A
add/drop multiplexer (ADM).

A device installed at an intermediate point on a transmission line that enables new signals to come in and existing signals to go out. Add/drop multiplexing can be done with optical or electronic signals. The device may deal only with wavelengths, or it may convert between wavelengths and electronic TDM signals.

adjacency.

A relationship formed between selected neighboring routers and end nodes for the purpose of exchanging routing information.

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