From BACnet Standards came to know below understanding . But still wondering Why MAC is made mandatory in BACnet ? even though having unique "Device instance"
Device Instance
The instance portion of the Object Identifier of a given device’s Device object. Unlike all other object types, each device may contain only one Device object. The instance number of this Device object must be field-configurable so that it may be assigned a unique instance number among all of the Device objects of all of the devices on a given BACnet internetwork.
A BACnet MS/TP device supports device DI in the range 0 to 4,194,302.
Medium Access Control (MAC)
The part of a network that handles access to the physical network (medium) for a particular datalink. In BACnet, each device has a unique MAC Address/Network Number combination that identifies it on the BACnet internetwork.
A BACnet MS/TP device supports device MAC addresses in the range 0-127 for masters and 0-254 for slaves.
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Additionally, there are many datalink layers, not just MS/TP (similar to the way TCP/IP has many datalink layers). Therefore there are a variety of MAC sizes, plus the additional routing layer (network number) to be able to find a Device ID that is within the connected network of various MAC layers (datalinks).
Using the Device Instance (ID) to determine the MAC (and network number) is BACnet's address resolution protocol.
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Thanks Steve Karg . Can you please clarify the below points as well
1) Why MAC address is not made unique across networks. (OR) How BACnet network works with the 2 devices having same MAC address .Refer the attached screenshot.
2) How to differentiate and create 2 separate MSTP networks . can you send , network diagram with the communication configuration . I wanted to create this set up in our lab
F.Y.I. The 'DADR' value is generally a virtual MAC address, not a registered one (- with an OU assigned/included).
But otherwise, proper MAC/physical/burned-in addresses should be unique; unless the unlikely case that Carrera Technology supposedly once had whereby the country (/Singapore?) that sold them bulk NICs had apparently copied the firmware verbatim - they all had the same MAC address assigned/burnt onto them; network-conflict city (!). ;P
👍
1
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
From BACnet Standards came to know below understanding . But still wondering Why MAC is made mandatory in BACnet ? even though having unique "Device instance"
Device Instance
The instance portion of the Object Identifier of a given device’s Device object. Unlike all other object types, each device may contain only one Device object. The instance number of this Device object must be field-configurable so that it may be assigned a unique instance number among all of the Device objects of all of the devices on a given BACnet internetwork.
A BACnet MS/TP device supports device DI in the range 0 to 4,194,302.
Medium Access Control (MAC)
The part of a network that handles access to the physical network (medium) for a particular datalink. In BACnet, each device has a unique MAC Address/Network Number combination that identifies it on the BACnet internetwork.
A BACnet MS/TP device supports device MAC addresses in the range 0-127 for masters and 0-254 for slaves.
MAC is needed in BACnet for the same reason as hardware MAC is needed for TCP/IP - see ARP (address resolution protocol).
https://en.wikipedia.org/wiki/Address_Resolution_Protocol
Additionally, there are many datalink layers, not just MS/TP (similar to the way TCP/IP has many datalink layers). Therefore there are a variety of MAC sizes, plus the additional routing layer (network number) to be able to find a Device ID that is within the connected network of various MAC layers (datalinks).
Using the Device Instance (ID) to determine the MAC (and network number) is BACnet's address resolution protocol.
Thanks Steve Karg . Can you please clarify the below points as well
1) Why MAC address is not made unique across networks. (OR) How BACnet network works with the 2 devices having same MAC address .Refer the attached screenshot.
2) How to differentiate and create 2 separate MSTP networks . can you send , network diagram with the communication configuration . I wanted to create this set up in our lab
Last edit: Ravi teja 2024-05-14
F.Y.I. The 'DADR' value is generally a virtual MAC address, not a registered one (- with an OU assigned/included).
But otherwise, proper MAC/physical/burned-in addresses should be unique; unless the unlikely case that Carrera Technology supposedly once had whereby the country (/Singapore?) that sold them bulk NICs had apparently copied the firmware verbatim - they all had the same MAC address assigned/burnt onto them; network-conflict city (!). ;P
Is any guide/manual to refer on below topics
Thanks in advance