thicknet

All posts tagged thicknet

Ivan’s recent very interesting post on LAN Data Link addressing takes me back.  Specifically, footnote #1, referring to “ThickNet” Ethernet:  “The coaxial cable had to be bright yellow”.  In the US, at least, we also used to call the stuff “Frozen Yellow Garden Hose”, for obvious reasons.

The original Ethernet physical medium was rather interesting.  I’ve often talked about my love of layer 1, but I got into the business in the twisted-pair era.  I did do a bit of ThinNet networking, but only a little.  And I had one encounter with ThickNet.  Twisted pair is fun to work with and easy to manage.  Coax is not.

The original “ThickNet” Ethernet used, as the name implied, a fairly thick coaxial cable.  The cable had to be physically routed in a path which put it in proximity to the stations that would use it.  Connections to the cable were originally made with a “tap”, requiring physical piercing of the cable to reach the center conductor.  A drop cable then extended down from the tap to the station using it.  Messy, and inconvenient.

“ThinNet” used a substantially smaller cable, and it was far more flexible.  Think about something close to your TV cable coax, but even more flexible, and using BNC connectors.  As with ThickNet, the routing of the cable was tricky, but instead of physical taps we used T-style connectors to add stations into the network.  My very first Ethernet network consisted of a ThinNet segment tied into a 10Base-T twisted pair segment with an adapter.

I’ve written a few times about my first full-time networking job at the San Francisco Chronicle.  Back when I worked there, people actually read the paper and its printing and distribution was a big deal.  After the 9/11 attacks, you may remember several authorities and news agencies in the United States were mailed powdered anthrax.  These events prompted our management to set up a “disaster recovery” site, where we would have enough equipment to produce the newspaper in the event our main building was incapacitated.

For a reason I never understood, they chose a building on the same block.  Behind the Chronicle building were a number of alleys, and the company owned a building back there.  It made no sense at all.  If an earthquake hit, and the main building was destroyed, presumably the building across the street would be too.  If anthrax were mailed to the main building, I assume the entire block would be shut down.  But anyways…

We set up this empty building with computers and phones, and added a frame relay connection so it could connect to the WAN if the main building were out.  But we still wanted a high speed connection for file transfers and backups, so I was tasked with somehow getting a faster connection to the HQ.  I called our cabling contractor, who also resold several wireless building-to-building alternatives, but they were all expensive.  Then I made a discovery.

In the basement of this historic building was our MDF, the main phone equipment and wiring room.  There was a large distribution frame for phone wiring to the entire building, three or four racks of phone equipment, a desk that looked like it was made by prisoners, and a grumpy phone lady who sat in there.  One day I also noticed a pipe with a tag hanging off of it.  It had the address of the disaster recovery building in it, and a disconnected piece of frozen yellow garden hose hanging down.  Could it be?

I went outside and saw a conduit running from the top of the HQ building to the disaster recovery site.  At this time, ThickNet was not being used by anyone, but 10Mbps would be more than sufficient for this DR site that would probably never be fully staffed.

One of my fellow engineers (who had worked at the paper forever) had a lab packed full of all kinds of esoteric electronic equipment.  I went spelunking in the dingy room and found two ThickNet transceivers.  Thankfully the ThickNet was terminated on both ends with connectors, so I didn’t need to drill and tap.  I hooked up the transceivers, connected the RJ45 ports to a nearby switch on each end, and then tested the connection.  It worked!  I had no idea how many years that frozen yellow hose had been in place, but it took one problem off my plate pretty easily.

The “DR” building sat unused for several years, but with keys to the building it made a nice place to take a nap occasionally.  The site was decommissioned eventually.  I wouldn’t be surprised if the frozen yellow garden hose is still in the conduit to this day.

A lot more detail on ThickNet can be found at Matt’s Tech Pages here.