[aprssig] Digipeater addresses/spec question

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Wed Jul 20 10:57:43 EDT 2011

On 7/20/2011 10:51 AM, Alexander Sack wrote:
> Yes I got that this from Bob's page on SSIDs (thanks).  But the spec
> seems to insinuate that AX.25 Source addresses have SSID's which is
> again the source of my confusion.

Yes, in AX.25, all station addresses in the header, including the 
source, destination, and all path components, have four bits reserved 
for the SSID.  When these packets are put into human-readable form, the 
-0 is typically suppressed and presented as just the callsign with no -SSID.

So, every station address in every packet on the air will contain an 
SSID from 0 through 15 inclusive.  But the human readable packets will 
suppress the -0 for convenience.

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

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