19 lines
3.0 KiB
Markdown
19 lines
3.0 KiB
Markdown
## Smartjack
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[](https://en.wikipedia.org/wiki/File:Network_Interface_Unit.jpg)
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Three smartjacks for [T-1](https://en.wikipedia.org/wiki/Digital_Signal_1 "Digital Signal 1") circuits, in two shelves; a [66 block](https://en.wikipedia.org/wiki/66_block "66 block") is on the left
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Several types of NIDs provide more than just a terminal for the connection of wiring. Such NIDs are colloquially called _smartjacks_ or [Intelligent Network Interface Devices](https://en.wikipedia.org/wiki/Intelligent_Network_Interface_Device "Intelligent Network Interface Device") (INIDs) as an indication of their built-in "intelligence", as opposed to a simple NID, which is just a wiring device. Smartjacks are typically used for more complicated types of telecommunications service, such as [T1 lines](https://en.wikipedia.org/wiki/Digital_Signal_1 "Digital Signal 1"). [Plain old telephone service](https://en.wikipedia.org/wiki/Plain_old_telephone_service "Plain old telephone service") lines generally cannot be equipped with smartjacks.
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Despite the name, most smartjacks are much more than a simple [telephone jack](https://en.wikipedia.org/wiki/Telephone_jack "Telephone jack"). One common form for a smartjack is a [printed circuit board](https://en.wikipedia.org/wiki/Printed_circuit_board "Printed circuit board") with a face plate on one edge, mounted in an enclosure.
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A smartjack may provide signal conversion, converting codes and protocols (e.g. framing types) to the type needed by the customer equipment. It may buffer and/or regenerate the signal, to compensate for signal degradation from line transmission, similar to what a [repeater](https://en.wikipedia.org/wiki/Repeater "Repeater") does.
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Smartjacks also typically provide diagnostic capabilities. A very common capability provided by a smartjack is [loopback](https://en.wikipedia.org/wiki/Loopback "Loopback"), such that the signal from the telephone company is transmitted back to the telephone company. This allows the company to test the line from the central [telephone exchange](https://en.wikipedia.org/wiki/Telephone_exchange "Telephone exchange"), without the need to have test equipment at the customer site. The telephone company usually has the ability to remotely activate loopback, without even needing personnel at the customer site. When looped back, the customer equipment is disconnected from the line.
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Additional smartjack diagnostic capabilities include [alarm indication signal](https://en.wikipedia.org/wiki/Alarm_indication_signal "Alarm indication signal"), which reports trouble at one end of the line to the far end. This helps the telephone company know if trouble is present in the line, the smartjack, or customer equipment. Indicator lights to show configuration, status, and alarms are also common.
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Smartjacks typically derive their operating power from the telephone line, rather than relying on premises electrical power, although this is not a universal rule. |