Table Of Contents
DOCSIS WFQ Scheduler on the Cisco CMTS Routers
Prerequisites for DOCSIS WFQ Scheduler
Restrictions for DOCSIS WFQ Scheduler
Information About DOCSIS WFQ Scheduler
Maximum Sustained Traffic Rate
Enhanced Rate Bandwidth Allocation
DOCSIS 3.0 Downstream Bonding Support with Bonding Group Dynamic Bandwidth Sharing
How to Configure DOCSIS WFQ Scheduler
Mapping DOCSIS Priority to Excess Ratio
Verifying the Service Flows and Queues
Verifying the DOCSIS Priority to Excess Ratio Mapping
Feature Information for DOCSIS WFQ Scheduler
DOCSIS WFQ Scheduler on the Cisco CMTS Routers
First Published: December 18, 2008
Last Updated: November 9, 2009
Cisco IOS Release 12.2(33)SCB introduces the Data-over-Cable Service Interface Specifications (DOCSIS) Weighted Fair Queuing (WFQ) Scheduler on the Cisco uBR10012 Universal Broadband Router. The DOCSIS WFQ Scheduler is an output packet scheduler that provides output scheduling services on both WAN uplink interfaces and DOCSIS downstream interfaces.
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 for DOCSIS WFQ Scheduler" section.
Use Cisco Feature Navigator to find information about platform support and Cisco IOS, Catalyst OS, and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Contents
•
Prerequisites for DOCSIS WFQ Scheduler
•
•
•
•
Prerequisites for DOCSIS WFQ Scheduler
Table 1 shows the Cisco Cable Modem Termination System (CMTS) hardware compatibility prerequisites for this feature.
Note
Restrictions for DOCSIS WFQ Scheduler
•
Information About DOCSIS WFQ Scheduler
The DOCSIS WFQ scheduling engine is used to provide output packet scheduling services including absolute priority queueing, weighted fair queueing, minimum rate guarantee, shaping, and DOCSIS bonding group dynamic bandwidth sharing on the Cisco uBR10012 Universal Broadband Router. It replaces the existing Versatile Traffic Management System (VTMS) scheduler.
The DOCSIS WFQ Scheduler provides services on both WAN uplink interfaces and DOCSIS downstream interfaces. The scheduling parameters on WAN uplink interfaces are configured through the Modular QoS CLI (MQC). On cable downstream interfaces, queues are created for DOCSIS service flows with parameters configured by DOCSIS downstream QoS Type-Length-Values (TLVs).
For DOCSIS downstream interfaces, the DOCSIS WFQ Scheduler implements traffic shaping and physical link scheduling at two separate layers, which allows it to account for traffic overhead differently. This allows the scheduler to schedule accurately at the physical layer while conforming to DOCSIS specifications.
The DOCSIS WFQ Scheduler also allows significant enhancement to the queue scaling limits compared to the VTMS scheduler. Table 2 shows the queue scaling number comparisons.
Table 2 Queue Scaling Limits
Total Number of Queues Per System1
384,000
384,000
65,534
Total Number of CIR Queues
120,000
120,000
65,534
Number of Queues Per GE Link
162
162
323
Maximum Number of Packets in PXF
Small 1,703,936
Large 245,760
Small 52,428
Large 32,768
Small 52,428
Large 32,768
Queue Size on WAN Uplink
16-32k
16-32k
32-16k
Queue Size on DOCSIS Downstream
255
255
64
1 Includes network-control and default queues.
2 14 user-configurable queues, 1 class-default queue, and 1 system queue.
3 30 user-configurable queues, 1 class-default queue, and 1 system queue.
The following sections explain the DOCSIS WFQ Scheduler features:
•
•
Queue Types
The DOCSIS WFQ Scheduler feature supports the following types of queues:
•
•
•
Priority Queues
Priority queues are serviced with absolute priority over all the other queues. On DOCSIS downstream interfaces, the priority queues are configured by DOCSIS applications that request a priority service flow, for example, a packet cable voice service flow. On WAN uplink interfaces, the priority queues are configured by the MQC policy maps.
The following restrictions apply to priority queues:
•
•
CIR Queues
A CIR queue is guaranteed to be serviced with at least the Committed Information Rate (CIR). CIR queues are used to service DOCSIS service flows with non-zero minimum reserved rates. If the offered load to a CIR queue exceeds its CIR value, the excess traffic is serviced as best effort traffic.
The following conditions apply to CIR queues:
•
•
Best Effort Queues
The Best Effort (BE) queues share the interface bandwidth not used by the priority queue and the CIR queues. The sharing is in proportion to each queue's quantum value.
The following conditions apply to BE queues:
•
•
DOCSIS QoS Support
DOCSIS defines a set of quality of service (QoS) parameters, including traffic priority, maximum sustained traffic rate, minimum reserved traffic rate, maximum traffic burst, maximum downstream latency, and peak traffic rate.
These QoS parameters are used by the downstream service flows to specify the desired QoS. The downstream policer and scheduler provides services such as traffic shaping, bandwidth provisioning, traffic prioritization, and bandwidth guarantee.
The Cisco uBR10012 Universal Broadband Router supports the DOCSIS parameters by mapping the DOCSIS service flow parameters to the packet queue parameters and by providing appropriate QoS support for the packet queues.
The following DOCSIS QoS parameters are supported in the Cisco uBR10012 Universal Broadband Router:
•
•
•
Note
Traffic Priority
The downstream channel bandwidth available to the best effort traffic, namely the channel bandwidth minus the amount consumed by the priority traffic and the CIR traffic, is allocated to the best effort service flows in proportion to their DOCSIS traffic priorities. For example, if there are three service flows sending packets at a particular moment over the same downstream channel, and their DOCSIS traffic priorities are 0, 1 and 3, respectively, their share of the channel bandwidth will be 1:2:4. To achieve this bandwidth allocation, each flow is assigned a value known as its excess ratio which is derived from its DOCSIS priority. Table 3 shows the default mappings of DOCSIS priority to excess ratio.
Note
Table 3 DOCSIS Priority to Excess Ratio Mapping
0
4
1
8
2
12
3
16
4
20
5
24
6
28
7
32
Custom DOCSIS Priority to Excess Ratio Mappings
Cisco IOS Release 12.2(33)SCC introduces the option to configure custom priority to excess ratio mappings for downstream service flows that override the default mappings listed in Table 3.
Note
The option to configure priority to excess ratio mappings is available on a per downstream forwarding interface basis and is applicable to legacy cable, wideband and modular cable, and integrated cable interfaces.
The cable downstream qos wfq weights command is used to configure the mappings. For more details on this command, refer to Cisco IOS CMTS Cable Command Reference Guide.
Maximum Sustained Traffic Rate
The maximum sustained traffic rate (MSR) specifies the peak information rate of a service flow. The MSR of a service flow is mapped to the shape rate of the packet queue. When the maximum sustained traffic rate is not specified or set to zero, its traffic rate becomes limited only by the physical channel capacity set by DOCSIS specifications.
Minimum Reserved Traffic Rate
The minimum reserved traffic rate (MRR) specifies the minimum rate reserved for a service flow. The MRR of a service flow is mapped to the CIR of the packet queue, which ensures the minimum amount of bandwidth a queue gets under congestion. When the MRR is not specified, the CIR is set to zero as per DOCSIS specifications.
High Priority Traffic
High priority traffic flows are mapped to a Low Latency Queue (LLQ) on the data forwarding interface. The packets in LLQ are serviced with absolute priority over other queues on the same interface.
The following service flows require high priority service:
•
•
•
Enhanced Rate Bandwidth Allocation
The DOCSIS WFQ Scheduler supports the Enhanced Rate Bandwidth Allocation (ERBA) feature for service flows. The ERBA feature allows cable modems (CMs) to burst their temporary transmission rates up to the full line rate for short durations of time. This capability provides higher bandwidth for instantaneous bandwidth requests without having to make changes to existing service levels in the QoS profile.
The DOCSIS WFQ Scheduler allows each service flow to have one dedicated queue. When ERBA is enabled for the service flow, the peak rate is implemented as the queue shape rate within the scheduler, while the maximum sustained rate is set as the token bucket refill rate. When ERBA is turned off, the burst size and the peak rate value are not used.
The maximum traffic burst parameter is used to control a service flow burst duration, to burst up to the channel line rate or a configured peak rate, when it is within its maximum burst size allowance. On the Cisco uBR10012 Universal Broadband Router, the cable ds-max-burst command is used to control this behavior explicitly.
For more details on this behavior and the CLI, refer to Cisco IOS CMTS Cable Command Reference Guide.
Note
Table 4 summarizes the ERBA support.
For information about ERBA support on the Cisco CMTS routers, refer to Using Enhanced Bandwidth Rate Allocation (ERBA) Support for DOCSIS 1.0 Cable Modems at the following location: http://www.cisco.com/en/US/docs/cable/cmts/feature/guide/ufg_docs.html#wp1274325
Peak Traffic Rate
The peak-rate option of the cable ds-max-burst command allows you to specify the peak rate an ERBA-enabled service flow can use. The peak-rate value is a global value and is applied to all service flows created after the configuration of the cable ds-max-burst command. The default value of the peak-rate is zero.
If the DOCSIS 3.0 TLV 25.27 is specified for a service flow, the peak-rate value is set as the TLV value. However, if ERBA is not turned on for a service flow, the peak-rate value is ignored.
The peak-rate value can also be configured through cable service class command which forms part of the service class template. During modem registration or Dynamic Service Addition (DSA) operation, the service class name TLV 25.4 is sent to create the static or dynamic downstream service flow that matches the service class template. These downstream service flows are created with a specific peak-rate. If the peak-rate is not specified, then the value specified by the cable ds-max-burst command is used.
If a service flow has both service class and TLV 25.27 defined peak-rate, then the peak-rate value specified in the TLV is used.
For more details on the cable service class command, refer to Cisco IOS CMTS Cable Command Reference Guide.
DOCSIS 3.0 Downstream Bonding Support with Bonding Group Dynamic Bandwidth Sharing
DOCSIS 3.0 introduces the concept of downstream channel bonding. Each Bonding Group (BG) is made up of a collection of downstream channels, which can be used by one or more bonding groups. Each downstream channel can also serve as a primary channel in a MAC domain and carry non-bonded traffic, while being part of a BG.
Prior to DOCSIS 3.0 standards, the downstream service flows were associated with a single downstream interface, which in turn corresponded to a physical downstream on an RF channel. In DOCSIS 3.0, the downstream service flows are associated with the downstream bonding groups. These bonding groups can use multiple downstream RF channels.
On the Cisco uBR10012 Universal Broadband Router, the DOCSIS 3.0 downstream channel bonding is supported on the SPA RF channels. To efficiently utilize the underlying RF channel bandwidth and to provide QoS to the downstream service flows, DBS is supported for the interfaces using SPA RF channels.
DBS is the dynamic allocation of bandwidth for wideband (WB) and modular-cable (MC) interfaces sharing the same downstream channel. Due to the channel-sharing nature of the bonding groups, the bandwidth available to bonding groups or non-bonded channels is not fixed. The bandwidth depends on the configuration and the traffic load on the WB or MC.
Note
In DBS mode, the bandwidth of the shared RF channels is dynamically allocated among the WB and MC interfaces. The DBS enables efficient use of the underlying RF channel bandwidth even in the presence of highly bursty traffic. The DBS is configured at the WB or MC interface level. By default, bandwidth for a WB or MC channel is statically allocated (non-DBS).
DBS does not preclude static bandwidth configuration. If a static portion of bandwidth is configured on any RF channel that one or more DBS-enabled channels also utilize, that portion is subtracted from the RF channel bandwidth, making it dedicated to the non-DBS interface and thus unavailable to the DBS WB or MC interfaces.
For information about DBS support on the Cisco CMTS routers, refer to the Dynamic Bandwidth Sharing on the Cisco CMTS Router feature.
How to Configure DOCSIS WFQ Scheduler
You cannot configure the DOCSIS WFQ Scheduler feature as it is automatically loaded into the PXF engine. The parameters used by the scheduler include the interface bandwidth and the queue parameters.
This section describes the following required and optional procedures:
•
•
•
Mapping DOCSIS Priority to Excess Ratio
This section describes how to map DOCSIS priorities to custom excess ratios for downstream service flows. These custom mappings will override the default mappings.
SUMMARY STEPS
1.
2.
3.
4.
5.
DETAILED STEPS
Verifying the Service Flows and Queues
To verify the downstream (DS) service flows and parameters for a modem, use the show cable modem mac-address | ip-address qos command as shown in the following example:
Router# show cable modem 0018.f826.3453 qosSfid Dir Curr Sid Sched Prio MaxSusRate MaxBrst MinRsvRate ThroughputState Type7 US act 1 BE 7 0 3044 0 08 DS act N/A BE 7 0 2000000 100000 742976929 DS act N/A BE 0 0 3044 0 0To verify the detailed service flow configuration, use the show interfaces cable-interface service-flow sfid qos command as shown in the following example:
Router# show interfaces c7/0/0 service-flow 8 qosSfid Dir Curr Sid Sched Prio MaxSusRate MaxBrst MinRsvRate ThroughputState Type8 DS act N/A BE 7 0 2000000 100000 7430397To verify the detailed service flow statistics, use the show interfaces cable-interface service-flow sfid counters command as shown in the following example:
Router# show interfaces c7/0/0 service-flow 8 countersSfid Packets Bytes PacketDrop Bits/Sec Packet/Sec8 100913 121095600 374337 7431599 773To verify the service flow ID-to-queue ID (Queue Index) association, use the show cr10k-rp cable-interface sfid queue command as shown in the following example:
Router# show cr10k-rp mod 1/2/0:0 queueDocsis queues on the interface: 0Total DOCSIS Queues Allocated: 45Available/Maximal reservable rate(kbps): 3750/3750HQF BLT Info (LBLT Group 36):LBLT 36: wt/qntm 1/10000; PBLT 1236: BW 3750Kbps, flowbit prd/ofst 512/0, rsrc/flrsrc 3/3BE Queues:CIR Queues:LL Queues:To verify service flow queue information, use the show pxf cpu queue interface-name command as shown in the following example:
Router# show pxf cpu queue modular-cable 1/2/0:0Cable Interface Queues:QID Len/Max Dequeues TailDrops MinRt Wt/Quantum ShapeRt FlowId(Kbps) (Kbps)131147 0/255 190 0 0 1/240 0 58131148 0/255 33820 0 0 1/10000 0 32824Cable Service Flow Queues:* Best Effort QueuesQID Len/Max Dequeues TailDrops MinRt Wt/Quantum ShapeRt FlowId(Kbps) (Kbps)131241 0/255 0 0 0 1/240 0 32881* CIR QueuesQID Len/Max Dequeues TailDrops MinRt Wt/Quantum ShapeRt FlowId(Kbps) (Kbps)2049 254/255 131018 485751 99 1/1920 0 32880* Low Latency QueuesQID Len/Max Dequeues TailDropsVerifying the DOCSIS Priority to Excess Ratio Mapping
To verify the DOCSIS priority to excess ratio mapping configuration, use the show running interface command as shown in the following example:
Router# show running interface cable 8/0/0 | i qoscable downstream qos wfq weights 10 20 30 40 50 60 70 80To verify the excess ratio for each queue on an interface, use the show cr10k-rp interface queue be command as shown in the following example:
Router# show cr10k cable8/1/0 queue beForwarding Interface: Cable8/1/0Docsis queues on the interface: 8Total DOCSIS Queues Allocated: 25Available/Maximal reservable rate(kbps): 25232/26000HQF BLT Info (LBLT Group 86):LBLT 110: wt/qntm 1/10000; PBLT 1286: BW 26000Kbps, flowbit prd/ofst 32/3, rsrc/flrsrc 17/17BE Queues:Queue Index: 131268, GlobalQID 83, CBLT ID 131268MinRate(Kbps) 0, ExcessRatio 4, ShapeRate(bps) 10000000, QLimit 255 Service Flow(s): rp_sf_index 32880, lc_sfid 3, min_rate(bps) 0, max_rate(bps) 10000000 peak_rate(bps) 0Queue Index: 131376, GlobalQID 81, CBLT ID 131376MinRate(Kbps) 0, ExcessRatio 32, ShapeRate(bps) 0, QLimit 255 Service Flow(s): rp_sf_index 33115, lc_sfid 39, min_rate(bps) 0, max_rate(bps) 0 peak_rate(bps) 0Queue Index: 131377, GlobalQID 82, CBLT ID 131377MinRate(Kbps) 0, ExcessRatio 24, ShapeRate(bps) 5000000, QLimit 255 Service Flow(s): rp_sf_index 33116, lc_sfid 40, min_rate(bps) 0, max_rate(bps) 5000000 peak_rate(bps) 0Queue Index: 131378, GlobalQID 85, CBLT ID 131378MinRate(Kbps) 0, ExcessRatio 32, ShapeRate(bps) 0, QLimit 255 Service Flow(s): rp_sf_index 33120, lc_sfid 35, min_rate(bps) 0, max_rate(bps) 0 peak_rate(bps) 0Queue Index: 131379, GlobalQID 88, CBLT ID 131379MinRate(Kbps) 0, ExcessRatio 24, ShapeRate(bps) 5000000, QLimit 255 Service Flow(s): rp_sf_index 33121, lc_sfid 43, min_rate(bps) 0, max_rate(bps) 5000000 peak_rate(bps) 0Queue Index: 131398, GlobalQID 109, CBLT ID 131398MinRate(Kbps) 0, ExcessRatio 32, ShapeRate(bps) 0, QLimit 255 Service Flow(s): rp_sf_index 33170, lc_sfid 37, min_rate(bps) 0, max_rate(bps) 0 peak_rate(bps) 0Queue Index: 131399, GlobalQID 110, CBLT ID 131399MinRate(Kbps) 0, ExcessRatio 24, ShapeRate(bps) 5000000, QLimit 255 Service Flow(s): rp_sf_index 33171, lc_sfid 51, min_rate(bps) 0, max_rate(bps) 5000000 peak_rate(bps) 0Router#Additional References
The following sections provide references related to the DOCSIS WFQ Scheduler feature.
Related Documents
CMTS cable commands
Modular Quality of Service
Enhanced Bandwidth Rate Allocation
Dynamic Bandwidth Sharing
Standards
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
—
MIBs
RFCs
No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.
—
Technical Assistance
Feature Information for DOCSIS WFQ Scheduler
Table 5 lists the features in this module and provides links to specific configuration information. Only features that were introduced or modified in Cisco IOS Release 12.2(33)SCB or a later release appear in the table.
Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS, Catalyst OS, and Cisco IOS XE 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
CCDE, CCENT, CCSI, Cisco Eos, Cisco HealthPresence, Cisco IronPort, the Cisco logo, Cisco Nurse Connect, Cisco Pulse, Cisco SensorBase, Cisco StackPower, Cisco StadiumVision, Cisco TelePresence, Cisco Unified Computing System, Cisco WebEx, DCE, Flip Channels, Flip for Good, Flip Mino, Flipshare (Design), Flip Ultra, Flip Video, Flip Video (Design), Instant Broadband, and Welcome to the Human Network are trademarks; Changing the Way We Work, Live, Play, and Learn, Cisco Capital, Cisco Capital (Design), Cisco:Financed (Stylized), Cisco Store, Flip Gift Card, and One Million Acts of Green are service marks; and Access Registrar, Aironet, AllTouch, AsyncOS, Bringing the Meeting To You, Catalyst, CCDA, CCDP, CCIE, CCIP, CCNA, CCNP, CCSP, CCVP, Cisco, the Cisco Certified Internetwork Expert logo, Cisco IOS, Cisco Lumin, Cisco Nexus, Cisco Press, Cisco Systems, Cisco Systems Capital, the Cisco Systems logo, Cisco Unity, Collaboration Without Limitation, Continuum, EtherFast, EtherSwitch, Event Center, Explorer, Follow Me Browsing, GainMaker, iLYNX, IOS, iPhone, IronPort, the IronPort logo, Laser Link, LightStream, Linksys, MeetingPlace, MeetingPlace Chime Sound, MGX, Networkers, Networking Academy, PCNow, PIX, PowerKEY, PowerPanels, PowerTV, PowerTV (Design), PowerVu, Prisma, ProConnect, ROSA, SenderBase, SMARTnet, Spectrum Expert, StackWise, WebEx, and the WebEx logo are registered trademarks of Cisco Systems, Inc. and/or its affiliates in the United States and certain other countries.
All other trademarks mentioned in this document or website are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (0910R)
Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.
© 2009 Cisco Systems, Inc. All rights reserved.
Guest
