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What is a network interface device?

The network interface device (NID) defines the point at which you become responsible for the phone wiring within your home. Bell Canada is responsible for providing and maintaining service up to the point of the NID.

The NID is important because it contains something called a demarcation jack that is on the part of the line outside your home (and for which Bell is responsible). You can use this jack to test your phone line.

If you are having trouble with the phone line in your home, plug a phone into the demarcation jack. If the phone works, it means that the problem is not with Bell 's line, and therefore the problem is on the wiring inside your home, for which you are responsible.

Finding the NID and demarcation jack

The NID is generally a grey box on the outside of your home. If the wiring was installed in your home before 1988, then you will likely have a grey or black telephone protector box located inside your home, and the demarcation jack will be located within 1 metre of this box.

In a multi-unit or multi-storey building (such as an apartment building), the demarcation point is at the main jack (the first point of entry) inside each unit. The main jack will be labelled  Demarcation or Verification.

In most business premises, the demarcation point is located where the Bell network enters each commercial or office space.