Optical mesh network

Optical Mesh Networks new article content ... Transport networks, the underlying optical fiber-based layer of telecommunications networks, evolved from DCS (Digital Cross-connect Systems)-based mesh architectures in the 1980's, to SONET/SDH (Synchronous Optical Networking/Synchronous Digital Hierarchy) ring architectures in the 1990’s. In the first decade of the 21st century, technological advancements in optical transport switches [1] have allowed service providers to support the same fast recovery in mesh networks previously available in ring networks while achieving better capacity efficiency and resulting in lower capital cost. Optical transport networks today not only provide trunking capacity to higher-layer networks, such as inter-router connectivity in an IP-centric infrastructure, but also support efficient routing and fast failure recovery of high-bandwidth services. This is possible due to the emergence of optical network elements that have the intelligence required to efficiently control the network. Optical mesh networks will enable 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.

Table of contents History of transport networks Optical mesh networks Recovery in mesh networks Transparency Routing in optical mesh networks Applications Related network architectures See also Notes References External links

History of transport networks Transport networks, the underlying optical fiber-based layer of telecommunications networks, evolved from DCS (Digital Cross-connect Systems)-based mesh architectures in the 1980's, to SONET/SDH (Synchronous Optical Networking/Synchronous Digital Hierarchy) ring architectures in the 1990’s. In the first decade of the 21st century, technological advancements in optical transport switches [1] have allowed service providers to support the same fast recovery in mesh networks previously available in ring networks while achieving better capacity efficiency and resulting in lower capital cost.

Optical Mesh Networks Optical mesh networks refer to transport networks that are built directly off the mesh-like fiber infrastructure deployed in metropolitan, regional, national, or international areas (e.g, trans-oceanic) by deploying optical transport equipment that allow to switch traffic (at the wavelength or sub-wavelength level - see http://t0.gstatic.com/images?q=tbn:ANd9GcRyFcv5gmjqwp7Van74NIwhcGudEtduPBPbv7JFVeh0-Ntr1Eo&t=1&usg=__EENErkLLUticDo4Ji28jIxXZ7F0=) from an incoming fiber to an outgoing fiber (show a figure). As most of the core backbone networks evolve to mesh topologies utilizing intelligent network elements (optical cross-connects or optical switches [2]) for provisioning and recovery of services, new developments are required for the design, development, deployment, and management of mesh optical networks.

Recovery in optical mesh networks Multiple recovery mechanism that provide different levels of protection [3] or restoration [4] against different failure modes are available in mesh networks. Channel, link, and path protection are the most common protection schemes. P-cycles are another one. Restoration is another recovery method. In path-protected mesh networks, some connections can be unprotected, others can be protected against single or multiple failures in various ways. A connection can be protected against a single failure by defining a backup path, diverse from the primary path taken by the connection over the mesh network. The backup path and associated resources can be dedicated to the connection, or shared among connections, typically connections whose primary paths are not likely to fail at the same time, thereby avoiding contention for the shared resources. A number of other protection schemes such as the use of pre-emptible paths, or only partially diverse backup paths, can be implemented. Finally, multiple diverse routes can be designed so that a connection has multiple recovery routes and can receover even after multiple failures (examples of mesh networks across the Atlantic and Pacific oceans).

Transparency Traditional transport networks are made of optical fiber-based links between telecommunications offices, where multiple wavelengths are multiplexed to increase the capacity of the fiber. The wavelengths are terminated on electronics devices called transponders, undergoing an optical-to-electrical conversion for signal recovery, retiming and regeneration. Inside a telecommunications office, the signals are then handled to and switched by a transport switch (aka optical cross-connect or optical switch) and directed to an outgoing fiber link where they are carried as wavelengths multiplexed into that fiber link towards the next telecommunications office, or dropped at that office. The act of going through Optical-Electrical-Optical (O-E-O) conversion through a telecommunications office causes the network to be considered opaque. When the incoming wavelength do not undergo an optical-to-electrical conversion and are switched through a telecommunications office in the optical domain using all-optical switches, the network is considered to be transparent. Hybrid schemes can be considered with limited O-E-O conversions across the network. Transparent optical mesh networks have been deployed in metropolitan and regional networks. Long distance networks tend to be opaque.

Routing in optical mesh networks Routing is a key control and operational aspect of optical mesh networks. In transparent or all-optical networks, routing of connections is tightly linked to the wavelength selection and assignment process (so-called Routing and Wavelength Assignment or RWA). This is due to the fact that the connection remains on the same wavelength from end-to-end throughout the network (sometimes referred to as wavelength continuity constraint, in the absence of devices that can translate between wavelengths in the optical domain). In an opaque network, the routing problem is one of finding a primary path for a connection and if protection is needed, a backup path diverse from the primary path. Wavelengths are used on each link independently of each others. Several algorithms can be used, such as Shortest path, k-shortest path, Dijkstra'a algorithm, edge and node-diverse or disjoint routing, Suurballe's algorithm, and multiple heuristics.

Applications dynamic services such as bandwidth-on-demand, Just-In-Time bandwidth, bandwidth scheduling, bandwidth brokering, and optical virtual private networks IP-over-optical network architectures

Related network architectures Mesh networking in wireless networks

Notes [1]. [2] Also referred to as Optical Cross connect 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 grooms, multiplexes, and switches signals in the electrical domain, although some equipment do switching (only) fully in the optical domain without any O-E-O conversion. [3] PROTECTION refers to a pre-planned system where a recovery path is pre-computed for each potential failure (before the failure occurs) and the path uses pre-assigned resources for failure recovery (dedicated for specific failure scenarios or shared among different failure scenarios) [4] With RESTORATION, the recovery path is computed in real time (after the failure occurs) and spare capacity available in the network is used to reroute traffic around the failure.

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