Intelligent Design of Automatically Switched Optical Network Based on GMPLS

1 Introduction
Automatically Switched Optical Network (ASON) is a new type of network that can automatically connect to the network. It consists of three planes: control plane, transfer plane, and management plane. The control plane technology is its core. It can implement dynamic exchange using the control plane. GMPLS generic Multi-Protocol Label Exchange (MSTP) is a common Multi-Protocol Label Exchange Technology proposed by IETF, which is extended by MPLS Multi-Protocol Label exchange. The evolution relationship between ASON and GMPLS 1 shows that it has evolved from an automatic transmission Optical Network (ASTN) to an ASON, and then combined with the development process of GMPLS. In this paper, an intelligent OXC Node Based on GMPLS is designed to meet the control plane requirements of the automatic switching optical network. The simulation scheme is discussed and its functions are verified through simulation.
2. control plane of the Automatically Switched Optical Network
ASON consists of three planes: control plane, transfer plane, and management plane. The intelligent control plane is the key to achieving ASON. It is precisely because of the role of the control plane that ASON can intelligently configure network traffic, supports business classification, powerful protection, fault recovery, and comprehensive network management functions based on data types. Through the control plane, we can implement the exchange connection in ASON. ASON dynamic superposition network structure model, which includes four types of control layer components: Request proxy RA), optical connection controller OCC), management domain AD) and interfaces. We can see that ASON has four elements: transmission platform, exchange platform, networking intelligence and network management software. Optical Fiber Transmission Equipment is the transport carrier of ASON, which is structured and networked. optical cross-connection OXC) equipment forms an ASON exchange platform and is the core of smart optical networks, its own scalability and the combination of network software can provide network-wide scalability. The Transport Platform and the exchange platform constitute the optical transport plane of ASON. This network interconnection system is based on the Distribution Control Principle. Each network element is intelligent. It can understand the topology of the entire network and the status of related links from the dynamic routing protocol, and realize automatic route selection and exchange. GMPLS has become the best way to implement the control plane because of its applicability to optical fields. The GMPLS function can be considered to unify the control plane at different levels using unified signaling and protocols, so that devices with different technical backgrounds can use unified control management interfaces for interconnection. Here, we use the GMPLS series protocol for control signaling interaction, and achieve unified control between Inter-Domain and intra-domain control planes. We can also see that the ASON Control Plane is suitable for the use of distributed control combined with centralized control. Each Smart node runs its own management and control software, but it also communicates and interacts with adjacent nodes, and reports and interacts with the High-Level network management platform. In this way, network control and management are well completed.
3. Intelligent OXC Design Based on GMPLS
3.1 Overall Thinking
Overall idea: Smart routers supporting GMPLS and simple optical devices. The overall structure of the intelligent OXC node includes the OXC internal structure and the GMPLS-based control component structure. Common OXC structures and technologies include MEMS, waveguide, and liquid crystal. The basic structure of the smart node is composed of MEMS-based optical cross-connection matrix, input port, output port, and management control unit. The control plane function is mainly implemented by the management control unit module, which is also the focus of our design. Considering the expansion of GMPLS functional modules and software frameworks on the original OXC supporting MPLS. In terms of signaling control technology, we adopt an innovative combination of default wavelength and dedicated control channels, that is, the control channel and data channel can be separated, control signaling is mainly transmitted through out-of-band channels to ensure reliability. It also supports simultaneous data transmission and signaling at the default wavelength. In the default wavelength mode, when a node needs to transmit data, it first uses the default wavelength for transmission. When the data arrives at the IP engine, it will conduct massive stream identification while forwarding, if it is determined to be a massive stream, it will call the wavelength assignment protocol, specify and establish the corresponding optical path, and notify the node to transfer all the data to the established channel for direct transmission, instead of Route identification and forwarding, direct transmission is implemented. After the transmission is completed, the IP engine removes the optical path. In this way, it is obvious that the default wavelength transmits signaling and data at the same time. In the dedicated control channel mode, the node first initiates a connection request through the dedicated control channel. The GMPLS control plane establishes the corresponding optical path after responding to the connection request, and then returns a confirmation message to the initiated node, so that the node can transmit data. After the transmission is complete, send a request to remove the link to release the link. This comprehensive design ensures the robustness of the control channel. A dedicated channel can be used even if the default wavelength channel is congested or the channel is damaged, and vice versa; at the same time, this comprehensive method can support all the channel control modes we can currently adopt, such as independent control channels, embedded control channels and sub-carrier modulation channels. In general, it supports both optical packet switching and its deformation form optical burst switching, it is also compatible with previous IP Routers and can easily be upgraded to ultra-high capacity optical network routing switches in the future.
3.2 Hardware Structure
OXC is used in the dotted box. Here we choose a star Coupler With a tunable filter, a spatial switching matrix, and a wavelength converter. A coupler and a tunable filter are used to separate the input N-fiber WDM signal from each other in space, and then pass through the space optical switch matrix and wavelength converter, finally, the structure of M wavelength multiplexing by the coupler can realize the exchange of any one of M wavelengths from N to the corresponding optical fiber and the wavelength number of the fiber. Because of the use of a tunable filter, the broadcast transmission function is available. The wavelength converter supports Virtual wavelength channels. At the same time, it also has wavelength transfer. When the number of wavelengths increases, only a corresponding number of switching matrices need to be added. It also supports local signal upstream and downstream functions.
3.3 Software Structure
To achieve seamless integration of IP and WDM, GMPLS expands MPLS labels so that labels can be used not only to mark traditional data packets, TDM time slots, wavelengths, wavelength groups, and optical fibers can also be marked. In order to make full use of the resources of WDM optical networks to meet the needs of new business in the future, intelligent optical networks can be achieved, GMPLS also modifies and supplements signaling and routing protocols. To solve the management problems of various links in optical networks, GMPLS designs a brand new LMP protocol; to ensure the reliability of optical network operations, GMPLS also improves the protection and recovery mechanisms of optical networks. Due to these features, GMPLS has become a very good means to implement ASON Control. The software implements GMPLS management, routing, path calculation, signaling, neighbor discovery, and link management, among them, we mainly consider the RSVP with GMPLS extension in signaling, of course we can also use a CR-LDP with extension ). Specifically, the following functions are executed:
1) coordinate all functions of the GMPLS plane control module;
2) ability to communicate with EMS/NMS or external management systems;
3) Create and delete signaling and routing interfaces;
4) implement access control;
5) execute link settings and release requests;

6) provides interfaces between the control plane and the actual data plane, such as setting and releasing OXC.
It includes a state machine, a database, and two sub-modules: GMPLS controller and GMPLS adapter. The state machine is mainly used to manage LSP and facilitate misoperations and error handling. The database is used to maintain location and available resource information, and to track the existing connection status. The two submodules, one is used to execute the control function, and the other is used to provide interfaces between routes and orders.
4. Simulation Solution
Currently, there are two commonly used network-level simulation software that can be trusted: OPNET and NS 2. Both of them support MPLS, but there is no GMPLS module yet, therefore, we must extend the corresponding MPLS modules to support GMPLS simulation. Here we use OPNET. Based on the original MPLS module, based on the software framework we designed, the corresponding program is compiled through VC, you can perform a Hybrid Simulation Based on the powerful network element settings and network simulation functions of OPNET to obtain more realistic results. There are also two famous GMPLS simulation software: GLASS and DERIVEIT ASON-GMPLS-MPLS NETWORK SIMU-LATOR, we can also combine their simulation results for comparison and research.
5 conclusion
Based on the synthesis and comparison of the smart OXC proposed by our predecessors, we combine the IP routing function with OXC, in addition, the GMPLS control module we designed forms an intelligent node that can execute the corresponding control plane functions. Simulation shows that it can meet the networking requirements of the Automatically Switched Optical Network and can be used as the basic node of ASON. At present, such as OIF, IFTF, ITU-T and other major organizations are studying ASON, GMPLS is gradually applied to the ASON Control Plane Design. We believe that in the near future, ASON will obtain large-scale applications.
References
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[2] ITU-T Recommendation G.8080, Architecture for the Automatically Switched Optical NetworkASON). Geneva 2001,11
[3] ITU-T Recommendation G.807, Requirement for Automatic Switched Transport NetworksASTN). Geneva 2001, 7
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Zhou Tianhua is a master's degree in the Communication and Information Engineering Department of Guilin Institute of Electronics Industry. He is mainly engaged in research on IP/WDM optical networks.