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Appendix B
WHAT IS DIGITAL SELECTIVE CALLING (DSC)?
Digital Selective Calling (DSC) uses marine VHF radio and Global Positioning System (GPS) tech-
nologies to transmit and receive location information. DSC is used by mariners to assist them in two
major areas: Distress Calls and Position Reporting.
An emergency DSC Distress Call allows a vessel in trouble to transmit a substantial amount of infor-
mation in a single transmission or “call,” without the need for voice communication. When any nearby
rescuer receives the DSC signal, an alarm sounds and they immediately receive the position of the caller.
The rescuer may then choose to navigate (Go To) the caller’s position to assist or forward the call on
to the Coast Guard. When the Coast Guard receives the call, they can immediately access the caller’s
information (such as who they are and the type of vessel) in their database while they are in transit to
the caller’s position.
A non-emergency DSC Position Report allows mariners to exchange and display the positions of one
another. Once a DSC position is received, the mariner may choose to create a waypoint or to show the
received position on an electronic map.
Anytime a vessel receives a DSC call, they can store that location and quickly navigate to that
position using a Go To. This makes DSC a time saver, especially in an emergency situation. In order to
use DSC, users must fi rst register their VHF radio with the FCC and receive a Maritime Mobile Service
Identity (MMSI) number.
WHAT IS A MARITIME MOBILE SERVICE IDENTITY (MMSI)?
Maritime Mobile Service Identity (MMSI) basically allows a VHF radio to act like a phone. In order
to make a “call” on a phone, you fi rst need a phone number to dial. The 9 digit MMSI number acts like
a phone number when used in a Position Report and as a unique identifi er to the Coast Guard when
used in an emergency Distress Call. In order to to obtain a Maritime Mobile Service Identity (MMSI)
number, users must register their VHF radio with the FCC (Form 605). Garmin does not supply this
number! Information to obtain this number can be found on the next page.
Digital Selective Calling (DSC)
182C Manual Part 2.indd 70 6/4/2003, 2:54:23 PM