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 |
|---|---|
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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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PSD regulation states of APC channels
The APC channel PSD regulation feature operates in these ways:
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Monitoring: The APC system periodically checks the Power Spectral Density (PSD) discrepancy for each channel.
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Trigger: If the measured discrepancy exceeds the configured PSD correction tolerance, the regulation process is initiated.
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Regulation action: The Line Controller (LC) applies changes to reduce the discrepancy below the defined tolerance, ensuring a flat spectrum before the Erbium-Doped Fiber Amplifier (EDFA) at the LINE port.
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Status states: During regulation, the APC status transitions through various states before reaching the final state, IDLE.
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Command usage: The show olc channel-apc controller Ots0/0/0/0 regulation-info command displays the LC state.
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State interpretation: When regulation is in progress, some displayed values may represent final values, while others may not yet be updated.
APC status and internal states
APC status refers to the current state of APC throughout the entire path.
Description of APC status
This table lists and describes the APC status.
| APC status | Description |
| BLOCKED |
APC moves to the BLOCKED state if:
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| PAUSED |
APC is paused using the apc-pause command. |
| IDLE | APC regulation has been completed successfully. All channels in the network have achieved the target PSD provided by the link tuner or configured by the user. |
| WORKING | When APC detects a discrepancy between the current and target PSD, it regulates to converge the power to the target PSD. |
| DISABLED | APC is disabled. |
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PARTIAL-TOPOLOGY NODE-BLOCKED |
APC has limited visibility. APC manager does not have visibility to the full OLT-OLT topology. APC manager tries to correct the power levels on the agent nodes that are reachable and after the regulation is complete, APC moves to BLOCKED state. |
Description of APC internal states
Internal state is the state of APC on each individual node.
This table lists and describes the internal states of APC.
| APC internal state | Description |
| DISCREPANCY | The APC manager flags an agent node which needs correction when there is a discrepancy between target PSD and current PSD. This state is temporary and lasts until APC starts power correction and goes into CORRECTING state. |
| CORRECTING | APC correction is in progress on the node. |
| OOR | APC-OUT-OF-RANGE condition is raised on an agent node when APC fails to regulate and achieve the target PSD power level because
the requested gain or attenuation setpoint cannot be set due to one of these conditions:
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| IDLE | APC regulation has been completed successfully. All channels in the network have achieved the target PSD, either provided by the link tuner or configured by the user. |
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BLOCKED |
APC is unable to perform for these reasons:
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View APC status and information
Use this task to verify whether APC is working, blocked, idle, or paused. You can also view detailed parameters such as target PSDs, amplifier gain, attenuation settings, and discrepancies between current and target power levels for each node in the APC domain.
Procedure
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Step 1 |
Use the show olc apc command to view the APC status. This sample shows the output of the show olc apc command when APC is in Centralized mode Example:This sample shows the output of the show olc apc command when APC is in span-mode. Example:For information about APC statuses and APC internal states, see APC status and internal states. This sample shows the output of the show olc apc command when OSRI has shut down an amplifier in the link. Example:This sample shows the output of the show olc apc command when APC is disabled locally on a node. Example:This sample shows the output of the show olc apc command when Gain Estimation is in progress on a node. Example:This sample shows the output of the show olc apc command when amplifier auto power reduction is enabled on a node. Example:This sample shows the output of the show olc apc command when band failure has occurred and the APC manager has visibility only to a partial topology. Example: |
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Step 2 |
Use the show olc apc-local command to view the local status of APC on each node. This command shows if APC is enabled or disabled on the node. This sample shows the output of theshow olc apc-local command. Example: |
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Step 3 |
Use the show olc apc-local target-psd-profile command to view the target PSDs configured for all the setpoints. This sample shows the output of the show olc apc-local target-psd-profile command on a C band node. The output also displays the PSD configuration source and indicates whether the target PSD source is the link tuner or a configuration. Example:This sample shows the output of the show olc apc-local target-psd-profile command on an L band node. Example: |
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Step 4 |
Use the show olc apc-local regulation-info command to view the detailed information about APC on each node. This command provides this information:
This command also provides detailed information on the channels:
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Step 5 |
Use the tx|rx keyword with the show olc apc-local regulation-info controller ots R/S/I/P command to view the APC information for only the Tx or Rx direction. This sample shows the output of theshow olc apc-local regulation-info command. Example:
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You can assess and monitor the power regulation and discrepancies across the network nodes for effective optical network management.
Configure the target PSDs
If you enable link tuner, it sets the target PSDs for APC on all nodes in the path.
You can configure the target power spectral densities at 33 points across the band. Each PSD value divides the spectrum into 150-GHz steps. APC uses the PSD value when a channel frequency matches a configured point. If not, APC calculates the target PSD for a channel based on the two nearest steps.
Procedure
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Step 1 |
Use the psd <1-33> value command to set the target PSDs for single-band for each node on a C-band network. This sample configuration sets the PSD value to 15 dBm or 12.5 GHz for setpoints 1 and 2. Example: |
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Step 2 |
(Only for NCS 1010) Use the dual-band-psd <1-33> value command to set the target PSDs for dual-band for each node on a C+L band network. This sample configuration sets the dual-band PSD values to -50 and -49 on setpoints 1 and 2 respectively, on the 0/0/0/0 controller. Example: |
The target PSD profiles are now configured for the selected band on all nodes in the path.
Disable centralized APC
Procedure
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Use the apc disable command to disable APC for a link on the transmitting OLT node. Example:
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User configuration is applied instead of APC. All setpoints are set to either configured values or default values.
Manage centralized APC
Use this procedure to manage APC by enabling and disabling APC domains.
Procedure
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Step 1 |
Use the apc enable command on the transmitting OLT node to enable APC for a link. Example: |
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Step 2 |
Use the apc pause command on the transmitting OLT node to modify the network without APC compensating for the changes. Example:
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Step 3 |
Use the apc-local [ RX | TX ] disable command on an ILA node to disable APC locally. Example:Consider a scenario where the headend OLT encounters a headless event. If power correction is required at agent nodes, the APC manager is unavailable to initiate regulation. When APC is enabled, adjustments cannot be performed, and user configuration of target-psd does not take effect. Disabling APC locally on an agent node allows manual adjustment of parameters. Use the apc-local disable command to disable APC on an agent node. |
Configure target drop PSD and minimum PSD
Use this task to manually configure the target PSD for drop ports. You can also set the minimum PSD threshold. These actions ensure that channel power levels meet the required target and maintain optimal channel quality across the network.
The link tuner does not set the target PSD for drop ports. The default target PSD for drop ports is –8.0 dBm/12.5 GHz. The device applies drop PSD configuration for channels with cross connect settings. Use the drop-psd command to set the desired drop PSD.
If the PSD of a channel with minimal attenuation at the amplifier input on an OLT is less than the minimum PSD, APC marks the channel as failed. APC then replaces the channel using the ASE source.The default minimum PSD is –24 dBm/2.5 GHz. Use the psd-min command to set the desired minimum PSD.
Procedure
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Step 1 |
Use the drop-psd command to set the desired drop PSD. This sample configuration sets the target PSD at drop ports to –25 dBm/12.5 GHz. Example: |
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Step 2 |
Use the psd-min command to set the desired minimum PSD. This sample configuration sets the minimum PSD to –25 dBm/12.5 GHz. Example: |
Channel power levels meet the required target power profile.
View patchcord loss and path loss
In a C+L band configuration, optical applications require data about loss between the LINE-TX port of the L-band device to the LINE-TX port of the C-band device to launch correct power into the transmission fiber.
This data, also known as path loss, is calculated from these components:
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patchcord loss between the LINE-TX port of the L-band device and the L-Band-RX port of the C-band device.
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insertion loss between the L-Band-RX port of the C-band device and the LINE-TX port of the C-band device.
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insertion loss due to the Raman modules inside the C-band device.
Procedure
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Step 1 |
Use the show olc partner-band-loss command to view the patchcord loss and path loss values. This sample is an output of the show olc partner-band-loss when executed on a C-band device. Example:This sample is an output of the show olc partner-band-loss when executed on a L-band device. |
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Step 2 |
Use the show olc partner-band-loss controller ots R/S/I/P command to view the patchcord loss and path loss values for individual controllers. This sample is an output of the show olc partner-band-loss controller ots R/S/I/P when executed on a C-band device. Example:This sample is an output of the show olc partner-band-loss controller ots R/S/I/P when executed on a L-band device. |
You can accurately monitor and manage optical power levels in the network.
Configure APC alarm hold-off timer and discrepancy threshold
Use this task to configure APC alarm sensitivity and timing. You can avoid false or premature alarms during APC.
Procedure
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Step 1 |
Use the apc-alarm-hold-off-timer time command to configure the timer. You can configure the time interval that must pass after APC detects a discrepancy before the APC-TARGET-PSD-NOT-MET alarm is raised. The default value is 30 seconds. This sample configuration sets the APC alarm hold-off timer to 45 seconds. Example: |
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Step 2 |
Use the apc-alarm-discrepancy-threshold discrepancycommand to configure the discrepancy threshold. You can configure the allowed discrepancy threshold before APC-TARGET-PSD-NOT-MET alarm is raised. The default value is 1 dB. This sample configuration sets the APC alarm discrepancy threshold to 1.5 dB. Example: |
The APC alarm parameters are configured, reducing false or premature alarms during APC operation.
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