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What is OTN (Optical Transport Network)?

OTN: Optical Transport Network is a type of network as defined by the standardization arm of the International Telecommunication Union. It transmits, multiplexes, routes, monitors, and guarantees performance metrics and survivability of service signals in the optical domain.

OTN uses WDM technology as its foundation, ensuring its large transmission capacity while adding the powerful operation, maintenance, management and provisioning capabilities of Synchronous Digital Hierarchy.

Compared to traditional SDH, OTN has the following advantages.

1.Scalable capacity, crossover capacity can be expanded to tens of Tbits/s.

2.Transparency of customer signals, including network load and clock information, etc.

3.Asynchronous mapping eliminates the limitation of network-wide synchronization, enhances the error correction capability of forward error correction (FEC), simplifies system design, and reduces network costs.

4.Up to 6 levels of TCM monitoring and management capabilities.

Compared to traditional WDM:

1.Effective monitoring capabilities - OAM&P and network survivability capabilities.

2.Flexible optical/electrical layer scheduling capabilities and carrier-grade, manageable and operational networking capabilities.

It can be said to have all the advantages of both SDH and WDM network technologies.

The application of OTN also increases the flexibility of network configuration and can provide network protection and improve security. In addition to reducing network construction costs, the adoption of OTN can enhance the manageability of WDM equipment, enables fast fault location, offer service protection, facilitate rapid service implementation, support network segmentation, reduce spare parts types, provide investment protection, and offer comprehensive service support capabilities.

WDM technology: DWDM is like a highway (very large capacity, ultra-high speed, ultra-long distance transmission)

OTN technology: OTN is like a highway with overpasses, using WDM technology, OTN overhead, OTN cross.

WDM is equivalent to a subset of OTN, and the intelligent control plane is equivalent to traffic lights and traffic management systems.

Protection principle of OTN.

During normal operation, only the cross-connections corresponding to the working circuit board take effect. When a failure occurs in the working channel, the cross-connections of the working circuit board are disconnected and the cross-connections corresponding to the protection circuit board become active, and the business signals then operate on the protection channel.

When the working route is restored to normal, the service signal can be restored to the cross-connection corresponding to the specified line board according to the restoration type pre-configured on the network manager.

Comparison of two protection schemes for OLP OTN

OLP’s Advantages:

1.Fast deployment on top of existing routes, requiring only the replacement of expansion cards and addition of protection cards.

2.Cost-effective, no need to move current equipment.

3.Line dual-core failure ensures 100% automatic routing.


For the current network environment, conditions such as increased line attenuation and single-core interruptions are not highly sensitive for automatic switching. Therefore, manual intervention and on-duty personnel are required to make switching decisions according to the situation.

OTN Advantages:

1.Configure the conditions for routing switching according to the trigger type (e.g. LOS, LOF, LOM, AIS, TTI, LCK, etc.).

2.Meet the trigger condition 100% switch to the backup route.

3.High reliability and no need for manning.


1.The equipment needs to be replaced, which is time-consuming and labor-intensive, and there is currently not enough space in the cabinet.

2.High cost.

OTN inherits many of the advantages of SDH and WDM technologies as the dominant technology for optical transport networks. OTN technology demonstrates both the technological leap forward in optical networks and the business opportunities for operators and service providers. OTN networks can provide operators with unprecedented flexibility in architecture, customer irrelevance and service differentiation in the era of data/transport convergence while fully utilizing the transmission infrastructure.

Optical Transport Network