Cisco CMTS Feature Guide
Upstream Scheduler Mode for the Cisco CMTS
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Table Of Contents

Upstream Scheduler Mode for the Cisco CMTS

Contents

Prerequisites for Upstream Scheduler Mode Configuration

Restrictions for Upstream Scheduler Mode Configuration

Information About Upstream Scheduler Mode Configuration

How to Configure Upstream Scheduler Modes

Troubleshooting Tips

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Command Reference

cable upstream scheduling type


Upstream Scheduler Mode for the Cisco CMTS

Revised: February 5, 2007, OL-1467-08

This document describes how to configure optional upstream scheduler modes.

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

History for the Enhanced DOCSIS Upstream Scheduler Modes Feature

Release
Modification

12.3(13)BC

This feature was introduced.


Finding Support Information for Platforms and Cisco IOS Software Images

Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.

Contents

•Prerequisites for Upstream Scheduler Mode Configuration

•Restrictions for Upstream Scheduler Mode Configuration

•Information About Upstream Scheduler Mode Configuration

•How to Configure Upstream Scheduler Modes

•Additional References

•Command Reference

Prerequisites for Upstream Scheduler Mode Configuration

This feature applies to all Cisco CMTS routers.

Restrictions for Upstream Scheduler Mode Configuration

Note the following restrictions for this feature:

•To ensure proper operation, Call Admission Control (CAC) must be enabled. When the Low Latency Queueing (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.

•Unsolicited Grant Services with Activity Detection (UGS-AD) and Non Real Time Polling Service (nrtPS) are not supported.

Information About Upstream Scheduler Mode Configuration

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

How to Configure Upstream Scheduler Modes

This section describes the configuration tasks that are most commonly performed when using the upstream scheduler modes feature on the Cisco CMTS platforms.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface cable x/y
or
interface cable x/y/z

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

5. cable upstream n scheduling type [ugs | rtps] mode [llq | docsis]

6. end

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode. Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

interface cable x/y
or

interface cable x/y/z

Example:

Router(config)# interface cable 5/1

Router(config-if)#

Enters interface configuration mode for the specified cable interface.

Step 4 

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



Example:

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

Enables LLQ-type (packet-based) scheduling for UGS services, where n specifies the upstream port. Valid values start with 0 for the first upstream port on the cable interface line card.

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

Step 5 

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



Example:

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

Enables standard DOCSIS (TDM-based) scheduling scheduling for rtPS services, where n specifies the upstream port. Valid values start with 0 for the first upstream port on the cable interface line card.

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

Step 6 

end

Example:

Router(config-if)# end

Router#

Exits interface configuration mode and returns to privileged EXEC mode.

Troubleshooting Tips

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 below. For the complete syntax of this command, refer to the following document on Cisco.com:

•Cisco Broadband Cable Command Reference Guide

http://www.cisco.com/en/US/products/hw/cable/ps2217/products_command_reference_book09186a0080108e88.html 

Router# show int cab 4/0 mac-sched 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

     Queue[LLQ Grants] 0/64, 0 drops, max 0   <--- This queue is added in LLQ mode.

     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

Router#

Additional References

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

Related Documents

Related Topic
Document Title

Cisco CMTS command reference

Cisco Broadband Cable Command Reference Guide, at the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/cable/bbccmref/index.htm

Cisco IOS Release 12.2

Cisco IOS Release 12.2 Configuration Guides and Command References, at the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/index.htm

Configuring cable features

Cisco CMTS Feature Guide, at the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/cable/cab_rout/cmtsfg/index.htm

Installing and configuring Cisco uBR7100 Series Universal Broadband Routers

Cisco uBR7100 Universal Broadband Routers, at the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/cable/ubr7100/index.htm

Installing and configuring Cisco uBR7200 Series Universal Broadband Routers

Cisco uBR7200 Universal Broadband Routers, at the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/cable/cab_rout/index.htm

Installing and configuring the Cisco uBR10012 Router

Cisco uBR10012 Universal Broadband Router, at the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/cable/ubr10k/ubr10012/


Standards

Standard
Title

DOCSIS

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


MIBs

No new or modified MIBs are supported by this feature.

RFCs

No new or modified RFCs are supported by this feature.

Technical Assistance

Description
Link

The Cisco Technical Support website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

http://www.cisco.com/techsupport


Command Reference

This section documents new commands only.

cable upstream scheduling type

To enable various scheduler modes, use the cable upstream scheduling type command in interface configuration mode (cable interface only). To disable this feature, use the no form of this command.

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

no cable upstream n scheduling type [ugs | rtps] mode [llq | docsis]

Syntax Description

n

Specifies the upstream port. Valid values start with 0 for the first upstream port on the cable interface line card.

scheduling

Enables the scheduler options.

type

Enables the selection of Unsolicited Grant Services (UGS) or Real Time Protocol Services (rtPS).

ugs

Selects scheduling for UGS.

rtps

Selects scheduling for rtPS.

mode

Enables the selection of packet-based Low Level Queueing (LLQ) or TDM-based DOCSIS scheduling.

llq

Selects LLQ scheduling.

docsis

Selects DOCSIS scheduling.


Command Default

The only default is docsis.

Command Modes

Interface configuration (cable interface only).

Command History

Release
Modification

12.3(13(BC)

This command was introduced.


Usage Guidelines

See How to Configure Upstream Scheduler Modes.

Any combination of ugs, rtps, llq, and docsis is allowed.

Note the following restrictions:

•To ensure proper operation, Call Admission Control (CAC) must be enabled. When the Low Latency Queueing (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.

Examples

The following example shows how to enable LLQ-type (packet-based) scheduling for UGS services on upstream port 4 on a Cisco CMTS interface: 

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

The following example shows how to enable standard DOCSIS (TDM-based) scheduling for rtPS services on upstream port 4 on a Cisco CMTS interface: 

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

Related Commands

Command
Description

show interface cable mac-scheduler

Use this command to confirm whether LLQ scheduling is enabled. See Troubleshooting Tips.