Automatic Power Control
On a fiber, the power level may vary between channels. Over long distances and with multiple amplifications, these power level differences can reduce the quality of some channels. APC corrects the power level differences and ensures that power for different channels is according to the target power profile for the spectrum. APC compensates for the degradation of the network over time. APC activates if automatic link bringup is enabled.
Automatic Power Control (APC) is a network-level feature that is distributed among different nodes. An APC domain is a set of nodes that is controlled by the same instance of APC at the network level. An APC domain identifies a portion of the network that can be independently regulated. The source OLT node acts as the APC Manager or Domain Manager for all the nodes in the path. The subsequent nodes in the path act as APC agent nodes.
The manager node enables APC on agent nodes, monitors discrepancy, and initiates regulation if correction is required. To avoid large power fluctuations, APC adjusts power levels incrementally. APC performs power correction in steps of plus or minus 0.8 dB. This incremental correction continues until the optimal power level is reached.
Starting with R7.11.1, you can use APC as a span-level application by using span-mode APC.
APC is direction-specific. You can enable APC for each direction at the transmitting OLT node. The source node enables and controls different parameters in all ILA nodes on the path and the far-end OLT ingress EDFA.
Parameters configured by APC
This table lists the parameters that APC configures and controls in different nodes.
| Node | Parameters |
|---|---|
|
Transmitting OLT |
EDFA Gain EDFA Tilt VOA Attenuation WSS Attenuation |
| ILA |
EDFA Gain EDFA Tilt VOA Attenuation DGE Attenuation |
| Receiving OLT |
EDFA Gain EDFA Tilt WSS Attenuation |
When you enable APC, APC controls these parameters. APC overrides any manual configuration. When you disable APC, user configuration is applied.
Functions of APC
APC divides the C band spectrum into 32 equal parts. APC uses 33 frequencies across the C band to perform this division. We call these 33 frequencies, setpoints. Each setpoint is 150 GHz apart from the adjacent setpoints. You can configure a power profile across the spectrum using these setpoints. You can configure the target PSD for each OLT and ILA node on a link.
APC applies amplification and attenuation as required at channel level and composite signal level to ensure that the channels are at the target power level. You can configure the target power spectral densities for 33 points across the band. If you enable link tuner, link tuner sets the target PSDs for APC on all nodes in the path.
APC performs these functions:
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Monitors the current PSD against the target PSD for each channel (ASE and user channel) and changes the amplifier parameters including VOA, WSS, and DGE to achieve the target PSD.
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Detects optical network changes on the path and alters the amplifier parameters on the nearest nodes to compensate for the changes. APC performs these alterations in multiple steps.
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Collects measurements from other link nodes at the transmitting OLT to precisely locate optical network changes.
From Cisco IOS XR Release 7.9.1, NCS 1010 supports C+L band networks. Before Cisco IOS XR Release 7.9.1, APC did not start regulating the power levels in a link until the full topology was discovered by OSPF. From Cisco IOS XR Release 7.9.1, APC regulation begins as soon as it discovers any part of the topology. At a transmitting OLT, APC starts power correction at the OLT and subsequent ILA nodes even if the complete OLT-OLT link has not been discovered. When APC detects a partial topology, the NCS 1010 raises the PARTIAL-TOPOLOGY alarm. APC moves to BLOCKED state after regulation is complete.
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