Subscriber Network Interfaces

by Frequency Man (FreqMan)

Also known as Telephone Network Interfaces (TNI), Subscriber Network Interfaces (SNI) are now installed on all new homes.

These devices are installed so that the homeowner can check to see if a fault is in his wiring or in the telephone company lines.  In actuality, it is the spot where the local telephone company's lines are plugged into your house.

When you open one up, you will encounter two (or more) modular jacks, with matching modular plugs running into them.  The modular plugs are the telephone company's lines, and they will be plugged into the jacks, which are your actual phone lines.

For a homeowner to find a fault he must do this:

First, get a phone that he is sure is working.

Second, go down to his SNI and open it up.  He then will unplug the modular plug from the line that has a fault in it, and plug his working phone into it.  What he is doing is plugging the phone into the phone lines before they enter the house.

As you have probably figured, if the fault is not present when using the phone from his SNI, then the fault is in the wiring in his house.  If the fault is still present when using the phone from his SNI, then it is a problem with the local phone company's lines.

Although SNIs are a pretty good idea, and can be handy for locating phone troubles, most homeowners have no idea what the little green box on the side of their house is, or what it is for.  Chances are that many homeowners are not even aware of its presence.

The most common of these devices is the Model CAC 3000, manufactured by Siecor.  I know for a fact there are different models and brands, but I have yet to encounter one which wasn't a CAC 3000.

Even if you are not working with this model, this information will still be valuable for all types of SNIs.

SNIs are usually small green boxes, perhaps 10 inches by 10 inches, and are usually found bolted to the side of the house, usually screwed shut.  Sometimes they say "Subscriber Network Interface" on the front.  They have a little loop which you can put a padlock on, but almost none of them do.  Most of them have two sections you can open.  There is the "Customer Access" section, which is most often opened with a flat-head screwdriver, and there is the telco service access, behind an extra plastic shield.  This is usually opened with an Allen wrench and contains more complicated wiring and components.

This article is written to deal with the "Customer Access" section, which is a lot of fun to play with by itself.  So don't worry - even though this information isn't highly technical, you can still have plenty of fun from the "Customer Access" spot.

Fun Thing #1

Since you have a jack right there, there are many things you can do with your neighbors' lines.

When your neighbors go out of town, that is the best time to do some tinkering with their lines, so from here on I am going to assume that you are out of harm's way while playing with their SNI.

For a quick and easy phone call that you need to make, all you need to do is grab your phone, run over to your neighbor's SNI, unplug the modular plug leading into Line 1, (they will be labeled) and plug in your phone.  Dial away.  This is all easier if you are not using a cordless phone, because with a cordless you also need a power outlet, of course.  The reason for plugging into Line 1 and not Line 2 is because many people still only have one line, and it will be the one labeled Line 1 if this is the scenario.  Your calls will obviously be billed to whoever's SNI you are using, for those of you who don't catch on too quick.

Fun Thing #2

This is actually a variation of "Fun Thing #1."

Instead of having to run over to your neighbor's house every time you don't want to pay for a call, I suggest just running some phone line straight from their SNI to your house.  The best thing to do is dig a trench about two inches deep.  Take some hollow black tubing, the thin kind, and run the telephone wire through that.  Now place your protected phone wire in the trench and cover it up.  Plug one end into your neighbor's SNI jack, and the other end straight into a phone at your house.  Now you got your neighbor's phone line at your finger-tips.  Keep in mind that as long as your phone is plugged into their SNI, they can't use that line.  This is why I save this for when they go on a two month vacation to Myanmar.

Fun Thing #3

Purchase a phone line fork, so you can plug two phones into one jack.  Stick the fork into the modular jack for Line 1 of your neighbor's SNI.  Now you have two modular jacks.  In one of them, stick the line you have running to your house, like in "Fun Thing #2," and in the other one, stick the matching modular plug for Line 1 of that house.  This way, you can not only charge up their phone bill from your house, but you can also listen in on their phone conversations, and even add a little noise of your own if you wish.

Fun Thing #4

This is a little something you can built up gradually, as time goes on.

Buy some sheet metal, and set up kind of a switchboard for all your neighbors' lines.  Every time one of your neighbors go on vacation, or moves, or whatever, hook that person's line from their SNI to your switchboard, the way explained in "Fun Thing #3."  Eventually you will have quite an array of phone lines going into your house, and you can add in all sorts of gadgets to customize your switchboard to suit your needs.

As clearly stated, SNIs are a major telephone security flaw, and I love taking advantage of it.  It actually isn't the telephone companies' fault that this is so easy - it is the owner of the SNI.  SNIs are lockable, but never locked.  Hideable, but never hidden.  Handy, but never used.

These little green beauties are a lot of fun to play with in the summer, especially when all the folks in your neighborhood have taken off for their fun little summer vacation.  This is definitely the time to play with all these "Fun Things" I have told you about.  Not like you wouldn't have figured out what you could do with an SNI anyways, but at least these little tips help get your brain going.  After all, if we didn't use our brains, we would all end up like our neighbors.