diff --git a/documentation/FreeDATA-protocols.md b/documentation/FreeDATA-protocols.md
new file mode 100644
index 00000000..70d3385c
--- /dev/null
+++ b/documentation/FreeDATA-protocols.md
@@ -0,0 +1,132 @@
+# 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 (14 bytes)
+
+|field|bytes|
+|-|-|
+|session id|1|
+|origin|6|
+|destination|6|
+|crc|1|
+
+
+#### SESSION_OPEN_ACK
+
+IRS sends this in response to a SESSION_OPEN_REQ
+
+DATAC13 Mode (14 bytes)
+
+|field|bytes|
+|-|-|
+|session id|1|
+|origin|6|
+|protocol version|1|
+|snr|1|
+|crc|3|
+
+
+#### SESSION_INFO
+
+ISS sends this in response to a SESSION_OPEN_ACK
+
+DATAC13 Mode (14 bytes)
+
+|field|bytes|
+|-|-|
+|session id|1|
+|total bytes|4|
+|total crc|4|
+|snr|1|
+|crc|4|
+
+
+#### SESSION_INFO_ACK
+
+IRS sends this in response to a SESSION_INFO
+
+DATAC13 Mode (14 bytes)
+
+|field|bytes|
+|-|-|
+|session id|1|
+|total crc|4|
+|snr|1|
+|speed level|1|
+|frames per burst|1|
+|crc|4|
+
+
+#### 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|