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Understanding Traffic Shaping via H-QoS
Traffic shaping is used to reduce traffic burstiness for an outgoing interface by delaying some or all frames. It is commonly applied at the network edges to control traffic entering the network. With shaping, you can control the volume of traffic being sent into a network during a specified period (bandwidth throttling) or the maximum rate at which the traffic is sent (rate limiting). Traffic shaping can be performed in both directions: from the UNI to the network and from the network to the UNI.
With the Cisco Provider Connectivity Assurance Sensor GT (formerly Skylight performance element: GT), traffic shaping is achieved through Hierarchical Quality of Service. Quality of Service (QoS) is a way to optimize and/or guarantee traffic performance by differentiating between high- and lower-priority traffic and treating each differently. Traffic is differentiated by means of its assigned Class of Service, based on the value of the PCP field in its Ethernet frames. With QoS, the latency of high-priority traffic is improved through accelerated transmission to the network. Hierarchical QoS (H-QoS) is an extension of traditional QoS because it increases the usable bandwidth for lower classes of services by recycling the unused bandwidth (tokens) left over from higher classes of service. Multiple levels of Class of Service can be created:
- The first level is quality of service per Class of Service for a single customer service.
- The second level is quality of service for all Classes of Service for a single customer service.*
Because of the possibility to share bandwidth between classes of services, H-QoS is the preferred approach over traditional QoS. The Assurance Sensor GT includes an MEF 10.3 H-QoS bandwidth sharing implementation.
In the figure below, three classes of service share the same total bandwidth. Bandwidth sharing enables bandwidth to be handed down from higher classes of service to lower classes of service.
In this example of MEF token sharing, a coupling flag (CF) is used to share unused bandwidth (shown as a dotted line) from either Excess Information Rate (EIR) traffic or Committed Information Rate (CIR) traffic with a lower Class of Service. The bandwidth profile algorithm that enables sharing unused bandwidth between flows inside an EVC is defined by the MEF 10.3 (the MEF uses the term envelope).
Setting Up H-QoS
Implementing H-QoS involves multiple configuration tasks, as listed below:
- Configure queues to handle the unit’s H-QoS traffic
- Create queuing profiles for each port or LAG on the unit
- Create envelopes (EVC), which define MEF 10.3 token sharing between flows
- Create a policy to refer to a queue profile that maps traffic on a queue
Note: Before you begin, you must ensure that you have pre-determined
how many queues you plan to implement, as well as the parameters of
each.
Understanding BLUE
The BLUE algorithm is used by the Assurance Sensor GT's shapers for queue management. BLUE is an enhancement to the RED congestion avoidance algorithm; it offers the same benefits as RED and provides similar queue monitoring. The main difference between BLUE and RED is that BLUE also uses the queue packet loss and utilization history. Its use of a drop probability is more friendly with TCP global synchronization and reduces the number of TCP retransmissions.
Each shaper uses BLUE to manage queues based on link use. It maintains a marking probability (pm) that is used to either mark or drop the frames. If the queue is continually dropping the frames, pm is increased by the factor d* If the queue is empty or link is idle, pm is decreased by the factor d2.
Note: The value of d1 should be set significantly larger than that of d* This is because link is underused when congestion management is either too aggressive or too conservative, but frame loss occurs only when congestion management is too conservative.
BLUE uses also freeze_time, which determines the time interval between two successive updates of pm. It allows the changes in the marking probability to take effect before the value is updated again.
The BLUE algorithm is expressed as follows:
Upon Qlen > L1) event:
if ( ( now - last_update) > freeze_time )
pm := pm + d1
last_update := now
Upon Qlen < L2event:
if ( ( now - last_update) > freeze_time)
pm := pm - d2
last_update := now
To disable the BLUE algorithm
You might need to disable BLUE if your test equipment does not support it.
Access the page Traffic ▶ Shaping ▶ Port ▶ Shaper.
The Traffic Shaping Port Shaper Configuration page is displayed.Click the traffic shaper Name to edit its settings.
Remove the check mark from the Enable box, then click Apply.
Configuring Queues for H-QoS
The Assurance Sensor GT has six dedicated queues per port, as well as 12 user assignable queues. When in LAG mode, the queues dedicated to the LAG’s ports are unavailable because the LAG’s own queues are used instead.
Definitions: RPTQ stands for Ring Pass Through Queue. ADQ stands for Adequate Queuing Profile.
Note: You do not have to configure a queue for H-QoS if you do not plan to use the queue..
To configure queues for H-QoS
Access the page Traffic ▶ Shaping ▶ Queue ▶ Configuration.
The Traffic Shaping Queue Configuration page opens. All the unit’s queues are listed in a grid.Select a queue from the list to configure by clicking it.
The queue’s details are displayed.Use the information in the table below to configure the queue for H-QoS, then click Apply.
For more information on specific parameters, refer to the following table.
Queue Settings (Traffic ▶ Shaping ▶ Queue ▶ Configuration)
Parameter | Description |
---|---|
Outgoing Port | Traffic from this queue will egress on the port specified here. |
Type | The type of queue is displayed here Available options are: - User-assignable -Dedicated |
Name | The name assigned to this shaper |
Queue Scheduling | |
Priority (0 to 7) | Make a selection from the drop-down list to assign a strict scheduling priority to this queue: 7 is the highest and 0 the lowest priority. Note: When several queues have the same priority, scheduling is carried out in a round-robin fashion. |
Color | Make a selection from the drop-down list to assign a queue scheduling color to this queue. Queues without an enabled shaper can have a CIR or EIR priority. When the queue scheduling color is set to green, the queue priority is configured for CIR scheduling; when the queue scheduling color is set to yellow, the queue priority is configured for EIR scheduling. |
Bandwidth Profile Parameters | |
Shaping State | Make a selection from the drop-down list to enable or disable the shaper. The rate information you provide in this page is applied to control traffic flow. Note: The BLUE and queue scheduling features remain functional when the shaper is disabled. |
Shaping Mode | The shaping mode determines whether the queue's bandwidth profile action is performed on the frames as they enter the unit (ingress) or after an EVC mapping action is applied by a traffic policy (egress). For example, if a traffic policy is configured to push a VLAN tag, setting the shaping mode to Ingress will apply the bandwidth profile before the VLAN tag is pushed. Setting the shaping mode to Egress will apply the bandwidth profile to the traffic after the VLAN tag is pushed. Make a selection from the drop-down list to indicate either ingress or egress shaping. |
CIR Committed Information Rate | The average shaping rate of green frames, expressed as a multiple of 125 kbps This is the shaper's average output rate. |
Maximum CIR | The maximum CIR, expressed in kbps, that the shaper can achieve by using the shared tokens from its envelope. |
CBS Committed Burst Size | The shaping burst of green frames, expressed as a multiple of 1 KiB (1024 bytes). Acceptable values range from 1 to 2047 KiB. |
EIR Excess Information Rate | The average shaping rate of yellow frames, expressed as a multiple of 125 kbps This is the shaper's average output rate. |
Maximum EIR | The maximum EIR, expressed in kbps, that the shaper can achieve by using the shared tokens from its envelope. |
EBS Excess Burst Size | The shaping burst of yellow frames, expressed as a multiple of 1 KiB (1024 bytes) Acceptable values range from 1 to 2047 KiB. |
Coupling Flag | Enable this check box to allow overflow tokens not used for Service Frames declared Green can be used as Yellow tokens. |
Queue Management Parameters | |
Maximum Queue Size | The buffer's size, expressed in KiB (1024 bytes) Acceptable values range from 16 KiB to 1920 KiB. The Maximum Queue Size must be greater than the Yellow Threshold value. |
Yellow Threshold | When the queue length reaches this threshold, tail-dropping is performed on new packets with yellow marking. Acceptable values range from 16 KiB to the Maximum Queue Size value indicated above. |
BLUE State | Select to enable the BLUE queue management algorithm. The buffer is used to queue frames for later transmission. If the BLUE state is enabled, congestion management is ruled primarily by the BLUE queue management algorithm. Otherwise, it is managed through simple tail-drops. |
BLUE Queue Full Threshold | Once the queue fills to the specified percentage, the marking probability will be increased. The current range is from 5 to * The Blue Queue Full Threshold must be equal or greater than the Blue Queue Empty Threshold. |
BLUE Queue Empty Threshold | Once the queue empties to the specified percentage, the marking probability will be decreased. The current range is from 5 to * The Blue Queue Empty Threshold must be less than the Blue Queue Full Threshold. |
BLUE Marking Probability Freeze Time | This value determines the minimum interval time, expressed in microseconds (in increments of 10, between two successive updates of marking probability. Maximum of 655350 µs |
BLUE Marking Probability Increment | The marking probability is incremented by this value (expressed as a step percentage) in the event of a buffer overflow. Note: If this parameter is set to 0, the BLUE algorithm is disabled. Note: The percentage value you enter here is only an approximation; the actual configured value appears to the right of this field. Maximum of approximately 25% |
BLUE Marking Probability Decrement | The marking probability is decremented by this value (expressed as a step percentage) if the link is idle. Note: The percentage value you enter here is only an approximation; the actual configured value appears to the right of this field. Maximum of approximately 25% |
Viewing Traffic Shaping Queue Statistics
You can view a summary and detailed statistics for each traffic-shaping queue.
To view a summary of statistics for all traffic-shaping queues
- Access the page Traffic ▶ Shaping ▶ Queue ▶ Statistics.
The Traffic Shaping Queue Statistics page opens. All the unit’s queues are listed in a grid.
For more information on specific parameters, refer to the following table.
Tips: To edit a specific queue or view its details, select the queue from the list by clicking it. To clear the statistics in the Traffic Shaping Queue Statistics page, click the small broom icon on the right side of the table header.
Traffic Shaping Queue Statistics (Traffic ▶ Shaping ▶ Queue ▶ Statistics)
Parameter | Description |
---|---|
Name | The name assigned to this shaping queue. |
Port | The name of the port associated with this queue. |
Forward | The total number of frames that have been forwarded by this queue. This value includes frames counted as: Green forward no delay Yellow forward no delay Green forward with delay Yellow forward with delay |
Discard | The total number of frames that have been discarded by this queue. This value includes frames counted as: Green Discard full Yellow Discard full |
Discard-BLUE | The total number of frames that have been discarded by the queue management algorithm, BLUE. This value includes frames counted as: Green Discard BLUE Yellow Discard BLUE |
CIR Compliant | The total number of frames that have been forwarded by this shaper using the CIR bucket |
EIR Compliant | The total number of frames that have been forwarded by this shaper using the EIR bucket |
You can view a summary and detailed statistics for each traffic-shaping queue.
To view detailed statistics for a traffic-shaping queue
Access the page Traffic ▶ Shaping ▶ Queue ▶ Statistics.
The Traffic Shaping Queue Statistics page opens. All the unit’s queues are listed in a grid.Select the queue from the list whose statistics you wish to view by clicking it.
The queue’s details are displayed. For more information on specific parameters, refer to the following table.
Tips: To clear the statistics in the Traffic Shaping Queue Statistics page, click the Clear button located above the queue details.
To obtain the latest statistics from the unit, click the Refresh button located beside the Clear button.
Select the Poll Every n Seconds box and enter the number of seconds between each time the statistics are automatically refreshed.
Traffic Shaping Queue Detailed Statistics (Traffic ▶ Shaping ▶ Queue ▶ Statistics)
Parameter | Description |
---|---|
Name | The name assigned to this shaping queue |
Port | Name of the port associated with this queue |
Green Forward No Delay | The total number of green frames/bytes in the queue when the queue is near empty, i.e., the green frames/bytes that can be dropped from the queue without delay |
Yellow Forward No Delay | The total number of yellow frames/bytes in the queue when the queue is near empty, i.e., the yellow frames/bytes that can be dropped from the queue without delay |
Green Forward With Delay | The total number of green frames/bytes in the queue when the queue is not empty, i.e., the green frames/bytes that will be dropped from the queue with delay |
Yellow Forward With Delay | The total number of yellow frames/bytes in the queue when the queue is not empty, i.e., the yellow frames/bytes that will be dropped from the queue with delay |
Green Discard Full | The total number of green frames/bytes that have been discarded by this queue |
Yellow Discard Full | The total number of yellow frames/bytes that have been discarded by this queue |
Green Discard BLUE | The total number of green frames/bytes that have been discarded by the queue management algorithm, BLUE |
Yellow Discard BLUE | The total number of yellow frames/bytes that have been discarded by the queue management algorithm, BLUE |
CIR Compliant | The total number of frames that have been forwarded by this shaper using the CIR bucket |
EIR Compliant | The total number of frames that have been forwarded by this shaper using the EIR bucket. |
Configuring H-QoS Queuing Profiles
To configure an H-QoS queuing profile
- Access the page Traffic ▶ Shaping ▶ Queuing Profile.
The Traffic Shaping Queuing Profile page opens. All profiles created for this unit are listed in a grid. - Do one of these actions:
- Select an existing profile from the list by clicking it.
- Click Add to create a new profile.
The queuing profile’s details are displayed.
Tip: To only display the profiles associated with a single port or LAG, make a selection in the Port drop-down list at the upper-left corner of the page.
- Use the information in the table below to configure the H-QoS queuing profile, then click Apply.
For more information on specific parameters, refer to the following table.
Queuing Profile Settings (Traffic ▶ Shaping ▶ Queuing Profile)
Parameter | Description |
---|---|
Name | The name assigned to the queuing profile. The name you enter can contain alphanumeric characters or special characters such as underscores and asterisks. Spaces and accented characters are not supported. |
Port | Indicate the port or LAG (for ring mode) to which this queuing profile applies by making a selection in the drop-down list. Note: You cannot modify this value once the queuing profile has been saved. Tip: LAG- 1 is always used in SFP mode for both the GT and GT-S models. |
PCP-0 to PCP-7 | PCP refers to the Class of Service (CoS) or priority associated with traffic. There are eight defined CoS, with PCP-0 being the lowest priority traffic and PCP-7 being the highest. Specify the queue to which you wish to send traffic assigned to each CoS by making a selection in the drop-down list. This way, you indicate the mapping between the queues and the port or LAG. Each user-assignable queue is assigned to a single port or LAG. An error is raised if you attempt to assign queues belonging to different ports or LAGs. similarly, an error is raised if the queuing profile and the set of queues you are assigning do not have the same port number. |
To delete a queuing profile
Access the page Traffic ▶ Shaping ▶ Queuing Profile.
The Traffic Shaping Queuing Profile page opens. All profiles created for this unit are listed in a grid.Select the profile to delete from the list by clicking it.
The queuing profile’s details are displayed.Click Delete.
The selected queuing profile is permanently deleted; you are not prompted to confirm your actions.
Creating a Shaping Envelope
To create a shaping envelope
You can create from one to six bandwidth profile envelopes using the six dedicated port queues that belong to each port. For example, you can create one bandwidth profile envelope with six queues, six bandwidth profile envelopes with one queue each, or any combination in between.
The same logic applies to the pool of 12 user-assignable queues. You can create combinations ranging from 12 bandwidth profile envelopes of one queue, to a single bandwidth profile envelope of 12 queues.
Access the page Traffic ▶ Shaping ▶ Envelope.
The Traffic Shaping Envelope Configuration page opens. All envelopes created for this unit are listed in a grid.Do one of these actions:
Select an existing envelope from the list by clicking it.
Click Add to create a new envelope.
The envelope’s details are displayed.
Tip: To only display the envelopes associated with a single port, make a selection in the Port drop-down list at the upper-left corner of the page.
- Use the information in the table below to configure the envelope, then click Apply.
Traffic Shaping Envelope Settings (Traffic ▶ Shaping ▶ Envelope)
Parameter | Description |
---|---|
Name | The name assigned to the queuing profile. Acceptable values are between 1 and 31 characters in length. The name you enter can contain alphanumeric characters or special characters such as underscores and asterisks. Spaces and accented characters are not supported. |
Port | Indicate the port or LAG (for ring mode) to which this queuing profile applies by making a selection in the drop-down list. Note: You cannot modify this value once the queuing profile has been saved. Tip: LAG-1 is always used in SFP mode for both the GT and GT-S models. |
Type | The type of envelope is displayed here (user-assignable, dedicated or logical) once the envelope has been populated with queues. |
Shaping Mode | Make a selection from the drop-down list to indicate either ingress or egress shaping. |
Coupling Flag | Enable this check box to share the tokens in this envelope in the EIR. Note: All queues in an envelope must have the same coupling flag value, otherwise an error is raised. Note: If you do not enable this check box, no bandwidth will be transferred between the Committed Information Rate (CIR) and Excess Information Rate (EIR) flows. |
Available Queues and Ranking List | Select and rank the queues you wish to include in this envelope. You can assign a maximum of 12 queues to an envelope. Select the queues according to the ranking you wish to apply, starting with the first queue is assigned the highest rank, etc. Note: Queues from different types cannot be added to the same envelope; only one type per envelope is permitted. In addition, a queue cannot be added to more than one envelope. Note: You can only add queues with an active shaper to an envelope. |
To delete an envelope
Access the page Traffic ▶ Shaping ▶ Envelope.
The Traffic Shaping Envelope Configuration page opens. All envelopes created for this unit are listed in a grid.Select the envelope to delete from the list by clicking it. The envelope’s details are displayed.
Click Delete.
The selected envelope is permanently deleted; you are not prompted to confirm your actions. The system returns to the listing of envelopes in the previous page.
Configuring a Port Shaper
Use the Traffic ▶ Shaping ▶ Port ▶ Shaper page to view and configure the shaping parameters assigned to outgoing ports.
To view a summary of the outgoing ports' shaping parameters
- Access the page Traffic ▶ Shaping ▶ Port ▶ Shaper.
The Traffic Shaping Port Shaper Configuration page opens. All the unit’s outgoing ports are listed in a grid. For more information on specific parameters, refer to the following table.
Tip: To edit a specific port's bandwidth profile parameters or view its details, select the port from the list by clicking it.
Traffic Shaping Port Shaper Configuration (Traffic ▶ Shaping ▶ Port ▶ Shaper)
Parameter | Description |
---|---|
Port | The name assigned to this outgoing port |
State | The current state of this outgoing port: enabled or disabled |
CIR (kbps) | The shaping rate of outgoing frames, expressed as a multiple of 125 kbps Range: 0 to port speed |
CBS (KiB) (1024 bytes) | The shaping burst of outgoing frames, expressed in kibibytes Range: 1 KiB to 2047 KiB |
Use the Traffic ▶ Shaping ▶ Port ▶ Shaper page to view and configure the shaping parameters of outgoing ports.
To configure a traffic-shaping port shaper
Access the page Traffic ▶ Shaping ▶ Port ▶ Shaper.
The Traffic Shaping Port Shaper Configuration page opens. All the unit’s outgoing ports are listed in a grid.Select the outgoing port from the list that you wish to configure by clicking it.
The outgoing port’s details are displayed.Make your changes, then click Apply.
For more information on specific parameters, refer to the following table.
Traffic Shaping Port Shaper Configuration (Traffic ▶ Shaping ▶ Port ▶ Shaper)
Parameter | Description |
---|---|
Enable | Click this box to change the current state of this outgoing port: enabled or disabled. |
Port | The name assigned to this outgoing port. You cannot modify this value. |
Bandwidth Profile Parameters | |
Committed Information Rate (kbps) | The shaping rate of outgoing frames, expressed as a multiple of 125 kbps Range: 0 to port speed |
Committed Burst Size (KiB) (1024 bytes) | The shaping burst of outgoing frames, expressed in kilobytes with 1 kibibyte granularity Range: 1 KiB to 2047 KiB |
CPU Traffic Debited from CIR | CPU traffic is never shaped. However, you can select this box to have the system debit CPU traffic from the outgoing port’s CIR bucket. Note: If you select this box, the bucket value could become negative. |
Viewing Traffic Shaping OAM Queue Statistics
Each outgoing port has five queues reserved for specific Operation, Administration and Maintenance (OAM) usage. The OAM queues are as follows:
- CPU
- Monitor1
- Monitor2
- Packet Generator
- Loopback
You can view a summary and detailed statistics for each traffic-shaping OAM queue.
To view a summary of statistics for all traffic-shaping OAM queues
Access the page Traffic ▶ Shaping ▶ Port ▶ OAM Queue Statistics.
The Traffic Shaping OAM Queue Statistics page opens. All the unit’s OAM queues are listed in a grid. For more information on specific parameters, refer to the following table.
Note: For each column in the table, the number of frames, bytes and the bit rate (expressed in Mbps) are displayed. The average CIR and EIR bit rates (expressed in Mbps) that you configured are also shown.
Tips: To edit a specific queue or view its details, select the queue from the list by clicking it.
To clear the statistics in the Traffic Shaping OAM Queue Statistics page, click the broom icon on the right side of the table header.
Traffic Shaping OAM Queue Statistics (Traffic ▶ Shaping ▶ Port ▶ OAM Queue Statistics)
Parameter | Description |
---|---|
Name | The name assigned to this shaping OAM queue |
Port | The name of the port associated with this OAM queue |
Forward | The total number of packets that have been forwarded by this OAM queue. This value includes packets counted as: Green forward no delay Yellow forward no delay Green forward with delay Yellow forward with delay |
Discard | The total number of frames that have been discarded by this queue. This value includes frames counted as: Green Discard full Yellow Discard full |
CIR Compliant | The total number of packets that have been forwarded by this shaper using the CIR bucket |
EIR Compliant | The total number of packets that have been forwarded by this shaper using the EIR bucket |
To view detailed statistics for a traffic-shaping queue
Access the page Traffic ▶ Shaping ▶ Port ▶ OAM Queue Statistics.
The Traffic Shaping OAM Queue Statistics page opens. All the unit’s queues are listed in a grid.Select the queue from the list whose statistics you wish to view by clicking it.
The queue’s details are displayed. For more information on specific parameters, refer to the following table.
Tips: To clear the statistics in the Traffic Shaping Queue Statistics page, click the Clear button located above the queue details. To obtain the latest statistics from the unit, click the Refresh button located beside the Clear button.
Select the Poll Every n Seconds box and enter the number of seconds between each time the statistics are automatically refreshed.
Traffic Shaping OAM Queue Detailed Statistics (Traffic ▶ Shaping ▶ Port ▶ OAM Queue Statistics)
Parameter | Description |
---|---|
Name | The name assigned to this shaping OAM queue |
Port | Name of the port associated with this OAM queue |
Green Forward No Delay | The total number of green frames/bytes in the OAM queue when the queue is near empty, i.e., the green frames/bytes that can be dropped from the queue without delay |
Yellow Forward No Delay | The total number of yellow frames/bytes in the OAM queue when the queue is near empty, i.e., the yellow frames/bytes that can be dropped from the queue without delay |
Green Forward With Delay | The total number of green frames/bytes in the OAM queue when the queue is not empty, i.e., the green frames/bytes that will be dropped from the queue with delay |
Yellow Forward With Delay | The total number of yellow frames/bytes in the OAM queue when the queue is not empty, i.e., the yellow frames/bytes that will be dropped from the queue with delay |
Green Discard Full | The total number of green frames/bytes that have been discarded by this OAM queue |
Yellow Discard Full | The total number of yellow frames/bytes that have been discarded by this OAM queue |
CIR Compliant | The total number of packets that have been forwarded by this shaper using the CIR bucket |
EIR Compliant | The total number of packets that have been forwarded by this shaper using the EIR bucket |
Configuring Default Queuing Profiles
The default queuing profiles are used to map traffic to a queue, based on the internal CoS value assigned to the data frames. Each default queuing profile is associated with an output port and contains a map of all possible CoS values (0-7) to either one or several queues.
To edit a default queuing profile
Access the page Traffic ▶ Shaping ▶ Port ▶ Default Queuing Profile.
The Traffic Shaping Default Queuing Profile page opens. All default profiles for this unit are listed in a grid. For more information on specific parameters, refer to the following table.Select the default queuing profile from the list that you wish to edit by clicking it. The queuing profile’s details are displayed.
Use the information in the table to configure the default queuing profile, then click Apply.
For more information on specific parameters, refer to the following table.
Traffic Shaping Default Queuing Profile (Traffic ▶ Shaping ▶ Port ▶ Default Queuing Profile)
Parameter | Description |
---|---|
Port | Indicates the port or LAG (for ring mode) to which this default queuing profile applies Note: You cannot modify this value, since default queuing profiles are fixed. Tip: LAG-1 is always used in SFP mode for both the GT and GT-S models. |
CoS Mappings | |
PCP-0 to PCP-7 | PCP refers to the Class of Service (CoS) or priority associated with traffic. There are eight defined CoS, with PCP-0 being the lowest priority traffic and PCP-7 being the highest. Specify the queue to which you wish to send traffic assigned to each CoS by making a selection in the drop-down list. This way, you indicate the mapping between the queues and the port or LAG. Each dedicated queue is assigned to a single port or LAG. |
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