Fairness Across DOCSIS Interfaces

First Published: April 14, 2015

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

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Contents

Hardware Compatibility Matrix for Cisco cBR Series Routers


Note

The hardware components introduced in a given Cisco IOS-XE Release are supported in all subsequent releases unless otherwise specified.

Table 1 Hardware Compatibility Matrix for the Cisco cBR Series Routers

Cisco CMTS Platform

Processor Engine

Interface Cards

Cisco cBR-8 Converged Broadband Router

Cisco IOS-XE Release 3.15.0S and Later Releases

Cisco cBR-8 Supervisor:

  • PID—CBR-CCAP-SUP-160G

  • PID—CBR-CCAP-SUP-60G1

  • PID—CBR-SUP-8X10G-PIC

Cisco IOS-XE Release 3.15.0S and Later Releases

Cisco cBR-8 CCAP Line Cards:

  • PID—CBR-LC-8D30-16U30

  • PID—CBR-LC-8D31-16U30

  • PID—CBR-RF-PIC

  • PID—CBR-RF-PROT-PIC

Cisco cBR-8 Downstream PHY Modules:

  • PID—CBR-D30-DS-MOD

  • PID—CBR-D31-DS-MOD

Cisco cBR-8 Upstream PHY Modules:

  • PID—CBR-D30-US-MOD

1 Effective with Cisco IOS-XE Release 3.17.0S, CBR-CCAP-SUP-60G supports 8 cable line cards. The total traffic rate is limited to 60Gbps, the total number of downstream service flow is limited to 72268, and downstream unicast low-latency flow does not count against the limits.

Prerequisites for Fairness Across DOCSIS Interfaces


Note
The term ‘Bonding Group (BG)’ is used in this document to refer to all the integrated-cable (IC) and wideband-cable (WC) interfaces in the context of Fairness Across DOCSIS Interfaces feature context. The IC 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 percent2 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. The weights (DOCSIS traffic priority (traffic priority + 1)) of all the BGs are equal for downstream BE service flows. The bandwidth, available for BE traffic, can be used to admit additional CIR flows.


Note
For information about DOCSIS traffic priority, see DOCSIS WFQ Scheduler on the Cisco CMTS Routers guide.

On-demand CIR Acquisition

When multiple bonding groups sharing the RF-channel bandwidth and the current bonding group's guaranteed bandwidth is insufficient, this feature can "borrow" neighbor bonding group's non-reserved guaranteed bandwidth for current bonding group's CIR.

This feature is only used by multicast service flow.

Fairness Across Bonding Groups

Fairness Across DOCSIS Interfaces feature use the weight value of the aggregated active flow count, that is EIR demand, to periodically re-balance the reservable bandwidth. So that the service flows with the same weight in different bonding groups will have roughly the same throughput.

OFDM Channels

OFDM Channel

DOCSIS 3.1 introduces modes for higher throughput and higher spectral efficiency while still allowing backward compatibility to DOCSIS 3.0. OFDM Channel support includes 1 OFDM channel per port with channel bandwidth from 24 MHz to 192 MHz wide. Effective from Cisco IOS-XE Release 3.18.0SP, a bonding group can consist of SC-QAMs and OFDM channels. An OFDM channel can have multiple profiles configured, and each profile may have different rate. The OFDM Channel rate can vary constantly depending on the profiles being used. For more information on OFDM channels, see OFDM Channel Configuration Guide.

OFDM Channel Rate

An OFDM channel can have multiple profiles configured, and each profile can have different rates. For example, with a 96MHz OFDM channel that is configured with profile A (Control Profile) with modulation 1024-QAM, profile B with modulation 2048-QAM, and profile C with modulation 4096-QAM, the profile rates of profile A, B, and C are 616Mbps, 680Mbps, and 736Mbps respectively.

Effective with Cisco IOS-XE Release 3.18.0SP, if an OFDM channel has both Control Profile (profile A) and Data Profiles (profile B, C, and so on) configured, the lowest Data Profile rate is used for Fairness Across DOCSIS Interface calculation. Otherwise, the Control Profile rate is used.

Interface Bandwidth

Effective from Cisco IOS-XE 3.18.0SP Release, a Wideband-Cable (WB) interface can consist of both SC-QAMs and OFDM channels. If it contains OFDM channels, the highest profile rates are used to calculate the interface bandwidth.

For example, with a 96MHz OFDM channel that is configured with profile A with modulation 1024-QAM, profile B with modulation 2048-QAM, and profile C with modulation 4096-QAM, the profile rates of profile A, B, and C are 616Mbps, 680Mbps and 736Mbps respectively. Here, 736Mbps is used to calculate interface bandwidth.

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

This section describes how to enable Fairness Across DOCSIS Interfaces feature on the cable interfaces. The configuration is applied to all WB or IC interfaces on the router.

Restriction:

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.

Procedure
     Command or ActionPurpose
    Step 1enable


    Example: 
    Router> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.
     
    Step 2configure terminal


    Example: 
    Router# configure terminal
     

    Enters global configuration mode.

     
    Step 3cable acfe enable


    Example: 
    Router(config)# cable acfe enable
     

    Enables Fairness Across DOCSIS Interfaces feature on the cable interfaces.

     
    Step 4exit


    Example: 
    Router(config)# exit
     

    Exits global configuration mode and returns to privileged EXEC mode.

     

    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.

    Procedure
       Command or ActionPurpose
      Step 1enable


      Example: 
      Router> enable
       

      Enables privileged EXEC mode.

      • Enter your password if prompted.
       
      Step 2configure terminal


      Example: 
      Router# configure terminal
       

      Enters global configuration mode.

       
      Step 3cable acfe max-eir-ratio eir-ratio


      Example: 
      Router(config)# cable acfe max-eir-ratio 20
       

      Configures the maximum EIR ratio between the BE bandwidth among adjacent BGs.

       
      Step 4exit


      Example: 
      Router(config)# exit
       

      Exits global configuration mode and returns to privileged EXEC mode.

       

      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.

      Procedure
         Command or ActionPurpose
        Step 1enable


        Example: 
        Router> enable
         

        Enables privileged EXEC mode.

        • Enter your password if prompted.
         
        Step 2configure terminal


        Example: 
        Router# configure terminal
         

        Enters global configuration mode.

         
        Step 3cable acfe constant-eir-demand value


        Example: 
        Router(config)# cable acfe constant-eir-demand 20
         

        Configures the constant EIR demand as 20 for a BG.

         
        Step 4exit


        Example: 
        Router(config)# exit
         

        Exits global configuration mode and returns to privileged EXEC mode.

         

        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 .
        Restriction:

        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.

        Procedure
           Command or ActionPurpose
          Step 1enable


          Example: 
          Router> enable
           

          Enables privileged EXEC mode.

          • Enter your password if prompted.
           
          Step 2configure terminal


          Example: 
          Router# configure terminal
           

          Enters global configuration mode.

           
          Step 3interface {wideband-cable | interface-cable }slot/subslot /port :interface-num


          Example: 
          Router(config)# interface wideband-cable 1/0/0:0
           

          Specifies the interface to be configured.

          Note    The valid values for the arguments depend on CMTS router and cable interface line card. See the hardware documentation for your router chassis and cable interface line card for supported values.
           
          Step 4cable acfe max-bonus-bandwidth bonus-bandwidth


          Example: 
          Router(config-if)# cable acfe max-bonus-bandwidth 1000000
           

          Configures the maximum usable bonus bandwidth for a BG.

           
          Step 5end


          Example: 
          Router(config)# end
           

          Exits interface configuration mode and returns to privileged EXEC mode.

           

          Verifying the Fairness Across DOCSIS Interfaces

          To monitor the Fairness Across DOCSIS Interfaces feature, use the following procedures:

          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 1875 Kbps
Total downstream reserved/reservable bandwidth 20000/1500 Kbps
Total downstream guaranteed/non-guaranteed bonus bandwidth 20760/9741 Kbps
Router#

          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” is 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.

          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 1/0/0:0

Interface Wi1/0/0:0
BGID: 28673

Resource - Downstream Bandwidth
-------------------------------
App-type    Name       Reservation/bps    Exclusive
1                      0                  Not configured
2                      0                  Not configured
3                      0                  Not configured
4                      0                  Not configured
5                      0                  Not configured
6                      0                  Not configured
7                      0                  Not configured
8                      20000000           Not configured
Max Reserved BW = 1500000 bps
Total Current Reservation = 20000000 bps
Guaranteed Bonus BW = 20760000 bps
Non-guaranteed Bonus BW = 9741000 bps
Subset BGs: In1/0/0:8 In1/0/0:9 In1/0/0:10 In1/0/0:11 In1/0/0:12
Superset BGs: N/A
Overlapping BGs: Wi1/0/0:8 Wi1/0/0:9 Wi1/0/0:10
Router#

          Effective with Cisco IOS-XE Release 3.18.0SP, Capacity BW is also displayed. It is summation of the channel capacity of the RF channels in this interface, and the capacity of OFDM channels is calculated considering the lowest profile rate. 

          Router#show cable admission-control interface wideband-Cable 2/0/0:1

Interface Wi2/0/0:1
BGID: 8194

Resource - Downstream Bandwidth
-------------------------------
App-type    Name       Reservation/bps    Maximum        Rejected
1                      4000               90%            0
2                      0                  N/A            0
3                      0                  90%            0
4                      0                  N/A            0
5                      0                  N/A            0
6                      0                  90%            0
7                      0                  N/A            0
8                      0                  87%            0
Max Reserved BW = 11424000 bps
Total Current Reservation = 4000 bps
Guaranteed Bonus BW = 884352000 bps
Non-guaranteed Bonus BW = 225904000 bps
Capacity BW = 1428000000 bps
Subset BGs: In2/0/0:0 In2/0/0:1 In2/0/0:2 In2/0/0:3 In2/0/0:4 In2/0/0:5 In2/0/0:6 In2/0/0:7 In2/0/0:158 Wi2/0/0:0
Superset BGs: N/A

          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 integrated-Cable 1/0/0
EIR Rebalance invoked: 450963
Adaptive CIR granted: 20
Adaptive CIR rejected: 1
Total clusters: 9
RF FlexBW
8 36376
9 36376
10 32625
......

          The BG clusters span across multiple channels and are used as a means to share the underlying RF channel bandwidth dynamically.

          Use the show controllers integrated-Cable acfe cluster command to show Per-controller statistics and clusters and checking the bandwidth information as follows: 

          
Router# show controllers integrated-Cable 1/0/0 acfe cluster 0
Integrated-Cable 1/0/0 status:
Topology changed: No

========Cluster 0========
Number of RF: 2
RF FlexBW 	WB 	ExcessBW	Quanta
0  35625			- 		35438 			35438
											0  	187 		187
1  35250 		0 	35250 		35250

Number of BG: 2
Intf	Demand	CIR	Max		CstrMin	Alloc	NBonus	Ratio
WB0 	1000 	0 	70875 	35250 	35437 	35438 	14855190400
IC0 	1000 	0 	35625 	0 					35438 	187 			14855609600

          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
!

          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

          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. 

          !
interface integrated-Cable1/0/0:0
cable bundle 1
 cable rf-bandwidth-percent 10
!
interface Wideband-Cable9/0/0:0 
 cable bundle 1 
 	cable rf-channels channel-list 0 
 	bandwidth-percent 1 
 	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 IC interface has only 1 BE flow, then IC 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 IC interface, as it would exceed the bonus bandwidth. If the ‘max-eir-ratio’ is set to 10, then the IC 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 integrated-Cable1/0/0:0
cable bundle 1
 cable rf-bandwidth-percent 10
 cable acfe constant-eir-demand 2
!
interface Wideband-Cable9/0/0:0 
 cable bundle 1 
 	cable rf-channels channel-list 0 
 	bandwidth-percent 1 
  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

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          Feature Information for Fairness Across DOCSIS Interfaces

          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:/​/​tools.cisco.com/​ITDIT/​CFN/​. An account on http:/​/​www.cisco.com/​ is not required.


          Note

          The below table 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.

          Table 2 Feature Information for Downstream Interface Configuration

          Feature Name

          Releases

          Feature Information

          Fairness Across DOCSIS Interfaces

          Cisco IOS-XE 3.15.0S

          This feature was introduced on the Cisco cBR Series Converged Broadband Router.

          Fairness Across DOCSIS Interfaces

          Cisco IOS-XE 3.17.0S

          On-demand CIR acquisition and Fairness across bonding groups were supported.

          The following commands were modified:

          • show cable acfe summary
          • show cable acfe interface

          Hierarchical QoS

          Cisco IOS-XE 3.18.0SP

          This feature was introduced on the Cisco cBR Series Converged Broadband Router.

          2 The reservable bandwidth for CIR flows consists of static and dynamic portions. By default, the static portion of bandwidth is assigned from the legacy configuration. The dynamic portion of bandwidth comes from the headroom left on each RF channel for BE traffic.