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Optical mesh networks are a type of telecommunications network. Transport networks, the underlying optical fiber-based layer of telecommunications networks, have evolved from DCS (Digital Cross-connect Systems)-based mesh architectures in the 1980s, to SONET/SDH (Synchronous Optical Networking/Synchronous Digital Hierarchy) ring architectures in the 1990s. Technological advancements in optical transport equipment in the first decade of the 21st century, along with continuous deployment of DWDM systems, have led telecommunications service providers to replace their SONET ring architectures by mesh-based architectures. The new optical mesh networks support the same fast recovery previously available in ring networks while achieving better capacity efficiency and resulting in lower capital cost. Optical mesh networks today not only provide trunking capacity to higher-layer networks, such as inter-router or inter-switch connectivity in an IP, MPLS, or Ethernet-centric infrastructure, but also support efficient routing and fast failure recovery of high-bandwidth services. This was made possible by the emergence of optical network elements that have the intelligence required to automatically control certain network functions, such as fault recovery. Optical mesh networks enable Quality-of-Service protection and a variety of dynamic services such as bandwidth-on-demand, Just-In-Time bandwidth, bandwidth scheduling, bandwidth brokering, and optical virtual private networks that open up new opportunities for service providers and their customers alike. ==History of transport networks== Transport networks, the underlying optical fiber-based layer of telecommunications networks, have evolved from Digital cross connect system (DCS)-based mesh architectures in the 1980s, to SONET/SDH (Synchronous Optical Networking/Synchronous Digital Hierarchy) ring architectures in the 1990s. In DCS-based mesh architectures, telecommunications carriers deployed restoration systems for DS3 circuits such as at&t FASTAR (FAST Automatic Restoration)〔(FAST Automatic Restoration - FASTAR ).〕〔(FAST Automatic Restoration - FASTAR ).〕〔(FAST Automatic Restoration - FASTAR ).〕 and MCI Real Time Restoration (RTR),〔(Real Time Restoration (RTR) ).〕 restoring circuits in minutes after a network failure. In SONET/SDH rings, carriers implemented ring protection such as SONET Unidirectional Path Switched Ring (UPSR)〔(Unidirectional Path Switched Ring (UPSR) ).〕 (also called Sub-Network Connection Protection (SCNP) in SDH networks) or SONET Bidirectional Line Switched Ring (BLSR)〔(Bidirectional Line Switched Ring (BLSR) ).〕 (also called Multiplex Section - Shared Protection Ring (MS-SPRing) in SDH networks), protecting against and recovering from a network failure in 50 ms or less,〔(Is 50 ms necessary? )〕 a significant improvement over the recovery time supported in DCS-based mesh restoration, and a key driver for the deployment of SONET/SDH ring-based protection. There have been attempts at improving and/or evolving traditional ring architectures to overcome some of its limitations, with trans-oceanic ring architecture (defined in ITU-T Rec. G.841〔(ITU-T Rec. G.841 )〕), "P-cycles" protection,〔W. D. Grover, (Invited Paper) ("p-Cycles, Ring-Mesh Hybrids and "Ring-Mining:" Options for New and Evolving Optical Networks," ) Proc. Optical Fiber Communications Conference (OFC 2003), Atlanta, March 24–27, 2003, pp.201-203. ((related presentation )).〕 next-generation SONET/SDH equipment that can handle multiple rings, or have the ability to not close the working or protection ring side, or to share protection capacity among rings (e.g., with Virtual Line Switched Ring (VLSR)〔(Virtual Line Switched Ring (VLSR). )〕). Technological advancements in optical transport switches 〔Also referred to as optical cross-connects or optical switches. The term optical does not imply that the equipment handles signals completely in the optical domain, and most of the times, it does not and instead it grooms, multiplexes, and switches signals in the electrical domain, although some equipment (referred to as photonic cross-connect) do switching (only) fully in the optical domain without any O-E-O conversion.〕 in the first decade of the 21st century, along with continuous deployment of dense wavelength-division multiplexing (DWDM) systems, have led telecommunications service providers to replace their SONET ring architectures by mesh-based architectures for new traffic. The new optical mesh networks support the same fast recovery previously available in ring networks while achieving better capacity efficiency and resulting in lower capital cost. Such fast recovery (in the tens to hundreds of milliseconds) in case of failures (e.g., network link or node failure) is achieved through the intelligence embedded in these new optical transport equipment, which allows recovery to be automatic and handled within the network itself as part of the network control plane, without relying on an external network management system. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Optical mesh network」の詳細全文を読む スポンサード リンク
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