flyqaq/umcp

Lightweight communication protocol with guaranteed delivery

uMCP

Lightweight communication protocol with guaranteed delivery

uMCP - a free view on the DDCMP protocol, especially designed to work with small baudrates and channels with high error probability - for example, underwater acoustic channel etc. uMCP is designed for better usability of uWAVE and RedLINE underwater acoustic modems (but not only!).

It is very similar to DDCMP, but has some differencies:

• smaller overhead
• possible communication between tributary stations
• no NAKs, all error situations are managed by timeouts to decrease traffic
• easy pipelining

timeouts are causing transmission of REP (reply to message), remote system answers with ACK (which, in fact, contains remote system state)

• if error is due to lost ACK, it will be corrected by ACK retransmission from the remote system
• if error is due to lost DATA message, it will be corrected by DATA message retransmission to the remote system Retransmission performed without pipelining.

Message framing

SIGN : 8 bit (start signature) = 0xAD SID : 8 bit (sender ID) TID : 8 bit (target ID) PTYPE : 8 bit (packet type)

if PTYPE == STR || PTYPE == STA

• no extra data

else if PTYPE == REP TCNT : 8 bit

else if PTYPE == ACK TCNT : 8 bit RCNT : 8 bit

else if PTYPE = DTA || PTYPE == DTE TCNT : 8 bit RCNT : 8 bit

endif

HCHK : 8 bit (header checksum)

if PTYPE == DTA || PTYPE == DTE DCNT : 8 bit (data counter) DATA : 8 bit * DCNT

endif