets like this.

Any managed hub or switch can control the ports via snmp protocol from an network management application running on one or more systems. I'm sure snmp commands can be scripted from a language like PHP but that's above my pay grade.

Are you dealing with life-critical systems or otherwise covered by OSHA?

If you add up the all the extra electrical connections, power sources etc for a relay-based system in use on any scale I'd argue that a managed hub with a web interface is *much* more reliable and in the unlikely case that it does fail it will do so in *much* less interesting ways and be trivial to spare and fix.

This would be a decent solution b/c then I wouldn't be compelled to pour epoxy into unused switch ports :-( Have you seen 2 port ethernet switches? Can you reference a manufacturer?

Can't unplug. HW switches would be great! Please tell me more if you can.

Thanks- Rich

Somehow I think we are playing in different leagues. CISCO, HP and a pile of other venders make managed hubs and switches. The HP procurve stuff (except for the bottom end) has built-in WEB management interface. I'm not familiar with CISCO.

Look for an HP Procurve box on ebay and then check HP.com to find the manual and read it to see what it's management capability is. Procurve has a lifetime warranty so it's hard to go wrong. I'm partial to the HP 4000 switch.

I repeat my statement; a business grade hub is going to be more reliable than a pile of relays, cables and wall wort power supplies.

Buy two or three, there *real* cheap.

HP will fix them forever.

In article , Rich Noonan wrote: :I'm looking for a device which could act as an ethernet breaker switch :based on the application or loss of power to that device. On one hand :we could accomplish what we need with a low-cost switch and two cables. : However, in our application and environment this would introduce :several new problems. What I really need is a two port fast ethernet :repeater that I could cut power to and break the link. Of course, such :a thing doesn't exist (or does it?).

Your reference to "several new problems" makes it difficult for us to know what would be acceptable and what would not.

I don't know whether this will help you, but recently I have been investigating remote-controllable serial ports and remote controllable power switches. For my particular application, I was looking at ones that can be reached via ethernet. Especially for the power switches I also found devices that can be controlled via serial lines -- up to 2000 feet for one of the devices.

Typical remote control units have 1, 8, or 16 ports, with 4 and 32 port units not too hard to find, and with 2 port units available but not easy to find.

The choices are differentiated on their remote access method (serial / ethernet); their security (ssh?); their modularity; their flexibility (several are uLinux with SDKs); their number of ports; their physical size; the amperage the power controls handle; and, of course, upon their cost.

Links to several manufacturers can be found at

In addition to those, I suggest checking out their web page has not yet caught up to several recent security enhancements.)

I have several other units bookmarked; if you want a bookmark dump, send me an email note.

I have seen something that reminds me of what you're asking for, except it's completely the opposite!

Years ago I had some external (to a webserver) hardware SSL accelerators. They were designed to go inline with a webserver's Ethernet cable, and do the SSL work whenever traffic appeared on TCP:443.

These boxes had 2 RJ45 Ethernet connectors on the front panel. These jacks were connected to *both* the ethernet transceivers of the hardware in the box *and* to each other through some DPDT relays (i guess).

The idea was that *even* if power to your SSL box was cut, the webserver would stay online.

So, yes, it's completely the opposite of what you're looking for, but it makes the point that running ethernet through some relays might be okay :-)

/chris

How about removing the power to a 2-port switch? Would that solve your problem?

If this is something you have to do one at a time, can you unplug cables or flip hardware switches? I've seen CAT5 mechanical switches..

In article , Al Dykes wrote: :If you add up the all the extra electrical connections, power sources :etc for a relay-based system in use on any scale I'd argue that a :managed hub with a web interface is *much* more reliable and in the :unlikely case that it does fail it will do so in *much* less :interesting ways and be trivial to spare and fix.

Ummm... where are you going to find a managed *hub* with a web interface?

There were some managed hubs, but they weren't common at the best of times, and they predated widespread use of web interfaces. They used serial, or telnet + snmp, or custom GUIs.

These days, it is apparently difficult to find true hubs; according to some of the groups I follow, devices being marketed as hubs have often been switched over by the manufacturer to actually be switches under the cover.

In article , Rich Noonan wrote: :My imaginary solution is a fairly simple, two port device that would :sit inline on the PC ethernet link and when it lost power would break :the link. Do you know of such a device?

There are many "broadband routers" on the market, a number of which can be set to turn off NAT.

(snip)

I would think a simple relay would be more reliable than a relay switching a complex of electronics.

I think you can just short across each pair to turn it off. That is probably more reliable than opening the circuit. (Probably one pair is enough if you decide which one.) I am pretty sure it won't hurt anything, but you might want to verify that first. I think it will also have less effect on the impedance characteristics of the line, though it might be better not to try it at gigabit levels anyway.

-- glen

In article , Al Dykes wrote: :Somehow I think we are playing in different leagues. CISCO, HP and a :pile of other venders make managed hubs and switches. The HP procurve :stuff (except for the bottom end) has built-in WEB management :interface. I'm not familiar with CISCO.

I found the Procurve Hubs on HP's site, and you are right that they do have a Web interface. On the other hand, checking around to stores, I'm finding them available as Used, or "1 in stock" (at wildly different prices.)

:Look for an HP Procurve box on ebay

If you have to buy it on eBay now, then it it isn't a good choice for devices intended to be easily replaceable.

Hmm, Linksys BEFSR11 looks like a product that's still extant, and you can probably put it in static routing or DMZ mode if you need to... Under $50 at Amazon, probably cheaper elsewhere.

I'm not home right now, though even if I were I'm not sure I could put my hand on the printout. Of course, in this case, google isn't your friend, as "cat5 switch" gets you lots of electronic 10/100 switches, but no mechanical ones.

I do know they exist! 8*)

A long time ago, at a trade show far away...

There was a company called LanHopper that made managable (via console or out of band SNMP) mechanical ethernet "switches". I put switches in quotes as they were not what we consider switches today. The were full of relays. You could hook one port to any other port, or just physically disconnect a port.

Sounds like what the OP is looking for. Have no idea where they went or what happened to them.

Check blackbox.com

$US10

Do you have space in/near the machine controller where you can stash a

4-port switch without the danger of people plugging extra equipment in?

If yes, something like this would be possible: put in a 4-port switch connecting machine, one operator interface, and a cable to the upstream port on the next switch. Next switch connects to all other operator interfaces and whatever people want to plug in. To limit control, cut power to the second switch, or put a hardware/keylock switch in the cable between the two switches.

J.

Don't forget, you'll need a relay that can handle the signal, without disturbing the impedance too much.