Eliminating vendor lock-in: True SDN is based on open standards and interoperability across layers and across vendors. Multi-vendor interoperability means that operators are not locked into the same vendor for their IP layer and optical layer equipment.

Capacity/performance trade-off: Long-reach DWDM optics are larger than short reach client optics (particularly at the high end of data rates and performance). Thus, physical integration of DWDM optics on IP routers typically means cutting IP routing capacity, a trade-off most operators are unwilling to make. Control and management plane integration completely avoids this issue and allows both IP router and DWDM systems to operator at full capacity/performance.

Network visibility and analytics: Many operators are interested in "early win" applications that understand both layers in the network in read-only fashion and are able to automatically correlate them into a unified view. This correlated view then can be fed into existing management systems to improve planning accuracy, identify anomalies in structure and make more confident planning decisions.

Multi-layer Bandwidth-on-Demand (BoD): Software automation removes the operational complexity and manual processes of provisioning a service and enables operators to respond in near real-time to bandwidth/service requests from customers. Single-layer BoD services have become common in the past two years and include AT&T NetBond, Level 3 Adaptive Network Control and Telstra PEN, among others. Multi-layer BoD extends the automation and coordination across the IP and optical layers, allowing one-shot provisioning for a service that encompasses both the IP and the optical layers. This is especially needed for very high-speed services, as the ones needed for data center interconnect (DCI).

Multi-layer network optimization (cross-layer): Network optimization is about making networks run more efficiently and with greater utilization, allowing operators to accommodate traffic growth without a commensurate increase in capex. Operators often refer to this as allowing networks to run "hotter." One of the primary means of multi-layer network optimization is the router bypass application -- intelligently coordinating traffic across layers to consolidate and transport, switch or route traffic at the lowest-cost layer that meets the traffic requirements. Router ports are the most expensive ports on the network, so router bypass only moves traffic up to the IP layer when necessary, thus reducing optical-to-electrical-to-optical (OEO) transitions and saving those ports for their specific job of IP routing.

Multi-layer restoration: Optical networks employ 1+1 protection schemes that shift traffic from the working path to the protection path in case of optical failure. In the absence of a failure, however, the protection path sits idle with no traffic -- leaving 50% of potential capacity unused. Significant economic benefits can come from using the photonic layer in conjunction with the IP layer to perform restoration, thereby sharing resources across two layers (IP and photonic). By sharing resources and coordinating across IP and optical layers, operators can achieve carrier-grade levels of availability while dedicating less bandwidth/ports for IP transit traffic and failure redundancy.