Device Level Ring (DLR) is a Layer 2 protocol that provides media redundancy in a ring topology. The DLR protocol is intended primarily for implementation in CP 2/2 end devices that have multiple Ethernet ports and embedded switch technology. The DLR protocol provides for fast network fault detection and reconfiguration in order to support the most demanding control applications.
Since the DLR protocol operates at Layer 2 (in the OSI network model), the presence of the ring topology and the operation of the DLR protocol are transparent to higher layer protocols such as TCP/IP and CP 2/2, with the exception of a DLR object that provides a configuration and diagnostic interface for CP 2/2.
DLR Rings connected to switches
A DLR network includes at least one node configured to be a ring supervisor, and any number of normal ring nodes. It is assumed that all the ring nodes have at least two Ethernet ports and incorporate embedded switch technology.
Non-DLR multi-port devices – switches or end devices – may be placed in the ring, subjetc to certain implementation constraints (e.g., no MAC table filtering). Non-DLR devices will also impact the worst-case ring recovery time.
The DLR protocol definition includes a number of aspects:
- A set of end node behaviors, for ring supervisors and normal ring nodes;
- Protocol messages and associated state diagrams
- Implementation requirements for devices.