cuit to an RPR-based circuit. Traffic tunneling for efficient, secure sharing of transport bandwidth Traffic-tunneling technology enables data from multiple enterprise customers to efficiently share common transport bandwidth on the ring while maintaining security for each customer's data packets. Also, traffic tunneling maintains traffic segregation even when customers use overlapping addresses. Traffic tunneling entails the encapsulation of entering customer data packets with customer/ring-specific address information. The added addressing identifies the correct exit point on the ring (node and port) for each entering packet. The customer/ring- specific information is automatically removed at the destination. Routing along the ring is based solely on the added customer/ring- specific address information SO each customer receives only the data packets that belong to that enterprise. The tunneling process is Chapter 4 self-learning in that packets reach their intended destinations without the labor-intensive provisioning of end-to-end connections. Intelligent flow control to regulate traffic entry and enable class of service (CoS) / QoS support Extensive flow controls regulate traffic entry and ensure that the delivered information rate conforms to the subscriber's SLA. These mechanisms also prevent certain nodes or traffic sources from unintentionally taking precedence over and starving others. The flow control mechanisms fall into three categories: the token-bucket traffic entry model, the buffer insertion ring, and the ring access protocol. 4.6 Other Approaches Some vendors include a hardware-resident distributed algorithm that exe- cutes a distributed dynamic bandwidth allocation (DBA) protocol in the overhead of standard SONET frames. See Figure 4-14. This approach goes in the direction of RPR, but is not the exact same concept. According to pro- ponents, this method provides a scalable, adaptive, and granular approach to managing bandwidth in a near mathematically optical fashion on SONET access rings. 1 Th