other changes there are three nius nius are the cards inside of the two slot mounting cases not the case themselves in the first picture not two the single card in the left case looks to be either a hdsl or hdsl niu the left card in the left case is a hdsl niu more accurately those are htu r or h tu r or h tu r cards that terminates hdsl data and outputs a ds signal functionally similar to older t niu but are not compatible with a t system explanatory information on variants t c two concantenated t s etc from a service provider to a customer it would look something like dsx orb kft rptr kt rptr niu csu dsu cpe showing the spacing between the office repeater in the office repeater bay orb and the first line repeater as feet kft and spacing between subsequent repeaters as kft emphasis at least orginally on t as being a span system designed as a short haul interoffice transport for use inside the telephone companies and as part of t carrier system linking two d channel banks d bank dsx x dsx orb rptr rptr orb dsx x dsx d bank links to other analog carrier systems showing t development in context