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[aprssig] questions about the Bulletin Screen "billboard" concept

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Wed Nov 9 02:48:26 UTC 2011


(I'm not Bob, but here's my take on your questions.  Let's see how close 
I come to Bob's answers)

First, you might want to look at http://aprs.fi/bulletin/  And then, if 
you're curious as to the raw packets that generated that display, drill 
into the individual station's raw display by clicking on the callsign 
link and then the "raw" link right at the top of that Station info page.

On 11/8/2011 7:38 PM, Andrew P. wrote:
> I have some questions for WB4APR, about his concept of the 
> Mountain-Top Billboard display mode that the specs say an APRS client 
> should support (but apparently few do).

If you run Windows (or WINE on Linux), download a free copy of 
APRSISCE/32 (http://aprsisce.wikidot.com/) and check out the Messages / 
Bulletins / View display, assuming of course that you've actually 
received a few BLN* messages for which there is no APRS-IS filter.  You 
can use a t/m (get me all messages) and that will deliver not only 
"normal" APRS messages but also all Bulletins.

>
> How exactly should this information be presented to the human users? 
> The spec talks about multi-line bulletins, but I can't figure out how 
> the multiple lines are uniquely identified and ordered (other than 
> when in NTS format, pg. 75 of the APRS 1.01 spec). The rest of it more 
> or less makes sense, but please check my understanding (before I waste 
> a lot of time writing software that behaves incorrectly):

Multiline bulletins are what the spec calls a "Bulletin ID".  That N is 
the line number and you are correct below in that a single bulletin 
sourcing station can only have 10 lines (0..9) PER GROUP.  Since you 
have 5 characters available for the group name, you can actually have 
LOTS of lines of bulletin, but only 10 per group.  How big do you expect 
your bulletin board to be, anyway?

>
> 1. Amateur radio bulletins and announcements are identified by the 
> combination of the sending station callsign, the fourth character of 
> the addressee field (which bulletin or announcement), and the 
> 5-character group ID (which may be 5 spaces for non-grouped 
> distribution). Because of the fourth character limitations, any one 
> sending station is restricted to a maximum of 10 active bulletins (0 
> to 9) and 26 active announcements (A to Z).

Yep.  See above.

>
> 2. National Weather Service bulletins use a totally different 
> addressee format, which "sort of" can map into the above bulletin 
> identifying logic, but not very well (by item #1 analysis, they would 
> appear as only one bulletin '-' per group ["WARN", "WATCH", etc.], 
> updated frequently with new content). Do they support multi-line?

National Weather Service alerts don't even attempt (as far as I can see) 
to be a bulletin.  Bulletins MUST start with BLN and NWS messages start 
with NWS per http://www.aprs-is.net/Wx/

>
> 3. Are there any other special categories that should be treated 
> differently than just directly addressed messages? Should messages 
> directly addressed to the receiving station be posted on the bulletin 
> screen?

See "Message Groups" at the bottom of page 72 in aprs101.pdf - Group 
names are up to the user at the receiving end.  Also, from the top of 
page 73:

> The receiving station will read all messages with the Addressee field 
> set to ALL, QST or CQ.

>
> 4. The status display for bulletins should display each bulletin's 
> 1-line messages consolidated together in order, with some higher-order 
> sorting of whole bulletins and announcements. What is the recommended 
> default sort order for whole bulletins, in order of precedence? Time 
> of last update? Callsign? Bulletin/announcement ID?

Default sort order is on page 76 and states the following.  Personally, 
I inserted Group ID between callsign and Bulletin/Announcement ID.

> This includes sorting by originating callsign and 
> Bulletin/Announcement ID.

>
> 5. The bulletin board display should alert users when it is updated 
> with newer information. Does this include "no-op" changes (receiving 
> identical message text from a periodic re-broadcast)?

Personally, I don't alert on receiving identical text, but have a user 
selectable "Notify" option to receive a notification when new or updated 
lines are received.  And then I discovered that the Kenwood and T2/Nuvi 
units display ALL bulletins received, so I actually quit transmitting my 
routine bulletins via RF.  They're just too intrusive, IMHO.

>
> 6. Presumably, directed station queries (APRS1.01 pg. 79) should 
> _never_ appear on the Bulletin Screen.

Yep, if it doesn't start with BLN, it's not a bulletin.

>
> 7. Bulletins and announcements only stop showing up when the 
> originator stops sending them.

Or when the user gets tired of looking at the drivel.

>
> Also, for directly addressed messages with sequence numbers, should 
> the software immediately acknowledge receipt autonomously, or should 
> it wait for a human being to explicitly tell it to acknowledge receipt?

You must ack immediately from the software.  Failure to do so will 
result in many useless retries which will eventually time out at the 
transmitter and if you subsequently send an ack when the human reads the 
message, the sender has probably long since quit looking for it.  The 
ack represents receipt by the APRS station, not necessarily that the 
message was seen by said station's operator.

>
> Are there any updates in the APRS 1.1 or 1.2 specs that override any 
> of the above?

No overrides that I can recall, but there is a Reply-Ack extension at 
http://aprs.org/aprs11/replyacks.txt that you'll probably want to read 
and support.

>
> Looking forward to some good advice.

Be ready to do it, and re-do it.  What platform are you targeting your 
application to if I may ask?  And if you're planning to release it to 
the general amateur radio public, you should probably read G4ILO's 
excellent description of what you can expect from your user base:

http://blog.g4ilo.com/2010/10/advice-to-amateur-programmers.html

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

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