1 Introduction
After years of development, Automatically Switched Optical Network (ASON) technology has been continuously accumulating and improving. For most domestic operators, the traditional transmission network has a considerable scale. How to introduce ASON technology more reasonably and realize the smooth evolution of the transmission network is the main problem discussed in this paper.
2. The significance of introducing ASON technology
At present, the transmission network is basically based on the SDH ring network, which mainly faces the following problems:
(1) Network reliability is not high enough
The traditional SDH ring network mainly relies on the ring protection mechanism and cannot resist multiple points of failure. When multiple rings are serially connected or nested, security is more degraded, and perfect protection and recovery cannot be achieved for important services.
(2) Low resource utilization
More than 50% of the bandwidth of the entire network is reserved resources; cross-ring nodes in complex large networks can easily become bottlenecks and resource utilization will be lower.
(3) Poor end-to-end scheduling management capability of the service
Some circuits require manual cable deployment and connection through DDF, which makes circuit scheduling difficult. The dynamic deployment capability of service bandwidth is poor, and it is difficult to handle the scheduling requirements of bursty services such as broadband data.
(4) Unable to achieve business grade management
It is not possible to provide a corresponding level of protection for different businesses and users.
ASON technology introduces the concept of dynamic switching in traditional SDH technology, which increases the multiple protection and recovery modes of services, and can effectively resist multiple network faults and provide differentiated service levels. It also improves the utilization of the channel and enhances the fast configuration and scheduling capability of the circuit. At the same time, it is conducive to network upgrade and expansion, enabling a more flexible and secure MESH networking. Therefore, it is meaningful to introduce ASON technology in a timely manner.
3. The current bottleneck of ASON
There are still four bottlenecks in ASON's large-scale application:
(1) Standard protocol uncertainty
Although related standards such as ASON architecture, network interface and signaling routing protocol have been formed, there are still many aspects to be improved in automatic discovery, inter-domain routing, recovery algorithm and management plane.
(2) Problems with interconnection
ASON already has basic interoperability in connection establishment and teardown, but the real interconnection between vendors still needs to wait. At present, the deployment of ASON products can only use one manufacturer's equipment.
(3) Maturity of technology and system
ASON technology has not been applied to the long-term application of a large-scale network, and the security of the recovery mechanism has yet to be tested.
(4) The relationship between manual management and intelligent control
The introduction of intelligent functions means that manual intervention will be reduced, and network reliability will no longer rely solely on sound operation, maintenance and management processes, but on the reliability of intelligent software. The controllability of maintenance management still needs further study.
4. Necessary conditions for the network to introduce ASON
Although ASON still has some shortcomings, with the gradual maturity of technology, its future must be bright.
When the operator is preparing to start ASON, in addition to considering the above-mentioned technical bottlenecks, the following conditions must be met:
(1) ASON-compliant business topology model
The ASON network can only exert its advantages in the mesh distributed business model, but it does not make sense for the star centralized and converged services. The mobile voice service is a full-mesh circuit model above the switching end office, and more base station circuits are centralized to the central office; the mobile switching end office is generally concentrated in a few hub offices, so only the inter-office may be There is an ASON requirement. The fixed-line operators in the voice service are more similar to the hierarchical convergence structure from the exchange branch, the end office to the tandem office, and the long-distance bureau. The mesh model is not obvious, and the ASON demand is not urgent. The characteristics of the data service are different from the voice, and are relatively in line with the ASON business model. Therefore, different operators have different ASON requirements because their business models are different.
(2) Authenticity of fiber optic cable multi-route
The physical optical cable network is the basis for implementing ASON. If the optical cable network resources are not in place (for example, the node cannot guarantee more than three optical cable dimensions), the introduction of ASON will not really exert its advantages. For this case, it is not recommended. Introduce ASON. Otherwise, the protection mechanism of ASON cannot function. On the contrary, due to the increase of hidden dangers in the same route, additional manpower is needed to manage the risk group, which increases the maintenance cost and management difficulty.
(3) Network scale
For small traffic situations, ring connections show better bandwidth utilization. For the case of large traffic, the direct physical channel between the nodes provided by the lattice MESH network is effectively filled, which can show better bandwidth utilization. In addition, the node is less able to play the advanced nature of ASON technology, and the general business demand node reaches 15 before it can trigger the benefit point of ASON technology.
(4) Business particles
ASON technology only works for business particles above VC-4. If ASON supports VC-12 services, this is a considerable challenge for the distributed intelligent network element database. When the business is switched and restored, the recovery time will also be astronomical. Therefore, ASON products cannot support the business particles below VC-4 in a short time. Operators need to wait for the service bandwidth model to gradually evolve from small particle VC.12 voice service to large particle-based data service, and then consider the problem introduced by ASON.
5. Introduction strategy of ASON technology at this stage
5.1 Different levels of treatment
The application of ASON technology needs to consider different evolution strategies according to the different characteristics of long-distance network and metropolitan area network. The long-distance service network is basically a mesh service connection, which is in line with the ASON feature; the long-distance transmission network currently adopts a ring network. Due to the long loop, there is a high probability of two-point fault or multiple-point fault, and it is also necessary to strengthen protection. Therefore, it is meaningful to introduce ASON into the long-distance network. It is recommended to adopt a “bottom-up†evolution strategy. First, introduce ASON in key areas where business needs are urgent, and then use UNI interface or NNI interface to The local ASON network is interconnected, and finally the whole network is intelligent.
For the metropolitan transport network, the core layer, the tandem layer and the access layer are generally used. The introduction of ASON technology should start from the core layer of megacities, adopt a “top-down†approach, and gradually expand to the tandem layer, eventually covering the entire transmission network.
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