| The ''Network Interface Device (NID)'', also | | | | the telephone jack or the wiring. If moisture gets |
| referred to as the ''Subscriber/Network Interface | | | | into ANY phone jack anywhere in the home, it |
| (SNI)'' or the ''Point of Demarcation (Demarc)'', is | | | | can cause the connections to corrode and |
| the box, often grey and usually on the outside of | | | | eventually to short out, which could cause some |
| the structure, where the telephone company's | | | | or all phones to stop working. Bad splices, |
| wires start, the lightning protector is installed, and | | | | particularly if exposed to moisture, can also cause |
| your phone wiring terminates. (True to telephone | | | | a phone to stop working. |
| company tradition, the terms "NID" and "SNI" are | | | | *If you suspect a phone of being bad, try it at a |
| pronounceable acronyms -- they are usually | | | | friend or neighbor's home where you know the |
| spoken as "nid" and "sny" rather than "n.i.d." or | | | | phones are working. Also, if possible, try swapping |
| "s.n.i.") An important feature of the NID is a test | | | | the line and handset cords with known good cords |
| jack with a short phone cord. Unplugging this cord | | | | from another working phone. The vast majority |
| disconnects all of your internal wiring from the | | | | of phone problems can be traced to bad cords |
| telephone company's network, allowing you to | | | | and/or bad or corroded modular plugs. |
| plug a "known-good" phone into the NID to verify | | | | *If a phone stops working after a thunderstorm, |
| that the service is working up to your home or | | | | it's possible that lightning hit the phone line and |
| business. If it is, your "service" is fine but your | | | | caused a voltage surge that damaged the phone. |
| wiring or a device inside are causing the problem. | | | | The actual hit could have occurred several miles |
| (See ''line lockout'', below.) | | | | away, and traveled down the line to your phone. |
| *Home and small business phone wiring is usually | | | | *If a phone won't dial out, make sure that there |
| installed using one of these topologies: | | | | isn't a tone/pulse switch set in an incorrect |
| **Star or Home Run - each jack has a wire | | | | position (such as midway between the two |
| running back to the NID. | | | | positions). Note that pulse dialing won't work if you |
| **Daisy Chain - wires from the NID go from one | | | | are using some VoIP services, and tone dialing |
| outlet, to the next, to the next. (This may also be | | | | won't work on some telephone lines (although this |
| called a "ring" topology, except that it is not a | | | | is no longer a common occurrence in the United |
| true ring, since the last outlet doesn't loop around | | | | States). |
| and then go back to the NID.) | | | | *If a phone won't ring, check to make sure the |
| **Combination of the two - You may find a spur | | | | ringer volume or on/off switch isn't at the lowest |
| subtending from a point along a daisy chain, or | | | | or "off" setting. Also, some very old phones may |
| that some outlets have a home run back to the | | | | have frequency-tuned "harmonic" ringers intended |
| NID while others are part of a Daisy Chain | | | | for use on a party line, and won't work properly |
| *''Line lockout'' can trip you up when | | | | on today's private phone lines due to a difference |
| troubleshooting. When your telephone line is left | | | | in ringing frequency. |
| off the hook for more than a couple of minutes, | | | | *Telephone companies often offer a "wiring |
| the telephone company central office switch | | | | maintenance" plan. This plan covers repairs to |
| automatically places your line in "lockout." This | | | | wiring that meets their standards but has become |
| prevents your line from consuming resources that | | | | defective. More importantly, this plan prevents |
| might result in denials of service to other | | | | you from having to pay "nonproductive dispatch" |
| customers. Many faults in your telephone wiring or | | | | charges if the technician finds that the trouble is |
| equipment will cause the central office equipment | | | | inside your house. Or, to be more precise, if the |
| to ''act as if'' your phone is actually off the hook. | | | | technician does not find any trouble outside your |
| When this occurs, your line goes into lockout. The | | | | house (i.e., the dial tone is good up to your |
| troubleshooting implication is that your line may | | | | network interface). This is essentially extortion |
| not clear for several seconds ''after'' you find and | | | | money, but is better paid than not paid: you're |
| remove the cause of the problem. | | | | paying the telephone company to shut up, be |
| *Keep in mind that the problem may not be in | | | | nice, and help you when you have trouble. Your |
| the phone itself - instead, it may be a problem in | | | | reward is no finger-pointing. |