Difference between revisions of "BACnet Virtual Link Layer"
From BACnet Wiki
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Between the BACnet Network Layer and the underlying UDP Layer of the IP Stack. Contains functionality such as [[BBMD]] and Foreign Device to forward BACnet broadcasts to multiple IP Subnets. | Between the BACnet Network Layer and the underlying UDP Layer of the IP Stack. Contains functionality such as [[BBMD]] and Foreign Device to forward BACnet broadcasts to multiple IP Subnets. | ||
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| + | Warning, this subject is VERY complex. Please see [https://docs.google.com/spreadsheets/d/1neArwaeN1Ro4Q8kHVqnRYa_9P4QqCGTbsZ7FXKwiNEg/pubhtml this worksheet] for reference (be aware that the worksheet may not be 100% accurate). | ||
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Latest revision as of 11:20, 16 June 2016
Between the BACnet Network Layer and the underlying UDP Layer of the IP Stack. Contains functionality such as BBMD and Foreign Device to forward BACnet broadcasts to multiple IP Subnets.
Warning, this subject is VERY complex. Please see this worksheet for reference (be aware that the worksheet may not be 100% accurate).
See Annex J: pg 565 of 135-2004 Specification
| UDP Header | |||
| BVLC | Octets | Description | Comment |
| 1 | Type (0x81) | Fixed | |
| 1 | BVLC Function | Fixed | |
| 2 | BVLC Length | Fixed | |
| 4 (Optional) | IP address of Originating Device | Optional - Dependent on BVLC Function Code | |
| 2 (Optional) | Port # of Originating Device | Optional - Dependent on BVLC Function Code | |
| BVLC length - 4 | NPDU | ||
Example 1
| UDP Header | ||
| BVLC | Octets | Description |
| 1 | Type (0x81) | |
| 1 | BVLC Function (0x0b) | |
| 2 | BVLC Length | |
| BVLC length - 4 | NPDU | |
Example 2
| UDP Header | ||
| BVLC | Octets | Description |
| 1 | Type (0x81) | |
| 1 | BVLC Function (0x04) | |
| 2 | BVLC Length | |
| 4 | IP address of Originating Device | |
| 2 | Port # of Originating Device | |
| BVLC length - 10 | NPDU | |
| APDU BBMD BVLC BVLL DADR DNET Encoding I-Am LSAP MAC NPCI NPDU NSAP NSDU SA SADR SNET |
| Edit this box. |
