"As power utilities migrate their communications network infrastructure to newer packet-switched architectures, they have to accommodate mission-critical applications. This means the newer networks must have the same high levels of reliability they enjoyed in their legacy networks.
Because communications is essential to the operation of the electrical grid, the operational network requires the highest level of resiliency. Historically, a single technology was the key to this resiliency. For instance, for a SONET/SDH-based network, the utility would use a ring or redundant SONET/SDH link for backup."