By Li Bo
A s network technologies and smart terminals evolve, IP services have gradually become the killer app for MAN architecture, with large-granularity services steadily gaining in importance. Both of these trends require metropolitan transport networks (MTNs) to accommodate IP transformation, which promises capacity, granularity, and reliability. This makes OTN the inevitable choice for ultra-broadband MAN construction, thanks to its cost-effective bandwidth and ability to support flexible scheduling of fine-grained services.
However, OTN introduction into an SDH network presents huge O&M challenges; the O&M workload increases significantly, while equipment management, service provisioning, troubleshooting, and resource management are also very different. Legacy O&M procedures are modestly automated and will therefore prove inadequate for the upkeep of complicated OTN infrastructure.
O&M complexities for OTN architecture
First, OTN devices themselves are more complicated. A piece of SDH equipment is basically a box of optical-fiber connections, making its O&M more easy, while an OTN device will have numerous subracks within, with fiber inputs & outputs running from each subrack along different signal routes. When a fault occurs, it is virtually impossible to determine if its origin is an internal or external fiber.
OTN architecture also has multiple service layers, which complicates parameter configuration. Compared to the one-layer service model for SDH, which basically performs add/drop multiplexing of data frames, the OTN service model has six layers, which is why it takes at least ten times as long to configure a service for OTN.
A massive number of alarms are generated by OTN networks, with separate ones for each service layer. However, many are invalid, which makes it all the more difficult to determine and troubleshoot the genuines. If an optical fiber is severed, all the services it bears will be affected, leading to thousands of alarms. It typically takes several hours to one day to find the needle in this haystack.
OTN architecture is also opaque, especially when it comes to resource utilization, leading to wastage and idling. The standard week spent on service activation and provisioning would be at least two for OTN, thanks to the "crawling around in the dark" that is involved. If network resources prove inadequate, time will be expended on expansion.
The aforementioned complexities require more from the O&M team, in terms of skills & knowledge. Team members have to spend more of their time training, which is a drag on efficiency.
OTN capability, SDH simplicity
To address the aforementioned challenges, Huawei has announced a solution that simplifies the O&M process for OTN by making it more like the SDH process; this is accomplished through a network management system (NMS).
OTN equipment transparency
To deal with the internal complexities of OTN equipment, the NMS provides signal flowcharts, which provide a clear view of the service configurations within OTN devices; these may include optical-fiber connections between various boards & subracks as well as alarm and wavelength information. In other words, personnel need no longer physically check the equipment in question for relevant information.
A certain European operator had over 5,000 sets of WDM equipment on its MAN. Their biggest O&M headache had been dealing with incorrect optical-fiber connections or improperly plugged-in boards. Such faults took a long time to troubleshoot, resulting in long service interruptions, totaling an average of more than five hours per month.
Thanks to the Huawei NMS flowchart functionality, these types of faults have almost disappeared. Even when they do occur, they are largely resolved before complaints roll in.
E2E service scheduling
The NMS packages and streamlines the original six OTN layers (OTS, OMS, Och, OTUk, ODUk, and Client) into two layers (Och and Client). Users need only create Och and Client paths manually to complete OTN service provisioning. As for SDH, O&M personnel need only click the source and sink nodes on the NMS graphic interface, for which the routes between and parameters for are calculated automatically. This enables end-to-end O&M on par with what had been previously possible for SDH.
A certain large bandwidth-lease operator activated an average of 150 wavelength services per month in 2011 and that figure is expected to be over 300 in 2012 (over 15 services per business day). If O&M personnel configure new services for one layer after another, they could only activate five per day. Thanks to the simplified service model for OTN provided by Huawei, the operator has seen its service provisioning efficiency increase six fold to 30 services per business day.
Timely fault location
By analyzing the relationships between the six OTN service layers, Huawei has determined the correlations between alarms from these layers. It has also established the principles governing their analysis, which are employed in its NMS. The system can also quickly identify the alarms that have real impact on services and prioritize their troubleshooting accordingly.
Another operator in Europe had previously employed its own OSS for fault handling. When a network fault occurred, an alarm was reported to the OSS, through which O&M personnel would locate and resolve the fault.
In 2010, OTN was introduced into its MAN, with its network services ranging from the optical to the electrical layer. According to network tests, more than 1,000 alarms were reported to the OSS when optical-fiber breakage occurred. This made it impossible for the O&M personnel to locate such faults through the OSS, throwing the entire network into chaos. After deployment of Huawei NMS, breakage alarms have been reduced to roughly a dozen; those that do occur can be resolved more rapidly now that false alarms are much more rare.
Network resource conservation
Huawei NMS also enables management of network bandwidth resources via virtual resource pooling, while outputting bandwidth usage statistics that encompass different service granularities and dimensions. In this way, OTN resource utilization is visualized, which cuts down the time spent on service activation to a few minutes, while making capacity expansions more timely.
Huawei NMS makes OTN O&M as simple & efficient as that for SDH, while leveling the learning curve for O&M personnel, which ensures a smooth transition now and into the future.