Redundancy

Redundancy considerations begin at the link level before progressing to the node level. Any SONET/SDH link connecting a pair of PNNI nodes may utilize Automatic Protection Switching (APS) for SONET or Multiplexed Switching Protection (MSP) for SDH within the same line card or across a pair of line cards in each connected node to provide redundancy at the physical layer. When APS/MSP is not an option, or when you're using an electric interface such as a T3, PNNI's rerouting capabilities make full use of parallel trunks connecting two nodes.

All Cisco MSS products offer full processor card redundancy. Optional Y-RED redundancy provides card and trunk redundancy for optical or electrical interfaces when optical protection switching using APS or MSP is not a viable option. Y-RED redundancy does incur the extra expense of additional line cards and loss of chassis slots for other purposes.