gg ing ▁allowed ▁equivalent ▁four - wire ▁operation ▁on ▁a ▁single ▁cable ▁pair ▁in ▁two - wire ▁operation . ▁ ▁During ▁the ▁period ▁when ▁Type ▁N - 1 ▁was ▁in ▁w ides p read ▁use , ▁L enk urt ▁Corporation , ▁owned ▁and ▁controlled ▁by ▁General ▁Tele phone , ▁field ed ▁a ▁variant ▁compet itor , ▁the ▁Type ▁B N . ▁ ▁B N ▁used ▁the ▁same ▁pairs ▁and ▁repe aters ▁as ▁did ▁the ▁Bell ▁N - C X R , ▁but ▁used ▁four ▁channel ▁" groups ," ▁lower ▁single - side band ▁heter od yn ing , ▁and ▁ 2 4 ▁channels ▁per ▁car rier , ▁as ▁later ▁seen ▁on ▁Western ▁Electric ' s ▁Type ▁N - 3 . ▁ ▁Type ▁B N ▁was ▁used ▁at ▁times ▁by ▁Bell ▁Oper ating ▁Comp an ies ▁after ▁the ▁ 1 9 5 6 ▁H ush - a - phone ▁Dec ision ▁of ▁the ▁US ▁Supreme ▁Court , ▁a ▁land mark ▁case ▁which ▁challeng ed ▁AT & T ' s ▁" ben ign ▁mon opol y " ▁of ▁US ▁tele phone ▁equipment ▁industry . ▁ ▁Part ▁of ▁this ▁settlement ▁was ▁for ▁AT & T ' s ▁Bell ▁Oper ating ▁Comp an ies ▁to ▁buy ▁and ▁use ▁small ▁amounts ▁of ▁L enk urt ▁and ▁Collins ▁mic row ave ▁and ▁car rier ▁systems . ▁ ▁In ▁California , ▁Type ▁B N ▁was ▁used ▁almost ▁exclus ively ▁to ▁provide ▁tr unk ▁and ▁private ▁line ▁connections ▁between ▁Pacific ▁Tel . ▁& ▁Tel . ▁to ll ▁offices ▁and ▁local ▁General