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[aprssig] APRS<=>E-mail

Gregory A. Carter gcarter at openaprs.net
Mon Jan 5 18:33:38 UTC 2009


Thanks for looking that up Lynn...

So it may be possible to check to see if the user is actually online at the
time with messaging by looking at the destination address they have set
which would hopefully reveal what client they are using.  Of course this
would fail in the case of MIC_E packets but would generally be useful for
others.  If we couldn't detect what client they were using then we're
default to the RF limit.

Greg

NV6G
OpenAPRS.Net

On Mon, Jan 5, 2009 at 10:24 AM, Lynn W. Deffenbaugh (Mr) <
ldeffenb at homeside.to> wrote:

>  From the APRS101 spec approved 29 August 2000 under the NTS Radiogram
> section:
>
> 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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> >
>
>
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