Dumb DSC Question - Distress without MMSI

[CaptTom]

I've often repeated what I've read and heard, that the "Distress" button on a DSC radio doesn't work if you haven't entered an MMSI number.

Yesterday someone challenged me on that assertion. So I went looking for source information. My Uniden manual is pretty clear:

DISTRESS
Note: You must set the user MMSI in
order to send a Distress call.

But a lot of other sources equivocate. They may suggest it's not fully functional, or use words like "should" instead of "must". Even Uniden doesn't say what will (or won't) happen if you don't set the number.

The person I was speaking with suggested that you don't really need an MMSI number, because if your DSC radio has a GPS signal available over NMEA, or built in, it will transmit your location, then switch you to channel 16 when it receives the ACK. So who cares whether or not the CG can look up your name?

I'm not a conspiracy theorist, I don't have a problem with registering, and I will continue to strongly recommend it.

But now I'm curious. I don't repeat hearsay.

[DotDun]

Originally Posted by CaptTom

I've often repeated what I've read and heard, that the "Distress" button on a DSC radio doesn't work if you haven't entered an MMSI number.

Yesterday someone challenged me on that assertion. So I went looking for source information. My Uniden manual is pretty clear:

DISTRESS
Note: You must set the user MMSI in
order to send a Distress call.

But a lot of other sources equivocate. They may suggest it's not fully functional, or use words like "should" instead of "must". Even Uniden doesn't say what will (or won't) happen if you don't set the number.

The person I was speaking with suggested that you don't really need an MMSI number, because if your DSC radio has a GPS signal available over NMEA, or built in, it will transmit your location, then switch you to channel 16 when it receives the ACK. So who cares whether or not the CG can look up your name?

I'm not a conspiracy theorist, I don't have a problem with registering, and I will continue to strongly recommend it.

But now I'm curious. I don't repeat hearsay.

:: Admitting I don't under the protocol details! ::

I'm curious how a radio would respond with an ACK to a message without an "address" (DSC identifier/MMSI number). Does the response include the originally sent GPS location?? How else would a radio know the ACK is for it??

[funk-an-bord.de]

Up to 2003 it was possible (in Germany) to get a MMSI number from the registration authority,
but to run the radio without the MMSI.
That was useful for a charterbasis with e.g. 10 boats and 11 radios.
In case of a defect of a radio they could take another radio and put it into the boat.
Wilhelm

[CaptTom]

Originally Posted by DotDun

:: Admitting I don't under the protocol details! ::

I'm curious how a radio would respond with an ACK to a message without an "address" (DSC identifier/MMSI number). Does the response include the originally sent GPS location?? How else would a radio know the ACK is for it??

Good point. My thought was that maybe there's a "null" MMSI, like all zeros or all nines or whatever, that it starts out with. Clearly the protocol requires an MMSI number to be sent as part of the packet, but that doesn't mean it has to be legitimate.

Funk, just to be clear, nobody is suggesting you can't use the radio without an MMSI number. I'm just questioning what would happen (if anything) if you were to press the distress button on such a radio.

Ironically, I had another MMSI issue come up shortly after I wrote this. I went to program my new MMSI number into the radio I'd originally installed in my last boat. I did all the steps right, but halfway through, the CG did a broadcast on channel 16. The display changed and the half-updated MMSI number was stored. That was my last chance. I have an e-mail in to the vendor to see if they'll take pity on me, or will charge me $60 to reset it.

Moral of the story: put the radio on some odd-ball channel, or disconnect the antenna, before changing your MMSI!

[colemj]

We have received DSC distress alerts that contained all zeros for the MMSI #, as well as nonsensical GPS coordinates.

Mark

[fairbank56]

They will not transmit any DSC data without an MMSI programmed as per ITU recommendations.

Eric

12.4 MMSI
DSC equipment should not transmit any DSC call until own ship’s MMSI allocated to the ship by
the relevant administration has been configured and stored in the DSC equipment. Once stored, it
should not be possible for the user to change the MMSI without advice from the manufacturer.

[colemj]

That's interesting because I know we have received DSC alerts with all zeros. A few times, so I'm not confusing it with something else (although it may have been the same radio). Perhaps all zeros were actually entered into the field and someone was fooling around with it.

That recommendation states "DSC call". Is is possible that a DSC alert is considered differently than a call?

Mark

[fairbank56]

I know for a fact that Icom and Standard radios will not transmit distress calls without a number programmed. Iv'e tried it in controlled test environment. The calls you received either had bogus numbers programmed or some of the data stream was corrupt and your radio was unable to resolve the number. Here's a troubleshooting chart from an Icom M412 manual that clearly states distress calls cannot be transmitted without an MMSI programmed.

Eric

[Neptune's Gear]

Agreed, no transmission is the standard. IF the device meets the standard....some do not. Does the device have FCC or CE type approval? Does that device cover the base model (without DSC) or is it actually for the EXACT model you have? Lots of traps here... especially for the international marketplace.

[fairbank56]

Originally Posted by Neptune's Gear

Agreed, no transmission is the standard. IF the device meets the standard....some do not.

Name one model that does not.

Eric

[fairbank56]

Came across an article from a couple years ago about the Coast Guard complaining about the number of false DSC distress calls. About 100 a month, 90% with no lat/lon data and 60% using unregistered ID's. Guess people are just plugging in any old number they want into their radio's. No easy way to idiot proof the system.

Eric

[Neptune's Gear]

Originally Posted by fairbank56

Name one model that does not.

Eric

here you go;
New Dsc Vhf Marine Radio Lt-m507 With Gps Function - Buy Vhf Marine Radio,Dsc Vhf Marine Radio,Dsc Vhf Marine Radio Product on Alibaba.com
Plenty more from Asia...

[fairbank56]

So....where's the proof that it doesn't meet ITU DSC specs and is capable of transmitting a DSC distress call without a programmed ID?

Eric

[funk-an-bord.de]

According to the referecnce or fairbank56
I have searched for the ITU specification.
You can find it at:
http://www.itu.int/dms_pubrec/itu-r/...0-I!!PDF-E.pdf
On page 15 you find the MMSI input required in article 12.4

The recomendation of 1997 does not contain a required MMSI before starting to operate.
http://www.itu.int/dms_pubrec/itu-r/...2-S!!PDF-E.pdf
I was told it changed in 2002 or 2003.
...............
when reading the recomendation I found valuable information regarding the Class D and Class A controller.
Wilhelm

[ranger58sb]

Local CG Sector Baltimore has received apparently-DCS-radio-initiated distress calls, with no vessel location and with no vessel information. We happened to also receive one of those while underway; presumption at the time was a DSC radio sent the distress call, but had no GPS input nor MMSI info. I can't remember if we were seeing an MMSI number (or similar, or zeros, whatever) in the display.

-Chris