D-Link DGS-6600-48TS Configuration Guide - Page 185

Volume 3-Layer 2 Configurations / Chapter 19-Ethernet Ring Protection Switching (ERPS) Chapter Overview ERP2 Service Traffic (VLAN 1 ~ 10) RPL2 RPL1 ERP1 Service Traffic (VLAN 1 ~ 10) RPL2 RPL1 Multi-Ring/ladder network For the multiple rings topology of ERPS, one ERP instance ("Major-Ring" or "Parent-Ring") is connected with two or more instances ("Sub-Rings" or "Child-Ring") is called "Multi-Ring/ladder network". Topology of multi-ring is depicted below, major-ring and sub-ring are connected through two "Interconnection Nodes (Share Nodes)". Interconnection Nodes RPL1 Sub Ring RPL2 Sub-Ring links Major Ring R-APS Controlled Virtual Channel But, the shared link between interconnection nodes is only controlled (block/unblock) by major-ring in order to prevent loop when this link fails. The diagram below depicts the relation of service protected channel for major-ring and sub-ring, and they may the same exactly or overlap each other. Multi-ring/ladder network's Service Protected Channel Major-Ring Sub-Ring R-APS Controlled Virtual Channel of Sub-Ring "R-APS controlled virtual channel" is the "R-APS controlled channel" connection between two interconnection nodes of a sub-ring and also be treated as "service traffic" of major-ring. It is used to provide connectivity between two interconnection nodes and always be enabled. For the sub-ring with R-APS controlled virtual channel, the VLAN-ID of R-APS virtual channel always equal with VLAN-ID of R-APS controlled channel. Topology Change Propagation Sub-ring of multi-ring topology shall issue the topology change event to "Parent-Ring" (major-ring or sub-ring) in the interconnection node when performing flush FDB action. This process is called "Topology Change (TC) Propagation" which is depicted below and following description are steps. RPL Major Ring 1 Link Failure Sub Ring 3 RPL Major Ring 2 RPL RPL Major Ring 1 Sub Ring 2 RPL Link Failure Sub Ring 3 RPL Topology Change (sub-ring  major-ring) R-APS (SF) R-APS (Event, Flush)  only transmit three DGS-6600 Configuration Guide 185