Facing the huge communication market demand beyond imagination, operators are looking for a new way to build a new type of optical transmission network at a lower cost, enhancing network capacity expansion capability and networking flexibility. The emergence of automatic switched optical network ( ASON ) is achieved by fully absorbing the advantages of IP networks and technologies and integrating them into the optical transmission network. At the beginning of the design, it fully considered the development trend of the dominant grouping business, designed it to be similar to the IP network structure, with unlimited scalability and compatibility, through standard interfaces, equipment from different manufacturers can achieve interoperability , To facilitate the management of the entire network.
The traditional transmission network only involves signal transmission, multiplexing, cross-connection, monitoring and survivability processing, and does not include switching functions. In addition to the above functions, ASON can also realize dynamic, automatic transmission, switching and connection establishment functions . At the same time, in order to meet the current needs of circuit-switched and packet-switched services, ASON also introduced the concepts of signaling and routing to absorb the advantages of both types of networks while avoiding their respective shortcomings. In addition, ASON supports multiple customer signals and is a network independent of customers and technology.
ASON technical characteristics
ASON is an optical transmission network that meets the requirements of the G.8080 framework and completes automatic switching and connection control through the control plane. It uses optical fiber as the physical transmission medium and is composed of optical transmission systems such as SDH and OTN. The core of the ASON network is network intelligence, including functions such as call and connection control, routing, and automatic discovery to realize intelligent network control functions. The application advantages of ASON network are mainly reflected in the following aspects.
1. Fast circuit assignment. ASON technology supports the use of standard routing and signaling protocols to achieve dynamic end-to-end connection establishment and scheduling in optical networks. The SPC and SC functions enable rapid circuit configuration.
2. Dynamic allocation of network resources. Use traffic engineering to dynamically allocate network resources to routes to meet the continuous adjustment of the network structure and the imbalance of business growth in various regions. At the same time, it can also meet various temporary services; fully explore the potential of the network, improve network resource utilization and operator investment Output ratio.
3. The network structure is easy to expand and adjust. Due to the use of mesh network structure and distributed network intelligence, it is easy to increase the number of nodes and adjust the network structure.
4. Resist multi-point failures and enhance the survivability of the network. Provide MESH protection and recovery capabilities to resist multi-node failures. When two optical cables break in the traditional ring network, the service has been interrupted, and the mesh network can find multiple detours to ensure that the service is not interrupted. Improve network survivability and anti-disaster capabilities, especially distributed recovery capabilities can achieve rapid business recovery.
5. Fast protection and recovery mechanism supports multi-level services. Provide different protection and recovery levels for different services and improve network utilization; At the same time, it can support various new services to better implement customized services for users, provide more attractive services for key customers, and improve operators Overall competitiveness.
6. Increased network bandwidth utilization, saved network investment, and reduced CAPEX / OPEX. The ASON network enables operators to make better use of optical networks, improve network utilization, significantly reduce unit costs per megabit, simplify network structure, and reduce operating costs.
7. The network is easy to manage. All functions such as circuit management and configuration in the traditional SDH network management are manually performed on the EM / SNM, and the intelligence is poor. ASON network adopts distributed intelligence, automatic resource discovery and dynamic configuration of connections are allocated to each node to automatically achieve, reduce network management pressure, and facilitate network management.
8. Support a variety of new businesses. Because of its good scalability and transparent format, it can be continuously updated with the emergence of new services, which is convenient to introduce new services such as on-demand bandwidth services, wavelength wholesale, wavelength rental, optical dial-up services, dynamic routing distribution, optical virtual private networks, etc. Type, make the traditional transmission network evolve to the business network.
In short, the advantage of the ASON network compared with the traditional network is that it can flexibly deploy services between any nodes of the network, dynamically allocate network resources, improve network resource utilization, and enhance the flexibility and survivability of the network.
ASON International Standardization
The international standardization organizations currently tracking and researching ASON technology mainly include the International Telecommunication Union Telecommunication Working Group (ITU-T), Internet Engineering Working Group (IETF), Optical Internet Forum (OIF) and Telecommunications Management Forum ( TMF), there is overlap between the standardization organizations, but also complement each other.
ITU-T is the main standardization organization in the communications industry. Its main work in the field of ASON is to define a standard automatic optical network architecture. The difference from other standardization organizations is that it studies optical networks from the perspective of the overall structure. Then decide how to achieve it. ITU-T is mainly responsible for the content of ASON architecture. In addition, it provides frame structure and protocol specifications in distributed call and connection management, routing protocol, automatic discovery, etc., and also protects recovery, connection permission control, management plane, etc. The aspect is regulated.
The IETF's work is mainly to define the control protocol for intelligent optical networks. The working groups related to ASON technology research include three working groups such as CCAMP, MPLS and IPO. Their main work is to propose a generalized multi-protocol label switching (GMPLS) A series of draft standards, including signaling protocol (RSVP-te / CR-LDP), routing protocol (OSPF / IS-IS), link management protocol (LMP), etc.
OIF is currently mainly concerned with IP clients, and OIF has standardized the user interface (UNI) of intelligent optical networks. For external network-to-network interfaces (E-NNI), OIF also has a preliminary definition.
TMF mainly solves the management problems of different technologies. It focuses on ITU-T G.7718 and supports the management of the ASON control plane. Many definitions of TMF can be used for ASON management, which provides an information model about the control plane. ITU-T's current approach is to divide the ASON management problem, and only define the functions and requirements of the management plane, and the definition of management objects and management information model is left to TMF to complete.
The China Communication Standards Association Transport Network Working Group is mainly based on the ITU-T framework and related recommendations in the formulation of standards for automatic switched optical networks, while taking into account the relevant specifications of IETF and OIF. In 2003, the Transport Network Working Group began to formulate a series of "Automatically Switched Optical Network Standard (ASON) Technical Requirements" series of standards. In this series of standards, the entire ASON technical requirements are divided into architecture and overall requirements, terms and definitions, DCN, letter Commands, routing, automatic discovery, protection recovery, management plane, UNI, E-NNI, etc., have now completed the formulation of some standards such as architecture, definition of terms, DCN, signaling, UNI, management plane, automatic discovery, etc.
In summary, the standardization work for ASON has been basically completed, and the functions of all aspects of ASON have been basically mature. Only in the interoperability of E-NNI interfaces, there are still imperfections, and protection based on inter-domain protection cannot be very good. Good interworking, this will be the problem to be solved in the next standardization work.
ASON equipment status
ASON equipment is gradually maturing. In general, the transmission plane currently focuses on SDH-based ASON equipment, whose switching particles are above the VC4 granularity, and some manufacturers have implemented ASON scheduling based on VC12 particles, and also have wavelength-based intelligent scheduling in WDM networks; At the control level, the basic control level functions are already available, such as connection management and routing. For the interface at the control level, the E-NNI interface has been interconnected between manufacturers, and the E-NNI interface can be used to implement end-to-end services. Scheduling, but the protection and recovery mechanism of the E-NNI interface is not perfect; for the ASON management system, the management of the equipment at the transmission level is relatively mature, and the management at the control level is basically perfect; for the signaling network, both in-band and out-of-band methods are available Provided, but there are certain problems in the inter-band communication; for protection and restoration, a more complete protection and restoration mechanism has been provided.
Specifically, the following main characteristics of the current status of ASON equipment.
1. Provides a large-capacity cross matrix to realize business grooming in the direction of multiple optical ports, can support 320G / 640G cross capacity, and can even reach 1.28T.
2. Provide rich service interfaces, including STM-1, STM-4, STM-16, STM64 and GE interfaces.
3. Supports distributed control, including distributed signaling, routing, and automatic discovery functions. It can realize the creation, query and deletion of soft permanent connection (SPC) and exchange connection (SC); support the routing information release and update, channel route calculation function; support neighbor automatic discovery and other functions.
4. Support various types of network protection and recovery functions, including more mature and perfect SDH network protection functions, control plane-based protection functions, distributed dynamic rerouting recovery functions, and a combination of protection and recovery. Various protection and recovery technologies can realize the survivability of resisting multiple failures and enhance the robustness of the network.
5. In terms of ASON signaling communication network, it supports both in-band and out-of-band signaling communication methods. Some manufacturers support the expansion of in-band signaling channels.
6. Through the ASON network management system to achieve end-to-end, across the ASON network business unified scheduling.
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