MMSI Group Usage

Re: Mail Call, The Port Hole Fall 2012 Tom O’Flaherty has put forth an interesting set of questions related to MMSI group usage and both Norm Dyck (Maritime Radio Course Director) and I have been scratching our heads over them. However, here are our answers to Tom’s queries:

Tom asks: “Let’s assume that a group gets a group number. And all the members put this number in their radios. I realize that one member must be authorized to apply for the number. Now suppose that a member wishes to make an announcement to the group. Presumably they pick a working channel, access the group MMSI number stored in their radio, and send this out. Again I presume that all members within range and with radios ON will hear a ringing tone. Is this the same tone as for an individual calling? “

Tony replies: Since I’m not aware of any standards with respect to audible signalling tones, I believe you’ll find that tone composition varies amongst manufacturers. One would hope that the tone signalling of an incoming group call would differ from an individual call but this will only be known after placing a few group calls with your own radio.

Tom asks: “Each group member may (or may not) see from their display that it is the group number, and maybe group name calling. If each of the members hit their transmit buttons, does their radio flip to the selected working channel? Most important, would they say anything? If so, would the initial sender be swamped with acknowledgements and comments? What would be the protocol for each member of a group who hears the call? At what point would the caller assume that most members in range had “answered” and the caller could now make an announcement?”

Tony replies: The group caller selects a working frequency and as soon as a called party answers by hitting their transmit button they should be automatically using that working frequency though, again, the method of responding may vary by manufacturer. With regard to the original caller being swamped by responses, think of this as a telephone-type conference call in which the caller usually establishes the protocol. It is possible that two call recipients may reply at the same time but this will be the exception rather than the rule. Once all parties have acknowledged the call then the original caller should submit to a kind of roll call in which he or she addresses each party, either by personal name or vessel name, and the recipients “take turns” in replying. It is important to understand that, amongst recreational boaters, the use of Channel 70 and the application of MMSI numbers for group calling is still largely unexploited. I would encourage Squadrons, yacht clubs and cruise participants to set up a group calling program in advance of embarking on a cruise. Try it out. And please come back to me with your comments so that they may be shared with other boaters!

P/C/C Tony Gardiner, SN Norvan Squadron Pacific Mainland District

3 thoughts on “MMSI Group Usage

  1. As I have two DSC-capable radios (Icom IC422 and 604) on my boat, I did some tests today:

    The Distress Alert (not personally tested today, but previously heard) is the two-tone radiotelephone alarm signal,and loud!

    The alert sound for all other calls (individual, group, position request, etc.) is a somewhat less annoying “beep-beep”.

    On the 604 (Class D), I see “Group call from “. On the 422 (SC-101), I just see “GRP CALL”

    On the 422, I press “DSC” a couple of times, to cancel the beeps, and transmit the acknowledgement, then both radios change channels. On the 604, I press “CLR” to silence the beeps, then “enter” a couple of times to acknowledge the call and change channels.

    Pressing Transmit on either radio will cancel the DSC operation, and transmit on the whatever channel the radio was on before the DSC call.

    Since the radio originating the group call doesn’t know how many radios are likely to respond, it will switch channels in response to the first acknwoledgement.

  2. Perhaps we need to establish a group ‘conference call’ set of procedures. For instance, as all radios called will have switched to the caller’s desired channel, check-in might proceed alphabetically- as each boat or person more or less chimes in, in that order. Round robin responses would follow the same pattern to ease the over-dubbing possible. Each squadron group could establish its own protocols ahead of time.

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