| 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
+-----+-----+-----+-----+-----+-----+-----+-----+