ITU-T X.87 PDF

This Recommendation specifies Multiple Services Ring (MSR) based on Resilient Packet Ring (RPR) and a way of multi-service provision over RPR. MSR is defined to work at the client of RPR MAC layer and uses Fairness Algorithm (FA) of RPR MAC to support services of Class A, Class B and Class C. MSR is used in configurations where a tributary service is managed such that over provisioning does not occur. Architecturally, the link and broadcast topologies are also supported. The features of tributary (Service, just like Ethernet, Frame Relay and G.702, etc.) based 1+1, 1:1 and 1:N standby within 50 ms, tributary (Service) based Bandwidth management with symmetry and asymmetry, tributary based multicast and Frame Sequence Number for Performance Monitoring of tributary are highlighted in this Recommendation. MSR provides a packet-based transport model to multiple services and multiple topologies.

This Recommendation is based on RPR as a MAC client and is used in configurations where topology and standby is provisioned. What this Recommendation emphasizes is tributary, but not a payload of tributary; standby (1+1, 1:1 and 1:N) and multicast of tributary, but not multicast of MAC; MSR priority, but not MAC priority. The data frame, control frame and network management frame in this Recommendation are all required to map to the payload of RPR data frame. Some control frames RPR defined are also used in X.87/Y.1324, just like topology discovery, protection and FA in RPR. All of these frames specified in this Recommendation have no relations to and are independent of the control frames (just like frames of topology discovery, fairness, protection) of RPR MAC layer. No change is made for all Ethernet-based protocols (including IEEE 802.3 Ethernet), all PDH standards, Frame Relay standards, G.702/ISDN standards and ETSI DVB specifications. This Recommendation is located at a dual-directional symmetric counter-rotating rings based on RPR.

NOTE – It is intended that this Recommendation can be extended, in future amendments, to support additional new types of data service.