- Default DOCSIS 1.0 ToS Overwrite
- DOCSIS 1.1 for the Cisco CMTS Routers
- DOCSIS WFQ Scheduler on the Cisco CMTS Routers
- Dynamic Bandwidth Sharing on the Cisco CMTS Router
- Fairness Across DOCSIS Interfaces
- Modular Quality of Service Command-Line Interface QoS on the Cisco CMTS Routers
- Service Flow Admission Control for the Cisco CMTS Routers
- Subscriber Traffic Management for the Cisco CMTS Routers
- Prerequisites for Fairness Across DOCSIS Interfaces
- Restrictions for Fairness Across DOCSIS Interfaces
- Information About Fairness Across DOCSIS Interfaces
- How to Configure Fairness Across DOCSIS Interfaces
- Verifying the Fairness Across DOCSIS Interfaces
- Configuration Examples for Fairness Across DOCSIS Interfaces
- Additional References
- Feature Information for Fairness Across DOCSIS Interfaces
Fairness Across
DOCSIS Interfaces
First Published: June 20, 2011
The Fairness Across DOCSIS Interfaces feature introduces an adaptive mechanism to effectively distribute reservable bandwidth for committed information rate (CIR) flows and fair bandwidth for best-effort (BE) service flows across adjacent bonding groups (BGs).
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://tools.cisco.com/ITDIT/CFN/. An account on http://www.cisco.com/ is not required.
Contents
- Prerequisites for Fairness Across DOCSIS Interfaces
- Restrictions for Fairness Across DOCSIS Interfaces
- Information About Fairness Across DOCSIS Interfaces
- How to Configure Fairness Across DOCSIS Interfaces
- Verifying the Fairness Across DOCSIS Interfaces
- Configuration Examples for Fairness Across DOCSIS Interfaces
- Additional References
- Feature Information for Fairness Across DOCSIS Interfaces
Prerequisites for Fairness Across DOCSIS Interfaces
Table below shows the hardware compatibility prerequisites for this feature.
 Note | The hardware components introduced in a given Cisco IOS Release will be supported in all subsequent releases unless otherwise specified. |
Note | The term ‘Bonding Group (BG)’ is used in this document to refer to all the integrated-cable (IC), modular-cable (MC), and wideband-cable (WC) interfaces in the context of Fairness Across DOCSIS Interfaces feature context. The IC and MC interfaces are considered as a single-channel BG. |
Restrictions for Fairness Across DOCSIS Interfaces
- The CIR flows cannot reserve all the RF bandwidth. The CIR flows can only reserve 90 percent3 of the RF bandwidth that is not statically reserved by the “bandwidth-percent”, in addition to the legacy CIR bandwidth.
- It is recommended that the CIR reservation be cleared before disabling Fairness Across DOCSIS Interfaces feature to ensure that the CIR reservation is not more than the static reservable bandwidth specified by the “bandwidth-percent” in legacy configuration. This is to prevent CIR over-subscription after disabling Fairness Across DOCSIS Interfaces feature.
- The effect of Fairness Across DOCSIS Interfaces feature depends on topology and flow distribution. In certain cases, Fairness Across DOCSIS Interfaces feature may not achieve BE fairness or maximum CIR utilization.
- Fairness Across DOCSIS Interfaces feature applies only to dynamic bandwidth sharing (DBS) enabled IC and WB interfaces.
Information About Fairness Across DOCSIS Interfaces
The Fairness Across DOCSIS Interfaces feature is an enhancement over the DOCSIS WFQ scheduler. It enables downstream CIR service flows to be admitted on the interfaces over the thresholds defined in the legacy configuration (that is, “bandwidth-percent” or “max-reserved-bandwidth”). For example, the feature enables large CIR flows (like multicast service flows) to be admitted when the current parameters cannot guarantee enough bandwidth. However, its success rate depends on the allocation and reservation of the bandwidth for cable interfaces within common RF channels.
This feature also ensures fair bandwidth for downstream BE service flows across cable interfaces with common RF channels. The per-flow bandwidth of all active service flows on the adjacent BGs are balanced periodically in proportion to their DOCSIS traffic priority (traffic priority + 1) for downstream BE service flows. This bandwidth, available for BE traffic, can also be used to admit additional CIR flows.
Note | For information about DOCSIS traffic priority, see DOCSIS WFQ Scheduler on the Cisco CMTS Routers guide. |
How to Configure Fairness Across DOCSIS Interfaces
This section describes the following tasks that are required to implement Fairness Across DOCSIS Interfaces feature:
- Configuring Fairness Across DOCSIS Interfaces
- Configuring Maximum Excess Information Rate Ratio
- Configuring Constant Excess Information Rate Demand
- Configuring Maximum Bonus Bandwidth
Configuring Fairness Across DOCSIS Interfaces
This section describes how to enable Fairness Across DOCSIS Interfaces feature on the cable interfaces. The configuration is applied to all WB, MC or IC interfaces on the router.
We recommend that you clear the CIR reservation before disabling the Fairness Across DOCSIS Interfaces feature to ensure that CIR reservation is not more than the static reservable bandwidth specified by the “bandwidth-percent” in the legacy configuration.
Configuring Maximum Excess Information Rate Ratio
This section describes how to configure the maximum Excess Information Rate (EIR) ratio between the BE bandwidth among adjacent BGs.
The EIR ratio is used to maintain the maximum EIR bandwidth difference between BGs. It helps to prevent BGs (which has only a few active BE service flows) from getting very low or zero EIR bandwidth. Otherwise, these BGs will not be able to admit CIR flows as they get only very low EIR bandwidth.
For example, there are two BGs sharing the same RF channel, with BG1 having 1000 active BE service flows and BG2 having none. If “max-eir-ratio” is not used, BG1 gets all the bandwidth leaving no bandwidth for BG2. When a voice CIR tries for bandwidth at BG2, it will get rejected. If “max-eir-ratio” is set at 10, BG2 gets about 10 percent of the QAM that is sufficient to admit the voice CIR. The ‘max-eir-ratio’ is a trade-off between perfect fairness and CIR utilization. It means, compromising 'flow fairness' to prevent some BGs from getting all the bandwidth leaving the other BGs with none.
Configuring Constant Excess Information Rate Demand
This section describes how to configure the constant excess information rate (EIR) demand for a bonding group (BG). EIR demand is a unitless value that is used to determine relative bandwidth ratio between BGs.
An active EIR flow with DOCSIS priority-0 is given 1000 units of demand in ACFE module. Therefore a BG with constant-eir-demand set to 1 will get no more than 1/1000 of the bandwidth of a single service flow.
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enable
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configure
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acfe
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exit
DETAILED STEPS
Configuring Maximum Bonus Bandwidth
This section describes how to configure the maximum usable bonus bandwidth for a BG.
Bonus bandwidth is the additional bandwidth provided by the Fairness Across DOCSIS Interfaces feature to each BG for CIR reservation. In the default maximum bonus bandwidth configuration, a single BG can reserve all the underlying RF bandwidth. When the maximum bonus is set, the AC module will not admit CIR flows above that setting even if the scheduler has guaranteed more bandwidth. This will effectively prevent BGs from being starved for CIR flows.
Note | The cable acfe max-bonus-bandwidth command configuration is applicable only for the new incoming CIR flows. It will not terminate the existing CIR flows that exceeds the max-bonus-bandwidth . |
If the maximum bonus bandwidth is less than the current CIR reservation on an interface, no new CIR flows are admitted until the CIR reservation drops below the maximum bonus bandwidth configuration.
Verifying the Fairness Across DOCSIS Interfaces
To monitor the Fairness Across DOCSIS Interfaces feature, use the following procedures:
- Verifying Reservable Bandwidth
- Verifying Global Fairness Across DOCSIS Interfaces Status and Statistics
- Verifying Per-Controller Fairness Across DOCSIS Interfaces Status and Statistics
- Verifying Per-Interface Fairness Across DOCSIS Interfaces Status and Statistics
- Troubleshooting
Verifying Reservable Bandwidth
To display the reserved and reservable bandwidth for a particular interface, use the show interface {wideband-cable | modular-cable | integrated-cable} command as shown in the example:
Router# show interfaces wideband-cable 1/0/0:1 downstream Total downstream bandwidth 3235 Kbps Total downstream reserved/reservable bandwidth 0/200 Kbps Total downstream guaranteed/non-guaranteed bonus bandwidth 66618/9972 Kbps !
The “reservable bandwidth” is a part of the guaranteed bandwidth from the legacy configuration. When the Fairness Across DOCSIS Interfaces feature is disabled, values of both the “guaranteed bonus bandwidth” and “non-guaranteed bonus bandwidth” are zero. When the feature is enabled, the “reservable bandwidth” and “guaranteed bonus bandwidth” represents the maximum CIR that can be reserved on the interface. Unicast CIR flows exceeding this limit are rejected. The additional “non-guaranteed bonus bandwidth” allows the multicast CIR flows to pass the AC module. However, the service flow may not be created successful because the bandwidth comes from the shared pool.
Note | The “guaranteed bonus bandwidth” and “non-guaranteed bonus bandwidth” are part of the bandwidth provided by the maximum bonus bandwidth configuration. The “non-guaranteed bonus bandwidth” is expected to be used only by multicast service flows in Cisco IOS Release 12.2(33)SCF. |
To display the reserved and reservable bandwidth for a particular interface, use the show cable admission-control interface command as shown in the example:
Router# show cable admission-control interface wideband-cable 1/0/0:1 verbose Interface Wideband-Cable1/0/0:1 Configured AC Max Reservable Bandwidth = 6000000 bps Resource - Downstream Bandwidth ------------------------------- Bkt Name Minor # of Major # of Excls # of Non-Ex Curr. Curr. Conf # of No Level Times Level Times Level Times Level Resv Ovrsb Level Rej 1 0 0 0 0 0 0 0 * 0.0 0.0 G 0 2 0 0 0 0 0 0 0 * 0.0 0.0 G 0 3 0 0 0 0 0 0 0 * 0.0 0.0 G 0 4 0 0 0 0 0 0 0 * 0.0 0.0 G 0 5 0 0 0 0 0 0 0 * 0.0 0.0 G 0 6 0 0 0 0 0 0 0 * 0.0 0.0 G 0 7 0 0 0 0 0 0 0 * 0.0 0.0 G 0 8 0 0 0 0 0 0 100* 50.0 0.0 G 0 Note: * indicates that the thresholds are implicit WB-NB CIR for Wideband-Cable1/0/0:1 CIR Values for Cable8/1/4 Bkt SFAC BW Rsvd CIR Reject # 0 0 0 0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 6 0 0 0 7 4500000 3000000 0 Available Guaranteed Bonus BW (bps): 30375000 Available Non-guaranteed Bonus BW (bps): 0 WB Multicast CIR Utilization Bkt SFAC BW Rsvd CIR Reject # 0 0 0 0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 6 0 0 0 7 1500000 0 0 Available Guaranteed Bonus BW (bps): 30375000 Available Non-guaranteed Bonus BW (bps): 0
Verifying Global Fairness Across DOCSIS Interfaces Status and Statistics
To display the global status and statistics of the Fairness Across DOCSIS Interfaces feature, use the show cable acfe summary command as shown in the example:
Router# show cable acfe summary ACFE state: Enabled EIR Rebalance period (secs): 5 EIR Rebalance invocations: 254 CIR Acquire rate/limit: 100/100 CIR Acquire invocations: 0 CIR Acquire throttled: 0 CIR Oversubscriptions: 0 Maximal EIR ratio: 10 Constant EIR demand: 2
Verifying Per-Controller Fairness Across DOCSIS Interfaces Status and Statistics
To display the status and statistics for each controller interface, use the show cable acfe controller command as shown in the following example:
Router# show cable acfe controller modular-cable 1/0/0 EIR Rebalance invoked: 301832 Adaptive CIR granted: 0 Adaptive CIR rejected: 0 Total clusters: 2 !
The BG clusters span across multiple channels and are used as a means to share the underlying RF channel bandwidth dynamically.
RF FlexBW 0 30375 1 30375 RF FlexBW 2 30375 3 30375
Verifying Per-Interface Fairness Across DOCSIS Interfaces Status and Statistics
To display the status and statistics for each interface, use the show cable acfe interface command as shown in the following example:
Router# show cable acfe interface wideband-cable 1/0/0:1 EIR Demand (raw/scale): 0/1 Per-Flow EIR BW (kbps): 19125 Guar Bonus BW (kbps): 19125 Non-guar Bonus BW (kbps): 38250 Reserved Bonus BW (kbps): 0 !
The EIR demand is the number of active BE service flows for each BG within a specific time period weighted by DOCSIS priority. The EIR portion is adjusted periodically in proportion to the EIR demand for each BG within the same BG cluster.
AC Max Reserved Bandwidth: 200 kbps Bucket Reservations (kbps): !
For information on Bucket Reservations, see the Service Flow Admission Control for the Cisco CMTS Routers guide.
Troubleshooting
The following debug commands help you troubleshoot an improper configuration:
- debug cable acfe —Enables debug operation for the Fairness Across DOCSIS Interfaces feature. You should run the debug cable acfe command first to enable other debug options listed below.
- debug cable acfe algorithm —Provides debugging information on internal operations of algorithms.
- debug cable acfe all —Provides debugging information of all cable events.
- debug cable acfe filter —Provides debugging information after applying the filter to limit the debug output.
- debug cable acfe filter controller —Provides debugging information on specific controllers.
- debug cable acfe cluster —Provides debugging information on specific clusters.
- debug cable acfe hccp —Provides debugging information on high availability and Hot Standby Connection-to-Connection Protocol (HCCP) activities.
- debug cable acfe process —Provides debugging information on process activities.
- debug cable acfe read—Provides debugging information from the system.
- debug cable acfe topology —Provides debugging information on cluster topology.
- debug cable acfe verbose —Provides debugging information on all internal data.
- debug cable acfe write —Provides debugging output to the router.
For detailed information on these and other debug commands, see the Cisco IOS CMTS Cable Command Reference guide.
Configuration Examples for Fairness Across DOCSIS Interfaces
This section lists the following sample configurations for the Fairness Across DOCSIS Interfaces feature on a Cisco CMTS router:
- Example: Fairness Across DOCSIS Interfaces
- Example: Maximum EIR Demand Ratio
- Example: Constant EIR Demand
- Example: Maximum Bonus Bandwidth
Example: Fairness Across DOCSIS Interfaces
The following sample configuration shows Fairness Across DOCSIS Interfaces feature enabled on the router:
Current configuration : 39682 bytes ! ! Last configuration change at 04:30:02 UTC Wed Jan 19 2 ! NVRAM config last updated at 04:23:17 UTC Wed Jan 19 2 ! version 12.2 ! cable clock dti cable acfe enable ! . . .
Example: Maximum EIR Demand Ratio
The following sample configuration shows maximum EIR demand ratio configured on the router:
Building configuration... Current configuration : 54253 bytes ! version 12.2 ! cable clock dti cable acfe enable cable acfe max-eir-ratio 20 !
The effect of the cable acfe max-eir-ratio command is demonstrated using a simple BG cluster, a 37.5 Mbps RF bandwidth shared by an MC and WB interface. The interfaces are configured as given in the following configuration example:
! interface Modular-Cable1/0/0:0 cable bundle 1 cable rf-bandwidth-percent 10 ! interface Wideband-Cable1/0/0:0 cable bundle 1 cable rf-channel 0 bandwidth-percent 10 end !
On this RF channel, 20 percent of the bandwidth is reserved by the ‘bandwidth-percent’ allowing Fairness Across DOCSIS Interfaces feature to use 27 Mbps, that is: (100 - 20) * 90 * 37.5). If the ‘max-eir-ratio’ is above 100 and the WB interface has 99 active BE flows and the MC interface has only 1 BE flow, then MC interface gets only 270 kbps, that is 1/(1+99)*27 of the bonus bandwidth. The BE traffic enjoys perfect fairness here. However, it is not possible to admit a unicast CIR flow beyond 270 kbps on the MC interface, as it would exceed the bonus bandwidth. If the ‘max-eir-ratio’ is set to 10, then the MC interface is treated to have 99/10 flows on it, resulting in a higher bonus bandwidth allocation. The ‘max-eir-ratio’ is a trade-off between perfect fairness and CIR utilization.
Example: Constant EIR Demand
The following sample configuration shows constant EIR demand on the router:
Building configuration... Current configuration : 54253 bytes ! version 12.2 ! cable clock dti cable acfe enable cable acfe max-eir-ratio 20 cable acfe constant-eir-demand 2 !
! interface Modular-Cable1/0/0:0 cable bundle 1 cable rf-bandwidth-percent 10 cable acfe constant-eir-demand 2 ! interface Wideband-Cable1/0/0:0 cable bundle 1 cable rf-channel 0 bandwidth-percent 10 cable acfe constant-eir-demand 2 end !
Example: Maximum Bonus Bandwidth
The following sample configuration shows the maximum bonus bandwidth enabled on the router:
Building configuration... Current configuration : 274 bytes ! interface Wideband-Cable1/0/0:0 cable bundle 1 cable rf-channel 0 bandwidth-percent 10 cable acfe max-bonus-bandwidth 10000 end !
In this per-interface configuration, even if the Fairness Across DOCSIS Interfaces feature guarantees more than 10 Mbps for a WB interface, the AC module will not pass more than 10 Mbps bandwidth above the legacy reservable bandwidth.
! . . .
Additional References
Related Documents
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Related Topic |
Document Title |
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Cisco IOS commands |
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Cisco IOS CMTS Cable Command Reference |
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Dynamic Bandwidth Sharing |
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DOCSIS WFQ Scheduler |
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Service Flow Admission Control for the Cisco CMTS Routers |
Standards
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No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
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MIBs
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No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature. |
To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs
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RFC |
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No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature. |
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Technical Assistance
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Description |
Link |
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The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
Feature Information for Fairness Across DOCSIS Interfaces
Table below lists the release history for this feature.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note | The table below lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature. |
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Feature Name |
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Feature Information |
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Fairness Across DOCSIS Interfaces |
12.2(33)SCF |
The Fairness Across DOCSIS Interfaces feature introduces an adaptive mechanism to effectively distribute reservable bandwidth for CIR flows and fair bandwidth for BE service flows across adjacent BGs. The following commands were introduced or modified:
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