Cisco IOS Software Releases 12.1 Mainline

Cisco IOS X-Release 12.1CX, No. 1287

Product Bulletin, No. 1287

Cisco IOS X-Release 12.1CX


This Product Bulletin describes the content and delivery information concerning Cisco IOS(TM) software releases 12.1(4)CX and 12.1(7)CX. It should be used in conjunction with Product Bulletin titled, Release Notes for Cisco ubr7200 Series IOS for Cisco IOS Release 12.1CX. 12.1CX is a short lived Early Deployment (ED) release parented to the 12.1EC train and supporting the Cisco ubr7200 platform. This release contains all new features delivered in 12.1EC up to 12.1(4)EC for the 12.1(4)CX release and up to 12.1(7)EC for the 12.1(7)CX release, with the exception of Hot Standby 1+1 Redundancy, which is not supported in 12.1CX.

The platform and features delivered with this ED release will be incorporated into the `Nitrogen' release of the 12.2B train, and subsequent Cisco IOS 12.2B releases. It is important to note that there are no planned maintenance releases for this ED release. In addition, please note the migration path to the latest 12.2B release. Customers must prepare to upgrade using this migration path


New Features in Cisco IOS Release 12.1(4)CX

Baseline Privacy Interface Plus Enhancement

The Plus (+) version of the Baseline Privacy Interface (BPI+) in DOCSIS 1.1 provides a set of extended services within the MAC sublayer that increase performance and system security. Digital certificates provide secure authentication for each cable modem, to prevent identity theft on the basis of MAC and IP addresses. Advanced encryption provides a secure channel between the cable modem and CMTS, and secure software download allows a service provider to upgrade the software on cable modems, without the threat of interception, interference, or alteration of the software code.

Dynamic Service Flows

The dynamic creation, modification, and deletion of service flows allows for on-demand reservation on Layer 2 bandwidth resources. The CMTS can now provide special QoS to the cable modem dynamically for the duration of a voice call or video session, as opposed to the static provisioning and reservation of resources at the time of cable modem registration. This provides a more efficient use of the available bandwidth.


The cable modem concatenates multiple upstream packets into one larger MAC data frame, allowing the cable modem to make only one timeslot request for the entire concatenated MAC frame, as opposed to requesting a time slot for each individual packet. This reduces the delay in transferring the packet burst upstream.

Enhanced QoS

Extensive scheduling parameters allow the CMTS and the cable modem to communicate QoS requirements and achieve more sophisticated QoS on a per-service flow level.

Different new time-slot scheduling disciplines help in providing guaranteed delay/jitter bound on shared upstream. Activity detection helps to conserve link bandwidth by not issuing timeslots for an inactive service flow. The conserved bandwidth can then be reused for other Best Effort Data slots.

packet classification helps CMTS/cable modem to isolate different types of traffic into different DOCSIS service flows. Each flow could be receiving a different QoS service from CMTS.


The MAC scheduler fragments data slots to fill the gaps in-between UGS slots. Fragmentation reduces the jitter experienced by voice packets when large data packets are transmitted on the shared upstream channel and preempt the UGS slots used for voice. Fragmentation splits the large data packets so that they fit into the smaller timeslots available around the UGS slots.

Multiple Subflows per SID

This feature allows the cable modem to have multiple calls on a single hardware queue. This approach scales much better than requiring a separate SID hardware queue on the cable modem for each voice call.

Payload Header Suppression

Payload header suppression allows the CMTS/cable modem to suppress repetitive or redundant portions in packet headers before transmitting on the DOCSIS link. This helps to conserve link bandwidth, especially with types of traffic, such as voice, where the header size tends to be as large as the size of the actual packet.

Service Classes

The QoS attributes of a service flow can be specified in two ways: either by explicitly defining all attributes, or implicitly by specifying a service class name. A service class name is a string which the CMTS associates with a QoS parameter set.

The service class serves the following purposes:

· It allows operators to move the burden of configuring service flows from the provisioning server to the CMTS. Operators provision the modems with the service class name; the implementation of the name is configured at the CMTS. This allows operators to modify the implementation of a given service to local circumstances without changing modem provisioning. For example, some scheduling parameters might need to be set differently for two different CMTSs to provide the same service. As another example, service profiles could be changed by time of day.

² It allows CMTS vendors to provide class-based-queuing if they choose, where service flows compete within their class and classes compete with each other for bandwidth.

² It allows higher-layer protocols to create a service flow by its service class name. For example, telephony signaling might direct the cable modem to instantiate any available provisioned service flow of class G.711.

Note The service class is optional: the flow scheduling specification may always be provided in full; a service flow may belong to no service class whatsoever. CMTS implementations MAY treat such "unclassed" flows differently from "classed" flows with equivalent parameters.

Any service flow can have its QoS parameter set specified in any of three ways:

· By explicitly including all traffic parameters.

· By indirectly referring to a set of traffic parameters by specifying a service class name.

· By specifying a service class name along with modifying parameters.

The service class name is "expanded" to its defined set of parameters at the time the CMTS successfully admits the service flow.

Detailed Information

The DOCSIS 1.1 specification provides the following functional enhancements over DOCSIS 1.0 coaxial cable networks:

· Enhanced Quality of Service (QoS) to give priority for real-time traffic such as voice and video

² The DOCSIS 1.0 QoS model (a Service IDs (SID) associated with a QoS profile) has been replaced with a service flow model that allows greater flexibility in assigning QoS parameters to different types of traffic and in responding to changing bandwidth conditions

² Support for multiple service flows per cable modem allows a single cable modem to support a combination of data, voice, and video traffic

² Greater granularity in QoS per cable modem in either direction, using unidirectional service flows

² Dynamic MAC messages create, modify, and delete traffic service flows to support on demand traffic requests

² Supported QoS models for the upstream are:

² Best effort-Data traffic sent on a non-guaranteed best-effort basis

² Committed Information Rate (CIR)-Guaranteed minimum bandwidth for data traffic

² Unsolicited Grants (UGS)-Constant bit rate (CBR) traffic, such as voice, that is characterized by fixed size packets at fixed intervals

² Real Time Polling (RTPS)-Real Time service flows, such as video, that produce unicast, variable size packets at fixed intervals

² Unsolicited Grants with Activity Detection (USG-AD)-Combination of UGS and RTPS, to accommodate real time traffic that might have periods of inactivity (such as voice using silence suppression). The service flow uses UGS fixed grants while active, but switches to RTPS polling during periods of inactivity to avoid wasting unused bandwidth.

² Enhanced time-slot scheduling mechanisms to support guaranteed delay/jitter sensitive traffic on the shared multiple access upstream link

² Payload Header Suppression (PHS) conserves link-layer bandwidth by suppressing unnecessary packet headers on both upstream and downstream traffic flows

² Layer 2 fragmentation on the upstream prevents large data packets from affecting real-time traffic, such as voice and video. Large data packets are fragmented and then transmitted in the timeslots that are available between the timeslots used for the real-time traffic.

² Concatenation allows a cable modem to send multiple MAC frames in the same timeslot, as opposed to making an individual grant request for each frame. This avoids wasting upstream bandwidth when sending a number of very small packets, such as TCP acknowledgement packets.

² Advanced authentication and security throughX.509 digital certificates and Triple Data Encryption Standard (3DES) key encryption

² Secure software download allows a service provider to remotely upgrade a cable modem's software, without risk of interception or alteration

DOCSIS 1.1 cable modems can coexist with DOCSIS 1.0 and 1.0+ cable modems in the same network—the Cisco uBR7200 series provides the levels of service that are appropriate for each cable modem

For more detailed information about the platforms and features being delivered in 12.1(4)CX, please see the Cisco IOS Release 12.1(4)CX Release Notes at the following location (* Please see note below regarding restricted access to the 12.1(4)CX release):

New Features in Cisco IOS Release 12.1(7)CX

Additional DOCSIS 1.1 SNMP Support

Release 12.1(7)CX adds support for the following new or changed MIBs:

  • DOCS-QOS-MIB —Describes the quality of service (QoS) attributes. This is revision 04 of the MIB.

  • DOCS-SUBMGT-MIB —Describes the subscriber management attributes. This is revision 02 of the MIB.

  • RFC2933 —Describes the IGMP protocol attributes, as defined in RFC2933.

  • DOCS-CABLE-DEVICE-MIB —Describes the operation of the CM and CMTS. Only the syslog and Event tables are supported by this MIB, which was released as RFC2669.

  • DOCS-CABLE-DEVICE-TRAP-MIB —Defines the traps supported by CMs and the CMTS and is the extension of the RFC2669 (DOCS-CABLE-DEVICE-MIB).

  • DOCS-IF-EXT-MIB —Extemds the RFC2670 (DOCS-IF-MIB) to provide information about whether CMs and CMTS support DOCSIS 1.0 or DOCSIS 1.1.

In addition, the CLI supports a new command (cable submgmt default) to set the default value of attributes in DOCS-SUBMGT-MIB. This command can be included in the Cisco IOS configuration file so that the new values are automatically set after a reboot or reload of the Cisco uBR7200 series router.

Advanced Spectrum Management Features for the Cisco uBR-MC16S Spectrum Management Card

The Cisco uBR-MC16S cable interface line card has a DOCSIS-based cable interface that supports one downstream and six upstreams. It incorporates a daughterboard with hardware-based spectrum management features that provide the following features:

  • Integrates a DOCSIS cable interface line card with an onboard spectrum analyzer that continuously analyzes the upstream spectrum quality in the DOCSIS frequency range of 5 to 42 MHz

  • Includes hardware-assisted frequency hopping, providing for more intelligent and faster frequency selection than software-only solutions

  • Reduces the response time to ingress noise that could cause modems to drop offline

  • Eliminates blind frequency hopping by initiating frequency hops to known clean channels

  • Improves frequency agility to help eliminate dropped packets and thereby maintain full upstream data rates

  • Supports frequency agility in dense-mode combining environments across a shared spectrum

  • Restricts frequency hopping to a set of discrete frequencies or to a range of frequencies, as desired

  • Allows frequency hop conditions to be customized for specific plant environments and requirements

  • Optionally schedules frequency hops to take advantage of known usage patterns or plant conditions

  • Optionally dynamically reduces channel width to allow cable modems to remain online, even in noisy upstream conditions

Baseline Privacy Interface Plus Enhancement

The Plus (+) version of the Baseline Privacy Interface (BPI+) in DOCSIS 1.1 provides a set of extended services within the MAC sublayer that increase performance and system security. Digital certificates provide secure authentication for each cable modem, to prevent identity theft on the basis of MAC and IP addresses. Advanced encrypt

For further information regarding these new features in 12.1(7)CX, please see the document, Release Notes for Cisco uBR7200 Series Routers for Cisco IOS Release 12.1CX.


Cisco IOS Release 12.1(4)CX supports the features listed in the DOCSIS 1.1 specification SP-RFIv1.1-IO3-991105. Additional features will be supported as they are added to the specification and as the specification is finalized.

In particular, the following DOCSIS 1.1 features are not supported in Cisco IOS Release 12.1(4)CX:

  • CMTS-initiated dynamic service MAC messages (CM-initiated messages are supported)

  • Dynamic Channel Change (DCC)

  • Pre equalization coefficients for 16 QAM upstream operation

  • non-Real Time Polling (nRTPS)

  • SNMPv3

  • RFC 2669


  • DOCS-QOS-MIB version 4 (version 2 of the MIB is supported)

In addition, 1+1 redundancy and the HCCP protocol are not supported during DOCSIS 1.1 operation.


Cisco IOS software release 12.1CX follows the standard Cisco support policy as indicated in the following link.

Product Numbers

Table 1: Cisco IOS Release 12.1(4)CX Feature Sets, Images, and Memory Recommendations
  • Platform Software Feature Set Product Code Image Flash DRAM


    (for 12.1(4)CX)



    (SU7M3K4-12104CX for the 12.1(4)CX release)


    16 MB

    64 MB

Download Information

Cisco IOS Releases 12.1(4)CX and 12.1(7)CX are available at the link below. (* Please see the note below regarding restricted access to the 12.1CX releases)

Access to 12.1CX Releases

Cisco IOS Release 12.1(4)CX and 12.1(7)CX are restricted releases. Please contact Cable Product Managers at for the proper access code to download this release. Without this access code, you will not be able to download the software or documentation.

Special Note for Customers

Cisco IOS release 12.1(4)CX and 12.1(7)CX are being released for use in test envronments that those that wish to perform initial testing of the DOCSIS 1.1 standard. Use or deployment of this release in any production environment is discouraged, due to the following facts:

1) This release does not contain support for the full DOCSIS 1.1 standard

2) This release does not have any planned maintenance. There will not be any follow-on releases for bug fixes or enhancements for 12.1(4)CX or 12.1(7)CX. The maintenance and enhancement path for this release is the 12.2B release, which should be avaible in the 2nd quarter of 2002.