8 7 6 5 4 3 2 1 1 H G F E D C B A H G F E D C B A 0 0 0 0 0 0 0 0 - spare 0 0 0 0 0 0 0 1 - spare 0 0 0 0 0 0 1 0 - user-to-user service 0 0 0 0 0 0 1 1 - spare to 1 1 1 1 1 1 1 1 - spare