VOICE UNIT FOR MODE 3
Services
The voice unit shall provide for a simplex, “push-to-talk” audio and signalling interface between the user and the VDL. Two separate mutually exclusive voice circuit types shall be supported.
VDL MODE 4
VDL Mode 4 radio channels
A VDL Mode 4 station should be capable of receiving additional channels simultaneously as required by operational services.
Subnetwork layer and SNDCF
Details on subnetwork layer functions and SNDCF are contained in the Manual on VDL Mode 4 Technical Specifications.