Research on Protection restoration application strategy in automatic switched Optical network

First, the introduction

Automatic Switched Optical Network (ASON) is a new generation of optical transmission network technology which is constantly adapting to the rapid development of the business. Ason Network as a distributed intelligent optical transport network, its biggest feature is in the transmission plane and management plane based on the introduction of intelligent control plane, the use of signaling, routing, automatic discovery and other technologies. The introduction of Ason technology in optical transport network will bring many advantages to operators. More recognized advantages include: fast delivery of the business, provide a variety of protection and recovery mechanisms, provide new types of business, and so on, and the provision of multiple protection recovery mechanism is the current operator planning and construction of Ason network focus on the problem, but also the focus of the features of the manufacturers.

Based on the existing protection and recovery standards and development situation, this paper focuses on the protection and recovery in the network application strategy analysis and research.

Ii. Protection and recovery mechanisms

1. Protection mechanisms

A protection mechanism is a mechanism that establishes one or more protected connections in advance in order to protect one or more working connections. These protected capacities cannot be rerouted, even if they are not used, and the cross connections used for protection by intermediate nodes have been configured in advance and need not be changed for protection.

In the protection mechanism, because the protection channel/link is the advance establishment, does not need through the Ason signaling in the fault occurrence to direct any intermediate node the connection controller to change, therefore the business restores fast (generally less than 50ms), applies to the higher level business , however, because the capacity used for protection cannot be rerouted even if it is not used, this makes the protection mechanism require more redundant resources, typically exceeding 100%. Currently, protection schemes can be grouped into the following categories.

(1) Special protection

L 1+1 Protection: The business is delivered at the same time on two completely disjoint channels/links (work Channel/link and Protection Channel/link) and selects the best quality signal at the receiving end.

L 1:1 Protection: The business is only delivered on the work channel/link, while the Protection channel/link does not transfer the service or transfer the lower priority business. When the work channel/link fails, the business is switched from the work Channel/link to the Protection Channel/link, while the lower priority service on the protection channel/link is discarded.

(2) Shared protection

L 1:n Protection (n>1): N working channel/link Sharing 1 protection channel/link. There is a low probability that the N-channel/link fails at the same time. If more than one work channel/link fails, protect the highest priority work Channel/link.

L M:N Protection (M

2. The recovery mechanism

A recovery mechanism is the mechanism by which a new connection is established through the rerouting mechanism in place of the failed connection, which consumes the redundant shared capacity of the network. Unlike protection, some or all of the connections that support the connection in a network change when a failure occurs that requires recovery.

As recovery leverages shared redundant capacity to create new connections instead of failed connections, it typically involves dynamic resource creation and routing calculations (routing calculations can be done in advance), thus requiring more time to switch than protection (typically hundreds of ms) and not suitable for high level business , but it is also because of the dynamic use of shared redundancy capacity, which makes the resource utilization ratio of the recovery mechanism higher, and only needs the redundant capacity of 50%~70%.

Depending on the time that routing calculations and resource allocations occur, recovery can be divided into preset and real-time two ways. In the preset mode, the recovery route or resource (time slot) is identified and stored in the corresponding node before the failure occurs, and the corresponding recovery route or resource information is invoked to cross connect directly when the fault occurs; In real time mode, After the fault occurred, the computing software did the routing calculation and resource allocation according to the resources of the network at that time, then completed the cross connection. The real-time way can reflect the current usage of network resources, so the provisioning of routing resources is more flexible than the preset method, but its recovery speed is slower than the preset way.

According to the business processing after the fault repair, the recovery mechanism can be divided into two kinds: return and not return. The way to return is to refer to the business from the protection connection back to the original work connection after the fault is repaired, this can be done to maintain the initial optimal design of the network; In contrast to the former, the business does not return to its initial working connection and remains above the protection connection, even if the failure is repaired. This does not require the node to save information about the initial work connection.

Iii. current status of protection and restoration functions

At present, there is a big gap between the protection and recovery function of Ason equipment in various factories. In my analysis, the main reasons for these gaps are two aspects: first, the protection of recovery standards have yet to be developed, the current standards are mainly put forward the definition of protection and the basic functional requirements, and the specific implementation of the method has not been stipulated, and for interconnection and interoperability involved in the problem has not been standardized Secondly, the protection recovery is closely related to the demand of the operators, and the different demands of different operators guide the research and development direction of the protection and restoration function of the manufacturers.

From the supported protection recovery types, see: 1+1 Protection and prefabricated/real-time restores are relatively simple and demanding, so they are the basic protection recovery mechanisms that most manufacturers can achieve at present, while 1:1 or m:n involve more complex strategies such as priority, business preemption and so on, and the demand is not clear, Most manufacturers are therefore not supported.

From the time Performance view: the protection mechanism, especially the switching time of the 1+1 protection, can be controlled within 50ms, while the recovery mechanism's business recovery time is very different, which is due to its own characteristics in the implementation of the detection mechanism, routing algorithm efficiency and preset degree (routing or Resource).

From the combination of protection recovery approach: this aspect should be the manufacturer in the protection of the restoration function of the most distinctive aspects. Permanent 1+1 Protection (when the failure to use the standby circuit at the same time to regenerate into another standby circuit), protection failure to restore, traditional ring protection/SNCP protection after failure to restore, the traditional ring protection/SNCP protection and Ason protection of the segmented combination, etc. However, a variety of combinations in order to provide more choices for operators, but also to the interconnection caused by the obstacles, the specificity of manufacturers will inevitably lead to a reduction in standardization.