What are DLR and REP?

DLR and REP ... what are they and how are they different.

Device Level Ring (DLR)

DLR is an EtherNet/IP™ protocol that is defined by the Open DeviceNet® Vendors’ Association (ODVA). DLR provides a means to detect, manage, and recover from single faults in a ring-based network.

DLR allows automation devices to be placed in a ring with a convergence time of less than 3ms

The Resilient Ethernet Protocol (REP)

REP was originally designed for Fast Ethernet (FE 10/100) ports. Link down detection time on FE ports is 10 milliseconds (ms) and convergence time is about 50 ms. 
On Fiber GE ports, link down time is 10 ms, but on GE copper interfaces, the IEEE 802.3 specification mandates the link drop detection and recovery times to be 750 ms for a master and 350 ms for a slave. 
As a result, link loss and recovery can be detected a lot more quickly on GE fiber interfaces than on corresponding copper interfaces. 
This in turn means that the convergence time for REP is a lot higher when using GE copper interfaces. 

REP is best suited for Switch to switch resiliency.