Automatic Link Calibration Overview
From Cisco IOS XR Release 7.11.1, NCS 1020 supports Automatic Link Calibration (ALC). ALC is an alternate to automatic link bring-up. When using ALC, the optical applications except APC remain idle when operating conditions change. After turning up the network, ALC saves optical parameters on all nodes as a baseline. ALC saves the following parameters as a baseline:
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Span loss data
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APC data
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C-band and OSC power measurements
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Link tuner data
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Gain estimator data
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OCM data
ALC is a link level application. ALC is initiated by the ALC manager which is the source OLT. The manager manages the downstream link. Similarly, the OLT at the other end of the link manages the upstream link.
ALC is a nework bring up operation. Link calibration is traffic impacting. When you are turning up a link
Prerequisites for ALC
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OLT to OLT Topology: OLT-OLT topology must be up and running from end to end. You should not have a Loss of Signal-Path (LOS-P) or a Loss of Channel (LOC) alarm on any node.
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Channel Map Configuration: You must configure channel maps on all nodes to align all nodes with the correct frequencies. Use hw-module location 0/0/NXR0 grid-mode flex[inline-ampli | terminal-ampli] channel-ididcentre-freqfrequencywidthwidth command to configure the channel map for all 32 channels.
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XC Creation: You must create Optical Cross-Connects (OXCs) on OLT nodes. These OXCs should cover the entire spectrum to ensure the correct routing of optical signals.
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Application Modes: You must set all applications to either manual mode or disabled mode, except for Automatic Power Control (APC). We recommend, all control loop applications should be in manual mode.
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Span-mode APC: You must configure APC in span mode on all nodes.
 Note |
If you use Cisco Optical Network Planner to design your network, the prerequisite configurations can be imported to the NCS 1020 nodes as an XML file. See Design and Analyze Networks for more information. |
ALC Process
The following sequence of events takes palce when ALC is initiated.
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The source Optical Line Terminal (OLT) starts the ALC procedure in the transmitting direction. The source OLT is the ALC manager for this direction. The ALC manager raises the Automatic-link-calibration procedure is running to indicate that the process is running.
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The OLT drops all user channels and forces the ASE channels from the Noise Loader (NL). These ASE channels are used for the ALC calibration.
Note
The Automatic Link Calibration (ALC) process needs a stable and reliable C-band source which covers entire spectrum. When the ALC process begins, it drops all active user channels and forces ASE noise channels from the noise loader. This is done to ensure that the calibration isn't affected by user traffic, which can fluctuate and cause inconsistencies. This allows the ALC process to accurately calibrate the power levels across the entire C-band spectrum, ensuring optimal performance of the optical network.
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ALC initiates an OTDR scan on the receive (Rx) and transmit (Tx) interfaces in the downstream direction. After the scan is completed, the location of the sor file is saved.
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ALC enables the Automatic Power Control (APC), Link Tuner, and Gain Estimator applications to run in parallel.
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The Power Spectral Density (PSD) and gain are initially calculated using the Optical Supervisory Channel (OSC) span loss. This step is temporary and is used to bring the C-band up.
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Once the C-band is up, the C-band based span loss is measured and the PSD and Gain are recalculated.
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Using the PSD computed by the LinkTuner and the gain-range computed by the Gain Estimator, the APC regulates the channels. Once this is completed, the APC moves to the IDLE state.
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After APC moves to the IDLE state on all nodes, ALC initiates the baseline.
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After saving the optical parameters, ALC completes the procedure and the ALC status changes to IDLE.
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The ALC Manager clears the Automatic-link-calibration procedure is runningalarm.
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The ALC manager rleases the ASE channels, and user channels become active.
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ALC changes APC mode from Centralized-mode to Span-mode.
Restrictions for ALC
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ALC impacts network traffic, and the time it takes to converge depends on the number of nodes in the network.
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ALC does not support Raman networks.
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ALC saves baseline data only if the procedure completes successfully. If the ALC procedure fails due to network errors, the collected baseline data is not saved.
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Do not enable or disable any optical applications or initiate gain estimator after ALC is complete.
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Do not initiate ALC on a link without cross connect configuration across the entire spectrum.
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Baseline data is preserved across reloads.
Note
To clear the baseline data, you must either perform a commit replace on the respective nodes or configure the no option of all the applications, for example, no apc-span-mode RX and no apc-span-mode TX to clear the APC baseline data on a node.
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