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[aprssig] Directional SSID

Stephen H. Smith wa8lmf2 at aol.com
Wed Jul 13 22:13:38 UTC 2005


n0yxv at gihams.org wrote:

>Can somebody point me toward the right web page to explain Directional SSID's,
>or what ever they are called? I found it in a config file that looks like
>below.
>
>// Path used when SSID routing is used (Up to 8 hops)
>// (Direction) Path
>// xpath [path]
>
>NorthPath              =
>
>SouthPath              =
>
>EastPath               =
>
>WestPath               =
>
>
>NorthPath              =
>
>SouthPath              =
>
>EastPath               =
>
>WestPath               =
>
>
>--
>  
>
It's a feature of APRS intended to be a shortcut way for users to 
express particular desired paths that never caught on.   

As a digipeater sysop, you would enter paths consisting of specific, 
actual callsigns of digipeaters , located north, south, east or west  
relative to your own digi,  in your digipeater's software or firmware.  
Users could then select this path (instead of generic paths like 
WIDEn-N) by changing the SSID of the destination callsign in their 
setups.  This would allow the user to, for example, beacon "North up the 
coast" without having beacons propagate inland or to the south,  without 
having to know the actual callsigns involved (the digi would know them 
instead). . 


Quoting from the APRS 1.01 standards document, available from:
      ftp://ftp.tapr.org/aprssig/aprsspec/spec/aprs101/APRS101.pdf*
*or  
      www.ui-view.org/files/APRS101.pdf    

pages 25 and 26:

"If the Destination Address SSID is non-zero, the packet follows one of 15
generic APRS digipeater paths.

The SSID field in the Destination Address is  encoded as follows:       
APRS    Digipeater
SSID    Path

-0    Use VIA path   
-1    WIDE1-1   
-2    WIDE2-2       
-3    WIDE3-3   
-4    WIDE4-4       
-5    WIDE5-5   
-6    WIDE6-6
-7    WIDE7-7   
-8    North path
-9      South path
-10    East path
-11    West path
-12     North path + WIDE
-13    South path + WIDE
-14    East path + WIDE
-15    West path + WIDE    "

In order for this to work, digipeater software or firmware had 
explicitly support this kind of SSID routing. Most never did.

1)  Practically no one ever used this technique (particularly because it 
isn't supported by the KPC3+ TNC used in such a large percentage of all 
digipeaters).

2)  Plain WIDE-type paths defined in this standard, (as distinguished 
from WIDEn-N paths) are now obsolete and being phased out. 

3)  In today's crowded APRS environment, no one should be using ( or 
facilitating the easy use of) paths with 4-7 hops in them.


Best Suggestion:   Just leave these items blank.

For more information on APRS digipeating conventions and how they have 
evolved and changed over the last few years, visit my web page at:
     http://webs.lanset.com/wa8lmf/DigiPaths   
 



Stephen H. Smith             wa8lmf (at) aol.com
                                                    
Home Page:                   http://wa8lmf.com

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