In this paper we introduce a formal specification of parts of the service differentiation mechanisms of the recent IEEE 802.17 Resilient Packet Ring (RPR) standard, and assess RPR's suitability for use in a DiffServ environment. We propose a simple mapping between RPR's traffic classes and three standardized DiffServ Per Hop Behavior groups. When using this mapping, we discuss, by use of an analytical example and simulation results, the behavior of the traffic assigned to each PHB group in terms of its throughput (all PHBs) and delay properties (for the EF PHB only). For the simulation part, we use our OPNET implementation of the RPR standard.