In telecommunications, the term network interface device (NID) is interchangeable with network interface unit (NIU)
Meanings of the term
A network interface, also commonly referred to as a smart jack, is typically in the basement, first floor telco room, garage, or even outside the building. NIUs are multi-functional devices, which include a protector block to prevent high-voltage surges from affecting premise equipment and inside wiring. It also usually allows the carrier to initiate a loop-back test from the central office to test the integrity of the local loop.
- A device that performs interface functions, such as code conversion, protocol conversion, and buffering, required for communications to and from a network.
- A device used primarily within a local area network (LAN) to allow a number of independent devices, with varying protocols, to communicate with each other.
An NID converts each device protocol into a common transmission protocol.
The transmission protocol may be chosen to accommodate directly a number of the devices used within the network without the need for protocol conversion for those devices by the NID.
Common practice
The NIU belongs to the PSTN provider. Together with the CSU it represents the PSTN demarcation point. The CSU is the first piece of Customer Premise Equipment (CPE). If the NIU fails the PSTN provider is responsible for repairs; if the CSU fails the customer is responsible for repairs.