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T1 RJ-48C Wiring and the Smart Jack

Again I find myself wiring up T1 circuits for a Telco provider that my company is going to use. I also find myself scouring the Internet for color codes for the T1 cable at the “Smart Jack”. The smart jack is where the demarcation point or demarc resides. So what is a demarc and what exactly is the smart jack… The demarc is where the Telco ends their responsibility and yours begins. The Telco needs a way to start your responsibility for wiring and internal maintenance, that is the threshold of the demarc. The smart-jack is a way that the phone company can loop or loopback the signal so that they can remotely check that everything is OK on their side.

Your interface with the smart jack is an RJ-48C connector, which is basically an RJ-45. When wiring the RJ-45 use the wiring spec of the TIA/EIA 568B color code. This color code is as follows…

RJ-48C Wiring

However only Pin 1, Pin2, Pin 4 and Pin 5 are used… You only need to wire the 4 pins crimped to the RJ-45 connector. In the end the White/Blue and Blue pair of wires is your Transmit Ring and Tip and the White/Orange and Orange pair of wires is your Receive Ring and Tip. This basic wiring is what comprises a 4-wire T1 circuit with current Telco service today.

If you wanted to create a simple hardware loopback; you could simply connect Pin 1 to Pin 4 and connect Pin 2 to Pin 5. This would connect the Receive Ring with the Transmit Ring and connect the Receive Tip with the Transmit Tip. A connection like this would loop all data back to the Telco. You can fabricate a device like this with an RJ-45 connector and two wires. When you want to check your wiring you can; look at the smart jack (if you have access to it) and watch the ‘Alarm’ go off when you connect the loopback or call the Telco and have them verify the alarm is off. This is a simple way to check your T1 circuit all the way to your device.