Upstream Scheduler Mode for the Cisco CMTS Routers

First Published: December 18, 2008

Last Updated: June 20, 2011


Note
Cisco IOS Release 12.2(33)SCA integrates support for the Upstream Scheduler Mode feature on the Cisco CMTS routers. This feature is also supported in Cisco IOS Release 12.3BC, and this document contains information that references many legacy documents related to Cisco IOS 12.3BC. In general, any references to Cisco IOS Release 12.3BC also apply to Cisco IOS Release 12.2SC.

This document describes how to configure optional upstream (US) scheduler modes.

With this feature, you can select Unsolicited Grant Services (UGS), Real Time Polling Service (rtPS) or Non-Real Time Polling Service (nrtPS) scheduling types, as well as packet-based or Time Division Multiplex (TDM) based scheduling. Low latency queueing (LLQ) emulates a packet-mode-like operation over the TDM infrastructure of DOCSIS. As such, the feature provides the typical trade-off between packets and TDM. With LLQ, you have more flexibility in defining service parameters for UGS, rtPS or nrtPS, but with no guarantee (other than statistical distribution) regarding parameters such as delay and jitter.

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 the Upstream Scheduler Mode for the Cisco CMTS Routers

The table below shows the hardware compatibility prerequisites for this feature.

Table 1 Upstream Scheduler Mode for the Cisco CMTS Hardware Compatibility Matrix

CMTS Platform

Processor Engine

Cable Interface Cards

Cisco uBR10012 Universal Broadband Router

Cisco IOS Release 12.2(33)SCA and later releases

  • PRE2

Cisco IOS Release 12.2(33)SCB and later releases

  • PRE4

Cisco IOS Release 12.2(33)SCH and later releases

  • PRE5

Cisco IOS Release 12.2(33)SCA and later releases

  • Cisco uBR10-MC5X20S/U/H

Cisco IOS Release 12.2(33)SCC and later releases

  • CiscoUBR-MC20X20V

Cisco IOS Release 12.2(33)SCE and later releases

  • Cisco uBR-MC3GX60V1

Cisco uBR7246VXR Universal Broadband Router

Cisco IOS Release 12.2(33)SCA and later releases

  • NPE-G1
  • NPE-G2

Cisco IOS Release 12.2(33)SCA

  • Cisco uBR-MC28U/X
  • Cisco uBR-MC16U/X

Cisco IOS Release 12.2(33)SCD and later releases

  • Cisco uBR-MC88V2

Cisco uBR7225VXR Universal Broadband Router

Cisco IOS Release 12.2(33)SCA and later releases

  • NPE-G1

Cisco IOS Release 12.2(33)SCB and later releases

  • NPE-G2

Cisco IOS Release 12.2(33)SCA releases

  • Cisco uBR-E-28U
  • Cisco uBR-E-16U
  • Cisco uBR-MC28U/X
  • Cisco uBR-MC16U/X

Cisco IOS Release 12.2(33)SCD and later releases

  • Cisco uBR-MC88V
1 Cisco uBR-MC3GX60V cable interface line card is not compatible with PRE2.
2 Cisco uBR-MC88V cable interface line card is compatible only with NPE-G2.

Restrictions for Upstream Scheduler Mode for the Cisco CMTS Routers

  • To ensure proper operation, Call Admission Control (CAC) must be enabled. When the LLQ option is enabled, it is possible for the upstream path to be filled with so many calls that it becomes unusable, making voice quality unacceptable. CAC must be used to limit the number of calls to ensure acceptable voice quality, as well as to ensure traffic other than voice traffic.
  • Even if CAC is not enabled, the default (DOCSIS) scheduling mode blocks traffic after a certain number of calls.
  • UGS with Activity Detection (UGS-AD) is not supported by the LLQ scheduler mode but remains supported by the default DOCSIS scheduler mode.
  • Upstream bandwidth request rate limiting feature is supported only on the Cisco UBR-MC20X20V, Cisco uBR-MC3GX60V, Cisco uBR-MC88V, and Cisco uBR-MC5X20H cable interface line cards.

Information About Upstream Scheduler Mode for the Cisco CMTS Routers

With UGS, a service flow is created that enables a cable modem to transmit fixed-size bursts of data at a guaranteed rate and with a guaranteed level of jitter by providing periodic transmission opportunities to the cable modem for fixed-sized frames. This kind of service flow is particularly suitable for VoIP applications.

With rtPS, a service flow is created that provides a periodic opportunity for a cable modem to request permission to transmit data by polling a single cable modem for a bandwidth request, rather than all the cable modems. This satisfies applications that have a requirement for real-time data transmission, and enables the cable modem to transmit data bursts of varying length. This kind of service flow is particularly suitable for MPEG VoIP.

Starting with Cisco IOS Release 12.2(33)SCG, rtPS requests, by default, are internally treated as priority 7—the highest priority for all Best Effort traffic. This high priority reduces the latency of rtPS traffic under congestion.

With nrtPS, a service flow is created that provides a periodic opportunity for a cable modem to request permission to transmit data by polling a single cable modem for a bandwidth request, rather than all the cable modems. The data bursts may be of varying length. This kind of service flow is particularly suitable for non-interactive services such as file transfers.

Upstream Peak Traffic Rate

The Cisco uBR10012 universal broadband routers support upstream traffic peak rates (DOCSIS 3.0 TLV 24.27). This feature is supported on the Cisco uBR10012 universal broadband routers with the Cisco uBR10-MC5X20H and Cisco UBR-MC20X20V cable interface line cards and supports DOCSIS 2.0 and DOCSIS 3.0 cable modems. The upstream peak traffic rate is configured using the cable service class command. To view the peak traffic rate value for a specific service flow, use the show cable modem qos verbose and show cable service-class verbose commands.

Some of the DOCSIS 1.x and DOCSIS 2.0 cable modems, which are not fully DOCSIS 1.x or DOCSIS 2.0 compliant, may fail to come online when they receive upstream peak rate TLV 24.27 from the Cisco CMTS. To overcome this, you can configure the cable service attribute withhold-TLVs command with peak-rate keyword to restrict sending of this type, length, value (TLV) to non-DOCSIS 3.0 cable modems.

Upstream Bandwidth Request Rate Limiting

The Cisco CMTS US scheduler may report high CPU consumption because of extensive incoming bandwidth request processing. The Cisco IOS Release 12.2(33)SCF introduces the upstream Bandwidth Request Rate Limiting (BRRL) feature, which controls the CPU consumption of the US scheduler by monitoring the number of incoming bandwidth requests, and dropping excessive bandwidth requests.


Note
Only the best effort (BE) service flows are subjected to bandwidth request rate limiting.

By default, the BRRL feature is enabled for the Cisco uBR-MC3GX60V line card.

By default, all the bandwidth requests with service flow priority from 0 to 7 are processed by the BRRL feature. However, the BRRL feature also enables you to configure a service flow priority that is exempted from BRRL. Any bandwidth request received with this configured priority or above, is exempted from BRRL processing and is therefore not dropped even if the CPU consumption by the US scheduler is high. For example, if the configured exempted priority is 5, any bandwidth request with priority 5, 6, or 7 is not dropped even if the CPU consumption is high.

Use the cable upstream rate-limit-bwreq exempted-priority command to configure the exempted service flow priority. If the exempted-priority is set to value zero, all the bandwidth requests are exempted from rate limiting, or in other words BRRL feature is disabled.

How to Configure Upstream Scheduler Modes

     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 3 Use one the following commands:

    • interface cable slot/subslot/port

    • interface cable slot/port


    Example: 
    Router(config)# interface cable 5/1
     

    Enters interface configuration mode for the specified cable interface.

     
    Step 4 cable upstream n scheduling type ugs mode [llq |docsis]


    Example: 
    Router(config-if)# cable upstream 4 scheduling type ugs mode llq
     

    Enables LLQ-type (packet-based) scheduling for UGS services.

    Note    Any combination of ugs, rtps, nrtps, llq, and docsis is allowed. The only default value is docsis .
     
    Step 5 cable upstream n scheduling type rtps mode [llq |docsis]


    Example: 
    Router(config-if)# cable upstream 4 scheduling type rtps mode docsis
     

    Enables standard DOCSIS (TDM-based) scheduling for rtPS services.

    Note    Any combination of ugs, rtps, nrtps, llq, and docsis is allowed. The only default value is docsis .
     
    Step 6end


    Example: 
    Router(config-if)# end
     

    Exits interface configuration mode and returns to privileged EXEC mode.

     
    What to Do Next

    To confirm whether the scheduler is operating in LLQ or DOCSIS mode, use the show interface cable mac-scheduler command. A new queue is added when LLQ mode is enabled, as shown in the following example: 

    Router# show interface cable 4/0 mac-scheduler 0
     DOCSIS 1.1 MAC scheduler for Cable4/0/U0
     Queue[Rng Polls] 0/128, 0 drops, max 1
     Queue[CIR Grants] 0/64, 0 drops, max 0
     Queue[BE(7) Grants] 0/64, 0 drops, max 0
     Queue[BE(6) Grants] 0/64, 0 drops, max 0
     Queue[BE(5) Grants] 0/64, 0 drops, max 0
     Queue[BE(4) Grants] 0/64, 0 drops, max 0
     Queue[BE(3) Grants] 0/64, 0 drops, max 0
     Queue[BE(2) Grants] 0/64, 0 drops, max 0
     Queue[BE(1) Grants] 0/64, 0 drops, max 0
     Queue[BE(0) Grants] 0/64, 0 drops, max 0

	 !This queue is added in LLQ Mode
	 Queue[LLQ Grants] 0/64, 0 drops, max 0 
     Req Slots 153607143, Req/Data Slots 0
     Init Mtn Slots 1305584, Stn Mtn Slots 145897
     Short Grant Slots 47, Long Grant Slots 2939
     ATDMA Short Grant Slots 0, ATDMA Long Grant Slots 0
     ATDMA UGS Grant Slots 0
     Awacs Slots 0
     Fragmentation count 3
     Fragmentation test disabled
     Avg upstream channel utilization : 0%
     Avg percent contention slots : 98%
     Avg percent initial ranging slots : 1%
     Avg percent minislots lost on late MAPs : 0%
     Sched Table Adm-State: Grants 0, Reqpolls 0, Util 1%
     UGS    : 0 SIDs, Reservation-level in bps 0
     UGS-AD : 0 SIDs, Reservation-level in bps 0
     RTPS   : 0 SIDs, Reservation-level in bps 0
     NRTPS  : 0 SIDs, Reservation-level in bps 0
     BE     : 2 SIDs, Reservation-level in bps 0
     r4k ticks in 1ms 131000
     Total scheduling events 0
     No search was needed 0
     Previous entry free 0
     Next entry free0
     Could not schedule 0
     Recovery failed 0
Curr time 8282 entry 90

    How to Configure Exempted Priority for BRRL feature

       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 upstream rate-limit-bwreq exempted-priority priority


      Example: 
      Router(config)# cable upstream rate-limit-bwreq exempted-priority 5
       

      Configures the exempted priority:

      • priority—Service flow priority. Bandwidth requests with this service flow priority value (and above) are exempted from BRRL. The valid range is from 0 to 7.
       
      Step 4end


      Example: 
      Router(config)# end
       

      Exits configuration mode and returns to privileged EXEC mode.

       

      Additional References

      The following sections provide references related to the Cisco CMTS routers.

      Related Documents

      Related Topic

      Document Title

      Cisco CMTS command reference

      Cisco CMTS Cable Command Reference

      http:/​/​www.cisco.com/​c/​en/​us/​td/​docs/​cable/​cmts/​cmd_ref/​b_​cmts_​cable_​cmd_​ref.html

      Standards

      Standard

      Title

      DOCSIS

      Data-Over-Cable Service Interface Specifications, DOCSIS 2.0, Radio Frequency Interface Specification, CM-SP-RFIv2.0-I08-050408

      Technical Assistance

      Description

      Link

      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.

      http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

      Feature Information for Upstream Scheduler Mode for the Cisco CMTS Routers

      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.

      Table 2 Feature Information for Upstream Scheduler Mode for the Cisco CMTS Routers

      Feature Name

      Releases

      Feature Information

      Upstream Scheduler Mode for the Cisco CMTS Routers

      12.3(13)BC

      This feature was introduced for all Cisco CMTS routers. The cable upstream scheduling type command was introduced.

      Upstream Scheduler Mode for the Cisco CMTS Routers

      12.2(33)SCA

      This feature was integrated into Cisco IOS Release 12.2(33)SCA. Support for the Cisco uBR7225VXR universal broadband router was added.

      Upstream Peak Traffic Rate

      12.2(33)SCC

      The upstream peak rate traffic (DOCSIS 3.0 TLV 24.27) is supported on Cisco uBR10012 universal broadband routers.

      The following command outputs display the upstream peak traffic rate:

      • show cable modem qos verbose
      • show cable service-class verbose

      Suppressing Downstream and Upstream Peak Rate TLVs for pre DOCSIS 3.0 Cable Modems

      12.2(33)SCB10

      This featuer restricts sending of the DOCSIS 3.0 TLVs to DOCSIS 1.x and DOCSIS 2.0 cable modems.

      The cable service attribute withhold-TLVs command was introduced.

      Upstream Bandwidth Request Rate Limiting

      12.2(33)SCF

      In the Cisco IOS Release 12.2(33)SCF, this feature was introduced for all Cisco CMTS routers.

      The cable upstream rate-limit-bwreq exempted-priority command was introduced.