Rockwell Automation Ethernet Design Considerations Reference Manual - Manual (Page 52)

52 Rockwell Automation Publication ENET-RM002C-EN-P - May 2013
Chapter 3 Ethernet Infrastructure Features
Segments can be wrapped into a ring. Identification of edge ports requires
additional configuration.
Device-level Ring (DLR)
The DLR protocol is a layer 2 protocol that provides link-level, physical
redundancy that provides network convergence in the 1…3 ms range for simple
automation device networks. The other resiliency protocols apply to only
infrastructure (switches and routers). DLR provides resiliency directly to an end
device directly (such as an I/O module, drive, or controller).
Some control applications, such as safety and motion require network
convergence times faster than what switch-oriented resiliency protocols can
provide. Most control applications suffer connection timeouts with switch-
oriented resiliency protocols.
Blocking
Forwarding
Forwarding
A
X
Y
B
C
A
X
Y
B
C
Link Failure
Blocking
Forwarding
X
A B
Y
Forwarding
Link Failure
X
A
C
C
B
Y