MeshCom 4.0 uses the AX.25 protocol for the payload data as defined for APRS. (aprs101.pdf APRS PROTOCOL REFERENCE Version 1.0 2000, Page 12)
Find use:
- Identifier - APRS data type identifier
- Message ID - 32-bit LSB->MSB unique value
- MAX-HOP - max. 7 (mask 0x07) default 5 is used which allows 4 more passes.
- 0x80 - Identifier whether this message has already run via MQTT server.
- 0x40 - Identifier that this message is to be supplemented per MeshClient with the callsign of the forwarding station. For measurement and control purposes.
- Source address - This field contains the callsign and SSID of the transmitting station.
- Destination Address - This field may contain an APRS destination callsign or "*" for transmissions to ALL.
- Digipeater - There can be 0 to 8 digipeater call signs in this field. Note: These digipeater addresses can be overwritten by a generic APRS digipeater path (specified by the SSID of the destination address).
- Information - This field contains transport data. The first character of this field is the APRS data type identifier, which indicates what type of data follows.
- Frame Check Sequence - The FCS is a sequence of 16 bits used to check the integrity of a received frame.
- Gateway ID - The gateway that passes the message to the MQTT server appends the 32-bit MAC address to ensure compatibility with MeshCom 2.0.
Messages:
Text messages:
:|MMMMMM|HH|OE0XXX-99|>*|:|Hello Mike, I am trying to send an APRS message|0x00|FCS#|GGGGG
Position messages:
!|MMMM|HH|OE0XXX-99|>*|!|4800.00|N|/|01600.00|E|#| BBB /A=HHH|0x00|FCS#|GGGGGGG
Protocol elements:
| Short code | Field name | Variable type |
|---|---|---|
| : or ! | Identifier | |
| MMMMMM | Message ID | 32-bit LSB->MSB |
| HH | MAX-HOP | 8-bit bit mask 0x07 |
| Message via MQTT server | Bit mask 0x80 | |
| Insert path in mesh (with comma as separator) | Bit mask 0x40 | |
| 4800.00 | Latitude | Degree/decimal x 100 |
| 01600.00 | Longidude | Degree/decimal x 100 |
| N | N ord / S outh | char |
| / | APRS SYMBOL group (/ or \) | char |
| E | E ast / W est | char |
| # | APRS SYMBOL | char |
| BBB | Battery status in % | int 0 - 100 |
| /A=HHH | GPS sea level (m) | int 0 - 9999 |
| Message completion | closes the APRS message area | 0x00 |
| FCS# | Checksum incl. identifier and 0x00 from message completion | unsigned int 16-bit |
| GGGGGGG | Gateway ID (only for MeshCom 2.0 compatibility) | 32-bit LSB->MSB |
|... is only used to show the separations here in the text
Text messages with Path from Mesh:
:|MMMMMM|HH|OE0XXX-99,OE3XXX-12,OE3YY-12|>*|:|Hello Mike, I am trying to send an APRS message|0x00|FCS#|GGGGG