DSC poling question

[estarzinger]

I am aware that with many DSC VHF you can pole them for their position if you know the MMSI. My questions are:

(a) do they (most or all dsc radios) return the position information automatically or does the operator/owner have to push a button to say "yes, respond with my position"

(b) if they do it automatically, do they tell the owner/operator that someone has pulled their position or can it be done without the owner/operator knowing?

[ranger58sb]

Near as I can tell, I have to manually agree to reply.

-Chris

[rodney_k]

On my Standard Horizon DSC VHF (CPV-350), the position reply can be set to auto reply or manual reply. In either case, an alarm sounds when the radio is queried. The interrogating vessel's MMSI is also displayed. The interrogating vessel name is displayed if its MMSI has been entered in to the VHF's memory.

[ranger58sb]

Originally Posted by ranger42c

Near as I can tell, I have to manually agree to reply.

-Chris

Yep, just found the instruction and ours will automatically respond if I set it that way too. Sorry I answered too soon earlier...

-Chris

[colemj]

Originally Posted by estarzinger

I am aware that with many DSC VHF you can pole them for their position if you know the MMSI. My questions are:

(a) do they (most or all dsc radios) return the position information automatically or does the operator/owner have to push a button to say "yes, respond with my position"

(b) if they do it automatically, do they tell the owner/operator that someone has pulled their position or can it be done without the owner/operator knowing?

On both our Standard Horizon fixed mount 2150 and handheld 851:

(a) the owner has the choice whether to set it to automatically respond with position or require a manual response (or turn the polling off completely).

(b) in automatic mode, the radio keeps a log of time of position polling and who polled (either MMSI# or name, if number is associated with a name in address book).

Mark

[estarzinger]

ok, that's all . . . that's what I thought. . . . but I had been told by an "Expert" that the USCG and law enforcement could position poll and get an automatic response without any indication on the targeted vessel.

[goboatingnow]

Originally Posted by estarzinger

ok, that's all . . . that's what I thought. . . . but I had been told by an "Expert" that the USCG and law enforcement could position poll and get an automatic response without any indication on the targeted vessel.

The USCG understanding of the operation of dsc leaves a lot to be desired
Dave

[Captain Bill]

Originally Posted by estarzinger

ok, that's all . . . that's what I thought. . . . but I had been told by an "Expert" that the USCG and law enforcement could position poll and get an automatic response without any indication on the targeted vessel.

They can with AIS, not DSC if I understand it correctly.

[goboatingnow]

Originally Posted by Captain Bill

They can with AIS, not DSC if I understand it correctly.

Huh , AIS transmits your position , they don't poll it. If you select silent mode , no position is reported

Dave

[colemj]

Was your "expert" wearing a tin-foil hat?

Mark

[estarzinger]

Originally Posted by colemj

Was your "expert" wearing a tin-foil hat?

Mark

^^ actually no, he was not a nut case. He operated a fleet of commercial work boats, and is a pretty sensible guy. It may be that he is confusing DSC and AIS, or he may have all his radios set to automatic response so he can poll them . . . I am not sure.

[Captain Bill]

Originally Posted by goboatingnow

Huh , AIS transmits your position , they don't poll it. If you select silent mode , no position is reported

Dave

That's what I used to think until I researched it a little more. I thought it was a transmitter and a reciever, but kept wondering why they were refered to as TRANSPONDERS. Transponders reply to quieries, like the 4096 transponder I used to have in my airplane. If it got hit by a radar beam it transmitted your ID number so I was wondering why a simple transmitter-reciever was being referred to by the manufacturers as a transponder. On researching that I found that AIS "transponders" can in fact be interrogated and will respond if you send them the right signal. Guess who has access to the equipment to transmit that signal?

[goboatingnow]

Originally Posted by Captain Bill

That's what I used to think until I researched it a little more. I thought it was a transmitter and a reciever, but kept wondering why they were refered to as TRANSPONDERS. Transponders reply to quieries, like the 4096 transponder I used to have in my airplane. If it got hit by a radar beam it transmitted your ID number so I was wondering why a simple transmitter-reciever was being referred to by the manufacturers as a transponder. On researching that I found that AIS "transponders" can in fact be interrogated and will respond if you send them the right signal. Guess who has access to the equipment to transmit that signal?

AIS is mistakenly described as a transponder, it's is actually a transceiver. Lets leave aside the discussion of class A AIS , which has extensive telecommand control including optionally using DSC ch 70.

For class B , if you disable the transmitter( ie silent mode) , no one can " request" or get your position. Despite what the tin foil hat brigade think , AIS specification is in the public domain and s was never really designed as a security system. ( because its exceptionally easy to spoof )

Dave

[Captain Bill]

Originally Posted by goboatingnow

AIS is mistakenly described as a transponder, it's is actually a transceiver. Lets leave aside the discussion of class A AIS , which has extensive telecommand control including optionally using DSC ch 70.

For class B , if you disable the transmitter( ie silent mode) , no one can " request" or get your position. Despite what the tin foil hat brigade think , AIS specification is in the public domain and s was never really designed as a security system. ( because its exceptionally easy to spoof )

Dave

You may in fact be protected in silent mode, but message 19 (Extended Class B position Report) is only transmitted when polled by a coast station. Since it only transmitts that message when polled, that makes it a transponder. Now if I only knew what "Coast Station" was I would know who was checking up on me.

[goboatingnow]

Originally Posted by Captain Bill

You may in fact be protected in silent mode, but message 19 (Extended Class B position Report) is only transmitted when polled by a coast station. Since it only transmitts that message when polled, that makes it a transponder. Now if I only knew what "Coast Station" was I would know who was checking up on me.

Yes message 19 is a holdover from the unimplemted. aIS class B SOTDMA specification. ( as it uses two slots. ) AIS class B can respond to message request 18, 19, 24 all of which provide position reports. 18, 24 are single slot protocols and can be requested from any equipped class A system , because message 19, is a two slot system , only the base station as defined in the ITU/IMO spec can guarantee reception of message 19. ( CSTDMA is a single slot system only )

Again if you turn off the transmitter you cannot respond to the few class B telecommands. In fact to my knowledge some leisure AIS units don't even implement these features.

It's certainly not what you feel it is.

Dave