BacNet: What is the difference between MSTP and IP BacNet cards?

BACnet IP:

BACnet IP uses a standard UDP/IP stack to send and receive messages. For the most part, the same packet that would be found on an MS/TP link is encapsulated in a UDP/IP packet and called BACnet IP. Devices use IP addresses and Ethernet MAC addresses just like other UDP/IP network devices. There is no concept of master/slave token passing since Ethernet is automatically peer to peer in nature. Devices simply transmit to their intended recipient at will, and let Ethernet deal with packet collisions and retries as needed.


MS/TP stands for Master Slave  Token Passing. Each device on the link is considered the “master” when it has the token. If it does not have immediate need to use the token, it is required to pass the token along to the next device. This is the “token passing” part. All devices on the link which do not currently have the token are regarded as slaves,  and are expected to listen to any messages the current master may have for it. Because all devices take turns being master, the link is effectively peer to peer.

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