[amsat-bb] Non standard APRS implementation in AI SAT

[Nitin Muttin]

We have not reached out to aprs.fi to show the APRS activity from  AISAT-1 heard by satgates. We have reached out to findu.com for the same. If we are missing something please advice.
73
Nitin [VU3TYG] 

    On Monday, 8 April, 2019, 8:47:17 pm IST, John Langner WB2OSZ via AMSAT-BB <amsat-bb at amsat.org> wrote:  
 
 

There was a discussion, in another group, about why nothing from AISAT was getting showing up on aprs.fi.

K4KDR provided some samples of the signals so they could be analyzed.

The direwolf "-dp" option was used to produce a hexadecimal dump, of the frame, so we could see what is going on.


---------------------------------

Notice the extra comma after the last address.

 
 K4KDR-6>CQ,AISAT*,::CQ-0    :=3747.66N/07736.67W`de K4KDR scott23192 at gmail.com Virginia  FM17es{847
------
U frame UI: p/f=0, No layer 3 protocol implemented., length = 111
 dest    CQ      0 c/r=0 res=3 last=0
 source  K4KDR  6 c/r=0 res=3 last=0
 digi 1  AISAT*  0  h=0 res=3 last=0    <--  The “h” bit indicates that the
                                          digipeater address has been used
                                          It should be 1 in this case.  There should NOT be
                                          the * character in the address field.
                                                                                                                                                                                
 digi 2          0  h=0 res=3 last=1
 
 
I reformatted this so the bytes would be in groups of 7 so it is easier to read.
 
  000:  86 a2 40 40 40 40 60          “CQ”      
            96 68 96 88 a4 40 6c      “K4KDR”  SSID 6
            82 92 a6 82 a8 54 60      “AISAT*”      <--  WRONG!!!!!
        
                                            The * character is used only for the
                                            human readable monitoring format.
                                            It should not be a character in the
                                            station address.
 
        40 40 40 40 40 40 61          “      “      WRONG!!!  Field should not
                                                be here if not needed.
        03 f0                                    expected control, protocol
        3a 43                                                                                      :C
  020:  51 2d 30 20 20 20 20 20 3a 3d 33 37 34 37 2e 36  Q-0    :=3747.6
  030:  36 4e 2f 30 37 37 33 36 2e 36 37 57 60 64 65 20  6N/07736.67W`de
  040:  4b 34 4b 44 52 20 73 63 6f 74 74 32 33 31 39 32  K4KDR scott23192
  050:  40 67 6d 61 69 6c 2e 63 6f 6d 20 56 69 72 67 69  @gmail.com Virgi
  060:  6e 69 61 20 20 46 4d 31 37 65 73 7b 38 34 37    nia  FM17es{847
 
 
-----------------------------------

This is my analysis:

(1) Digipeating does not work normally.  A digipeater should only change the via path.  The information part should not be changed.  Why is it converted into “message” format?

(2) Only the needed digipeater fields should be present.  If they are not needed leave them out.  Don’t fill them with blanks.

(3) A station address should never contain the * character.  That is only in the human readable standard monitoring format.  The * after a station indicates that the H bit is set.

(4) When a digipeater uses up an address in the via path, it must set the “H” bit to 1.  If it responded to an alias, it should substitute its own callsign.

Here is an example of expected behavior:

K4KDR-6>CQ,ARISS:=3747.66N/07736.67W`de K4KDR scott23192 at gmail.com Virginia  FM17es
K4KDR-6>CQ,RS0ISS*:=3747.66N/07736.67W`de K4KDR scott23192 at gmail.com Virginia  FM17es

- ARISS is recognized as an alias by RS0ISS.
- RS0ISS substitutes its own call and marks that digipeater field as being used.
- The * is not a character in the address.  It is the human readable way to indicate that the “H” bit is set.
- Only the via path is changed.
- The Information part is not changed at all.



------------------
  
73,
John WB2OSZ

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