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 network with some chain structures. The services carried are mostly traditional TDM circuit services, which have good security and QoS guarantees. However, with the rapid development of data services, especially IP services, there has been an explosive growth in demand for bandwidth. Businesses now require larger bandwidths, more flexible allocation, and improved reliability and performance. As service networks expand and network scales grow, the limitations of the existing ring-based transmission network become increasingly evident.
Automatically Switched Optical Network (ASON) technology was introduced to address these challenges and adapt to the growing demands of modern data services. In recent years, as ASON technology has matured, many foreign operators have deployed it, while domestic operators have started implementing ASON in provincial trunk networks and metropolitan area networks. Some operators plan to deploy ASON nodes in long-distance transmission networks. This paper explores how ASON technology can be applied in long-distance transmission networks by leveraging its unique features.
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 each plane are:
a) The transport plane provides bidirectional or unidirectional information transfer between endpoints, performing tasks such as optical signal transmission, multiplexing, protection switching, and cross-connection. It can be based on SDH or OTN equipment.
b) The control plane enables the establishment, maintenance, and termination of end-to-end connections through signaling and routing. It also supports protection and recovery when failures occur, and can automatically discover adjacent relationships and link information to support connection setup and recovery.
c) The management plane oversees the operation of both the transport and control planes, ensuring their cooperation. It includes functions such as performance management, fault management, configuration management, billing, and security management.
Introducing a control plane in ASON offers several advantages:
a) It allows for rapid service configuration to meet urgent business needs.
b) It supports traffic engineering, enabling dynamic resource allocation and better network utilization.
c) A dedicated control plane protocol can be used across various transmission technologies.
d) It provides mesh protection and recovery capabilities, enhancing network survivability.
e) It supports multi-vendor environments and connection control.
f) It enables the introduction of new services like closed user groups and virtual private networks, offering customized solutions for key customers.
1.2 ASON Supports Business Types and Classifications
Since ASON is built on various transmission technologies, it adds an independent control plane to the SDH and OTN layers, supporting a wide range of services, including different rates and signal formats. ASON can provide fixed bandwidth channels between client network elements, defined at the input and output access points of the optical network.
The types of services supported include:
a) SDH services, supporting VC-n and VC-n-Xv as defined by G.707.
b) OTN services, supporting ODUk and ODUk-n-Xv as 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 FICON, ESCON, and FC.
The mesh network is a typical structure for ASON. Compared to ring and tree networks, it offers higher efficiency and flexibility. However, early DXC-based mesh networks had long recovery times, typically in the minute range. ASON makes mesh protection and recovery feasible. ASON-based mesh networks offer multiple QoS levels, though there is no universal standard for classification.
a) Diamond level: 1+1+ rerouting, with less than 30ms switching time.
b) Gold level: 1:1 protection with less than 50ms switching time.
c) Silver level: Reroute protection with recovery time in the range of hundreds of milliseconds to seconds.
d) Copper grade: No protection or recovery guarantee.
e) Iron level: Additional services that may be preempted by high-priority services.
ASON can provide new services like Bandwidth-on-Demand (BoD), Optical Virtual Private Networks (OVPN), and Assigned Bandwidth Services (PBS). However, due to lack of standardization and client equipment compatibility, full commercialization remains challenging.
3. ASON's Technical Advantages and Challenges
1.3.1 ASON's Technical Advantages
Compared to traditional transmission technology, ASON offers several advantages:
a) It shifts from a ring to a more flexible mesh network, improving network protection and reducing reserved bandwidth.
b) It dynamically allocates bandwidth, improving resource utilization and reducing costs.
c) Its control plane uses standardized protocols, enabling multi-vendor interoperability and faster service provisioning.
d) It supports new services such as wavelength rental, optical dial-up, and OVPN.
e) It provides different protection and recovery methods tailored to user requirements, making it more cost-effective than SDH networks.
f) It supports automatic resource and topology discovery, allowing for dynamic network optimization.
1.3.2 Problems with ASON
Despite its progress, ASON still faces challenges, particularly in performance and interoperation.
1) ASON's performance is not yet satisfactory. Although distributed recovery should be faster, current implementations often take tens of seconds to recover, even slower than centralized DXC systems. Issues like insufficient bandwidth and signaling delays contribute to this problem.
2) Multi-vendor interoperability remains a challenge. While OIF tests show promise, real-world integration is still limited, especially in complex topologies where accurate network information is essential.
Current intelligent node equipment based on SDH electrical cross-connect is mature and widely used, offering efficient protection and recovery for large-granular services.
Application Strategy Analysis of ASON Technology in Long-Distance Networks
2.1 Analysis of Problems in Long-Distance Transmission Networks
Long-distance transmission networks, often based on SDH and WDM, face challenges due to increasing bandwidth demands and service complexity. Traditional ring networks are not well-suited for multiple failures, leading to poor availability and inefficient resource use. Manual circuit scheduling across rings is time-consuming and error-prone. Additionally, the need for more flexible and reliable services, along with the lack of SLA support, highlights the limitations of current networks.
2.2 ASON Introduction Strategy in Long-Distance Backbone Networks
ASON represents the future of transmission networks. With the maturity of ASON technology and the growth of data services, widespread deployment is expected. However, operators must carefully plan the transition from SDH to ASON to protect existing investments and ensure smooth evolution.
2.2.1 Evolution Strategy Choice
There are two strategies for transitioning from SDH ring networks to ASON:
1) Hybrid Networking: ASON mesh networks are deployed in the core, while the edge remains in ring structures. This allows for gradual expansion and unified management of circuits.
2) Separate Networking: ASON operates independently, handling only services within its coverage area, while SDH handles others. This approach ensures end-to-end service management but requires careful planning.
2.2.2 Network Model Selection
Although IP technology is becoming the dominant carrier network, ASON integration with IP networks is still evolving. The overlapping model is currently the most feasible, with peer-to-peer models being studied further.
2.2.3 Network Size Selection
Due to E-NNI standard limitations, ASON networks are initially built with single control domains. Operators should start with small-scale deployments, gradually expanding as standards mature.
2.2.4 Application Location of ASON and Existing SDH Network
ASON is built on existing WDM infrastructure and complements SDH networks. It supports all SDH services and offers greater flexibility and reliability. Operators can continue using SDH infrastructure while introducing ASON for new services.
2.3 Problems to Be Aware of When Introducing ASON
Operators should plan ASON node placements in advance, avoid unnecessary adjustments, and consider interconnection issues with other network layers. Testing and gradual implementation are essential to ensure stability and compatibility.
3. Conclusion
ASON is the future of next-generation optical networks. Despite current limitations in standardization and product maturity, its adoption in long-distance transmission networks is inevitable. Operators must plan strategically, use standardized equipment, and implement ASON step-by-step to minimize costs and maximize benefits.
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