1 Introduction
After years of development, ASON technology has been continuously accumulating and improving. For most domestic operators, the traditional transmission network already has a considerable scale. How to introduce ASON technology more reasonably to achieve a smooth evolution of the transmission network is the main issue discussed in this article.
2. The significance of introducing ASON technology
At present, the transmission network is basically based on the SDH ring network, mainly facing the following problems:
(1) The 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 further reduced, and important services cannot be fully protected and restored.
(2) Low resource utilization
The entire network has more than 50% of the bandwidth as backup resources; cross-ring nodes in complex large networks can easily become a bottleneck, and resource utilization will be lower.
(3) Poor end-to-end scheduling management capabilities
Some circuits require manual routing of cables and connection through DDF, making circuit scheduling difficult. The dynamic deployment capability of service bandwidth is poor, and it is difficult to handle the scheduling needs of burst services such as broadband data.
(4) Unable to achieve business classification management
It is impossible to provide corresponding protection levels for different services and users.
The ASON technology introduces the concept of dynamic switching in the traditional SDH technology, adding multiple protection and recovery methods for the business, which can effectively resist network multi-point failures and provide differentiated business service levels. And improve the utilization rate of the channel, and enhance the circuit's rapid configuration scheduling ability. At the same time, it is conducive to the upgrade and expansion of the network, and can realize a more flexible and safe MESH networking. Therefore, it is meaningful to introduce ASON technology in a timely manner.
3. The current bottleneck of ASON
ASON large-scale application also has the following four bottlenecks:
(1) Uncertainty of standard agreement
Although the relevant standards in ASON architecture, network interface and signaling routing protocol have been formed, but still need to be improved in many aspects such as 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 manufacturers still needs to wait. Currently, only one manufacturer's equipment can be used to deploy ASON products.
(3) Maturity of technology and system
ASON technology has not been applied for a long time in a truly 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 depend only on perfect 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 network introduction of ASON
Although ASON still has some shortcomings, as the technology gradually matures, its future must be bright.
When preparing to start ASON, operators should not only consider the above technical bottlenecks, but also meet the following necessary conditions:
(1) Business topology model in line with ASON
The ASON network can only play its advantages in the mesh distributed business model, but it has no meaning for the star centralized and convergent business. 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 it is only possible between hub offices There is an ASON requirement. In terms of voice services, fixed-line operators are more similar to the hierarchical aggregation structure from switching branch offices, end offices to tandem offices, and long-distance offices. The mesh model is not obvious, and the demand for ASON is not urgent. The characteristics of the data service are different from the voice, which is relatively in line with the business model of ASON. Therefore, different operators have different requirements for ASON due to their different business models.
(2) The authenticity of optical fiber mesh multi-route
The physical optical cable network is the basis for achieving ASON. In the case where the optical cable network resources are not yet fully in place (such as the node cannot guarantee more than 3 optical cable dimensions), the introduction of ASON will not really play its advantages. For this situation, it is not recommended Introduce ASON. Otherwise, the protection mechanism of ASON will not work. On the contrary, due to the increase of hidden risks in the same route, additional manpower is required to manage the risk group, which increases the maintenance cost and management difficulty.
(3) Network scale
For the case of small traffic, the ring connection shows better bandwidth utilization. For the case of large traffic, the direct physical channels between the nodes provided by the mesh MESH network are effectively filled, which can show better bandwidth utilization. In addition, there are few nodes that cannot take advantage of the advanced nature of ASON technology. The general business demand node can only reach 15 points before triggering the benefits of ASON technology.
(4) Business particles
ASON technology only works for business particles above VC-4. If ASON supports VC-12 service, this is a considerable challenge for the distributed intelligent network element database. When the service is switched back, the recovery time will be astronomical. Therefore, ASON products cannot support 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 services to large-particle data services, and then consider the problems introduced by ASON.
5. The introduction strategy of ASON technology at this stage
5.1 Different treatment at different levels
The application of ASON technology needs to consider different evolution strategies according to different characteristics of long-distance network and metropolitan area network. The long-distance service network is basically a mesh service connection, which conforms to the characteristics of ASON. The long-distance transmission network currently generally uses a ring network. Due to the long loop, there is a high probability of two-point or multi-point failure, and protection needs to be strengthened. Therefore, it is meaningful to introduce ASON in the long-distance network. It is recommended to adopt the "bottom-up" evolution strategy. First, introduce ASON in the key areas with urgent business needs, and then use the UNI interface or NNI interface to convert multiple The local ASON networks are interconnected, and eventually the entire network becomes intelligent.
For metro transport networks, the current three-layer structure of the core layer, tandem layer and access layer. The introduction of ASON technology should start at the core layer of megacities, adopt a "top-down" approach, and gradually expand to the junction layer, eventually covering the entire transmission network.
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