atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services T1's, CSU's and DSU's t1 / smart jack / demarc confusion

Just had the pleassure of installing my first solo t1, didn't go very well. The circuit id was clearly printed inside the telco network interface box mounted to the side of the residence (right next to the ped). by telco network interface, i mean the PASSIVE grey plastic box with the screw terminals inside. This box had a 2 circuit capacity and had 2 female rj-45 sockets per circuit that had 3" pig tails plugged into them, with the other end running to the copper screw down terminals. I ran a demarc extension with cat5e inside the house to the comm. cabinet and terminated both ends to 568B to a cisco 2811 router csu/dsu. the term smart jack to me has always meant an electronic interface that "converts" the raw telco signal into a tcp/ip recognizable format. During trouble shooting with the telco I was told everything from sunday that didn't make sense. My question: Do you need a smart jack (in the sense that I explained above) before you plug in to your router csu / dsu - OR can you in some cases just run directly into the router without the smart jack? I ended up leaving the site not sure if I dropped the ball or if the telco did. I was certain that the smart jack needed to be installed before the router could be pinged. Please let me know where I'm wrong.

No, the term "smart jack" simply means that a loopback condition is created when a plug isn't inserted to keep the circuit alive. All it does is connect the transmit pair to the receive pair just to create artificial traffic so that the telco doesn't automatically take it out of service.

Remember that outdoor T1 network interfaces have four connections; one pair for transmit and one pair for receive. These need to be connected to pairs 1,2, 4 and 5 at the terminal equipment's jack. You should invest in the proper jack, one that is designed to provide an RJ48X interface to terminate you cable run so that if the equipment is unplugged for testing, the circuit won't be disrupted.

If you follow the 1,2,4,5 wiring and it doesn't work, try reversing the transmit and receive pairs. The telco here is notorious for having them reversed.

Unfortunately, we won't be able to assist you further unless you complete your profile; it's just a courtesy thing that we request so that we know the level of support that will be necessary.

A smart jack is a form of T1 demarcation, but isn't the only form. Your router's csu/dsu is converting the tcp/ip data into the T1 data stream, where the far end reconverts it back.

This is a rather simple explanation. For youe senario to work, both routers must use indentical protocols and T1 configurations (as ordered from the provider), and the T1 provider must supply the ciruit as requested (ordered). This doesn't always happen the first time, and without a T1 tester, troubleshooting is extremely hard.

both john and ed both naile dit. You do not need a "smartjack" it basically gives the provider a loopable test point on site. Is this a PRI or regular T1? JOhn is also correct without some type of T1 tester like a tberd or something along those lines troubleshooting will be very difficult. You can have you provider out to prove the t1 to their demarc, at least you will know the ckt is goof to your site

The smartjack is contained in the housing outside. When you open the door, you'll notice two small security-type screws on the top corners. These open and allow access to the smartjack which is inside the door. They are typically a two position mount.

If you are familiar with your 568A & B color codes, it's fairly easy to hookup. Look at what color wire is in which position in the head attached to the pigtail. Look at the end that attaches to your equipment. You're essentially making a patch cord, so match them one-for-one.

Some CPE techs around town simply crimp an 8P8C on the end, unplug the pigtail and plug their patch cord directly into the port.

One way you can check your wiring is to use a multimeter. Plug your equipment in, and unplug the pigtail at the smartjack outside. Measure the resistance on the black to red wires. If you see something close to a short (around 10-20 ohms usually) you're good. Repeat for the yellow & black pair.

I used to trust the RLOS led on the smartjack. I had a circuit that wouldn't come up one day but everything looked good. I then discovered that the smartjack only needs to see one of the wires of the pair for the LED to go out.