Load Balancing, Dynamic Channel Change, and
`Dynamic Bonding Change on the Cisco CMTS
`Routers
`
`First Published: February 14, 2008
`Last Updated: October 15, 2012
`
`Load Balancing (LB) for the Cisco CMTS allows system operators to distribute cable modems across
`radio frequency (RF) downstream (DS) and upstream (US) channels on the same cable interface line
`card, or across multiple cable interface line cards in some circumstances. Load balancing maximizes
`bandwidth and usage of the cable plant.
`
`Note
`
`Cisco IOS Release 12.2(33)SCA integrates support for this 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.
`
`Load balancing supports multiple methods to achieve greater bandwidth availability and performance of
`the Cisco CMTS with subscriber benefits. These include static and dynamic load balancing schemes,
`inter-line card and intra-line card support, in some circumstances, configuration of load balancing
`groups (LBGs) that entail multiple interfaces, multiple load balancing policies, and the option to
`configure multiple additional load balancing parameters.
`
`The load balancing policies can be configured on the Cisco CMTS, indexed by an ID, to limit the
`movement of CMs within a Load Balancing Group (LBG). The CM will forward TLV43.1 in its
`registration request (REG-REQ) message, which is then parsed and stored in the Cisco CMTS. A policy
`defines whether and when CMs can be moved within their load balancing groups.
`
`During dynamic load balancing, the specified policy of the CM is checked to determine whether the CM
`is allowed to move. However, existing static load balancing using a frequency override technique and
`passive load balancing still take action at ranging time.
`
`Effective with Cisco IOS Release 12.3(17a)BC, and later 12.3 BC releases, load balancing is enhanced
`and supported with Dynamic Channel Change (DCC). DCC in DOCSIS 1.1 dynamically changes cable
`modem upstream or downstream channels without forcing a cable modem to go offline, and without
`reregistration after the change.
`
`Americas Headquarters:
`Cisco Systems, Inc., 170 West Tasman Drive, San Jose, CA 95134-1706 USA
`
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`
`Finding Feature Information
`
` Load Balancing, Dynamic Channel Change, and Dynamic Bonding Change on the Cisco CMTS Routers
`
`Effective with Cisco IOS Release 12.3(17b)BC4, and later releases, load balancing is enhanced to
`distribute downstream load balancing with upstream channel loads in the same upstream load balancing
`group. This improves upon the prior load balancing limitation, in which load balancing was implemented
`on the basis of the entire downstream channel load.
`
`Effective with Cisco IOS Release 12.2(33)SCB, and later releases, load balancing is enhanced to use
`rules and policies to decide on moving the CMs within their LB groups. These policies are created on
`the Cisco CMTS and chosen on a per-CM basis using type-length-value (TLV) portion (43.1, Policy ID)
`of REG-REQ. These policies prohibit a modem from being moved or restricted.
`
`A policy contains a set of rules. When the policy is defined by multiple rules, all rules apply in
`combinations. A rule can be defined as “enabled”, “disabled”, or “disabled during time period.” Each
`rule can be used by more than one policy.
`
`Effective with Cisco IOS Release 12.2(33)SCF1, DOCSIS 3.0 static modem count-based load balancing
`is enhanced to use the dynamic bonding change (DBC) to modify the following parameters of
`DOCSIS 3.0 cable modem with multiple transmit channel (MTC) mode or multiple receive channel
`(MRC) mode without primary channel change:
`
`• Transmit channel set (TCS)
`
`(cid:129) Receive channel set (RCS)
`
`(cid:129) Downstream IDs (DSID) or DSID-associated attributes
`
`(cid:129) Security association for encrypting downstream traffic
`
`These parameters and additional load balancing schemes are supported on the Cisco CMTS, and
`described in this document. This document describes all implementations of load balancing on the
`Cisco CMTS, dependent upon the Cisco IOS release installed and the desired parameters.
`
`Effective with Cisco IOS Release 12.2(33)SCG1, the Cisco uBR-MC3GX60V line card and up to five
`shared port adapters (SPAs) can be configured to the same LBG. You can:
`
`(cid:129)
`
`Include all the downstreams and upstreams of the SPA cards and the Cisco uBR-MC3GX60V line
`card in the LBG.
`
`(cid:129) Configure the MAC domain to include the SPA cards and the Cisco uBR-MC3GX60V line card.
`
`(cid:129) Configure the fiber-node to include all the downstreams and upstreams of the SPA cards and the
`Cisco uBR-MC3GX60V line card.
`
`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 Configuring Load Balancing, Dynamic Channel Change, and
`Dynamic Bonding Change on the Cisco CMTS Routers” section on page 286
`
`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.
`
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` Load Balancing, Dynamic Channel Change, and Dynamic Bonding Change on the Cisco CMTS Routers
`
`Contents
`
`Contents
`
`(cid:129) Prerequisites, page 231
`
`(cid:129) Restrictions, page 233
`
`(cid:129)
`
`Information on the Load Balancing on the Cisco CMTS Feature, page 238
`
`(cid:129) How to Configure Load Balancing on the Cisco CMTS, page 254
`
`(cid:129) Configuration Examples for Load Balancing on the Cisco CMTS, page 277
`
`(cid:129) How to Configure Dynamic Channel Change for Load Balancing, page 269
`
`(cid:129) Example: Configuring Dynamic Channel Change for Load Balancing, page 282
`
`(cid:129) Additional References, page 284
`
`(cid:129) Feature Information for Configuring Load Balancing, Dynamic Channel Change, and Dynamic
`Bonding Change on the Cisco CMTS Routers, page 286
`
`(cid:129) Glossary, page 288
`
`Prerequisites
`
`The Load Balancing, Dynamic Channel Change, and Dynamic Bonding Change feature is supported on
`the Cisco CMTS routers in Cisco IOS Releases 12.3BC and 12.2SC. Table 1 shows the hardware
`compatibility prerequisites for this feature.
`
`Note
`
`The hardware components introduced in a given Cisco IOS release are supported in all subsequent
`releases unless otherwise specified.
`
`Table 1
`
`Load Balancing, Dynamic Channel Change, and Dynamic Bonding Change Hardware
`Compatibility Matrix
`
`Cisco CMTS Platform
`Cisco uBR10012
`Universal Broadband
`Router
`
`Processor Engine
`Cisco IOS Release 12.2(33)SCA and later
`(cid:129) PRE21
`Cisco IOS Release 12.2(33)SCB and later
`(cid:129) PRE4
`
`Cable Interface Cards
`Cisco IOS Release 12.2(33)SCA and later
`(cid:129) Cisco uBR10-MC5X20U/H
`Cisco IOS Release 12.2(33)SCC and later
`(cid:129) Cisco UBR-MC20X20V
`Cisco IOS Release 12.2(33)SCE and later
`(cid:129) Cisco uBR-MC3GX60V2
`
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`Prerequisites
`
` Load Balancing, Dynamic Channel Change, and Dynamic Bonding Change on the Cisco CMTS Routers
`
`Table 1
`
`Load Balancing, Dynamic Channel Change, and Dynamic Bonding Change Hardware
`Compatibility Matrix (continued)
`
`Cisco CMTS Platform
`Cisco uBR7246VXR
`Universal Broadband
`Router
`
`Processor Engine
`Cisco IOS Release 12.2(33)SCA and later
`(cid:129) NPE-G1
`
`(cid:129) NPE-G2
`
`Cisco uBR7225VXR
`Universal Broadband
`Router
`
`Cisco IOS Release 12.2(33)SCA and later
`(cid:129) NPE-G1
`Cisco IOS Release 12.2(33)SCB and later
`(cid:129) NPE-G2
`
`Cable Interface Cards
`Cisco IOS Release 12.2(33)SCA and later
`(cid:129) Cisco uBR-MC28U
`Cisco IOS Release 12.2(33)SCD and later
`(cid:129) Cisco uBR-MC88V3
`Cisco IOS Release 12.2(33)SCA and later
`(cid:129) Cisco uBR-MC28U
`Cisco IOS Release 12.2(33)SCD and later
`(cid:129) Cisco uBR-MC88V
`
`1. PRE = Processor Routing Engine
`2. Cisco uBR-MC3GX60V cable interface line card is only compatible with PRE4.
`3. Cisco uBR-MC88V cable interface line card is only compatible with NPE-G2.
`
`Prerequisites for Load Balancing on the Cisco CMTS
`
`The Load Balancing on the Cisco CMTS feature has the following prerequisites:
`
`(cid:129) Load balancing can be done only on upstreams and downstreams that share physical connectivity
`with the same group of cable modems.
`
`(cid:129) When performing load balancing among downstreams, you must also configure the known
`downstream center frequency to be used on each downstream interface, using the cable downstream
`frequency command. (This is an information-only configuration on cable interfaces that use an
`external upconverter, but it is still required for load balancing so that the Cisco CMTS knows what
`frequencies it should use when moving cable modems from one downstream to another.)
`
`Prerequisites for Dynamic Channel Change for Load Balancing
`
`(cid:129) DCC can be done only to a cable modem that is physically connected to both source and target
`upstream or downstream channels, or both.
`
`(cid:129) Upstreams and downstream channels that share the same physical connectivity must have different
`center frequencies separated by channel width.
`
`(cid:129) The difference between the physical layer parameters on the source and target DCC channels must
`be within the threshold required by the desired DCC initialization technique.
`
`(cid:129) DOCSIS 1.1 must be enabled for a modem to behave properly for the DCC operation. Note that not
`all DOCSIS 1.1 certified modems are DCC-capable, as the CableLabs DCC ATP tests need
`enhancement for complete coverage.
`
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` Load Balancing, Dynamic Channel Change, and Dynamic Bonding Change on the Cisco CMTS Routers
`
`Restrictions
`
`Prerequisites for Dynamic Bonding Change for DOCSIS 3.0 Static Modem
`Count-Based Load Balancing
`
`(cid:129)
`
`Initialization techniques 1 to 4, when used, require the Cisco CMTS to include the upstream channel
`descriptor (UCD) TLV (TLV46.5) in the DBC-REQ message.
`
`(cid:129) Bandwidth must be sufficient on the target bonding group to support DBC. This is determined by
`the admission control APIs.
`
`(cid:129) Fiber nodes must be configured before configuring DOCSIS 3.0 static modem count-based load
`balancing
`
`Restrictions
`
`The following sections describes the restrictions applicable for the Load Balancing, Dynamic Channel
`Change, and Dynamic Bonding Change feature:
`
`(cid:129) Restrictions for Load Balancing on the Cisco CMTS, page 233
`
`(cid:129) Restrictions for Dynamic Channel Change for Load Balancing, page 235
`
`(cid:129) Restrictions for DOCSIS 3.0 Static Modem Count-Based Load Balancing, page 236
`
`Restrictions for Load Balancing on the Cisco CMTS
`
`The Load Balancing on the Cisco CMTS feature has the following restrictions:
`
`(cid:129) Load balancing can be done only on a per-chassis basis—all interfaces in a load balancing group
`must be provided by the same chassis.
`
`(cid:129) A downstream or upstream can belong to only one load balancing group.
`
`(cid:129) All downstreams and upstreams in a load balancing group must share physical connectivity to the
`same group of cable modems. Downstreams can be in a separate load balancing group than
`upstreams, but all downstreams or all upstreams that have the same RF physical connectivity must
`be members of the same load balancing group.
`
`(cid:129) You can configure only one load balancing group per shared physical domain (upstream or
`interface). You cannot configure multiple load balancing groups to distribute downstreams or
`upstreams that share physical connectivity.
`
`(cid:129)
`
`(cid:129)
`
`In later Cisco IOS releases, such as Cisco IOS Release 12.3(17a)BC, you can create a maximum of
`80 load balancing groups on each chassis (the older limitation was 20). However, in prior Cisco IOS
`releases, you can reuse those load balancing groups on different sets of cable interfaces, as long as
`they are in different domains. If downstream channels are not included in a load balancing group,
`then each downstream channel can be considered a separate domain.
`If an upstream port is operational, using the no shutdown command, and is not being used and not
`connected, load balancing attempts to use the port even though there are no cable modems registered
`on that port. When the upstream port is up, it is put into INIT state and load balancing includes this
`port as a potential target. However, if the load balancing sees multiple failures moving to this
`upstream, it is set to DISABLE state and the port is avoided later on in load balancing processes.
`
`(cid:129) The load balancing algorithms assume a relatively even distribution of usage among modems. In the
`situation where one cable modem creates the bulk of the load on an interface, the load balancing
`thresholds should be configured for a value above the load created by that single modem.
`
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`Restrictions
`
` Load Balancing, Dynamic Channel Change, and Dynamic Bonding Change on the Cisco CMTS Routers
`
`(cid:129) Load balancing is done on cable modems in real time, using current load-usage statistics. You cannot
`perform load balancing according to the time of day or using a schedule.
`
`(cid:129) You cannot select particular cable modems to be automatically moved for load balancing, although
`you can exclude cable modems from load balancing operations altogether on the basis of their MAC
`address or organization unique identifier (OUI). (You can use the test cable load-balance command
`to manually move a particular cable modem among upstreams, but this is done typically to test the
`configuration of the load balancing groups.)
`
`(cid:129)
`
`If you have configured upstream shared spectrum groups while doing downstream load balancing,
`the downstream in each MAC domain must not use overlapping upstream groups. For example, the
`downstream in one MAC domain could use an upstream spectrum band of 10 to 30 MHz, while the
`downstream in a second MAC domain could use an upstream spectrum band of 30 to 42 MHz. Each
`MAC domain has its own upstream shared spectrum group, allowing the load balancing group to
`contain the downstreams for both MAC domains.
`
`Note
`
`A MAC domain is one downstream and its associated upstreams.
`
`(cid:129) All upstream ports coming from the same splitter must be using different center frequencies that are
`separated by the channel width. For example, if the upstreams are using a channel width of 3.2 MHz,
`the center frequencies for all upstreams must be separated by at least 3.2 MHz.
`
`(cid:129)
`
`In Cisco IOS Release 12.2(15)BC1, the dynamic load balancing method uses the Downstream
`Frequency Override message to move cable modems between downstream channels, which results
`in cable modems going offline and having to reregister, resulting in a short, temporary loss of
`connectivity for the customer. This is because the DOCSIS 1.0 specification requires cable modems
`to reregister whenever the downstream is changed using the Downstream Frequency Override
`message. Cable modems should not go offline when they are moved between upstreams. This
`behavior is modified in Cisco IOS Release 12.3(17a)BC, with the introduction of four initialization
`techniques for Dynamic Channel Change (DCC). See the “Configuring DCC for Load Balancing on
`the Cisco CMTS” section on page 269.
`
`(cid:129) As required by cable interface bundling, all interfaces in a load balancing group must also be in the
`same Hot Standby Connection-to-Connection Protocol (HCCP) interface bundle.
`
`(cid:129)
`
`If you have configured load balancing, the provisioning system must not assign specific upstream
`channels or downstream frequencies to individual cable modems in their DOCSIS configuration
`files. Any cable modems requiring specific upstream channels or downstream frequencies must be
`excluded from load balancing operations (using the cable load-balance exclude command).
`
`(cid:129) Do not use the utilization method of load balancing on cable interfaces that have a small number of
`cable modems and where a single modem is responsible for the majority of the interface load. In this
`condition, the Cisco CMTS could end up continually moving cable modems from one interface to
`another in an endless attempt to load balance the interfaces. To avoid this, configure the utilization
`threshold to a value that is higher than what can be caused by any single cable modem.
`
`(cid:129)
`
`In Cisco IOS Release 12.2(15)BC1, you should not configure an interface for both dynamic load
`balancing and Hot-Standby Connection-to-Connection (HCCP) N+1 redundancy, because cable
`modems will go offline after a switchover. You can configure the interface for HCCP N+1
`redundancy when you are using only static and passive load balancing.
`
`(cid:129) Load balancing, however, does not continue after a switchover from a Working to a Protect interface.
`Load balancing resumes when the Cisco CMTS switches back to the Working interface. (One
`possible workaround is to preconfigure the Protect interface with the appropriate load balancing
`commands, but you must be certain that the downstreams and upstreams in each load balancing
`group after the switchover have the same physical connectivity.)
`
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` Load Balancing, Dynamic Channel Change, and Dynamic Bonding Change on the Cisco CMTS Routers
`
`Restrictions
`
`(cid:129) When deployed with channel restriction features, if the target upstream channel attribute masks are
`against that of the CM, then the CM on the higher load upstream will not be load balanced, as the
`current load balancing moves CMs only to the target upstream. However, CMs that do not have an
`attribute mask can still be load balanced. You should consider the following while deploying the
`load balancing groups: the target upstream will always be the upstream that has the lowest load. If
`some other upstreams have the same load, the upstream with the lowest index will be chosen as the
`target upstream.
`
`(cid:129) A TLV in CM configuration file restricts dynamic load balancing on per modem basis. Still, existing
`static load balancing using frequency override technique and passive load balancing takes action at
`ranging time.
`
`(cid:129)
`
`If you remove the last rule of a DOCSIS policy, the policy itself will be removed.
`
`(cid:129) The Cisco CMTS load balancing feature moves a cable modem based on the load of the channels in
`a load balancing group, without checking if the cable modem supports the extended frequency range
`(5Mhz-85Mhz). This may result in moving a cable modem that supports standard frequency range
`(5Mhz-65Mhz) to a channel that has extended frequency configured. To overcome such scenarios,
`operators should not mix upstreams that have standard and extended frequencies configured into the
`same load balancing group, unless all modems in the group support extended frequency range.
`
`Restrictions for Dynamic Channel Change for Load Balancing
`
`(cid:129) DCC initialization 0 is the default technique for load balancing DCC. Legacy line cards can only
`use DCC initialization technique 0.
`
`(cid:129) DCC initialization techniques 1-4 are strictly for downstream channel changes within a distributed
`line card (intra-card), and can not be used for load balancing between cards (inter-card). For load
`balancing between cards (inter-card), DCC initialization technique 0 will be used in all cases,
`regardless of what technique is set for the LB group or what card types are used.
`
`(cid:129) For load balancing between multiple cable interface line cards (inter-card implementation), DCC
`initialization technique 0 is to be used in all cases, regardless of what technique is set for the load
`balancing group or which cable interface line card types are used.
`
`(cid:129) The source and target upstreams and downstreams must share physical connectivity with the modem
`desired for a DCC transaction.
`
`(cid:129)
`
`Independent downstream change is not supported, and cross-MAC domain upstream changes must
`occur with the associated downstream changes.
`
`(cid:129) The source and target downstream interfaces must belong to the same virtual bundle and the same
`load balancing group if DCC is used for load balancing.
`
`(cid:129) For DCC initialization techniques 1 to 4, all the configuration variables of the cable modem must
`remain constant with the exception of the configuration variables that are explicitly changed by the
`Dynamic Channel Change request (DCC-REQ) messages encoding.
`
`(cid:129) DCC initialization techniques 2 to 4 must not be used if the propagation delay differences between
`the old and new channels exceeds the ranging accuracy requirement defined in DOCSIS, for
`example, ±0.25 usec plus ± ½ symbol time.
`
`For example, for a symbol rate of 1.28 Msps, the timing offset difference between the source and
`target upstream channel is ± floor[(0.250 us + 0.5*0.781us)/(1/10.24)] = ± 6.
`
`(cid:129) The attenuation or frequency response differences between the old and new upstream channels
`causes the received power at the Cisco CMTS to change by more than 6 dB.
`
`(cid:129) DCC initialization technique 3 must not be used if the conditions for using technique 2 are not met.
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`Restrictions
`
` Load Balancing, Dynamic Channel Change, and Dynamic Bonding Change on the Cisco CMTS Routers
`
`(cid:129) DCC initialization technique 4 must not be used if the conditions for using technique 2 cannot be
`met.
`
`(cid:129) Micro-reflections on the new upstream channel result in an unacceptable BER (greater than 1e-8)
`with preequalization coefficients set to the initial setting.
`
`(cid:129) DCC is used only for dynamic downstream load balancing on DOCSIS 1.1 and later CMs. Upstream
`Channel Change (UCC) is always used for dynamic upstream load balancing on DOCSIS 1.x CMs.
`For DOCSIS 2.x CMs, UCC is used when the ucc option is configured. For DOCSIS 3.x CMs, DCC
`is used irrespective of whether the ucc option is configured or not.
`
`(cid:129) Prolonged interruption of the multicast traffic is expected if the cable modem moved by DCC is the
`first one in a dynamic multicast group on the target interface. The downstream multicast service flow
`cannot be reestablished until the Cisco CMTS receives an Internet Group Management Protocol
`(IGMP) join message from the customer premises equipment (CPE) as the result of the Cisco CMTS
`IGMP query, where the IGMP query interval is set to one minute. This is an IGMPv2 limitation.
`
`(cid:129)
`
`In Cisco IOS Release 12.2(33)SCB4 and earlier releases, after a DCC with initialization technique 1
`or higher, IP connectivity to a CPE with multiple IPs assigned to a single MAC address, is lost.
`
`Effective with Cisco IOS Release 12.2(33)SCB5, multiple statically-assigned IP addresses to a CPE
`can be pinged. However, this works only if all the security features, such as verification of
`IP addresses for cable modems and CPE devices on the upstream, and other security mechanism are
`disabled.
`
`(cid:129) The TCS and RCS assigned to the DOCSIS 3.0 cable modems are restricted by the upstream and
`downstream bonding groups configured by the Cisco CMTS.
`
`(cid:129) Load balancing and DCC are not supported for CMs that are enabled for Layer 2 VPN (L2VPN)
`support.
`
`DCC Restrictions with N+1 Redundancy and Inter-Card Load Balancing
`
`(cid:129)
`
`Inter-card load balancing is not supported with cable interface line cards using N+1 redundancy.
`Refer to general DCC restrictions for additional information.
`
`(cid:129) Dynamic load balancing should not be used together with N+1 redundancy. Cable modems with
`outstanding DCC transactions go offline after a switchover event.
`
`Note When cable modems go offline during a switchover event, the load balancing feature activates. Cable
`modems move in relation to the switchover event. When the cable modems return online, load balancing
`may need to initiate again.
`
`To facilitate load balancing during a switchover, you can increase the dynamic load balance threshold,
`if a certain percentage of cable modems that reset during switchover is configured in the system. An
`alternate method is to use static load balancing with N+1 redundancy. For more information, see the
`“Types of Load Balancing Operations” section on page 244.
`
`Restrictions for DOCSIS 3.0 Static Modem Count-Based Load Balancing
`
`(cid:129) Effective with Cisco IOS Release 12.2(33)SCF, static modem count-based load balancing is
`supported on MTC and MRC-only CMs. Single-channel, narrowband CMs will continue to be
`supported with dynamic load balancing as in the Cisco IOS Release 12.2(33)SCE and earlier
`releases. MRC-only modems are supported by dynamic load balancing on upstream channels.
`
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` Load Balancing, Dynamic Channel Change, and Dynamic Bonding Change on the Cisco CMTS Routers
`
`Restrictions
`
`Note
`
`DOCSIS 3.0 static modem count-based load balancing is not supported on:
`
`(cid:129) Multiple line cards.
`
`(cid:129) Load balancing groups and downstream channels shared across multiple line cards. However,
`autonomous load balancing-based CM steering and load balancing group assignment is supported
`across multiple line cards.
`
`(cid:129)
`
`In Cisco IOS Release 12.2(33)SCF, DOCSIS 3.0 static modem count-based load balancing does not
`support service flow method of load balancing.
`
`Restrictions for Dynamic Bonding Change for DOCSIS 3.0 Static Modem Count-Based Load
`Balancing
`
`(cid:129) The Cisco CMTS can use only DBC messaging to move modems within a MAC domain and applies
`only to CMs operating in MTC mode or MRC-only mode without a primary downstream change.
`
`(cid:129) The Cisco CMTS moves the MRC-only CMs with a primary channel change using DCC with
`initialization technique 0.
`
`(cid:129) The Cisco CMTS moves CMs across MAC domains using only DCC with initialization technique 0.
`
`(cid:129) The Cisco CMTS must ensure minimum interruption to existing QoS services while considering an
`initialization technique that is suitable for the cable plant conditions.
`– Initialization Technique 0—(Reinitializing the MAC) results in the longest interruption of
`service. This technique is used when QoS resources are not reserved on the new channel(s),
`when the downstream channel of an MRC CM is changed, or when the upstream channel of a
`CM to which a transmit channel change (TCC) was assigned in the registration process, is
`changed.
`
`Note
`
`Initialization technique 0 is used only with DCC, and not with DBC.
`
`– Initialization Technique 1—(Broadcast initial ranging) may result in a lengthy interruption of
`service, which is mitigated by the reservation of QoS resources on the new channel(s). The
`service interruption can be further reduced if the Cisco CMTS supplies the UCD TLV in the
`DBC request in addition to providing more frequent initial ranging opportunities on the new
`channel.
`– Initialization Technique 2—(Unicast ranging) offers the possibility of only a slight interruption
`of service. To use this technique, the Cisco CMTS must include the UCD TLV in the DBC
`message if the upstream channel is changing.
`– Initialization Technique 3—(Broadcast or unicast ranging) offers the possibility of only a slight
`interruption of service. Use this technique when there is uncertainty when the CM may execute
`the DBC command and thus a chance that it might miss station maintenance slots. However, the
`Cisco CMTS should not use this technique if the conditions for using techniques 1 and 2 are not
`completely satisfied.
`– Initialization Technique 4—(Use the new channel directly) results in the least interruption of
`service.
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` Load Balancing, Dynamic Channel Change, and Dynamic Bonding Change on the Cisco CMTS Routers
`Information on the Load Balancing on the Cisco CMTS Feature
`
`Restrictions for MRC-Only Cable Modems
`
`(cid:129) MRC-only cable modems use single channel non-bonded upstreams (similar to narrowband (NB)
`modems) and multi-channel bonding groups on the downstream.
`
`Note
`
`The following restrictions apply only to DOCSIS 2.0 and DOCSIS 3.0 CMs in MRC-only mode.
`
`(cid:129) CMs are moved across upstream channels using DCC.
`
`(cid:129) CMs are moved across downstream channels b using DBC, if there is no change in the primary
`downstream channel; otherwise DCC with init tech 0 is used.
`
`(cid:129) CMs are moved to different downstream channels through DBC, if there is a change in the upstream
`channel and downstream channel bonding group, but not in the primary downstream channel and the
`upstream channel change is ignored.
`
`However, if there is a change in the primary downstream channel also, DCC with init tech 0 is used
`to balance the CMs.
`
`(cid:129) MRC-only modems are treated similar to CMs operating in MTC mode, to move modems across
`downstream channels. For change in upstream channel, MRC-only CMs are treated similar to
`single-channel NB CMs.
`
`Information on the Load Balancing on the Cisco CMTS Feature
`
`This section describes the operation, concepts, and benefits of the Load Balancing on the Cisco CMTS
`feature.
`
`(cid:129) Feature Overview, page 238
`
`(cid:129) Benefits of Load Balancing, page 253
`
`Feature Overview
`
`The Load Balancing on the Cisco CMTS feature allows service providers to optimally use both
`downstream and upstream bandwidth, enabling the deployment of new, high-speed services such as
`voice and video services. This feature also can help reduce network congestion due to the uneven
`distribution of cable modems across the cable network and due to different usage patterns of individual
`customers.
`
`By default, the Cisco CMTS platforms use a form of load balancing that attempts to equally distribute
`the cable modems to different upstreams when the cable modems register. You can refine this form of
`load balancing by imposing a limit on the number of cable modems that can register on any particular
`upstream, using the cable upstream admission-control command.
`
`However, this default form of load balancing affects the cable modems only when they initially register
`with the Cisco CMTS. It does not dynamically rebalance the cable modems at later times, such as when
`they might change upstream channels in response to RF noise problems, or when bandwidth conditions
`change rapidly because of real-time traffic such as Voice over IP (VoIP) and video services. It also does
`not affect how the cable modems are distributed among downstream channels.
`
`This feature has been enhanced to make use of DOCSIS policies and rules to limit the movement of CMs
`within a Load Balancing Group. A policy defines whether and when CMs can be moved within their load
`balancing groups.
`
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` Load Balancing, Dynamic Channel Change, and Dynamic Bonding Change on the Cisco CMTS Routers
`Information on the Load Balancing on the Cisco CMTS Feature
`
`A policy consists of a set of rules. Each rule can be defined as “enabled”, “disabled”, or “disabled during
`time period.” Multiple policies can share a single rule. However, if you remove the last rule of a policy,
`that will also remove the policy.
`
`Each rule can be used in any number of policies. When it is defined by multiple rules, all rules apply in
`combinations. Each rule helps to prohibit load balancing using a particular CM and to prohibit load
`balancing using a particular CM during certain times of the day.
`
`Following are the general guidel