Why are Coax-to-Ethernet converters causing the entire network to stop working?

Question

I have installed nine of these Coax-to-Ethernet passive converters, which allow me to use existing coax cables to transmit Ethernet traffic from IP cameras. This was necessary due to the inability to run new Ethernet cables to those locations.

These usually work as advertised. However, I have encountered situations where, if the converter gets disconnected from one end of the coax, or if the coax is not terminated properly, causing a poor connection, our entire network stops passing traffic.

Note that we have multiple Ethernet switches uplinked together, and all the coax converters are connected to a single switch used only for this purpose, which is then uplinked to our main network switches.

When this issue happens, if I try to ping any address on the network, no matter if I'm connected to the switch that hosts these converters or any other switch in the network, the pings come back as "timed out" and computers can't talk to each other.

It's as if these adapters cause some sort of packet flood or loop which the switches don't know how to handle, if there is not one present on each end of the coax.

As soon as I unplug the offending coax adapter from the switch, the network starts working again with no lost packets. Usually the problem is due to the coax being improperly terminated, thus there is no connection to the other end. Fixing this usually eliminates the problem.

However, the last time, it seemed multiple of these adapters were causing the problem. I could plug any of the adapters into the switch and within a few seconds I would start to see some packets dropped, then major packet losses would begin.

I'm trying to understand what principle is in play here, so that I can mitigate this to the greatest extent possible.

I wish I could eliminate these converters, but that's not possible due to the existing wiring being impossible to replace.

Answer 1

Basically with these adapters the unterminated coax just creates an Ethernet loopback plug with delay proportional to cable length.

As mentioned by the previous question how these adapters work, they most likely just have a hybrid transformer to terminate the coaxial cable and to split/combine the single transmission line into separate transmit and receive paths for the twisted pair side.

As you said most problems happen when there is nothing connected at the far end of the cable when the coax is not properly terminated.

As per the theory of transmission lines, improperly terminated cables will cause a reflection at the end of the cable when it is not properly terminated.

It is possible that signals sent from the Ethernet switch reflect back at the end of the cable and the Ethernet switch determines that the link is up and it can send packets out and it will receive the reflected packets.

So at the first packet the switch sent out to coax will get echoed back and received by the switch and switch has to send it back again to coax, creating infinite retransmissions of the same packet over and over again.

So you must reconsider your options which is least impossible and least costly, just replacing the cable for reliable network, or spending money and time getting the network to operate with several of these quirky adapters as you likely have constant problems, or purchasing proper adapters.