Evolution of Intelligent automatic switched Optical Network

Absrtact: The development of telecommunication service needs new and more intelligent Optical Network support, Nortel Network Company's Optera series product has the main performance of new optical network, conforms to ITU-T's automatic switched Optical network standard--G.ASTN. Firstly, the structure of the automatic Switched Optical network is introduced, signaling components, routing, and then comparing some of the relevant standards, the main advantages of the ITU-T recommendations in the network structure, and IETF standard signaling and routing protocols have considerable advantages; Finally, the optical service network of Nortel Network is introduced.

Keywords: astn,ason, routing, signaling transmission, mesh recovery

In general, backbone networks are optical networks capable of carrying complex, predictable voice and network services. Internet services at the edge of the network are exploding, giving new service providers an exciting prospect. Moreover, optical transmission services, which were used primarily to reduce the cost of network planning, can now be directly faced with end users, requiring a new, more intelligent optical network to meet these challenges.

The new optical network should have the following main features:

· Standardized Routing and signaling transmission structure;

· Based on the network topology structure;

· Network topology structure and automatic resource detection;

· Flexible mesh recovery mechanism based on SONET/SDH loop;

· The planning and application of shared bandwidth recovery and the allocation of resources for graded services;

· Through the rapid connection of equipment performance and multiple vendors, internal service providers to work together;

· User signal bandwidth on demand.

I. Structure of G.ASTN

Nortel Network Company's Optera series products with the above new Optical network features, in line with the ITU-T automatic optical switching Network standards (G.ASTN). G.ASTN's structural framework is shown in Figure 1, where the optical business layer supports a variety of business particles from STM-1 to wavelength bandwidth. The G.ASTN supports users directly connected to optical crossover devices (OXC) or through Optera Metro 4100/4200 and Optera Metro 5100/5200 to the access network. The G.astn control layer is composed of the optical connection controller, which overlaps with the transmission network, and each optical connection controller corresponds to the Optera Connect network node one by one. The G.ASTN control layer provides routing and signaling transmission through optical network according to the requirements of the edge users.

The routing setup is divided into two steps: first, each Optera node searches for the effective resources, then connects with the neighboring nodes, and reports the local topology information to the relevant optical connection controller (OCC), so the optical connection controller automatically searches the optimized transmission network topology and resources; The optical connection controller dynamically updates the topology database to adapt to the corresponding topological changes by routing protocol, maintains the newest topological structure database by each automatic switching transmission network (ASTN) controller, and carries on the dynamic routing computation for the connection establishment. This latest network state allows for current information utilization while collecting historical information to meet capacity planning needs, activating optimized triggers, and limiting routing capacity.

Ii. Signalling components

The network component is a common basic component used to describe the network function structure, which has nothing to do with the concrete implementation technology. At the ASTN control level, there are four main types of components: Request Agent (RA), optical connection controller, admin domain and interface.

The ASTN control layer includes the following signaling interfaces.

(1) User network interface (UNI)

This interface allows the user to create and remove connections when generating signals that are based on MPLS (LDP or RSVP) scenarios that apply to the optical network. It applies to user systems (such as routers), or to higher-level transport network elements. Uni can also be used by network administrators to send user connection signals to users who do not have the Uni signaling function. The parameters that end users may use include QoS, protection levels, bandwidth, calendar features, routing diversity, and other attributes.

(2) Node to node interface (NNI)

This is the internal interface of the ASTN network, which transmits user requests over the network to establish a connection between the intermediate nodes on the optical channel. The parameters of this interface include clear routing descriptions, protection capabilities, and routing restrictions, and well-defined nni interfaces can support the normal functioning of the different levels of nodes defined in the ASTN network.

(3) Internal interface (Irdi:inter-domain Interface)

This interface is not displayed for ASTN networks under different network management, and is a nni with uni function, which is used to exchange simple addresses and topologies. It is the key to achieve rapid transmission of services across multiple management areas. The internal interface is completely open to the internal connection of the ASTN network, and can realize the true end-to-end connection between different carriers.

(4) Connection control Interface (CCI)

This is an interface between the ASTN controller (the aforementioned optical connection controller) and the Optera connect switching structure, which is used to configure the crossover of the switching device and to obtain information about the current exchange status. CCI allows for multiple capacity exchange and internal complexity.

The performance of uni and Nni can enhance service capabilities, including End-to-end dial-up Signaling channel protection, persistent software connections, background connection optimization, connection tracking, and calendar connection settings.

Third, Route selection

Each Optera connect node searches for valid resources and then connects to neighboring nodes and reports local topology information to the associated optical connection controller via CCI. Similarly, the optical connection controller automatically searches for global transmission network topologies and resources, such as bandwidth, between optical connection controllers. This has been done through the Open Shortest Path First (OSPF) protocol extended to the Optical network form. Once they establish a topology database, the ASTN controller dynamically updates their topology database using a routing protocol such as CR-LDP or Rrsvp-te. Similarly, any change in IP address will spread to maintain accessibility.