Network interface device
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In telecommunications, the term network interface device (NID) is a device that serves as the demarcation point between the carrier's local loop and the customer's network. The terms network interface unit (NIU) and smartjack are interchangeable with network interface device.
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[edit] Meanings of the term
According to the ATIS Telecom Glossary 2000 (An updated version of the Federal Standard 1037C standard) a NIU is a device that “performs interface functions, such as code conversion, protocol conversion, and buffering, required for communications to and from a network.”[1] A network interface, also commonly referred to as a smart jack, is a device that serves as the demarcation point between the end user's inside wiring and local access carriers' facilities.[2] According to the TR-73569 standard put forth by Bellsouth[3], an NIU must have these functions:
- Conversion: Convert protocols and codes such as framing types to information usable by the channel service unit (CSU).
- Logical Loop back: Allow a logical loop to be placed in the front of the jack, to allow for remote testing. This allows for the line to be tested without an on site tech being required to put up a hard loop at the back of the jack. When the device is allowing strait-away traffic is is in “normal” state, while when in loop back mode, it is referred to as being in maintenance state.[3]
- Signal Regeneration: The device will amplify the signal coming in much like a repeater. The regeneration must take place in front of the loop back according to this standard, because the loopback causes the non-repeated distance to effectively double, and will cause a loss of signal that would not be there when the device is in normal operation.
- Alarm indication signal (AIS): All smartjacks that comply to the TR-73569 standard need to have an AIS generator inside the device. This allows the local exchange carrier (LEC) to know that the jack is still functioning properly, and that the consumer just removed his CSU from the line.
- DC Isolation of the LEC and the end-user. The NIU is a powered device, and requires two surge protectors to comply with the TR-73569 standard: one on the send pairs, and one on the receive pairs. From there, the wire pairs enter the DC isolators.
[edit] Common practice
The NIU belongs to the public switched telephone network (PSTN) provider. Together with the CSU it represents the PSTN demarcation point.[citation needed] The CSU is the first piece of customer-premises equipment.[citation needed] If the NIU fails, the PSTN provider is responsible for repairs. If the CSU fails, the customer is responsible for repairs if it is owned by the customer, or the PSTN provider is responsible for repairs if the CSU is leased from the PSTN.[citation needed]
[edit] References
- ^ Federal Standard 1037C. U.S. Department of Commerce and National Telecommunications and Information Administration. Retrieved on 2008-02-11.
- ^ T1/E1 Bit Error Rate Testing. GL Communications. Retrieved on 2008-02-09.
- ^ a b Functional Criteria for the DS1 Interface Connector. Bellsouth. Retrieved on 2008-02-09.
