Cisco cBR Converged Broadband Routers DOCSIS Software Configuration Guide for Cisco IOS XE Dublin 17.12 - DOCSIS 3.0 Multicast Support [Cisco cBR Series Converged Broadband Routers] - Cisco
DOCSIS WFQ Scheduler on the Cisco CMTS Routers
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 that are documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. The Feature Information Table at the end of this document provides information about the documented features and lists the releases in which each feature is supported.
Contents · Hardware Compatibility Matrix for Cisco cBR Series Routers, on page 1 · Prerequisites for DOCSIS WFQ Scheduler, on page 1 · Restrictions for DOCSIS WFQ Scheduler, on page 2 · Information About DOCSIS WFQ Scheduler, on page 2 · How to Configure DOCSIS WFQ Scheduler , on page 7 · Additional References, on page 8 · Feature Information for DOCSIS WFQ Scheduler, on page 9
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.
Prerequisites for DOCSIS WFQ Scheduler
No specialequipment or softwareis needed to use the DOCSIS WFQ Scheduler feature.
DOCSIS WFQ Scheduler on the Cisco CMTS Routers 1
Restrictions for DOCSIS WFQ Scheduler
DOCSIS WFQ Scheduler on the Cisco CMTS Routers
Restrictions for DOCSIS WFQ Scheduler
· The DBS feature is only applicable to DOCSIS 3.0 downstream channel bonding.
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, traffic shaping, and DOCSIS bonding group dynamic bandwidth sharing on the Cisco cBR-8 converged broadband router.
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).
The default queue size for the DOCSIS service flows (with bandwidth greater than 150 Mbps) is based on the bandwidth on the cable downstream interfaces (see Table below). Additionally, the queue limit for all service flows can also be adjusted using the cable queue-limit command, buffer size in service class or downstream buffer control TLVs.
Note The default queue size change, and the cable queue-limit command do not affect the DOCSIS high priority queues.
Table below is an example of the queue size based on Annex B 256 QAM channels.
Table 1: Bandwidth, Queue Sizes, and Queue Limits
Channel Bandwidth (Mbps) Default Queue Size
Queue Size 1 ms
1
37.5
63
63
2
75
255
63
3
112.5
255
63
4
150
255
63
5
187.5
319
63
6
225
383
63
7
262.5
447
63
8
300
511
63
12
450
767
63
20 30 40 200 ms ms ms ms 63 92 123 617 123 185 247 1235 185 277 370 1852 247 370 494 2470 308 463 617 3087 370 555 741 3705 432 648 864 4323 494 741 988 4940 741 1111 1482 7411
DOCSIS WFQ Scheduler on the Cisco CMTS Routers 2
DOCSIS WFQ Scheduler on the Cisco CMTS Routers
Queue Types
Channel Bandwidth (Mbps) Default Queue Size
Queue Size 1 ms
14
525
16
600
895
63
1023
63
20 30 40 200 ms ms ms ms
864 1296 1729 8646
988 1482 1976 9881
The DOCSIS WFQ Scheduler also allows significant enhancement to the queue scaling limits. The following sections explain the DOCSIS WFQ Scheduler features:
Queue Types
The DOCSIS WFQ Scheduler feature supports the following types of queues:
· Priority queues · CIR queues · Best Effort 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:
· Only one priority queue is allowed per WAN uplink interface. · Only one priority queue is allowed for low latency service flows created for each DOCSIS downstream
interface. · All low latency flows on a DOCSIS downstream are aggregated to the single priority queue.
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.
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 excess ratio.
The following conditions apply to BE queues:
· On DOCSIS downstream interfaces, BE queues are created by DOCSIS service flows that do not request a minimum reserved rate.
· Each DOCSIS flow without a minimum reserved rate uses its own BE queue.
DOCSIS WFQ Scheduler on the Cisco CMTS Routers 3
DOCSIS QoS Support
DOCSIS WFQ Scheduler on the Cisco CMTS Routers
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.
The downstream service flows use the QoS parameters to specify the desired QoS. The downstream policer and scheduler provides services such as traffic shaping, bandwidth provisioning, traffic prioritization, and bandwidth guarantee.
The DOCSIS service flow parameters are mapped to the packet queue parameters and provided with appropriate QoS support for the packet queues to support the DOCSIS parameters
The following DOCSIS QoS parameters are supported:
· Traffic priority · Maximum sustained traffic rate · Minimum reserved traffic rate
Note The maximum traffic burst size and the peak traffic rate are supported as described in the http://www.cisco.com/ c/en/us/td/docs/cable/cbr/configuration/guide/b_cmts_quality_of_services/docsis_wfq_scheduler.html#con_ 1085732.
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 service flow is assigned a value known as its excess ratio which is derived from its DOCSIS priority. Table below shows the default mappings of DOCSIS priority to excess ratio.
Note When traffic priority for a flow is not explicitly specified, a default priority value of 0 is used as per the DOCSIS specification.
Table 2: DOCSIS Priority to Excess Ratio Mapping
DOCSIS Traffic Priority Excess Ratio
0
4
1
8
2
12
3
16
4
20
DOCSIS WFQ Scheduler on the Cisco CMTS Routers 4
DOCSIS WFQ Scheduler on the Cisco CMTS Routers
Custom DOCSIS Priority to Excess Ratio Mappings
DOCSIS Traffic Priority Excess Ratio
5
24
6
28
7
32
Custom DOCSIS Priority to Excess Ratio Mappings
This option is introduced to configure custom priority to excess ratio mappings for downstream service flows that override the default mappings listed in the above Table.
Note The configured values are used only for new service flows that are created after the configuration has been applied. All the existing service flows maintain their previous excess ratio values.
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.
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:
· Service flows with DOCSIS downstream latency TLV set to a value above zero. For example, PacketCable Multimedia Specification (PCMM) voice calls.
· PacketCable downstream service flows. · Service flows with Unsolicited Grant Service (UGS) type--non-PacketCable voice calls--upstream
flows.
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Enhanced Rate Bandwidth Allocation
DOCSIS WFQ Scheduler on the Cisco CMTS Routers
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 cBR-8 Converged Broadband Router, the cable ds-max-burst command is used to control this behavior explicitly.
Note The ERBA feature is not applicable for high priority service flows and multicast service flows.
Table below summarizes the ERBA support for the Cisco cBR-8 router.
Table 3: Enhanced Rate Bandwidth Allocation Support for the Cisco cBR-8 Router
Policer Rate
Policer Exceed Policer Token Bucket Queue Shape Rate
Action
Size
Traditional Service Flow
Maximum Sustained Transmit Traffic Rate (unused)
A value computed internally by CMTS (unused)
Maximum Sustained Traffic Rate
ERBA-Enabled Maximum Sustained Drop Service Flow Traffic Rate
Maximum Traffic Burst Peak Traffic Rate TLV
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: DOCSIS 1.1 for the Cisco CMTS Routers
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.
DOCSIS WFQ Scheduler on the Cisco CMTS Routers 6
DOCSIS WFQ Scheduler on the Cisco CMTS Routers
DOCSIS 3.0 Downstream Bonding Support with Bonding Group Dynamic Bandwidth Sharing
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 TLV 25.27 from the Cisco CMTS during registration. In order to overcome this you can configure the cable service attribute withhold-TLVs command with the peak-rate keyword to restrict sending of this TLV to non-DOCSIS 3.0 cable modems.
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. DBS is the dynamic allocation of bandwidth for wideband (WB) and integrated cable (IC) 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 IC.
Note Bonding groups are implemented as WB interfaces and non-bonded channels as IC interfaces.
In the DBS mode, the bandwidth of the shared RF channels is dynamically allocated among the WB and IC interfaces. The DBS enables efficient use of the underlying RF channel bandwidth even in the presence of high burst traffic. The DBS is configured at the WB or IC interface level. By default, bandwidth for a WB or IC channel is statically allocated (non-DBS). 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. The parameters that the schedule uses include the interface bandwidth and 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.
DOCSIS WFQ Scheduler on the Cisco CMTS Routers 7
Verifying the Downstream Queues Information
DOCSIS WFQ Scheduler on the Cisco CMTS Routers
Procedure
Step 1
Command or Action enable Example:
Purpose
Enables privileged EXEC mode. Enter your password if prompted.
Step 2
Router> enable
configure terminal Example:
Enters global configuration mode.
Step 3
Router# configure terminal
interface wideband-cable slot/subslot/port Enters interface configuration mode for the
:wideband-channel or interface
indicated cable downstream interface.
integrated-cable slot/subslot/port :rf-channel
Example:
Step 4 Step 5
Router(config)# interface wideband-cable 2/0/0:0 or
Router(config)# interface integrated-cable 1/0/0:0
cable downstream qos wfq weigthts {weight1...weight8}
Configures the custom excess ratios for 8 priorities:
Example:
Note
Router(config-if)# cable downstream qos wfq weights 10 20 30 40 50 60 70 80
The custom values are used only for new service flows and not existing ones.
end Example:
Exits interface configuration mode and returns to privileged EXEC mode.
Router(config-if)# end
Verifying the Downstream Queues Information
To verify the downstream queue information for a modem, use the show cable modem [mac-address |ip-address ]service-flow command.
To check queue stats of all queues on an Integrated-Cable or Wideband-Cable interface, use the show cable dp queue interface command.
Additional References
The following sections provide references related to the DOCSIS WFQ Scheduler feature.
DOCSIS WFQ Scheduler on the Cisco CMTS Routers 8
DOCSIS WFQ Scheduler on the Cisco CMTS Routers
Feature Information for DOCSIS WFQ Scheduler
Technical Assistance
Description
Link
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Feature Information for DOCSIS WFQ Scheduler
Use Cisco Feature Navigator to find information about the 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 the www.cisco.com/go/cfn link. An account on the Cisco.com page is not required.
Note The following table lists the software release in which a given feature is introduced. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Table 4: Feature Information for DOCSIS WFQ Scheduler
Feature Name
Releases
Feature Information
DOCSIS WFQ Scheduler Cisco IOS-XE Release 3.15.0S This feature was introduced on the Cisco cBR Series Converged Broadband Routers.
DOCSIS WFQ Scheduler on the Cisco CMTS Routers 9
Feature Information for DOCSIS WFQ Scheduler
DOCSIS WFQ Scheduler on the Cisco CMTS Routers
DOCSIS WFQ Scheduler on the Cisco CMTS Routers 10
DITA Open Toolkit XEP 4.30.961; modified using iText 2.1.7 by 1T3XT