Computer cables can only be too short, but never too long. The same applies to networking cables. Sometimes it is just the last meter that is missing, but in many cases, some kilometers are missing. A standard 10/100 or 10/100/1000 Copper RJ45 connection can be 100 meters long. To be honest, this is not really a lot when thinking about connecting the world. Using fiber cables and media converters and switches is not a bad idea, but in many cases, not a solution that you can do immediately or for somewhat money. If there is no fiber cable, you need to install one. If you want to connect another building being 1 kilometer away it can be nerve-racking to get all approvals to dig and install the fiber cable.
Ethernet Extensions are cheap and immediate solutions for using what you have for connecting your networks. Almost always there are already telephony cables. With Black Box Ethernet Extensions you can use these for your network at tremendous bandwidth rates.
Basically, the following standards and protocols are available for doing Ethernet Extensions:
Black Box has beside the here listed example products others available with less distance or bandwidth that are available for you as economy versions. One should not exchange incoming Internet DSL lines from your Internet Service Provider with these devices. These are Ethernet Extenders to make your data go where no Ethernet data has gone before. But the basic technology is the same. Nearly all existing telephone lines can carry frequencies up to 1 MHz. But analog telephony only requires a maximum frequency of 3.3 KHz, leaving a large amount of the bandwidth unused. DSL makes use of this otherwise wasted space by piggybacking high-speed data traffic onto the unused bandwidth.
So by implementing Black Box DSL technology you just use what you already have. Because the telephony wires are there, there is no additional money investment necessary except for the Ethernet Extension devices. Since some of the Black Box solutions still transmit the analog telephony service parallel to Ethernet on the same wires, there is no argument to not use this technology.