[aprssig] APRS<=>E-mail

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Mon Jan 5 13:24:51 EST 2009

 From the APRS101 spec approved 29 August 2000 under the NTS Radiogram 

Each line may be up 67 characters long, including the 3-character NTS
format identifier. Lines in excess of 67 characters will be truncated.

Also from the Messages, Bulletins, and Announcements section:

The message text may be up to 67 characters long, and may contain any
printable ASCII characters except |, ~ or {.

 From the APRS-IS Specification:

All "packets" sent to APRS-IS must be in the TNC2 format terminated by a 
carriage return, line feed sequence. No line may exceed 512 bytes 
including the CR/LF sequence.

And that 512 bytes INCLUDES the TNC2 monitor format "header" information 
(prior to the colon) of SENDER>DEST,PATH:rest of packet.  If I remember 
correctly, the AX.25 path can handle up to 8 hops and then an IGate may 
add a qXX and it's own callsign, and a callsign-ssid is 9 characters, 
plus the commas means that the header maxes out at 120 bytes 
(sender+dest+8*path+qXX+IGate) (actually 114 if we assume a 3, not 9, 
character qXX code).  That would leave a maximum of 398 payload 
characters per the APRS-IS spec.  Oh, but we have to allow for the 9 
character message destination and an additional colon separator plus the 
ack at the end (assuming the e-mail forwarder is doing the decaying send 
until ack routine).  That'd leave us with 382 (10 for dest & colon and 6 
for {msgno per APRS spec).

Seems like 382 is the upper limit of message body for TCP/APRS-IS 
packets and 67 is the defined spec limit for APRS over RF messages.

Lynn (D) - KJ4ERJ - Thankful for Jason's suggestion to check the specs...

Jason KG4WSV wrote:
> On Mon, Jan 5, 2009 at 11:48 AM, Lynn W. Deffenbaugh (Mr)
> <ldeffenb at homeside.to> wrote:
>> To throw out numbers, I'd say 1K for non-RF users
> gack!  Think maybe you should check the APRS-IS design first?  I don't
> know the upper limit on packet size, but it would pay to check it out.
> Think "APRS messages", not "small email".
> -Jason
> kg4wsv
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