proNX Optical Director Span Loss Management, Alarms and Metrics

Span Loss Management

What is Span Loss

Span loss can be defined as the total system attenuation between line ports of adjacent TCX1000 Series devices in the network. This includes the loss from the transmission fiber and any additional losses from optical connections within the path. An example of additional losses is the attenuation introduced when optical patch panels are used to manage cabling within an installation.

The proNX Optical Director measures the span loss by reading the output power (dBm) at the Line Out port at one end of the fiber and the input power (dBm) at Line In port at the other end of the fiber. These measurements are continuously read at both ends of the span and reported to the proNX Optical Director. After proNX Optical Director reads these power levels, it calculates the span loss and adjusts internal set points on one or both TCX1000 Series devices to compensate for the loss while minimizing the added noise. For example, based on the measured span loss, the proNX Optical Director may determine that the input level on the downstream device is too low. In this case, proNX Optical Director adjusts the output level on the Line Out port of the local TCX1000 Series device to compensate for the span loss.

Span loss management is performed on all links between these TCX1000 devices:

• TCX1000-RDM20 to TCX1000-RDM20

• TCX1000-RDM20 to TCX1000-ILA

• TCX1000-ILA to TCX1000-ILA

Short Span Support

On short spans, if the measured span loss is such that the maximum input powers to the downstream TCX1000 Series device may be exceeded, the span control feature adjusts the launch power at the upstream site to automatically compensate. In this way, the span control seamlessly manages span losses as low as 0 dB.

Span Control Over Time

The span control continuously monitors the span loss between the line ports of the TCX1000-RDM20 and TCX1000-ILA and adjusts the internal set points to compensate for the loss, while adding the minimum amount of noise. In this way the span control automatically adjusts for variations in span loss over time, for example, from seasonal variations in loss or for additional losses added after a cable repair.

How Span Loss Out-Of-Range (OOR) Alarms Work

When a span is first brought into service, the span control configures the internal components of the TCX1000 Series devices to be optimized for that loss. In cases of very large changes in span loss, the optimization cannot be maintained over the full operating specification of the managed device with full optical performance. The proNX Optical Director provides a Span Loss Out-Of-Range (OOR) alarm, which indicates that either the TCX1000 Series device is being operated outside of specification or that the internal configuration is no longer optimized.

If the measured span loss is outside the allowable range for the managed device, a Span Loss Out-Of-Range (OOR) alarm is raised and logged by the proNX Optical Director. The proNX Optical Director span loss management feature ensures that the OOR alarm is unlikely to be raised except in the rare event that the span loss changes by a very large amount after initial commissioning.

For example, let us assume that we have two TCX1000 Series devices connected point-to-point. The local device is “device A” and the remote device is “device B. The proNX Optical director reads the output dBm power level at the device A transmit port (Line Out) and the dBm power level received at the device B Line In port. If, after subtracting the receive line power measured at device B from the transmit line power measured at device A, the resulting value is not within the allowable range, a Span Loss Out-of-Range alarm is raised in proNX Optical Director:

• Span Loss Out-Of-Range — This alarm is raised at the receive end Line In port on device B.

In the rare event that the OOR alarm is raised, you can remotely re-optimize the span by toggling the administrative state of the line port by setting the administrative state to Out-of-Service and then back to In-Service.

If the reported span loss is outside of the TCX1000 device specification, the optical connections in the span should be verified to identify why the accumulated losses are now out of range.

proNX Optical Director Span Loss Performance Metrics

The span loss is always measured within the OSC-band (1510 nm), which allows for zero-lambda turn-up, whereby the optical path between TCX Series sites is confirmed without having to turn up any wavelength services. This is valuable during installation. When wavelength services are provisioned on the link, both the OMS Span Loss and the OSC Span Loss are reported as performance metrics in the proNX Optical Director as described in Table 1.