Infinera Technology

Infinera has introduced a new transport network architecture, the Digital Optical Network, that exploits fundamental advances in both large-scale photonic integration and optical system design to create a disruptive shift in network architecture and economics. A Digital Optical Network enables carriers to deploy an optical service platform into metro, regional, and long haul core transport networks to maximize service flexibility, minimize bandwidth costs, simplify network operations, and consolidate network architectures.

 

From Digital to Analog: the emergence of the all-optical network

The emergence of the all-optical network

The introduction of Wavelength Division Multiplexing (WDM) into core networks enabled significant growth in network traffic by reducing bandwidth costs by over 98% in the past decade. Before the advent of WDM, optical transport required the use of digital repeaters along the network to regenerate optical signals degraded during fiber transmission.

These digital repeaters performed Optical-Electrical-Optical (OEO) conversions of the signals so the digital data could be Re-amplified, Re-shaped, and Re-timed (leading to the term "3R" regeneration), and also provided bandwidth management and performance monitoring at each site. The digital data would then be re-transmitted back into the optical domain, and the process would continue across the network.

The economic benefits of WDM over the use of digital repeaters derived from two key attributes. Firstly, WDM provided the ability to significantly scale fiber capacity by multiplexing many optical channels along a single fiber. Second, WDM enabled a significant reduction in the number, and cost, of OEO's used in repeaters by replacing these with optical amplifiers to increase optical reach and amortize costs across many channels.

In the process however, digital access to the data at repeater sites was lost, and optical transport networks became increasingly analog, relying on the amplification, manipulation and management of analog wavelengths, rather than of digital "bits" as used to be the case.

In becoming increasingly analog, optical networks lost their engineering simplicity while also introducing new cost pressures. Through the need to sustain "all-optical" transmission over extensive distances, system designers or carriers were required to move from the simple "plug and play" engineering of digital SONET/SDH repeaters to more complex measurement, engineering, and adjustment of analog optical transmission systems.

In addition, the need to compensate for optical transmission impairments required many special optical compensation elements, increasing system first-in-cost in the process. Finally, the manipulation of wavelengths, rather than digital bits, in an analog optical network significantly decreased network flexibility for functions such as traffic add/drop, bandwidth management, network diagnostics and SLA management. And when such functions were needed, WDM terminals with costly OEO conversions were required, thus negating the economic benefits of WDM in the process.

---

Introducing Digital Optical Networks: the return to digital

The return to digital

A Digital Optical Network redefines optical transport by providing the capacity of WDM with the traffic management flexibility and engineering simplicity of digital transport systems, and the network cost savings of large-scale photonic integration. This provides flexible access to the underlying digital data at any node, for the purpose of add/drop, bandwidth management, performance monitoring, or other value-added manipulation.

In the process of providing frequent cost-effective digital access, a Digital Optical Network reduces the "analog" optical portions of the network to allow "plug and play" operation, and significantly simplifies network planning, engineering, installation and operation. Such a network concept provides a profit enabling optical network architecture for service providers to reach more customers, more cost-effectively, with better network performance, while unifying network architectures and simplifying operations.

The implementation of a Digital Optical Network is uniquely enabled through the development and use of large-scale Photonic Integrated Circuits (PICs) to bring to the industry what has long eluded it—ultra-low cost OEO's. Application of large-scale monolithic integration concepts to the photonic domain permits upwards of sixty or more discrete optical components to be consolidated onto PICs, as we show in this figure. This significantly reduces OEO costs, allowing network bandwidth to be cost-effectively converted to the digital domain at any switching point.

In parallel, large-scale photonic integration brings "Moore's Law" economics of semiconductor manufacturing to optical networking, allowing future optical transport cost reductions to be viably sustained on a cost curve defined by volume manufacturing efficiencies, greater functional integration, increased device density, and manufacturing yield enhancements.

---

Building the Digital Optical Network

The fundamental building block of a Digital Optical Network is the Digital Node, which provides high capacity WDM optical transport and digital add/drop flexibility. A Digital Node utilizes PIC technology to provide ultra-low cost OEO access to the WDM bandwidth, allowing the optical signals to be converted into the electronic domain for value-added processing using silicon electronics and software, before conversion back into optics.

Optical bandwidth transiting through a digital node can therefore be easily and cost effectively managed to maximize service flexibility, enable rapid network reconfigurability, and simplify network engineering, turn-up, growth and operations.

Key network functions are cost-effectively enabled by software and electronics—not complex optical components:

• Digital signal clean-up and performance monitoring (PM) provided through frequent access to digital wrapper or SONET/SDH overhead provides valuable information on service SLA's and network performance, and enables faster and more accurate fault identification and trouble-shooting. Optical system performance is improved through frequent 3R regeneration by applying the performance gains of Forward Error Correction (FEC) and Electronic Dispersion Compensation (EDC) technologies more widely across the network. Value-added system software automates system turn-up, adjustment and operation, and significantly simplifies all aspects of ongoing system operations.

• Digital multiplexing, grooming and add/drop capabilities enable sub-wavelength bandwidth management at each node. This reduces the need for external bandwidth management within the core of the network, and allows both line-side and client-side traffic to be added/dropped, multiplexed, groomed, or protected. A Digital Node can be equipped with a wide range of SONET, SDH or Ethernet service interfaces for connection to new and existing customers. Finally, the application of a GMPLS control plane enables automated end-to-end service provisioning and topology auto-discovery across a Digital Optical Network, and provides a service platform for enabling the introduction of Intelligent Optical Networks.

The feature richness, flexibility and cost-effectiveness of a Digital Node enables the use of a common system platform across a wide range of core backbone applications in metro, regional, long-haul and ultra-long haul networks. Thus a Digital Optical Network can be implemented by deploying Digital Nodes anywhere carriers desire to provide "on-net" access to their networks. These can then be interconnected in a "building block" fashion using simple to engineer Digital Links using optical line amplifiers to extend the optical reach between Digital Nodes.

Migration to a Digital Optical Network can be implemented incrementally on a route-by route basis where required due to capacity exhaust or geographical expansion and to reduce the cost of add/drop sites. The Digital Optical Networks can then be extended as required by network growth, or to cost-effectively increase the carrier's by increasing the number of "on-net" sites on the network.