embedded systems - bacnet

NPDU Header
length	description
1	Version (0x01)
1	Control Flags
0, 3, or 4	possible destination specifier
0 or 4	possible source specifier
0 or 1	possible hop count

    | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
    +---+---+---+---+---+---+---+---+
 1: | m | 0 | d | 0 | s | r | prior | Control Flags
    +---+---+---+---+---+---+---+---+

Control Flags
bit	name	description
7	m	0 = NSDU contains: BACnet APDU, message type field absent.
6	0	0
5	d	Destination Specifier Present
4	0	0
3	s	Source specifier Present
2	r	Expecting Reply: Other than a BACnet-Confirmed-Request-PDU, segment of BACnet-ComplexACK-PDU or network layer message expecting a reply present.
1, 0	prior	Priority

if Destination Specifier is true, a destination address is present.

If the Destination MAC layer Address Length is zero, the message is a broadcast on the destination network, and the destination MAC Layer Address is not present.

offset	length	data	description
0048	2	ff ff	Destination Network Address: 65535
0050	1	0	Destination MAC Layer Address Length: 0 indicates Broadcast on Destination Network

If the Destination MAC layer Address Length is greater than zero, the destination MAC Layer Address is present.

offset	length	data	description
0048	2	4	Destination Network Address
0050	1	1	Destination MAC Layer Address Length: greater than 0 indicates the MAC Layer address present
0050	len	32	Destination MAC Layer Address

If Source specifier is true, a source address is present.

offset	length	data	description
0048	2	4	Source Network Address
0050	1	1	Source MAC Layer Address Length
0050	len	32	Source MAC Layer Address

Examples
From the same network (IP)

    |--7--|--6--|--5--|--4--|--3--|--2--|--1--|--0--|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    | BACnet Virtual Link Control                   |
    +-----+-----+-----+-----+-----+-----+-----+-----+
 0: | Type                                          | 81 = Type: BACnet/IP (Annex J)
    +-----+-----+-----+-----+-----+-----+-----+-----+
 1: | Function                                      | 0b = Function: Original-Broadcast-NPDU
    +-----+-----+-----+-----+-----+-----+-----+-----+
 2: | BACnet packet length                          | 00
 3: |                                               | 18
    +-----+-----+-----+-----+-----+-----+-----+-----+
    | Building Automation and Control Network NPDU  |
    +-----+-----+-----+-----+-----+-----+-----+-----+
 4: | Version                                       | 01 = (ASHRAE 135-1995)
    +-----+-----+-----+-----+-----+-----+-----+-----+
 5: |  m  |  0  |  d  |  0  |  s  |  r  | priority  | 20 (see above)
    +-----+-----+-----+-----+-----+-----+-----+-----+
 6: | Destination Network Address                   | FF
 7: |                                               | FF = broadcast
    +-----+-----+-----+-----+-----+-----+-----+-----+
 8: | Destination MAC Layer Address                 | 00 = broadcast on destination network
    +-----+-----+-----+-----+-----+-----+-----+-----+
 9: | Hop Count                                     | FF
    +-----+-----+-----+-----+-----+-----+-----+-----+

From a different network (MSTP)

    |--7--|--6--|--5--|--4--|--3--|--2--|--1--|--0--|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    | BACnet Virtual Link Control                   |
    +-----+-----+-----+-----+-----+-----+-----+-----+
 0: | Type                                          | 81 = Type: BACnet/IP (Annex J)
    +-----+-----+-----+-----+-----+-----+-----+-----+
 1: | Function                                      | 0b = Function: Original-Broadcast-NPDU
    +-----+-----+-----+-----+-----+-----+-----+-----+
 2: | BACnet packet length                          | 00
 3: |                                               | 1c
    +-----+-----+-----+-----+-----+-----+-----+-----+
    | Building Automation and Control Network NPDU  |
    +-----+-----+-----+-----+-----+-----+-----+-----+
 4: | Version                                       | 01 = (ASHRAE 135-1995)
    +-----+-----+-----+-----+-----+-----+-----+-----+
 5: |  m  |  0  |  d  |  0  |  s  |  r  | priority  | 28 dest present, source present (see above)
    +-----+-----+-----+-----+-----+-----+-----+-----+
 6: | Destination Network Address                   | FF
 7: |                                               | FF = broadcast
    +-----+-----+-----+-----+-----+-----+-----+-----+
 8: | Destination MAC Layer Address                 | 00 = broadcast on destination network
    +-----+-----+-----+-----+-----+-----+-----+-----+
 9: | Source Network Address                        | 00
10: |                                               | 04 = network 4
    +-----+-----+-----+-----+-----+-----+-----+-----+
11: | Source MAC Layer Address Length               | 01
    +-----+-----+-----+-----+-----+-----+-----+-----+
12: | Source Address                                | 32
    +-----+-----+-----+-----+-----+-----+-----+-----+
13: | Hop Count                                     | fe
    +-----+-----+-----+-----+-----+-----+-----+-----+

To the same network (IP)

    |--7--|--6--|--5--|--4--|--3--|--2--|--1--|--0--|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    | BACnet Virtual Link Control                   |
    +-----+-----+-----+-----+-----+-----+-----+-----+
 0: | Type                                          | 81 = Type: BACnet/IP (Annex J)
    +-----+-----+-----+-----+-----+-----+-----+-----+
 1: | Function                                      | 0a = Original-Unicast-NPDU
    +-----+-----+-----+-----+-----+-----+-----+-----+
 2: | BACnet packet length                          | 00
 3: |                                               | 11
    +-----+-----+-----+-----+-----+-----+-----+-----+
    | Building Automation and Control Network NPDU  |
    +-----+-----+-----+-----+-----+-----+-----+-----+
 4: | Version                                       | 01 = (ASHRAE 135-1995)
    +-----+-----+-----+-----+-----+-----+-----+-----+
 5: |  m  |  0  |  d  |  0  |  s  |  r  | priority  | 04 = reply expected
    +-----+-----+-----+-----+-----+-----+-----+-----+

To a different network (MSTP)

    |--7--|--6--|--5--|--4--|--3--|--2--|--1--|--0--|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    | BACnet Virtual Link Control                   |
    +-----+-----+-----+-----+-----+-----+-----+-----+
 0: | Type                                          | 81 = Type: BACnet/IP (Annex J)
    +-----+-----+-----+-----+-----+-----+-----+-----+
 1: | Function                                      | 0a = Original-Unicast-NPDU
    +-----+-----+-----+-----+-----+-----+-----+-----+
 2: | BACnet packet length                          | 00
 3: |                                               | 16
    +-----+-----+-----+-----+-----+-----+-----+-----+
    | Building Automation and Control Network NPDU  |
    +-----+-----+-----+-----+-----+-----+-----+-----+
 4: | Version                                       | 01 = (ASHRAE 135-1995)
    +-----+-----+-----+-----+-----+-----+-----+-----+
 5: |  m  |  0  |  d  |  0  |  s  |  r  | priority  | 24 = dest present, reply expected
    +-----+-----+-----+-----+-----+-----+-----+-----+
 6: | Destination Network Address                   | 00
 7: |                                               | 04 = network 4
    +-----+-----+-----+-----+-----+-----+-----+-----+
 8: | Destination MAC Layer Address Length          | 01
    +-----+-----+-----+-----+-----+-----+-----+-----+
 9: | Destination MAC Layer Address                 | 20
    +-----+-----+-----+-----+-----+-----+-----+-----+
10: | Hop Count                                     | 255
    +-----+-----+-----+-----+-----+-----+-----+-----+

filename:	embedded systems - bacnet - NPDU Header
filename:	embedded%20systems%20%2D%20bacnet%20%2D%20NPDU%20Header
last edit:	June 27 2015 18:34:12 (3235 days ago)
ct	= 1714988813.000000 = May 06 2024 05:46:53
ft	= 1435444452.000000 = June 27 2015 18:34:12
dt	= 279544361.000000