I-Am is only one of the possible Service Choices, used to determine the Device Identifier and Network Address of a BACnet Device
The Network Address is derived either from the MAC address (if the device is on the local network) or the NPCI if the device is on a remote network.
The following structure is only one possible example of an I-Am message. In particular, the first field has flags the would include other fields if the flags were set. See the entry on APDU for more information.
|1||0001 0000||0001 = PDU Type, 0000 = BACnet-Unconfirmed-Request-PDU||-|
|1||0||Service Choice 0 = I-Am||-|
|4||User||Device Identifier of device, of type||Application, Object Identifier|
|1-2||User||Max APDU Length Accepted||Application, Unsigned|
|2||0-3||Segmentation Supported||Application, Enumerated|
|3||Vendor Identifier||Official list here.||Application, Unsigned 16|
BACnet Specification, Section 16.10.3, Page 340
|APDU BBMD BVLC BVLL DADR DNET Encoding I-Am LSAP MAC NPCI NPDU NSAP NSDU SA SADR SNET|
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i-am I-Am iam IAM IAm