Sam Parthemer, Datalink Solutions Inc.
Problem
A customer`s existing cabling plant for data communications is commonly wired using RS-232 data cabling with RJ-12 six-conductor wallplates and the Uniform Service Ordering Code wiring scheme. The customer may now want to run 10Base-T on the same cabling, while retaining connection to the old RS-232 network. This cabling was installed before the Telecommunications Industry Association category system was devised, and it is uncertain that the existing plant can meet current Category 3 requirements. What can you do?
Solution
If you know that the existing USOC wiring is straight-through and correctly paired, you can make a patch cord that takes the USOC pairing directly into 10Base-T without rewiring the wallplates and the patch panels. You can then test the system to ensure it complies with the Category 3 standard. If it does, you will have created a backward-compatible network over which you can run 10Base-T Ethernet.
Procedure
1) Make up an appropriate number of patch cords that connect the 10Base-T network at one end to a USOC line cord at the other (see diagram). Note that pair 1 is intentionally left unwired to ensure no voice/ring voltage can get to the 10Base-T equipment if you mistakenly plug the conversion line cord into a telephone outlet.
2) To verify that the system meets Category 3 specifications, use a 10Base-T tester to measure loss, near-end crosstalk and other cabling parameters.
3) If the network cabling passes all Category 3 parameters, hook up the active equipment for 10Base-T Ethernet.
Sam Parthemer is a project manager and design technician at installation contractor Datalink Solutions Inc., San Diego, CA.
