SON: Next Generation Optical Network

Since the 1990s, Wavelength division multiplexing (WDM) has been deployed on a large scale in telecommunications networks, and the system's transmission capacity has increased by one times every 12-18 months. However, the control and management of optical networks remain in the traditional sense of SDH networks: The optical layer is simply a simple transport medium in the network, and its main function is to provide static high speed optical access to the top electronic devices such as IP routers and ATM switches, which are usually manually configured, The network intelligence mainly concentrates on the electronic layer, the optical transport layer is regarded as some inflexible "dumb" pipeline collection. In this traditional mode, the interconnection of electronic layer and light layer is obviously inefficient, complex, and prone to errors, which limits the flexibility, reliability and scalability of the network.

The Next Generation optical network "son" has changed this situation. There are many kinds of meanings of "son": Switched Optical Network (switched Optical network), Smart Optical Network (Intelligent Optical Network), software-based Optical Network (software-based Optical Network) , service-oriented Optical Network (business-oriented optical network) and so on. These meanings actually correspond to different levels of technology. For example, "swap" emphasizes hardware, meaning that network nodes are made up of large capacity, non-blocking and transparent optical cross connection (OXC) devices; "Smart" emphasizes distributed control, including automatic discovery of network neighbors, automatic topology discovery, distributed routing computation and Optical path management (build, dismantle and restore), etc. "Software-based" Emphasis is on reconfiguration and programmability; "Business-oriented" emphasizes network management, including virtual private network (VPN), service level agreement (SLA), Traffic Engineering (TE), security authentication, billing interface and so on.

Key--OXC of Next generation optical network

There is no doubt that OXC is the key hardware that forms the next generation optical network. Some companies, such as Ciena, Sycamore and Tellium, have introduced the OXC of electronic switching cores based on traditional ASIC technology, and the notable advantage of this oxc is that they can handle bandwidth units that are smaller than wavelength granularity, suitable for current market requirements, and easier to manage than Pangkung of OXC switching technologies. However, due to the wide use of WDM technology in current and future telecommunication networks, the electronic switching core is difficult to cope with the explosive growth of wavelength bandwidth. The current ASIC technology can only support the 512X512 port's electronic switching core, but the potential market requires at least twice times the capacity.

All-optical switching reduces the optical-electrical-optical conversion in the network, saves a lot of investment, and transparent optical exchange makes the user's rate easier to upgrade to a higher transmission rate in the future.

So far, there are many kinds of technologies to realize all-optical exchange, such as: micro-level electromechanical technology (MEMS), liquid crystal technology, bubble technology, thermal light technology, holographic technology and optical technology. The main parameters of these techniques are: Exchange matrix scale, scalability, switching speed, loss, power consumption, reliability, performance price ratio and so on. By synthesizing these parameters, MEMS is one of the most promising technologies at present. The MEMS optical Exchange matrix is composed of a tilted micro-mirror array, which can be two-dimensional or three-dimensional. The two-dimensional micro-mirror array is equivalent to the cross-bar switch, and is the first generation of MEMS optical exchange matrices. Three-dimensional micro-mirror array is usually composed of a pair of light from the input port after the mirror reflection two times, to reach the desired output port, each of the micro-mirror tilt position of two axes adjustable, can be accurately controlled in the thousand points within a few degrees.

Technical controversy of next generation optical network

--with inside signaling and with external signaling

In-band signaling is that the control plane and the data plane share the same physical medium, such as using the DCC channel of SDH multiplexing section or regenerating section, or using a specific wavelength channel as the control plane of a data communication network. The advantage of in-band signaling is that it saves data communication network investment, but the risk of control plane is the same as that of Datum plane, and the security and reliability are poor. The actual telecommunication network often uses the Out-of-band signaling, namely the control plane and the data plane are not in the same physical medium, guarantees the security and the reliability, 7th number signaling NET is one example.

--distributed control and centralized management

The dispute between distributed control and centralized management is a long-standing one, in fact, this is the contention between computer network and telecommunication networks. The computer network is a typical distributed control, it realizes the distributed dynamic routing through a series of routing protocols such as RIP, OSPF and BGP, so its scalability and reliability are better, and the telecommunication network is a typical centralized management, For example, the Telecommunications Management Network (TMN) enables network or business providers to quickly apply new business, innovate technology, reduce costs, and enhance competitiveness by defining standard interfaces for basic network functional component relationships.

The initial design of optical network was developed from the telecom network, however, in order to adapt to the explosive Internet development demand, IP over optical gradually became the research direction. Considering the business characteristics of the Internet, distributed control in optical network can effectively utilize network resources and realize fast protection and recovery. But this does not mean that optical network management can completely discard centralized management, the traditional TMN method has many advantages in business management, such as virtual private network (VPN), service level agreement (SLA), Traffic Engineering (TE), security authentication, billing interface and so on. Therefore, the next generation of optical network management should be distributed intelligence and centralized intelligence of the organic combination.

--overlapping model and equivalence model

The interconnection model of heterogeneous networks has been studied in IP networks and ATM networks, there are two main models: overlapping model (overlay models) and Peer-to-peer model, similarly, the control plane of optical network can be divided into these two models.

In the overlapping model, the address scheme, routing protocol and signaling Protocol of the electronic layer and the address scheme of the optical layer, routing protocol and signaling protocol are operated independently. Such a model allows the optical network to allow multiple service access, each business network has its own address scheme, routing protocol and signaling protocol. Optical networks provide point-to-point connections to the electronic layer, which in turn can be viewed as the client layer of the optical network.

Overlapping models can be divided into two sub models: the supply model (provisioned models) and the Exchange models (switched model). The optical path in the supply model is statically configured by the network management system, therefore, it is not necessary to exchange the routing information between the uni and the optical layer, this model is similar to the permanent virtual circuit (PVC) in ATM, the endpoint of the optical path in the Exchange model is specified by the Uni signaling, and the electronic layer can dynamically apply bandwidth to the optical network. Similar to the Switched virtual Circuit (SVC) in ATM. Obviously, the electron layer and the optical layer need to carry on some exchange of information, such as the electronic layer of accessibility information.

In the Peer-to-peer model, the electronic layer and the optical layer adopt a unified control plane, the address scheme, routing protocol and signaling protocol are the same, so there is no uni protocol. This model is the most popular common multi-protocol tag Exchange (GMPLS) recently. It has the following advantages: it inherits the advanced idea of MPLS control plane and IP routing protocol, avoids the redevelopment of a new set of optical network control Surface protocol, realizes software reuse, simplifies network management, and facilitates the control fusion of data network and transmission network.

But from the network operation, the electronic layer and the optical layer may belong to different operators, the transmission network does not want its own internal routing information and data network sharing, so the recent development direction should be exchange overlapping model, the peer model is the future development goals. Finally, it should be noted that "son" is not isolated and is consistent with the direction of many standardization organizations such as IETF, ITU, OIF and ODSI.