such as in GSM mobile system,
Idle mode is the mobile is standby, no traffic service, the mobile just use signalling channel to maintain connection with base station. Mobile listen and reply to base station through signalling channel every several seconds.
Traffic mode is mobile in used for talks, thus the mobile use traffic channel (that's time slot assgined), so the mobile transciver every frame, that is say in ms interval. At the same time, the signalling channel is used also.
You can try to find telecomm standards for the idle mode and traffic mode definition.