[aprssig] Maximum APRS Packet Lengths

Jim Alles kb3tbx at gmail.com
Tue Nov 29 06:03:36 CST 2016


#3, and 5: see
http://www.tapr.org/pipermail/aprssig/2008-November/027554.html

7. Where did this 67 character limit on messages come from?

This is a question for Bob.

http://www.aprs.org/localinfo.html

He was counting, like this:

>        1234567890------------============------------=========(D7)

http://www.aprs.org/ande/ANDEfirmware.txt

BText (B):  >ANDE alt._channel.__US_Naval_Academy        <== REV-2
>             Note, Underscores are used for BLANK characetrs here in
>             this spec to clearly indicate the exact number of spaces
>             The spacing is such to fit well on the Kenwood D7 display

http://www.cbradio.cz/doc/_HAM/Kenwood/TH-D7/aprs.pdf

Says Max. 45 Characters -  that is old, but that's not it.

http://aprs.qrz.ru/hard/th-d72/d/TH-D72A-brochures-eng-4.pdf

Has: Messaging • Messages: up to 100 (max. 67 characters each)

maybe, but I like this purpose-built device:

http://www.aprs.pl/hh2.htm

4x20, but it does 20 characters, then scrolls.

hmm.

http://www.aprs.org/dcc1998.html

I didn't get licensed til 10 years later...

Steve?

I should be at work already.

73,

.ja.



> So my questions:
>
> 1. Do we still want RF-gates including consumed hops in third-party
> packets, or is that deprecated in favor of the "}[SRCCALL]>[TNCID],[NETWORKID],[IGATECALL]*:"
> 42 byte format? (If we're going to clarify that as being deprecated, we
> should probably include AEA format while we're at it)
>
> 2. Are there any other Network IDs in actual use except for TCPIP for
> APRS-IS? (Remember that TCPXX is already deprecated)
>
> 3. Where did all of these different lengths for comment fields come from?!
>
> 4. Do we want to consider loosening up the maximum packet length for some
> of these data types?
>
> The way I figure, we could support 197 byte messages for APRS Messages.
> This is going to break sending long-winded messages to many devices, but 67
> is awfully restrictive compared to modern features like SMS... Clearly new
> software is deliberately constraining fields based on the spec. I'll need
> to test length limits on the D700 I've got sitting on my bench.
>
> 5. Does anyone happen to know the actual length limits on messaging for
> various devices out in the wild already?
>
> 6. If not messaging, do we want to loosen some of the comment fields? 23
> bytes for the BITS. Project Title seems like a strong contender for first
> to consider. Remember that we're talking about bytes here, not characters;
> many non-English languages using UTF-8 can burn through 23 bytes very
> quickly, so I'm talking about making Project Titles allowed up to something
> CRAZY like 190 so length just isn't an issue anymore.
>
> 7. Where did this 67 character limit on messages come from?! This really
> bothers me now.
>
>
> --
> Kenneth Finnegan, W6KWF
> http://blog.thelifeofkenneth.com/
>
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> aprssig at tapr.org
> http://www.tapr.org/mailman/listinfo/aprssig
>
>
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