FreeDATA/documentation/FreeDATA-protocols.md

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:BURST_ACK (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