2.6 KiB
FreeDATA - Protocols
ARQ Sessions
An ARQ Session represents a reliable data transmission session from a sending station (A) to a receiving station (B). It uses automatic repeat request on top of different codec2 modes according to the transmission channel conditions.
So lets say A wants to send some data to B. A typical scenario would be like this:
ISS->(1)IRS:<datac13> OPEN_REQ(session id, origin, dest)
IRS->(1)ISS:<datac13> OPEN_ACK (session id, proto version, speed level, frames, snr)
ISS->(1)IRS:<datac13> INFO(id, total_bytes, total_crc)
IRS->(1)ISS:<datac13> INFO_ACK(id, total_crc)
ISS->(1)IRS:BURST (ID, offset, payload),(ID, offset, payload),(ID, offset, payload)
IRS->(1)ISS:BURST_ACK (ID, next_offset, speed level, frames, snr)
ISS-->(1)IRS:Lost BURST (total or part)
IRS->(1)ISS:BURST_NACK (ID, next_offset, speed level, frames, snr)
ISS->(1)IRS:BURST (ID, offset, payload),(ID, offset, payload),(ID, offset, payload)
IRS->(1)ISS:DATA ACK NACK (ID, next_offset, speed level, frames, snr)
Frame details
SESSION_OPEN_REQ
ISS sends this first
DATAC13 Mode (12 bytes)
| field | bytes |
|---|---|
| session id | 1 |
| origin | 6 |
| destination_crc | 3 |
SESSION_OPEN_ACK
Sent by the IRS in response to a SESSION_OPEN_REQ
DATAC13 Mode (12 bytes)
| field | bytes |
|---|---|
| session id | 1 |
| origin | 6 |
| destination_crc | 3 |
| protocol version | 1 |
| snr | 1 |
SESSION_INFO
ISS sends this in response to a SESSION_OPEN_ACK
DATAC13 Mode (12 bytes)
| field | bytes |
|---|---|
| session id | 1 |
| total bytes | 4 |
| total crc | 4 |
| snr | 1 |
SESSION_INFO_ACK
IRS sends this in response to a SESSION_INFO
DATAC13 Mode (12 bytes)
| field | bytes |
|---|---|
| session id | 1 |
| total crc | 4 |
| snr | 1 |
| speed level | 1 |
| frames per burst | 1 |
Data Burst
ISS sends this to send data to IRS
Mode according to handshake speed level
Frames per burst according to handshake
Modulation
Each burst is composed of frames_per_burst frames:
|preamble|f1|f2|f3|...|postamble|
Each data frame
| field | bytes |
|---|---|
| session id | 1 |
| offset | 4 |
| payload | (the remaining payload length) |
DATA_BURST_ACK
Sent by the IRS following successful decoding of burst.
| field | bytes |
|---|---|
| session id | 1 |
| next offset | 4 |
| next speed level | 1 |
| next frames per burst | 1 |
| snr | 1 |
DATA_BURST_NACK
Sent by the IRS following unsuccessful decoding of burst or timeout.
| field | bytes |
|---|---|
| session id | 1 |
| next offset | 4 |
| next speed level | 1 |
| next frames per burst | 1 |
| snr | 1 |
DATA ACK NACK
Sent by the IRS after receiving data with a state information.
| field | bytes |
|---|---|
| session id | 1 |
| state | 1 |
| snr | 1 |