Policy Analysis on introducing ASON technology into transmission networks

1. Introduction

Automatic Switching Optical Network (ASON) technology has been accumulating and improving after years of development. For most carriers in China, Traditional transmission networks already have a large scale. How to introduce ASON technology more rationally to achieve stable evolution of transmission networks is the main issue discussed in this article.

2. Introduction of ASON technology

At present, the transmission network is basically based on SDH ring network and mainly faces the following problems:

1) Insufficient Network Reliability

The traditional SDH ring network relies mainly on the environmental protection mechanism and cannot resist multiple failures. When multi-ring concatenation Or nesting is performed, the security is reduced, and the protection and recovery of important services cannot be improved.

2) low resource utilization

Over 50% of the network's bandwidth is used as backup resources. In complex large networks, cross-link points can easily become bottlenecks and lower resource utilization.

3) Poor end-to-end scheduling and management capabilities

Some circuits require manual cabling and connection through DDF, making it difficult to schedule the circuits. The dynamic deployment capability of service bandwidth is poor, making it difficult to handle the scheduling needs of burst businesses such as broadband data.

4) unable to achieve hierarchical Business Management

Different services and users cannot be protected.

The ASON technology introduces the concept of dynamic switching in the traditional SDH technology, and adds multiple protection and recovery methods for services. It can effectively resist multiple network faults and provide differentiated service levels. It also improves the channel utilization and the fast configuration and scheduling capability of the circuit. At the same time, it is conducive to network upgrades and resizing, and can achieve more flexible and secure MESH networking. Therefore, it is meaningful to introduce ASON technology in a timely manner.

3. Current ASON bottlenecks

ASON large-scale applications still have the following four bottlenecks:

1) standard agreement uncertainty

Although the relevant standards in ASON architecture, network interfaces, and signaling routing protocols have been formed, however, automatic discovery, Inter-Domain Routing, restoration algorithms, and management plane still need to be improved.

2) interconnection Problems

ASON already has basic connectivity in connection establishment and removal, but the real interconnection between manufacturers still needs to wait. Currently, only devices from one manufacturer can be used to deploy ASON products.

3) technology and system Maturity

The ASON technology has not been applied to a real large-scale network for a long time, and the security of the Restoration Mechanism remains to be tested.

4) Relationship between manual management and Intelligent Control

The introduction of intelligent functions means that manual intervention will be reduced, and network reliability will not rely solely on the complete operation, maintenance and management processes, but on the reliability of intelligent software. The Controllability of maintenance management still needs further research.

4. Necessary Conditions for network introduction to ASON

Although ASON still has some shortcomings, with the gradual maturity of technology, its future must be bright. When preparing to start ASON, the operator should not only consider the above technical bottlenecks, but also meet the following conditions:

1) compliant with the ASON business topology model

The ASON network can only take advantage of the network-based distributed business model, but it does not make sense for Star-based centralized and aggregate-type businesses. The mobile voice service is a network-wide circuit model above the switch terminal, and more base station circuits are centralized at the local end; generally, mobile exchange bureaus are concentrated in a few hubs. Therefore, only the hubs may have ASON requirements. In terms of voice services, fixed-line telephone operators are more similar to the progressive aggregation structure from the exchange branch office, the terminal Bureau to the settlement Bureau, and the long-distance Bureau. The mesh model is not obvious, and the demand for ASON is not urgent. The characteristics of the data service are different from those of the voice service, which is in line with the ASON business model. Therefore, different carriers have different requirements for ASON because their business models are different.

2) optical fiber mesh multi-route authenticity

The physical optical fiber network is the basis for achieving ASON. If the optical fiber network resources are not fully available, more than three optical fiber cable dimensions cannot be ensured for the node ), introduction of ASON will not really give full play to its advantages. In this case, we do not recommend the introduction of ASON. Otherwise, the protection mechanism of ASON cannot play a role. Due to the increase of the hidden risks of the same route, it requires additional manpower to manage risk groups, increasing the maintenance cost and difficulty of management.

3) Network Scale

For small business volumes, the ring network connection shows better bandwidth utilization. In the case of large traffic volumes, direct physical channels between nodes provided by the grid MESH network are effectively filled to show better bandwidth utilization. In addition, a small number of nodes are unable to take advantage of the advanced technology of ASON. Generally, after 15 business needs nodes are reached, the benefits of ASON technology can be triggered.

4) Business Granularity

ASON technology only works for business particles above VC-4. To support the VC-12 service on ASON, it is a great challenge for the Distributed Intelligent Network metadatabase, and the recovery time will also be astronomical when the service is recovered. Therefore, ASON products cannot support the following business particles of VC-4 in a short time. Operators need to consider the introduction of ASON when the business Bandwidth Model gradually develops from small particle VC.12 voice service to large particle data service.

5. Introduction strategy of ASON technology at present

5.1 treat different levels differently

The Application of ASON technology needs to consider different evolution strategies based on different features of Long-Distance Networks and man. The long-distance service network is basically a mesh service connection and conforms to the ASON characteristics. The long-distance transmission network currently adopts the ring network. Due to the long loop, the probability of Two-point or multi-point faults is high, and protection needs to be strengthened. Therefore, it is meaningful to introduce ASON in the long-distance network. We recommend that you adopt the "bottom-up" evolution strategy, first introduce ASON in the key areas with urgent business needs, and then, based on the technical development, the UNI interface or NNI interface is used to connect multiple local ASON networks, and the entire network is intelligent.

For Metro Transmission Networks, the core layer, sink layer, and access layer are generally used. The introduction of ASON technology should begin with the core layer of a mega city and adopt a "top-down" approach to gradually expand to the junction layer, covering the entire transmission network.

The specific cause analysis is as follows:

1) The backbone layer includes the core layer and the Convergence layer)

The backbone layer provides connections between backbone nodes. Its business needs have the characteristics of mesh distribution, large business volume, and large business size, and meet the requirements of ASON applications.

In the backbone layer, the interconnection between multiple rings is very common. When the service needs to be connected to multiple rings, the security needs to be jointly guaranteed by multiple rings. Currently, SNCP is usually used to protect the security, as there are too many forwarding rings, the security is difficult to guarantee. The direct routing of ASON solves the above problems.

At the same time, from the perspective of the carrier's optical fiber resources, The Hub's core nodes are relatively rich. Therefore, the backbone layer is the first layer introduced by ASON.

2) access layer

The business volume at the access layer is generally small and focuses on concentrated businesses. The business particles are mostly below the VC-4, the most common is the VC-12. Most carriers have relatively limited access-side optical fiber resources, and most of them can only provide ring-and link-type connections. Therefore, it will be a long-term process to introduce the access layer to ASON.

5.2ASON and traditional optical network integration Analysis

A large number of SDH or MSTP networks have been built on existing networks. These networks are not smart. How can they coexist with ASON? Theoretically, the original transmission equipment can be upgraded to support UNI. However, it is practically impossible to replace all boards because of this transformation.

"Intelligent proxy" is also recommended by equipment vendors. by upgrading the management system, it has a smart centralized control plane to automatically establish connections within the control domain, the private control protocol is used in the control domain to add standard signaling interfaces for external use, so as to cooperate with other control domains. This approach is feasible, but it is difficult to implement it.

Gradually radiating through the "ASON Island" may be the final construction method. In the initial stage, an "ASON Island" is built in a centralized business area, and end-to-end services will pass through the smart domain and traditional SDH domain. The two networks of the same manufacturer can achieve unified management and full-process unified scheduling through the High-level network management system, and maintain local protection methods. As the scale of ASON equipment continues to expand, multiple "ASON islands" are interconnected through multiple paths, and the center of gravity of service load is shifted. ASON gradually becomes the mainstream of the network.

ASON and traditional networks will coexist for a long time.

6. Preparations for operators

6.1 Transmission Line Planning and Construction advance to grid development

Due to the long pipeline construction period, in order to meet the requirements of ASON, the network planning and construction of pipelines should be paid attention to in advance. To meet the existing business needs, take into account the grid layout of the pipeline and the communication and connection between pipelines, and gradually provide the optical cable line resources required by ASON without increasing investment.

6.2 When purchasing new equipment, operators should consider the upgrade capability to ASON.

Currently, many mainstream equipment manufacturers have launched ASON products. When intelligent control software is not loaded, it functions the same as traditional SDH devices and large DXC devices. When selecting equipment, carriers should give priority to products that can be smoothly upgraded to ASON under the same conditions.

6.3 consider the ASON upgrade factors in advance when formulating the Transmission System Planning Scheme

On the backbone layer, plan the construction based on the physical topology of the ASON target network in advance. Although the smart platform is not open for the moment, you can try to establish a single ADM multi-party network, while maintaining the ring network or 1 + 1 protection, plan the third and fourth protection routes for important business circuits in advance. When a network multi-point fault occurs and the traditional SDH automatic failover fails, the switch between the third and fourth protection paths is manually started. To a certain extent, network security is improved. Once ASON technology is mature, intelligent control can be provided in a timely manner to smoothly upgrade to intelligent optical networks.

You need to reserve enough device slots at the initial stage of network creation. When traditional SDH is directed to ASON, multiple route outlets are formed, occupying a certain slot. In the past, a node often had multiple ADM devices with multiple SDH rings. After the ASON device is used, a single set of devices will carry all the services of this site, there is a large demand for slots, device capacity, and cross matrix. Therefore, in network planning, we need to appropriately enlarge the redundancy of equipment, especially the central data center and the Central Data Center. Due to the large business volume and unpredictable development space, we must reserve sufficient capacity for expansion.

6.4 adjust the service granularity across the network to prepare for ASON

If the network opened a lot of fragmented VC-12 business, in the ASON presentation will encounter a lot of difficulties. Therefore, on the one hand, it is necessary to strengthen the unified planning and management of the entire network, and appropriately increase the number of high-speed interfaces above the VC-4 of core network equipment such as switches, to improve the service granularity together; on the other hand, in the whole network resource management work, the granularity of the circuit should be reset at any time, under the conditions of possible conditions, gradually back to the VC-12 business, clear VC-4 or higher level of business particles, prepare for the introduction of ASON.

7. Conclusion

ASON technology is a major breakthrough in transmission technology and an inevitable trend in the development of transmission networks. Operators should closely follow the technological development and maturity process to avoid blind large-scale introduction. However, we need to pay more attention to network planning, construction, and maintenance. With reasonable investment, we should make relevant preparations in advance to lay the foundation for the introduction of ASON technology and smooth upgrade of transmission networks.

1. ASON automatic switching Optical Network Technology and Its Development
2. Research on the Control Plane of ASON automatic switching Optical Network