Ethernet is the most common interface within enterprise networks. Although the optimal customer interface and LAN solution, Ethernet does not work well within metro networks. Most RPR edge systems offer an Ethernet interface as the customer interface. SONET/SDH can be used to transport RPRs that use the SONET/SDH physical layer. A 2.5G RPR can be carried as two optical carrier (OC)–48/synchronous transfer mode (STM)–16 channels (inner and outer rings) inside an OC–192/STM–64 SONET/SDH ring. This allows customers to utilize their existing transport infrastructure to deliver legacy TDM services, while RPR delivers data services efficiently. New SONET advancements such as virtual concatenation and the link-capacity adjustment scheme (LCAS) allow more precise and dynamic allocation of bandwidth dedicated to RPR services.

Figure 4. RPR over SONET with Ethernet Customer Interfaces