At present, the long-distance transmission network built by domestic telecom operators mainly adopts SDH-based ring network protection technology. The network structure is mainly ring network and supplemented by chain. The bearer service is mainly traditional TDM circuit service, its security and QoS. Have a good guarantee. However, with the rapid development of data services, especially IP services are exploding, business needs are showing more and more bandwidth, larger and larger bandwidth, more flexible bandwidth supply, circuit transmission performance and reliability. The requirements are getting higher and higher. The development of the service network and the expansion of the network scale have caused the current transmission network, which is mainly based on the ring network, to expose problems that are difficult to overcome. Automatically switched optical network (ASON) technology is proposed to adapt to the rapid growth of data services. In recent years, with the maturity of ASON technology, many foreign operators have built ASON, and domestic operators are in the provincial trunk network and metropolitan area network. ASON technology has been introduced, and some operators plan to deploy ASON nodes in the long-distance transmission network. This paper combines the characteristics of ASON technology and long-distance transmission network to explore the application strategy of ASON technology in long-distance transmission network.
1.1ASON technical features
Unlike traditional networks, ASON introduces a control plane that forms an architecture that is functionally composed of a transport plane, a control plane, and a management plane.
The main functions of the three planes are described as follows:
a) The transport plane provides bidirectional or unidirectional information transfer from one endpoint to the other, performing functions such as optical signal transmission, multiplexing, configuration protection switching, and cross-connection. The transmission plane can be composed of SDH-based or OTN-based equipment.
b) The control plane provides the ability to establish, tear down and maintain the end-to-end connection through signaling, and selects the appropriate route for the connection through routing; when the network fails, the control plane performs protection and recovery functions; the control plane can also automatically discover the adjacency Relationship and link information, releasing link state information to support connection establishment, teardown, and recovery.
c) The management plane implements the management functions of the transport plane, the control plane, and the system to ensure the cooperative work between all planes. The management plane provides the management functions specified in M.3010, including performance management, fault management, configuration management, and billing management. And security management.
Introducing a control plane in an ASON structure has the following features.
a) Support rapid service configuration to meet urgent business needs.
b) Support traffic engineering, allow dynamic allocation of network resources, meet the continuous adjustment of network structure and imbalance of business growth, and also meet various temporary services, improve network resource utilization, and explore network potential.
c) A dedicated control plane protocol can be applied to a variety of different transmission technologies.
d) Realize the recovery function according to the real-time transmission network status, provide Mesh protection and recovery capability, resist multi-node failure, and improve network survivability and disaster resistance.
e) Support 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, which can more customize the services of users and provide more attractive services for key customers.
1.2ASON supports business types and classifications
Since ASON is built on various transmission technologies, that is, an independent control plane is added on the transmission plane SDH and the optical transport network (OTN), it supports various rates and different signal characteristics that the current transmission network can provide. Business (such as format, bit rate, etc.). ASON can provide a fixed bandwidth transmission channel between two client network elements, and the channel is defined between the input access point and the output access point of the optical network. The ASON business has the following aspects.
a) SDH service, supporting SDH connection particles VC-n and VC-n-Xv defined by G.707.
b) OTN service, supporting OTN connection particles ODUk and ODUk-n-Xv defined by G.709.
c) Transparent or opaque optical wavelength services.
d) Ethernet services of 10 MbTI/s, 100 MbTI/s, 1 GbTI/s and 10 GbTI/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. The mesh network is the closest to the actual fiber network structure. In theory, the transmission efficiency is higher and the service configuration is more flexible than the ring and tree networks. Due to the technical implementation level, the recovery time of the Mesh network service composed of the early DXC equipment usually reaches the minute level and cannot be accepted by the operator. The emergence of ASON makes the Mesh network protection/recovery possible. The ASON-based Mesh network has multiple QoS levels. Most equipment vendors divide the service types according to the following methods. There is no universal standard for this service classification. A convention is common.
a) Diamond level: 1+1+ rerouting, that is, when a fiber is interrupted in the service path, the service is immediately switched to the alternate path, the switching time is less than 30ms, and the network finds a new protection path, and the fiber can still be used when the fiber fails twice. Guarantee to switch within 30ms.
b) Gold level: 1:1 protection, preset route protection, switching time is less than 50ms.
c) Silver level: Reroute protection, real-time calculation of recovery path, recovery time in the range of hundred 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 a variety of new services, such as bandwidth-on-demand (BoD), optical virtual private network (OVPN), and assigned bandwidth services (PBS), but due to lack of standardization and client equipment. It is still difficult to fully commercialize.
3ASON's technical advantages and problems1.3.1 ASON's technical advantages
Compared with traditional transmission technology, ASON has obvious technical advantages, mainly the following points.
a) The concept of ASON introduced into the exchange, the traditional ring network structure in the core backbone network will gradually shift to adopt a more flexible mesh network structure. The mesh network mode can improve the network protection survivability, simplify the network structure, save the reserved bandwidth of the protection path, and fundamentally solve the transmission delay and reliability problems.
b) ASON can dynamically allocate bandwidth on demand, improve network resource utilization, and reduce networking costs.
c) The control plane protocol adopted by ASON is a standard protocol, which can realize the connection, call control and even quick recovery of services in a multi-vendor environment, paving the way for solving the problem of multi-vendor device interconnection and realizing rapid service provision.
d) ASON can provide more new business types. These new services mainly include wavelength/sub-wavelength rental, wholesale, resale, optical dial-up services, bandwidth trading, OVPN and so on.
e) ASON technology provides different network protection recovery methods, so that different protection and recovery methods can be formulated as needed according to user requirements for different levels and different service quality levels. This approach is clearly more cost effective than traditional SDH networks.
f) ASON technology supports automatic resource discovery and automatic topology discovery, and has the ability to quickly establish services, which can dynamically optimize and adjust the network.
1.3.2 Problems with ASON
Although the development of ASON technology has made great progress, there are still some problems, mainly focusing on the improvement of performance itself 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 the network connection topology with complex network structure, service bearer The amount is relatively large. In the case of multiple end-to-end link failures, 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 when the system reroutes and establishes connections through distributed algorithms, the system selects routes and establishes connections one by one, so that when the bandwidth of the SCN is insufficient to guarantee ( Using in-band DCN, such as SDH multiplex section DCC overhead, can result in very long recovery times. The time for recalculating the route may not be the main one, but establishing a connection requires signaling back and forth communication, which takes up more time.
Multi-vendor interoperability still has not been completely solved
The OIF interoperability test brings confidence to people, but it takes time to truly realize the complete interconnection of ASON (like the current router). The main difficulty lies in the topology abstraction of routing and logic information, and it will be layered in the future. routing. The 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 the two device vendors. If sufficient information, such as service capabilities, cannot be provided, the user may be lost or unable to establish a connection.
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 the inter-ring transition 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 2ASON Technology in Long-distance Network2.1 Analysis of problems in long-distance transmission network
Among the many protection measures, the ring structure has been favored by various operators because of its simple and practical characteristics, and gradually expanded from the access level and relay level to the long-distance transmission level. The long-distance backbone network of China's telecom operators is widely used in 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, and a powerful WDM layer. The bandwidth provides the ability 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. The higher. The development of the service network and the expansion of the network scale have caused the organization structure of the current transmission network to expose problems that are difficult to overcome.
a) Security: The network has poor resistance to multiple points of failure. The traditional ring network cannot cope with multiple points of failure and the system availability is poor. Many loops have been built to meet or exceed 5000km. Although each ring uses a 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 the 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 strategyASON 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. Simple and effective protection. 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. , free 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.
2.3ASON 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 ConclusionASON 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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