Network Layer Protocol Data Unit

From BACnet Wiki
(Redirected from NPDU)
Jump to: navigation, search

See BVLL for the packet structure before the NPDU.


The NPDU consists of a NPCI followed by a NSDU


NPDU
NPDU
NPCI Octets Meaning Notes
1 Version (Always 0x01)
1 NPCI Control Octet Establishes if NSDU is a Network Layer Message or APDU
2 DNET Only present if DNET, DADR, Hopcount present flag set in NPCI Control Octet
1 DLEN Only present if DNET, DADR, Hopcount present flag set in NPCI Control Octet
Variable DADR Only present if DNET, DADR, Hopcount present flag set in NPCI Control Octet
2 SNET Only present if SNET, SADR present flag set in NPCI Control Octet
1 SLEN Only present if SNET, SADR present flag set in NPCI Control Octet
Variable SADR Only present if SNET, SADR present flag set in NPCI Control Octet. Is the 4 byte IP address and port number in BACnet/IP. (6 bytes total)
1 Hop Count Only present if DNET, DADR, Hopcount present flag set in NPCI Control Octet
NSDU Variable Network Layer Message if NPCI Control Octet bit 7 true, APDU if NPCI Control Octet bit 7 false



Common NPDUs - Control = 0x20

Implies a broadcast NPDU. Notice that there is no SNET and SADR in the BACnet network of the initiating device. These two fields are added by the first BACnet Router before the message is placed on the next BACnet network.


NPDU
Octets Meaning
1 Version (Always 0x01)
1 NPCI = 0x20
2 DNET = 0xFFFF (B'Cast)
1 DLEN = 0x00 - (B'Cast)
1 Hop Count
Variable APDU



Keyword List
APDU BBMD BVLC BVLL DADR DNET Encoding I-Am LSAP MAC NPCI NPDU NSAP NSDU SA SADR SNET

Device Profiles

Edit this box.

Glossary