Echelon OpenLDV - Manual (Page 68)

60 Sending and Receiving Messages with the OpenLDV API
SICB application buffer structure is defined as a structure of type ExpAppBuffer
in the OpenLDVdefinitions.h header file.
Some immediate commands use only the first byte of the SICB buffer—the cmd
field—of the application buffer, with no data payload. Other immediate
commands also include a data payload.
All other downlink and uplink message commands use the complete SICB
application buffer structure, as shown in Figure 6. The following sections
describe the application buffer structures.
Queue
Length
ExpMsgHdr
SendAddrDtl
or
RcvAddrDtl
or
RespAddrDtl
Command
UnprocessedNV
or
ExplicitMsg
Length
Application Layer
Header
Size=2
Message Header
Size=3
Network Address
Size=11
Message Data
Size=variable
Queue
Length
Layer 2 Header
NPDU
Command
CRC
Length
Application Layer Header
Size=2
Layer 2 Header
Size=1
Network Protocol Data Unit
Size=variable
CRC
Size=2
Layer 5 Buffer Structure Layer 2 Buffer Structure
Figure 6. SICB Application Buffer Detailed Structure
As described in Getting Started with the OpenLDV Driver on page 7, an
OpenLDV application can use a Layer 2 network interface or a Layer 5 network
interface:
• Layer 2 Network Interface – A network interface that communicates at
Layer 2 of the LonTalk protocol. This type of interface transports
LonTalk packets without processing them, and does not filter by network
address.
• Layer 5 Network Interface – A network interface that communicates at
Layer 5 of the LonTalk protocol. This type of interface transports
incoming LonTalk packets that are addressed to the network interface,
and transports outgoing packets that are addressed to other devices.