DIGITAL SELECTIVE CALLING  (DSC) 
A VHF or HF radiotelephone with DSC fitted can send a distress alert and position reports if connected to a GPS. It can also be used for urgency, safety information dissemination or routine calling and answering. The information is sent as a burst of digital code to either rescue authorities or to an addressee.  Subsequent contact is by voice.  DSC acts like a paging system with the alert being both audio and visual alarms. Included in the call is the caller’s Maritime Mobile Service Identity (MMSI) and what mode or channel is required for further communications. Once contact is made the conversations are public. A caller will need to know the 9-digit MMSI Number of the station being called.
DSC EMERGENCY FREQUENCIES
DSC Frequency Associated Frequency 
VHF Ch 70 VHF Ch 16
2187.5 Khz 2182Khz
4207.5 Khz 4125 Khz
6312 Khz 6215 Khz
8414.5 Khz 8291 Khz
12577 Khz 12290 Khz
16804.5 Khz 16420 Khz
DSC SERVICE (ROUTINE)
Ship Receive (Khz)  Ship Transmit (Khz)
4219.5 4208
6331 6312.5
8436.5 8415
12657 12577.5
16903 16805
22444 22374.5
DSC ALERT CONTENTS
*   MMSI number of the Caller
*  The Alert Priority   – Menu selectable from Listing,  Sinking,          Disabled, Abandoning,  Piracy, MOB, Fire, Flooding,                Collision and Grounding.
*  Last known position and time (preferably GPS)
*  The station(s) being called