I have an application in which I need to disconnect an ethernet channel most of the time unless there is a special set of circumstances. I have a processor to control the disconnection, and access to the ethernet (CAT5) cable and its conductors.
The application is in a pressure environment and that precludes me from using the obvious relays on the 4 cores of the cable. I have no software access to the routers on either end of the cable, so I can't simply program them to turn off the channel. So, I'm looking for some way of disabling the channel by only accessing the transmitted signals.
To put some context: We have a subsea application in which two separate ethernet circuits are used to transmit data between the surface and the equipment subsea. In normal use, one circuit is used for bidirectional control and monitoring of the subsea systems, and the other is a dedicated, one-way high-speed data link used for monitoring. In order to minimise the jitter and latencies on that link there will be only one data channel open and transmission will be as fast as possible with no other data on the link. Normally the two networks are totally unconnected at both the topside and bottom ends.
However, it's all too possible that one of the ethernet connections becomes broken. In this case we want to be able to bridge the two independant networks onto the remaining wire, albeit with some degradation in the link speeds. On a surface system, this would mean that we simply unplug the bottom end ethernet cable from its router and plug in into the other network, and do the same thing at the top end, so that both networks share the same bit of wire for the uplink. Everything should then work as before.
However, we can't find any volunteers to replug the networks in the subsea end of the link, so we need to make the switch automatically. That'd be easy enough in a 1-bar environment, because we'd just use changeover relays in the cable. However the whole system's running in an oil- filled box at whatever the pressure is at depth, which could be up to 600MSW (or 60 atm). So, I need to use solid state stuff to do the switching. I don't think that I can just stick semiconductor switches in the circuit either because they have quite a large on- resistance (although I've not tried it).
I was wondering if anyone here had any ideas?