Evolution of Optical Networking

Optical networking technology has evolved significantly over the past few decades to support the exponential growth in data traffic driven by increased internet usage. Early optical networks in the 1990s utilized Synchronous Digital Hierarchy (SDH) and Synchronous Optical Networking (SONET) to transmit data over fiber at speeds up to 10 Gigabits per second (Gbps). However, the proliferation of applications such as video streaming, cloud computing, and online gaming has led to demand for higher network speeds. This triggered the development of dense wavelength division multiplexing (DWDM) technology that multiplexed multiple optical carrier signals onto a single optical fiber to deliver transmission speeds of 40Gbps and beyond.

Today's networks require even greater capacity to support emerging technologies like 5G, Internet of Things (IoT), augmented/virtual reality, and more. This need led to the adoption of flexible grid in optical network design with flexible spectrum allocation. Flex grid along with advanced modulation formats enables speeds exceeding 100Gbps over a single wavelength. Furthermore, the use of space division multiplexing using few-mode and multicore fiber promises to deliver petabit capacities required for next-generation networks.

Advent of Optical Transport Networks

To meet evolving network demands, Optical Transport Network traditional SONET/SDH networks were upgraded to generalized flexible optical transport net utilizing Dense Wavelength Division Multiplexing (DWDM). An optical transport net uses reconfigurable optical add-drop multiplexers (ROADMs) to add or remove optical carrier signals carrying data without converting the signals to electronic form. ROADMs enable wavelength selective switching across the network, drastically simplifying network management.

Optical transport net employ multi-protocol label switching (MPLS) or generalized multi-protocol label switching (GMPLS) to set up end-to-end lightpaths automatically. This allows bandwidth-on-demand provisioning and restoration of services. The use of reconfigurable wavelength selective switches (WSS) and various modulation formats in DWDM systems provide flexibility to efficiently utilize the immense bandwidth of fiber. Furthermore, standards-based network management systems enable seamless integration of multi-vendor equipment.

Deployment and Architecture

Core optical transport net form the backbone of telecom infrastructures connecting national and global networks. They carry enormous volumes of data traffic at ultra-high speeds ranging from 10Gbps up to 400Gbps or faster using DWDM technology. The core network features mesh or ring topologies with ROADM nodes in metropolitan cities and major geographical points of presence.

Access and metro networks serve as the first and last mile connectivity feeding into the core. Metro networks employ wavelengths up to 100Gbps to connect cities and business districts. Access networks operate at lower wavelengths from 2.5Gbps up to 10Gbps to provide fiber connectivity to businesses and cell towers. Lastly, edge networks interface customer premises equipment at lower speeds to deliver connectivity to end users.

All-optical networks avoid costly optical-electrical-optical conversions, simplifying infrastructure and reducing latency. Careful network design using simulation and modeling tools ensures optimized capacity utilization. Strategically placed ROADM nodes provide automatic restoration and network survivability. The use of coherent detection and digital signal processing overcomes fiber non-linearities enabling long-haul transmission.

Applications and Use Cases

Optical transport networks power a diverse range of network applications and services. They deliver high-bandwidth connectivity between data centers to enable cloud, content delivery and peering applications. Long-haul DWDM links connect Cable Landing Stations for transoceanic traffic. Cell site backhaul provides fiber connectivity between cell towers and switching centers for mobile networks.

DWDM networks support nationwide projects like National Research and Education Networks (NRENs). Governments leverage DWDM capabilities for disaster recovery, security/surveillance, and smart city projects. Carrier Ethernet and IP services ride over the optical infrastructure. Industrial applications involving remote machinery control rely on carrier-grade transparency and resilience. OTN creates new revenue streams through dark fiber leasing, bandwidth-on-demand, and enterprise services.

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