Network providers face an optical networking problem: Their optical infrastructure was designed for circuit-switched traffic, but the bulk of their traffic consists of IP data. Managing these disparate layers of technology means extra expenses, as coordinating IP and optical creates delays when additional services are added or when network problems are encountered.
Traditional optical and IP design
Service providers carry data via high-data rate optical technology using dense wave division multiplexing (DWDM). Reconfigurable optical add-drop multiplexers (ROADMs) serve as switches. ROADMs add a frequency to the outgoing stream, drop a frequency from the outgoing stream, and redirect it to an end user or change the frequency of an incoming signal when it's retransmitted.
IP networks are superimposed over the optical network. Each network has its own data and control planes, and the two technologies are often managed by different departments within the organization, further complicating oversight. Changes are difficult and prone to error and delay.
To overcome these challenges, cloud providers and others that need to connect data centers have leased dark fiber to create point-to-point links between geographically distant centers. These single-purpose links are simpler than a routed network designed to reach multiple end nodes.
Routed optical networking approach shows promise
Recently, Cisco introduced a new way to manage how IP can be carried over optical. Instead of layering IP over optical, the routed optical networking architecture treats optical as a communications medium -- just like Ethernet, Wi-Fi or coax.
A node may be connected to others via multiple optical connections just as it would be through other media types. All multiplexed frequencies are terminated at each node's router with outgoing frequencies routed toward their destinations. All data between nodes is routed at Layer 3 using MPLS.
The idea of routed optical networking is propelled by two advances:
- high-end routers capable of routing data at optical rates; and
- new fiber endpoint technologies.
The latest generation of endpoint transceivers -- 400 Gb ZR/ZR+ DWDM optical transponders -- are pluggable modules that reduce space and energy use. Providers can upgrade older units without majorly updating their network.
Management is accomplished through a single IP control plane -- based on software-defined networking management across the entire network -- which eliminates the need to coordinate changes at two levels. The approach signals a significant shift in how network systems are connected. Expect to see wide adoption as the technology evolves.