cyphal_udp_header.dsdl

# Cyphal/UDP provides UNRELIABLE UNORDERED DEDUPLICATED (at most one) delivery of UNICAST or MULTICAST datagrams
# with GUARANTEED INTEGRITY (messages either delivered correct or not delivered).
#
# All Cyphal/UDP traffic is sent to port 9382.
# The subject multicast group address is composed as 239.0.0.0 (=0xEF000000) + subject_id (23 bits).
#
# All frames of a transfer must share the same field values unless otherwise noted.
# Frames may arrive out-of-order, possibly interleaved with neighboring transfers; implementations must cope.
#
# The origin UID is a 64-bit globally unique identifier (e.g., EUI-64). It allows nodes to use redundant interfaces
# without source address ambiguity, and also allows live interface migration.
#
# Unicast traffic is sent directly to the source endpoint of the destination node, which is discovered dynamically.
# The destination UID is not included explicitly since the IP endpoint is considered adequate for node identification.

uint5 version                   #=2 in this version.
uint3 priority                  # 0=highest, 7=lowest.

void5                           # Send zero, ignore on reception.
uint3 incompatibility           # Send zero, drop frame if nonzero.

uint48 transfer_id              # For multi-frame reassembly and dedup.
uint64 sender_uid               # Origin identifier ensures invariance to the source IP address for reassembly.

uint32 frame_payload_offset     # The offset of the frame payload relative to the start of the transfer payload.
uint32 transfer_payload_size    # Total for all frames.

uint32 prefix_crc32c            # crc32c(payload[0:(frame_payload_offset+payload_size)])
uint32 header_crc32c            # Covers all fields above. Same as the transfer payload CRC.

# Header size 32 bytes; payload follows.