[ax25-layer2] 7-byte address proposal

[Robert Bruninga]

Pete,

Yes, all of  your assumptions are correct including the potential
for problems.  I just put it on the table as a possible short-term 
workaround...  You are correct that the
position of the numeric digit is lost.  Hummh..., how about this...
two of the 6 extra bits are used to encode the "position" of the
digit in the field, and then 4 bits are still left for multiple calls
from the same station.  
00 could mean TBD
01 could mean 1st and 3rd as in 4X4xxx
10 could be the 2nd digit as in K4HG
11 could be the 3rd as in WB4APRS

Again, this is not a serious proposal, but just a background
idea... not intended to dissrupt the current discussions...
Thanks
Bob, WB4APR

>>> pete at ae5pl.net 08/02/06 4:00 PM >>>
Taking APRS out of the equation since that is an application written on
AX.25 and not a layer 2 application of AX.25, let's look at what you
proposed solely from an AX.25 standpoint.

If I have this right, your proposal is for 7 character callsigns to use
the SSID for the area number (area numbers are _currently_ used
throughout the world).  Also, upper and lower case ASCII letters would
be allowed in the address fields.  If this is not an accurate summary of
your proposal, please correct it.

Let's look at what this does and doesn't do for us (this is not a
critique, simply an exploration of causes/effects):

7 character callsigns are supported as long as there is an area number.

There is the possibility (however remote) for duplicates: AA5AAAA and
AAA5AAA and A5AAAAA would all be AAAAAA-5
Another example: AA50AAA (special event station) and AA0AAA-5 (SSID 5
for AA0AAA)

Some current AX.25 TNCs in converse mode (KISS mode _should_ be
transparent) and some applications might prevent transmission or
reception of lower-case letters in the address fields (usually by
converting them to upper case).

If upper and lower case can be used for 7 character callsigns, you know
anyone can and will use them for shorter callsigns (simply a potential
compatibility issue).

As you said, it is a kluge and like any kluge it has issues.  But it is
possibly a workable idea for the near future which would not have to be
in the next spec (2.3) beyond the allowance of upper and lower case
letters in address fields.

73,

Pete Loveall AE5PL 

> -----Original Message-----
> From: Robert Bruninga
> Sent: Wednesday, August 02, 2006 9:08 AM
> To: ax25-layer2 at lists.tapr.org 
> Subject: RE: [ax25-layer2] 7-byte address proposal
> 
> For 7 character addresses:
> 
> Clarify if this would work....  and correct me if I am wrong...
> 
> If I remember correctly the AX.25 spec limited the 
> TRANSMISSION of callsigns to be the UPPERCASE ASCII subset, 
> but made no mention of reception.  Thus, I have seen many 
> TNC's that will actually receive just fine, abd decode 
> mixed-case AX.25 addresses.
> 
> My thoughts for this would be to use mixed case as a means of
> transmitting an additional bit per character.    To use this, first
> remove the Numeric DIGIT and move it to the SSID field.  So a 
> 7 byte call such as WB4APRS would be come WBAPRS-4 This is 
> 100% backwards compatible.  Now, then, use the added
> 6 bits for up to 64 different callsign variants for that station.
> (Like SSID Used to do).

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