In the optical communication field, the OTN incorporates the operatability and manageability of a Synchronous Digital Hierarchy/Synchronous Optical Network (SDH/SONET) as well as the large capacity of a Wavelength Division multiplexing (WDM) network, and gradually becomes an underlying network for optical communication systems. The OTN defines a layered network model. An optical layer includes an Optical Transport Section (OTS) layer, an Optical Multiplex Section (OMS) layer and an Optical Channel (OCH) layer. In an electrical layer network, an Optical Channel Transmission Unit (OTU), an Optical Channel Data Unit (ODU) and an Optical Channel Payload Unit (OPU) are defined. Specifically, the OPU is used to carry client traffic, the ODU defines management and maintenance functions required in end-to-end transmission through an optical channel, and the OUT provides management and maintenance functions required in transmission of an ODU signal. The OTN has a significant advantage over the SDH/SONET in that the OTN provides 6 levels of Tandem Concatenation Monitoring (TCM) which provide functions of concatenation monitoring and failure locating in a multi-operator application context. The TCM involves functions such as connectivity monitoring, signal quality monitoring, failure and alarm conveying.
A Trail Trace Identifier (TTI) is a 64-byte string including a source node identifier and a destination node identifier for OTN frame transmission over the network. The TTI may be used to determine whether or not a frame signal arrives at an output port of a designated destination node from a designated source node in the network. A Bit Interleaved Parity (BIP-8) is used for traffic quality monitoring. As specified in the G.709, a source end performs a bit parity check on an OPU field of the Nth frame by using the BIP-8, and stores a check result into an BIP-8 field of the TCM of the (N+2)th frame. A destination end performs the same bit parity check on the OPU field, and compares a parity check result with the BIP-8 value extracted from the corresponding location. If the two values are identical, it is indicated that no error has been introduced in the network between the source end and the destination end; otherwise it is indicated that errors have been introduced in the network through which the traffic goes. In addition, the TCM defines a 4-bit Backward Error Indication (BEI) field used to convey errors detected in the network to the upstream source node. What is transferred by the BEI is the count of interleaved-bit blocks that have been detected in error at the destination end. The TCM also defines a 1-bit Backward Defect Indication (BDI) used to transfer a signal fail status of the network to the upstream source end, so that the source end may detect a failure in the network.
In the conventional technical solution, the G.709 defines 6 levels of TCMs. The multiple levels of TCMs are used to monitor status of the interior of each sub-network, and to locate a failure. Up to 6 levels of TCM may be performed simultaneously on a network node. In a conventional method, a centralized Network management system (NM system, and NM for short) assigns a corresponding TCM to each of the nodes in the entire network for monitoring, and then each of the nodes reports the network status information detected through the TCM to the NM. The NM in turn determines network failure information.
FIG. 1 is an application example in which the NM assigns TCM levels centrally, and illustrates a network configuration scenario as below: there is a large sub-network between nodes A1 and A2, with the nodes A1 and A2 as boundaries of the sub-network; and client traffic enters the sub-network from the node A1/A2, goes through the sub-network, and leaves the sub-network from the node A2/A1. There are multiple sub-networks included in the A1-A2 sub-network, such as the sub-networks respectively between A1 and A6, A1 and A4, as well as A3 and A5, as shown in FIG. 1, and these sub-networks may be constituted with devices of different vendors managed by the same operator. Respective sub-networks are also formed between B1 and B2, C2 and C2, as well as D1 and D2, and these sub-networks may be constituted with different devices managed by different operators. Thus, the client traffic goes through the sub-networks sequentially after entering the sub-network between A1 and A2 from the boundary node A1, and then leaves the sub-network from the boundary node A2. In such a multi-operator/multi-vendor network context, services provided by each of the sub-networks need to be monitored to allow precise locating of a failure. The NM assigns a TCM level to each of the sub-networks respectively according to the condition of the entire network, as illustrated in FIG. 1. The sub-network between A1 and A2 is monitored at TCM1, the sub-network between A1 and A6 is monitored at TCM2, the sub-network between A1 and A4 is monitored at TCM3, the sub-network between A4 and A5 is monitored at TCM4, the sub-network between B1 and B2 is monitored at TCM2, the sub-network between C1 and C2 is monitored at TCM3, and the sub-network between D1 and D2 is monitored at TCM2. The sub-network nodes report their detected network performance data to the NM, and the NM determines service performance of the individual sub-networks according to TTI, BIP-8, BEI, BDI, etc., as reported from the sub-networks corresponding to the respective TCMs.
In the prior art, the NM centrally configures at which level of TCM the information should be monitored on each sub-network and each node. This may not lead to significant disadvantages in the case of a small scale of the network and relatively simple networking context. However, as the openness of the network is improved and both the scale and the complexity of the network increase continuously, the technique solution that the NM fixedly assigns a TCM level at which each sub-network or each node monitors has a limited flexibility and increases the complexity of configuration and processing. Especially in the case that a TCM level has to be added or deleted due to a change in network distribution, the NM is required to reconfigure the TCM level for each network node, and to determine network failure information by querying new TCM performance data, resulting in complex processing.
FIG. 2 is an example in which the NM reassigns TCMs due to a change in network topology/sub-network monitoring. When a change in the network distribution occurs, i.e., a change in the B1-B2 sub-network segment as shown in FIG. 2 occurs, the D1-D2 sub-network segment can not be monitored at TCM2 if the B1-B2 sub-network is still monitored at TCM2. At this point, the NM is required to reassign TCM levels at which the individual sub-networks and network nodes are monitored. In this example, the NM assigns TCM4 to the D1-D2 sub-network for monitoring network service quality. The NM analyzes network service quality information reported from the respective network nodes according to the updated TCM levels, and then locates a failure. Thus, each time a change in network distribution or sub-network partition occurs, it is required to reconfigure the TCM levels and re-extract the performance data, resulting in complex processing.
Moreover, in addition to being downloaded to each sub-network, TCM level assignment information from the NM has to be downloaded to each network element node, and the NM may receive from each network element node only TCM monitored information (including TTI Identifier Mismatch (TIM) alarm information, BIP-8 error statistics, BEI error statistics, a BDI backward defect indication, etc.). Such monitoring information may not indicate which TCM level the information belongs to and which pair of network element nodes the information is processed by. Which TCM level the TCM monitored information belongs to has to be acquired by the NM in a unidirectional control.