[aprssig] APRS-IS Duplicate Packets

[Lynn W. Deffenbaugh (Mr)]

Just for the record, and why trailing whitespace is significant (a poor 
design decision IMHO), consider the Yaesu VX-8 device below from the 
Mic-E specification (http://aprs.org/aprs12/mic-e-types.txt).  Yes, the 
... represents the entire packet and the _b (underscore blank) comes at 
the very end!  Adding trailing blanks is just as bad as it makes it very 
difficult to ascertain the actual last character.  Was it the blank, or 
the last non-blank before that?

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

Mic-E TEXT FORMAT:   "T......Mv".

Where T is the Mic-E TYPE byte (" ",">","]","`","'")
Where ........ is free field text
Where aaa}.... like Taaa}....Mv is optional altitude
Where "M" represents the Manufacturer Byte 
Where "v" represents a version number
<snip>
NEW FORMATS FOR ALL FUTURE APPLICATIONS:

`......Mv  OTHER Mic-E  - display "McE-msg" or "Mic-Emsg"
'......Mv  OTHER Mic-E  - display "McE-trk" or "McTrackr"

As combinations of "Mv" bytes are added to this table, manufacturers
are encouraged to display the correct radio type if known.  The
following additional bytes have been declared:

`......_b  Yaesu VX-8 (b = SPACE) (message capable)
`......_"  Yaesu FTM-350 (message capable)
`......_#  Yaesu VX-8G   (message capable)   [new in 2010]
'......|3  Byonics TinyTrack3 (TT3)  
'......|4  Byonics TinyTrack4 (TT4)
T......\v  Hamhud  ? (awaiting confirmation?)
T....../v  Argent  ? (awaiting confirmation?)
T......~v  OTHER (to be used when all other "M" MFR's are used up)



Pete Loveall AE5PL Lists wrote:
> The servers are properly eliminating dupes.  Unfortunately, the packets you presented are not dupes.  Upon closer inspection (on jfindu.net's ListPackets.aspx page), the packets gated to APRS-IS by N4XI-11 and WB9TLH-15 contain trailing spaces while packets from the other IGates do not contain those trailing spaces.  If your packets contain trailing whitespace, this can occur by IGates or the server(s) they are connected to improperly trimming packets of data content (there is some attempt by javAPRSSrvr to reduce these duplicates, but if the trimmed packet shows up first, as in this case, there is not much that can be done).  If your packets do not contain trailing white space, then these IGates are improperly appending the white space.
>
> In my experience of monitoring APRS-IS traffic, the most common occurrence is when the packet contains trailing whitespace and some software or device in the path (either on air or on APRS-IS) is improperly modifying packet content by trimming the whitespace.
>
> 73,
>
> Pete Loveall AE5PL
> pete at ae5pl dot net
>
>   
>> -----Original Message-----
>> From: Max Harper
>> Sent: Monday, May 03, 2010 1:29 AM
>>
>> I have noticed for some time now that the APRS-IS is not filtering out
>> all
>> duplicate packets. I currently have a filter that only sends me packets
>>     
>
>   
>> KG4PID-15>APN391,NV4B-7*,WIDE2-1,qAR,KB4YTM-
>> 1:@030210z3417.45N/08742.32W_000/000
>> g000t069r000p157P157h97b10081.DsVP
>> KG4PID-15>APN391,NV4B-7,WD4INS-4,WIDE2*,qAR,WB9TLH-
>> 15:@030210z3417.45N/08742.32W
>> _000/000g000t069r000p157P157h97b10081.DsVP
>>     
>
>   
>> KG4PID-15>BEACON,SPKSCH*,WIDE2-2,qAR,N8DEU-5:>Digi / Weather
>> kg4pid at yahoo.com
>> KG4PID-15>BEACON,NV4B-7,WIDE1,WAVTN*,WIDE2-1,qAR,N4XI-11:>Digi /
>> Weather kg4pid@
>> yahoo.com
>>