ASON Technology Introduction
Currently, the long-distance transmission networks built by domestic telecom operators mainly rely on SDH-based ring network protection technology. The network structure is primarily a ring with some chain structures, and it mainly supports traditional TDM circuit services, which ensure good security and QoS. However, as data services, especially IP services, have experienced rapid growth, business demands are showing an increasing need for bandwidth, larger capacity, more flexible bandwidth allocation, and higher transmission performance and reliability. As service networks develop and the network scale expands, the existing transmission network, which is based on ring structures, has exposed challenges that are difficult to overcome.
Automatically Switched Optical Network (ASON) technology was introduced to adapt to the fast-growing demand for data services. In recent years, with the maturation of ASON technology, many foreign operators have implemented ASON in their networks. Domestic operators have also started deploying ASON in provincial trunk networks and metropolitan area networks, with some planning to introduce ASON nodes into long-distance transmission networks. This paper explores the application strategy of ASON technology in long-distance transmission networks, combining its features with those of the long-distance transmission network.
1.1 ASON Technical Features
Unlike traditional networks, ASON introduces a control plane, forming a three-plane architecture: transport plane, control plane, and management plane.
The main functions of the three planes are as follows:
a) The transport plane provides bidirectional or unidirectional information transfer from one endpoint to another, performing tasks such as optical signal transmission, multiplexing, configuration protection switching, and cross-connection. The transport plane can be composed of SDH-based or OTN-based equipment.
b) The control plane enables the establishment, tear-down, and maintenance of end-to-end connections through signaling and selects appropriate routes for connections through routing. When a network failure occurs, the control plane performs protection and recovery functions. It can also automatically discover adjacency relationships and link information, releasing link state information to support connection setup, tear-down, and recovery.
c) The management plane implements management functions for the transport plane, control plane, and system, ensuring cooperation between all planes. It provides management functions defined in M.3010, including performance management, fault management, configuration management, and billing management, along with security management.
Introducing a control plane in an ASON structure offers several advantages:
a) Support for rapid service configuration to meet urgent business needs.
b) Support for traffic engineering, enabling dynamic allocation of network resources, meeting continuous adjustments in network structure and imbalances in business growth, as well as supporting various temporary services, improving network resource utilization, and exploring network potential.
c) A dedicated control plane protocol can be applied to various different transmission technologies.
d) Realize recovery functions based on real-time network status, providing mesh protection and recovery capabilities, resisting multi-node failures, and enhancing network survivability and disaster resistance.
e) Support for connection control in a multi-vendor environment.
f) New supplementary services, such as closed user groups and virtual private networks, can be introduced to provide SLA networks, allowing more customized services for users and offering more attractive services for key customers.
1.2 ASON Supports Business Types and Classifications
Since ASON is built on various transmission technologies, meaning an independent control plane is added to the transmission plane (SDH and OTN), it supports various rates and signal characteristics that the current transmission network can provide, such as format and bit rate. ASON can provide a fixed bandwidth transmission channel between two client network elements, with the channel defined between the input access point and output access point of the optical network. ASON services include:
a) SDH services, supporting SDH connection particles VC-n and VC-n-Xv defined by G.707.
b) OTN services, supporting OTN connection particles ODUk and ODUk-n-Xv defined by G.709.
c) Transparent or opaque optical wavelength services.
d) Ethernet services at 10 Mb/s, 100 Mb/s, 1 Gb/s, and 10 Gb/s.
e) Storage Area Network (SAN) services based on Fiber Optic Connection (FICON), Enterprise System Connectivity (ESCON), and Fibre Channel (FC).
The mesh network is a typical network structure of ASON. It is closest to the actual fiber network structure. In theory, it offers higher transmission efficiency and more flexible service configuration than ring and tree networks. Due to technical implementation limitations, early DXC-based mesh networks had recovery times reaching the minute level, which was not acceptable to operators. The emergence of ASON made mesh network protection and recovery possible. ASON-based mesh networks offer multiple QoS levels. Most equipment vendors classify service types according to the following methods, though there is no universal standard. A common convention exists.
a) Diamond Level: 1+1+ rerouting, where if a fiber is interrupted, the service immediately switches to an alternate path, with a switch time of less than 30ms. The network finds a new protection path, and even if the fiber fails twice, it guarantees a switch within 30ms.
b) Gold Level: 1:1 protection, pre-set route protection, with a switch time of less than 50ms.
c) Silver Level: Reroute protection, real-time calculation of recovery paths, with recovery times ranging from hundreds of milliseconds to seconds.
d) Copper Grade: No protection, no guarantee of recovery.
e) Iron Level: Additional transmission services, which may be preempted by high-priority services.
In terms of service type, ASON can provide various new services, such as Bandwidth-on-Demand (BoD), Optical Virtual Private Network (OVPN), and Assigned Bandwidth Services (PBS). However, due to a lack of standardization and client equipment, these services are still difficult to fully commercialize.
3. ASON's Technical Advantages and Problems
1.3.1 ASON's Technical Advantages
Compared to traditional transmission technology, ASON has obvious technical advantages, mainly the following points.
a) The concept of ASON introduces a shift from the traditional ring network structure in the core backbone network to a more flexible mesh network structure. Mesh networks improve network protection survivability, simplify the network structure, save reserved bandwidth on protection paths, and fundamentally solve transmission delay and reliability issues.
b) ASON can dynamically allocate bandwidth on demand, improving network resource utilization and reducing networking costs.
c) The control plane protocol used by ASON is a standard protocol, which allows for service connection, call control, and quick recovery in a multi-vendor environment, paving the way for solving multi-vendor device interconnection and enabling rapid service provisioning.
d) ASON can provide more new service types, such as wavelength/sub-wavelength rental, wholesale, resale, optical dial-up services, bandwidth trading, and OVPN.
e) ASON technology provides different network protection and recovery methods, allowing for tailored protection and recovery strategies based on user requirements for different service quality levels. This approach is more cost-effective than traditional SDH networks.
f) ASON technology supports automatic resource discovery and automatic topology discovery, with the ability to quickly establish services and dynamically optimize and adjust the network.
1.3.2 Problems with ASON
Although ASON technology has made great progress, there are still some problems, mainly focusing on performance improvement and interconnection.
1) ASON performance is not satisfactory. In theory, distributed recovery can provide faster network recovery. However, from the products provided by various vendors, in complex network topologies with large service volumes, the system recovery speed is relatively slow, sometimes even reaching the level of ten seconds. The recovery performance of ASON has not even reached the level of centralized DXC.
In many vendors' designs, when multiple links fail or the system reroutes and establishes connections through distributed algorithms, the system selects routes and establishes connections one by one, which can result in very long recovery times, especially when using in-band DCN (such as SDH multiplex section DCC overhead). The time for recalculating the route may not be the main issue, but establishing a connection requires back-and-forth signaling communication, which takes up more time.
Multi-vendor interoperability still has not been completely solved. While OIF interoperability tests bring confidence, it takes time to truly realize complete ASON interconnection (like current routers). The main difficulty lies in the abstraction of routing and logical information, and future layering of routing. Current interoperability is the simplest, purely interconnected 2 isolated nodes, without considering more complex network topologies. If it is a complex network topology, appropriate network abstraction information must be considered. The network profile information mainly refers to the number, location, and network capacity of the network connection nodes of two device vendors. If sufficient information, such as service capabilities, cannot be provided, the user may lose the connection or be unable to establish it.
At present, intelligent node equipment (ASON) based on SDH electrical crossover has been basically mature, and there is a successful large-scale commercial record. The intelligent node is integrated with the backbone and aggregation layers to reduce inter-ring transitions and simplify the increasingly complex network. At the same time, it provides an efficient and flexible protection and recovery method to meet the protection and recovery requirements of large-granular services, so that the network has sufficient intelligence, high flexibility, and reliability.
Application Strategy Analysis of 2 ASON Technology in Long-distance Network
2.1 Analysis of Problems in Long-distance Transmission Network
Among many protection measures, the ring structure has been favored by operators due to its simple and practical characteristics, gradually expanding from the access level and relay level to the long-distance transmission level. China’s telecom operators’ long-distance backbone network widely uses a layered structure consisting of a chain-shaped WDM system and a ring-shaped SDH system. This structure uses a simple network topology and fast and effective protection mechanism of the SDH layer, along with powerful WDM layer bandwidth, providing the capability to build a transport platform for the entire telecommunications network. With the development of IP data services and large customer bandwidth leasing services, the required transmission bandwidth is increasing, the particles are getting larger and larger, the required bandwidth supply mode is more and more flexible, and the transmission performance and reliability of the circuit are coming higher and higher. The development of the service network and expansion of the network scale have caused the current transmission network structure to expose problems that are difficult to overcome.
a) Security: The network has poor resistance to multiple points of failure. Traditional ring networks cannot cope with multiple points of failure, resulting in poor system availability. Many loops have been built to meet or exceed 5000km. Although each ring uses self-healing ring function, when two faults occur in the ring, it will inevitably affect the existing service. Protection measures to improve circuit safety and reliability.
b) Complexity: Traditional ring network services are complex and flexible, and many end-to-end circuits need to be routed through multiple rings. The long-distance circuit across the ring requires that the ring network passing through has available channels, and the circuit scheduling between the rings is completed on the distribution frame, which is manual, complicated, and inefficient.
c) Efficiency: Since the SDH ring network protection mode must reserve 50% capacity for protection, the utilization rate of the existing network is low, and the system utilization rate can be 50%.
d) Network expansion: The SDH ring network structure is difficult to adjust, and the transmission channel is difficult to plan and cannot adapt to the expansion of the network scale.
e) Maintenance: As the network continues to increase, the maintenance pressure increases. Maintenance personnel must have an in-depth understanding of the existing network. The flow of personnel will have a great impact on network maintenance, and network resource management is cumbersome, and circuit adjustment takes a long time.
f) Service provisioning capability: The inherent service provisioning mode of SDH cannot adapt to the characteristics of burstiness, self-similarity, routing and data flow asymmetry of IP services.
g) Service level: The existing network lacks the distinction of service security level. The types of service recovery provided are only ring/line protection and non-protection. There is no SLA. It cannot meet the requirements of traffic engineering (TE), differentiated services (DiffServ), and specific quality of service (QoS). It is difficult to support customers and networks SLA between.
h) Business protection granularity: The SDH layer has been unable to meet the bandwidth requirements of large IP (2.5G, 10G) IP services, while the WDM layer lacks a fast and flexible protection method.
Long-distance Backbone Network ASON Introduction Strategy
ASON represents the development direction of the transmission network. With the further maturity of ASON technology and the rapid development of data services, ASON technology will be applied on a large scale. However, telecom operators have invested huge amounts of money in the traditional SDH transmission network. The existing operation and maintenance system is also organized according to traditional technologies. At the same time, the SDH transmission network has good adaptability to small-granule services, and SDH can be implemented simply and effectively. Therefore, we must carefully consider the strategy of the transport network from the existing SDH network to ASON smooth evolution, in order to maximize the protection of existing investments, make full use of the existing network potential, and ensure the development of the network.
2.2.1 Choice of Evolution Strategy
There are two strategies for the evolution of the transport network from the existing SDH ring network to ASON.
1) Single plane structure of ASON and SDH hybrid networking
The ASON mesh network is built in the core part of the transport network. The edge part is still in the ring network. The newly created ASON domain and the edge ring network coexist. The new services will pass through the intelligent ASON domain and the traditional SDH domain. The ASON domain and the traditional SDH network of the same manufacturer can realize unified management and unified scheduling of circuits through the high-level network management system, and the networks of different manufacturers cannot be uniformly managed. As the scale of application of ASON devices in the network continues to expand and gradually extends from the core to the edge, the traditional SDH domain will continue to shrink. Ultimately, the entire network will be unified into intelligent ASON, and the subnets will be unified across different vendors. The E-NNI interface is interoperable.
2) Double plane structure of ASON separate networking
ASON is independent of the traditional SDH network, and organizes a new transport plane. It only solves the services of the ASON coverage area. The services outside the coverage area are solved by the traditional SDH network. The existing services in the coverage area are cut from the existing SDH network to the ASON, freeing up network capacity to solve new business beyond the coverage area. End-to-end management of services is achieved by avoiding services traversing intelligent ASON domains and traditional SDH domains. With the gradual expansion of the ASON scale, a two-plane structure in which ASON and the traditional SDH network coexist will be formed, and each of the two planes has a division of labor and mutual protection.
As domestic operators have built SDH long-distance transmission networks, it is recommended to use strategy 1) to deploy ASON, which can take into account existing network investment and improve the effective utilization and reliability of network resources.
2.2.2 Selection of Network Model
Although IP Internet as a carrier-class bearer network still has problems such as excessive bandwidth consumption, low device reliability, insufficient network stability, and QoS cannot be strictly guaranteed, IP technology is the only possibility from the current state of the art and development trends. Become a unified technology for carrying networks. With the rapid expansion of IP network scale, the impact of ASON in solving IP trunking circuits will become more and more significant, and MPLS will be deployed on a large scale in IP networks, which will make the coordination problem between IP network and ASON more prominent. These issues will make it possible for ASON to eventually adopt a peer-to-peer model to achieve complete integration with the IP network.
However, according to the current support level of equipment manufacturers for the three models, the overlap model is basically mature and has a successful large-scale commercial record, and the peer model has not been fully studied. From the perspective of network development, IP network and transmission network as two professional networks are designed, constructed and operated and maintained separately as a reasonable and feasible operation mode. Therefore, in the initial stage of ASON construction and in a long period of time, the overlapping model will be an effective and feasible network model.
2.2.3 Choice of Network Size
Since the E-NNI standard is not yet fully mature, there is a big difference in the support capabilities and standardization level of E-NNI among various manufacturers' devices, which limits the current ASON structure that can only adopt a single control domain. Using a single control domain structure, on the one hand, there is doubt that the ASON control plane can effectively support hundreds of nodes to form a large-scale network (no example); on the other hand, there is a lack of competitive risk in using single-manufacturer equipment. Therefore, the use of a single control domain structure to cover large-scale ASON covering the whole country and extending to prefecture-level cities is very risky. In order to avoid the above risks, operators can adopt some compromise solutions to build ASON in the initial stage of network construction, and gradually improve the network after E-NNI standards mature. For example, ASON with a relatively small coverage area is used in the early stage, and only static interconnections of transmission planes are used between different control domains, and protection is implemented by using a traditional protection mechanism for a small number of cross-domain services.
Before making network planning, you must determine which physical locations in the network are necessary to deploy ASON nodes. Generally, nodes with small traffic in long-haul networks and many nodes at the edge of the network are not suitable for ASON in the initial stage of network construction due to insufficient optical cable and WDM resources. For the network core node, the traffic is large, and the number of inbound and outbound routes is more than three. You can consider deploying as an ASON node. Therefore, in the initial stage of network construction, ASON is organized in the core important nodes, and the edge general nodes use the ring network to access the ASON core network.
2.2.4 Application Location of ASON and Existing SDH Network
The ASON built by the operator at the long-distance transmission network level is a multi-service bearer network that is built on the existing WDM network. It is on the same level as the existing SDH network. Although the concept of intelligent optical network technology evolved from the all-optical network-based automatic switched transport network architecture (ASTN), the physical layer it faces is still a mature SDH network, suitable for existing SDH transmission channels. Access. The physical layer of intelligent optical network technology is still the transmission channel (VC) based on SDH technology. The exchanged particles are also VC and VC-XC. The SDH performance monitoring and alarm features are still protected and restored by the intelligent optical network at the physical layer. The basis, so it can be said that the intelligent optical network is based on the development and extension of SDH technology. In terms of service bearer, it can carry all the services of the existing SDH network; it is more complete than the SDH network in terms of network flexibility and reliability; in terms of network management, the introduction of the control plane is more powerful than the SDH network. The intelligence of the network is further improved.
In summary, the intelligent optical network is developed from the original network technology such as SDH. It is an innovative development rather than a revolution. Therefore, operators can continue to utilize the existing SDH network infrastructure when developing new service platforms using intelligent optical network equipment in long-distance transmission networks. As the current ASON technology only supports the transmission of services above the VC4 (155M) level, the new ASON is mainly used to carry new services such as IP services and leased line services of the VC4 level. It is carried by the original ring network. With the development of ASON technology, a part of the VC4 or higher leased line or data service currently carried in the ring network can be filled into the ASON according to a certain principle, and the spare time slot can be used for the bearer of the low-order service. For some of the very important 2M services of the whole granularity, it is also possible to aggregate the services into VC4 or higher and then enter the ASON. In this way, the interworking between the multiplex device and the ASON can be ensured.
2.3 ASON Introduces Problems to Be Aware Of
a) At present, the transmission network of domestic operators is divided into three levels: interprovincial trunk line, provincial trunk line and local/metropolitan area network. Therefore, when introducing ASON technology into long-distance transmission network, it is necessary to first make a unified plan in advance, and clear the inter-provincial, The setting of the ASON node in the province avoids the influence of the later adjustment on the network.
b) Since the ASON technology is suitable for applications under the mesh network structure, the operator needs to increase the transmission route according to the development needs of the service network, and gradually transition the existing network structure from the ring network to the mesh network.
c) The introduction of ASON technology into the long-haul network should also fully consider the ASON interconnection problem with other layers of the network, and try to avoid the ASON networking on all layers of the network.
d) After the introduction of the ASON device, some networks do not immediately open their intelligent functions. Instead, they wait until the service reaches a certain scale or after the test network is verified, and then upgrades the transmission device to the real ASON device. In this case, you must thoroughly test the ASON device in advance, including the stability of the device and compatibility with traditional SDH devices.
e) Since the ASON technology is not yet fully mature, the process of introducing ASON requires a strategy step by step. In view of the fact that the UNI interface technology and the E-NNI interface technology are not perfect, the UNI interface can be gradually introduced. In the initial stage of ASON construction, most of the service network devices do not have the UNI interface capability. The fixed connection should be provided for the service network mainly by means of soft permanent connection (SPC). With the continuous integration of the service network and ASON, the UNI is relatively mature. The service network can directly control the ASON through the UNI interface to dynamically initiate requests, and provide new network services such as BoD and OVPN.
3 Conclusion
ASON represents the development direction of next-generation optical networks. Although it is limited by standardization and product maturity in its current application, the introduction of ASON technology in long-distance transmission networks has become an inevitable trend. Due to the wide coverage of long-distance transmission network, the variety of services carried, and the large amount of services, operators need to consider network planning software to achieve global planning when constructing ASON for long-distance transmission networks, and choose to apply higher standardization. Manufacturer equipment, so that operators can minimize the initial investment cost, and realize the evolution to ASON relatively quickly and safely, so as to gain an advantage in the competition.
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