Monday, August 20, 2012

Telephone Jones and the Bridge to Nowhere

Today started like any normal Monday looking at the random tickets from over the weekend.  Then I decided to work on installing a new phone for our new IT team member.  Keep in mind that I am still supporting an ancient (that's being nice) Rolm/Siemens 9006i CBX (Computer Branch eXchange) for a phone system.  So unlike my lucky colleagues in the IP Telephony realm, a new phone is still a production number when it comes to layer 1.

For those not familiar with traditional phone systems, you have to have a copper path from the phone to the port on the phone system.  There are no intermediate switches like on the network side.  These paths are created using jumper wires between phone blocks like shown to the left.  As you can see, there is not much room for labeling.  To add insult to injury, through use, even with permanent markers, the labels tend to fade or disappear completely.  Of course this is why every telephony engineer carries a toner set and knows how to use it.

Today's adventure started at the user's cubical.  There were four telephone jacks labeled 22 A, 22 B, 22 C, and 22 D.  Generally when the jacks all have the same number and just a different letter, it is one 8 conductor (CAT5/CAT5e/CAT6) cable that has been split across four jacks.  Usually A represents the blue/white pair, B the orange/white pair, C the green/white pair and D the brown/white pair.  In my case the port labeled B was available so I plugged in my toner and ran off to the IDF to find the other end.

This is where it got fun.  Normally when toning out a cable, you will find one place on the other end that you hear the tone.  That being said, when I heard tone (keep in mind the labels had worn off) I assumed I was on the right cable.  I punched down my jumper from the phone system to the orange/white pair and went back to the cubical to check the phone.  Nothing.  The phone was as dead as it was before I plugged it in.

Thinking that maybe the B pair was damaged, I hooked the toner up to the D pair and repeated the process.  So this time though I found the tone on a different orange/white pair.  Remember when I said that D should go to brown/white?  Well at this point I got puzzled.

In my environment it is common for lines to have been abandoned without removing the old jumpers.  This turned out to be the case this time.  As I continued my troubleshooting I found the tone in 7 different places on the 66 block.  I noticed that there was a jumper cable on all of the terminals that had tone.  After following the jumper I found that all 7 locations were bridged for an old modem or fax line.

The solution to my problem was to remove the bridging jumper and voila my tones worked right and I was able to get my phone setup.  Unfortunately this whole process took 3 hours with interspersed other morning fires in the mix.

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