This enables providers to extend the distance between optical repeaters, which helps reduce both capital and operational expenses while simplifying the network topography with the ability to skip amplifier sites. FEC is used to significantly increase system margin for a given Bit Error Rate (BER) and signal power, which allows longer spans in the network. FEC dramatically improves tolerance to network impairments present in high-capacity transmissions, correcting and detecting errors in the optical link. A key advantage of OTN is that it defines an out-of-band FEC scheme applied to the signal before transmission. Let’s explore some of these key advantages in more detail. Operators can thus leverage next-gen technologies over a programmable optical infrastructure to quickly respond to today’s unpredictable bandwidth requirements. Today, operators gain a competitive edge from the significant advantages offered by OTN, including improved performance with Forward Error Correction (FEC), simplified operations, faster service turn-up, maximized efficiencies, and differentiated services. It is important to note that even packet optimized technologies like 400ZR and OpenZR+ are based on OTN structures that are optimized for Ethernet only clients. Muxponders aggregate and groom lower rate services and are used in compact DCI platforms today to transport multiple 100GE/400GE services. An OTN muxponder multiplexes lower speed clients onto a DWDM channel within a hardware module or compact platform, enabling cost-effective point-to-point connectivity. OTN is also widely deployed among networks leveraging module-based or central fabric-based OTN hardware. Transponders that are widely deployed today use OTN to map a client to a Dense Wavelength Division Multiplexing (DWDM) channel. For example, today’s coherent modems leverage OTN mapping to transport client service(s) over a high-capacity coherent wave. OTN mapping or encapsulation is used to provide high-bandwidth agile photonic connections. The Optical Transport Unit (OTU) contains the ODU overhead and payload, provides the section-level overhead (such as BIP8), and supports General Communication Channel (GCC) bytes for overhead communication between network nodes.Īs shown in Figure 3, OTN technology is used in various ways within an optical network. The ODU represents the OTN path service within an OTN network.įigure 2: The Optical Transport Module (OTM) is the information structure The Optical Channel Data Unit (ODU) contains the OPU overhead and payload area, plus additional overhead such as BIP8, GCC1/2, Tandem Connection Monitoring (TCM), and so on. The OPU overhead is associated with the mapping of client data into the payload area. The payload area of the OPU structure is comprised of end-user services such as IP, Ethernet, or any other protocol. The Optical Channel Payload Unit (OPU) contains the payload frames. It has two parts: a digital structure and an optical structure. The Optical Transport Module (OTM) is the information structure transported across the optical interface. The OTN wrapper is made up of several components in a hierarchy as depicted in Figure 1. Hundreds of thousands of OTN ports have been deployed and are carrying mission-critical traffic from the edge into the metro and core of the network, as well as in submarine applications. To date, OTN technology has been extensively deployed in networks across the globe, with increasing scope across a wide spectrum of applications. OTN-enabled technology often underpins next-generation optical networks with its ability to support flexible packet technologies that include new Ethernet interfaces, Multi-Protocol Label Switching (MPLS), Segment Routing, and Time Sensitive Networking (TSN) to name a few. In fact, OTN has been optimized to support Ethernet-today’s most popular client service-from 1GE to 400GE. Since its inception in 2001, OTN has continued to evolve beyond a simple SONET/SDH wrapper. The enhanced multiplexing capability of OTN allows different traffic types, including IP, Ethernet, storage, digital video, and SONET/SDH, to be carried over an OTN framing structure-a key reason for the adoption of OTN. OTN is commonly called a ‘digital wrapper’ as it wraps each client/service transparently into a container for transport across optical networks, preserving the client’s native structure, timing information, and management information.
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