IP and optical integration has long been a dream in the telecommunications industry: A quick Google search turns up discussions of "IP over glass" going at least as far back as 1998.

The concept of IP over glass was to eliminate the ATM and Sonet/SDH layers and transport IP packets directly over WDM, thus saving on network layers and equipment. Forebodingly, Enron was a leading champion of this architectural concept, which died out along with the energy trader.

During the 2000s, IP over DWDM (or IPoDWDM) introduced the direct, physical integration of DWDM optics on IP routers. Despite the obvious capex savings benefit of removing the need for back-to-back transponders in the network, IPoDWDM suffered from a major capex drawback of its own. Long reach optics have historically been larger than comparable generation short reach interfaces. As a result, operators have preferred to pack their routers with smaller short reach interfaces to get the most use of their costly IP router processing capacity. They’ve kept the DWDM optics on separate hardware.

Today, a new wave of IP and optical integration interest is taking hold, one which, in our view, has much greater promise than the previous two generations. Commonly called IP+optical, the new trend calls for a coupling of control and management of the IP and optical layers but with the data planes being kept in separate hardware devices.

Such software-level integration yields many of the operations and some of the capex savings of physical integration while avoiding the uneconomical faceplate trade-offs that reduce the value of full physical integration. The Open Networking Foundation (ONF), in a recently published technical paper entitled Optical Transport Use Cases, describes the values of control integration of IP and optical layers as follows:

Although IP+optical integration does not require it from a technical standpoint, SDN, with its emphasis on software programmability, openness, and standardization, is emerging as the best long term means to accomplish IP+optical integration. This is because an SDN-based IP+optical network architecture opens the possibility of integration that is both multi-layer and multi-vendor.

For this reason, Heavy Reading believes that IP and optical integration and carrier SDN progress will be closely aligned moving forward.

— Sterling Perrin, Senior Analyst, Heavy Reading