 The Delhi Metro uses cab signalling along with a centralised automatic train control system consisting of automatic train operation , Automatic Train Protection and automatic train signalling modules . A 380 MHz digital trunked TETRA radio communication system from Motorola is used on all lines to carry both voice and data information . For Blue Line Siemens Transportation Systems has supplied the electronic interlocking <unk> , the operation control system <unk> OC 500 and the automation control system <unk> 700 M. An integrated system comprising optical fibre cable , on @-@ train radio , CCTV , and a centralised clock and public address system is used for telecommunication during train operations as well as emergencies . For Red and Yellow lines <unk> has supplied signalling system and for line Green and <unk> Bombardier Transportation has supplied <unk> 350 signalling system . 
