ry routers and the utilization of lower-cost native Ethernet interfaces 10/100Base-T, 100Base-FX, and GbE interfaces Cost-effective data networking with carrier-grade reliability Capability for multiple packet edge streams per SONET ring to assign a dedicated STS3/6/9/12c stream to a hub site Capability to group multiple hub sites to STS-n stream As an elaboration of this approach, you could develop equipment that was fully hybrid, where, for example, the backbone ran a SONET OC-192c. A number of constituent subchannel OC-48cs (for example, three of them) could be utilized to support crossconnected user-side OC-x to the network- side OC-48s running on the OC-192 bearer with a TDM-to-TDM mapping, whereas other subchannel OC-48s (for example, one of them) could be uti- lized to support statistically aggregated user-side Ethernet interfaces to the network-side OC-48 on the OC-192 bearer with a Ethernet-to-packet (for example, RPR) mapping. Nortel Networks' OPTera Packet Edge combines three complementary, next-generation technologies: Self-healing IEEE 802.17 RPRs with distributed Layer 2 switching RPR converts a portion of a fiber ring (in STS-1 size chunks) into a logical Ethernet segment. The remaining bandwidth, if any, can be used for traditional circuit-oriented traffic (see Figure 4-12). This feature offers a self-healing topology that protects against fiber cuts and node failures by providing duplicate, geographically diverse paths for packet data transport. If a cable cut or other fault impairs a preferred primary route, Layer 2 protection switching automatically forwards the affected data packets to the alternate route on the opposite side of the ring. Switching to the protection route typically Chapter 4 Ethernet Figure 4-12 frames RPR environment. Ethernet Resilient Packet Ring Ethernet frames frames Logical view of the ring Ethernet frames requires about 50 ms SO no noticeable interruption in service occurs. The self-healing RPR architecture does not require setting aside half of its fiber-span capacity 