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Cisco DOCSIS 3.0 Downstream Solution Design and Implementation Guide
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Preface
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Solution Overview
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Cisco DOCSIS 3.0 Downstream Solution Components
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Cisco DOCSIS 3.0 Downstream Architecture
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Implementing and Configuring the Solution
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Monitoring and Troubleshooting Narrowband and Wideband Components
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Cisco DOCSIS 3.0 Downstream Solution Release 1.0 and 2.0 Component Compatibility Matrix
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Table Of Contents
Cisco DOCSIS 3.0 Downstream Solution Architecture
Benefits of M-CMTS Architecture
Gigabit Ethernet Switch Functionality
DOCSIS Timing Interface Server Functionality
Wideband Cable Modem Functionality
Wideband Cable Modem Design and Operation
Cisco DOCSIS 3.0 Downstream Solution
Primary-capable SPA downstream channels
Extensible MAC domain support via Channel Grouping Domain
Virtual bundle support for modular cable interfaces
CMTS Interfaces Associated with a Cable Modem
Enhanced SPA downstream channel support
Load balancing support for DOCSIS 1.x/2.0 modems on SPA RF channels
Primary-capable downstream channel selection
High availability support for cable modems on SPA DS channels
DOCSIS 3.0 Support on a Wideband SPA
Support for Cisco SIP-600 and Gigabit Ethernet SPAs
Voice Support on Wideband Modems
DOCSIS 3.0 Downstream Bonding for Bronze Certification
Cisco DOCSIS 3.0 Downstream Solution Architecture
This chapter explains the architecture used for the Cisco DOCSIS 3.0 Downstream Solution in Cisco IOS Releases 12.2(33)SCB and 12.3(23)BC.
It explains the following topics:
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Gigabit Ethernet Switch Functionality
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The Cisco DOCSIS 3.0 Downstream Solution utilizes the modular CMTS architecture and enables cable operators to optimize their networks for additional bandwidth. The solution provides support for both narrowband and wideband modems allowing both types of modems to share the same SPA downstream channel. The DOCSIS 3.0 Downstream Solution is backward compatible with DOCSIS 1.x/2.0 services and networks.
The Cisco DOCSIS 3.0 Downstream Solution encompasses the following:
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Modular CMTS
The Cisco DOCSIS 3.0 Downstream Solution, Release 2.0, deploys along with the modular CMTS (M-CMTS) architecture. With a modular CMTS architecture, the downstream PHY (physical layer) is located in a separate network element called the edge QAM device, while the packet processing at Layer 2 (DOCSIS) and above is done in the M-CMTS core. In this release, the DOCSIS 3.0 Downstream Solution is provided over the M-CMTS downstream channels.
The CableLabs specification for the M-CMTS architecture defines changes to the edge QAM device that require it to be both DOCSIS-aware and synchronized to the DOCSIS subsystem. The Cisco implementation of the M-CMTS architecture meets this requirement by using the DTCC to acquire timing information from the DTI server and then distribute it within the CMTS.
Figure 3-1 shows the M-CMTS architecture used in the Cisco DOCSIS 3.0 Downstream Solution, Release 2.0 with a single wideband channel. In this example, three downstream RF channels are bonded together into one wideband channel. The Gigabit Ethernet (GE) switch is optional. The user can connect the Wideband SPA Gigabit Ethernet Interface directly to the GE Interface on the Edge QAM.
Figure 3-1 Cisco Cable Wideband M-CMTS Architecture
In the M-CMTS architecture used for the Cisco DOCSIS 3.0 Downstream Solution, Release 2.0, traditional CMTS functionality is divided into three network elements and an interface as follows:
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Benefits of M-CMTS Architecture
Some of the benefits of a modular CMTS architecture are described in these sections:
Cost-Effective Architecture
The Cisco DOCSIS 3.0 Downstream Solution, Release 2.0, can use the Multiple Systems Operator (MSO)'s existing network. Deployed Cisco uBR10012 routers that are used as a DOCSIS 1.x/2.0 CMTS can be upgraded to a modular CMTS by adding on hardware (the Cisco Wideband SIP and SPA) and upgrading software. Some existing external QAM array devices used for video-on-demand (VOD), with a software upgrade, may be able to be deployed as the edge QAM device. For edge QAM devices that have been tested for interoperability, see the "External Edge QAM Device" section on page 2-11.
MSOs can repurpose their existing network infrastructure, including existing fiber nodes, for wideband cable. The benefits of the M-CMTS architecture include:
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With traditional CMTS architecture, adding downstream RF channels for a wideband channel would mean also adding multiple upstreams. With the M-CMTS architecture, multiple downstream RF channels can be added without any additional upstreams. This independent scaling of downstream channels makes the Cisco DOCSIS 3.0 Downstream Solution more cost effective.
Multiservice Architecture
With M-CMTS architecture, the use of external edge QAM devices allows MSOs to use the same network resources for a video-on-demand (VOD) network and a Cisco wideband cable network. With updated firmware, some edge QAM devices can be used for VOD and for wideband channels though individual output QAM channels in the device cannot be shared.
The wideband channel comprising of one or more RF channels on the edge QAM device is used for downstream data traffic. The Upstream channels on Cisco uBR10-MC5X20 cable interface line card are used for upstream traffic. The DTI server is used for signaling messages.
In the Cisco DOCSIS 3.0 Downstream Solution, Release 2.0, traditional DOCSIS 1.x/2.0 services are supported by the CMTS on either the traditional Cisco uBR10-MC5X20 cable interface downstream channels or the edge QAM downstream channels. This release also supports multiservice architecture (see Figure 3-2) with converged IP triple play (voice, data, and video services) on wideband channels, which includes support for DOCSIS 3.0 services.
All services use the same IP/DOCSIS network and share the same RF network resources.
Figure 3-2 M-CMTS Multiservice Architecture
Gigabit Ethernet Switch Functionality
The Gigabit Ethernet switch is an optional device that receives downstream packets from the Cisco Wideband SPA and passes the packets to the edge QAM device. The Gigabit Ethernet switch is used for these purposes:
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If more than two EQAM devices are required for two Wideband SPAs, a Gigabit Ethernet switch is needed to connect the SPAs to the EQAM devices.
If video-on-demand (VOD) traffic and the RF channels for wideband channels are mixed on the same EQAM device, a Gigabit Ethernet switch is required.
When an RF channel for a wideband channel is configured using Cisco IOS commands on the
Cisco uBR10012 router, the rf-channel command mac-address keyword option specifies the MAC address for the next-hop interface on the switch if it is a Layer 2 Gigabit Ethernet switch. The rf-channel command ip-address keyword option specifies the IP address of the Gigabit Ethernet interface on the edge QAM device. The MAC address on the switch and the IP address on the EQAM device are used to route downstream traffic for the RF channel to the correct destinations.DOCSIS Timing Interface Server Functionality
The DTI server interfaces with the edge QAM devices and with the DTCC in the M-CMTS and facilitates communication between M-CMTS, edge QAM devices, and the cable modems by synchronizing timing and frequency between the three devices to nanosecond levels, supporting DOCSIS 3.0 standards. The M-CMTS core is synchronized to the edge QAM device to schedule, correct, and insert MPEG time stamps for video. A cable modem receives its synchronization from the edge QAM device so that it is synchronized to other cable modems to properly transmit to the upstream burst receiver.
Edge QAM Device Functionality
The edge QAM (EQAM) device receives wideband traffic as MPEG-TS over IP on its Gigabit Ethernet interfaces. The edge QAM device extracts the MPEG-TS packets from the MPEG-TS over IP stream and routes them to the proper QAM RF outputs to the HFC plant for transmission to the wideband cable modem.
The edge QAM devices are not involved in the active management of bandwidth or QoS for wideband channels. The edge QAM devices are not aware of the IP addressing used by the wideband cable modems.
Each modular CMTS can support up to four edge QAM devices. The Downstream External PHY Interface (DEPI) interfaces with the edge QAM device and modular CMTS and is used for encapsulation of frames in DOCSIS-MPEG Transport mode over IP to forward packets for primary-capable QAM channels to a synchronous EQAM. Each downstream channel associated with the edge QAM is a narrowband channel and is referred to as a modular-cable interface. The modular-cable interface must forward traffic using DEPI.
The total bandwidth for a single QAM channel can be statically allocated between one or more wideband and narrowband channels. When a wideband channel is configured on the CMTS, the wideband channel uses multiple specified logical RF channels on the Wideband SPA. Each RF channel is associated with a QAM output on the edge QAM device.The bandwidth of an RF channel can be divided between one or more wideband channels as long as the total allocated bandwidth for an RF channel (and QAM channel) does not exceed 100 percent. For more information on configuring RF channels, see the Cisco uBR10012 Universal Broadband Router SIP and SPA Software Configuration Guide.
The QAM channels on the edge QAM device do not have to be adjacent channels. If some of the QAM channels have already been assigned for non-DOCSIS purposes, the Cisco DOCSIS 3.0 Downstream Solution uses the channels that are available. The system does impose certain constraints. For example, if the QAMs are frequency stacked, certain QAMs will have to be adjacent.
Wideband Cable Modem Functionality
The wideband cable modem is a standalone device capable of interoperation with an industry standard DOCSIS 1.x/2.0- or DOCSIS 3.0-compatible CMTS, but it supports wideband operation when used with a wideband CMTS.
The wideband cable modem operates in one of two ways:
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This section focuses on the modem's role as a wideband cable modem. The explanations in this section are generic and apply to all wideband cable modems supported by the Cisco DOCSIS 3.0 Downstream Solution, Release 2.0.
Wideband cable modem functionality may vary depending on the wideband cable modem vendor. For implementation information on vendor-specific wideband cable modems, see the "Wideband Cable Modem Behavior" section in Chapter 4, "Implementing and Configuring the Solution."
Wideband Cable Modem Design and Operation
The wideband cable modem is backward-compatible with DOCSIS 2.0 and contains a complete DOCSIS 3.0 core. Figure 3-3 shows a simplified block view of the wideband cable modem.
Figure 3-3 Wideband Cable Modem Block View
The wideband cable modem has a wideband receiver that receives the multiple RF channels of a bonded channel. It also has a wideband framer that decodes the signal from the wideband receiver and extracts the packets for the 10/100/1000-Mbps Ethernet home network.
The wideband cable modem identifies itself as being wideband-capable during the configuration process. This allows the DOCSIS Trivial File Transfer Protocol (TFTP) provisioning server to enable or disable wideband mode, and to choose the appropriate configuration parameters.
A wideband channel uses the same DOCSIS frame format as a DOCSIS channel uses. The channel just has more bandwidth. A new extended header for wideband has been added to the DOCSIS protocol. The extended header defines the logical wideband channel and a sequence number that the wideband cable modem uses for resequencing the wideband packets.
The CISCO-CABLE-WIDEBAND-MODEM-MIB for the wideband cable modem is supported and is an extension to the existing cable modem MIB.
Cisco DOCSIS 3.0 Downstream Solution
Figure 3-4 illustrates the Cisco DOCSIS 3.0 Downstream solution.
Figure 3-4 Cisco DOCSIS 3.0 Downstream Solution
In Figure 3-4:
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Primary-capable SPA downstream channels
Each SPA DS channel may serve as a primary-capable channel as defined in DOCSIS 3.0. When configured as a primary-capable channel, the SPA DS channel carries the DOCSIS MMM messages including time synchronization (SYNC), bandwidth allocation map (MAP), Upstream Channel Descriptors (UCD), and possibly the primary MAC Domain Descriptor (MDD) messages, along with the non-bonded data traffic.
A SPA DS channel, whether primary-capable or not, can always be part of a bonded channel that carries bonded data traffic.
A SPA DS channel is made primary-capable via Channel Grouping Domain (CGD) configuration. The MAP and UCD messages carried by such a channel may contain the information of all or a subset of the upstream channels, as specified by CGD, in the MAC domain.
A SPA DS channel may only be a primary-capable downstream channel for a single MAC domain. However, the same SPA DS channel may be part of one or more bonded channels (wideband interface) that serve multiple MAC domains.
Modular-Cable Interfaces
Modular-cable (MC) interfaces are logical representations of the downstream channel's capability to carry non-bonded data traffic on the SPA DS channels. MC interfaces are instantiated when the Wideband SPA is inserted. However, for an MC interface to be operational, the underlying SPA DS channel must be configured as a primary-capable channel via the CGD. If a downstream channel is not primary-capable, then sending non-bonded traffic over this downstream is not supported.
RF Channel Bandwidth Allocation
When a SPA DS channel is used by both an MC interface and Wideband interfaces, or when it is used by more than one WB interface, its bandwidth is statically partitioned between both these interfaces. When a SPA DS channel's bandwidth is not allocated to the corresponding MC interface, 100 percent of this bandwidth is available for all the WB interfaces, which includes this SPA DS channel. However, if any amount of bandwidth of an RF channel is used for its modular-cable interface, then only 96 percent of the DS channel bandwidth is available for allocation, for both the MC interface and the WB interfaces that use this DS channel. The remaining 4 percent is reserved for MAPs and other MAC Management Messages, because this SPA DS channel could be enabled as a primary-capable channel to carry such messages.
Enhanced Channel Bonding Support
Because of the ability to use the same SPA DS channel as a primary-capable channel and as part of a wideband channel, a DOCSIS 3.0 modem may use the same tuner to receive the DOCSIS control traffic as well as the bonded traffic on that channel. This allows the modem to make full use of its tuner capability, namely allowing n channel bonding for an n-tuner modem, as long as the modem's primary channel is also part of an n-channel bonding group visible to that modem.
Extensible MAC domain support via Channel Grouping Domain
A Channel Grouping Domain (CGD) is a collection of primary-capable downstream channels that are associated with a common set of upstream channels. A CGD is always specified within the context of a MAC domain to which all the downstream and upstream channels belong. The downstream channel local to the MAC domain on the Cisco uBR10-MC5X20 line card is always primary-capable, but a SPA DS channel has to be made primary-capable by explicit CGD configuration. A CGD provides the additional flexibilty of associating a subset of the upstream channels within a MAC domain to any of the primary-capable downstream channels, including the local downstream channels. When an upstream channel is associated with a downstream channel, its information is included in the MAP and UCD messages sent through that downstream channel.
Multiple CGD configurations may be included in the same MAC domain, allowing the flexibility of the MAC domain to include various primary-capable downstream channels associated with common or different sets of upstream channels.
The operator can define the Channel Grouping Domain in a flexible manner to support a variety of downstream-upstream combinations on a fiber node. Here are a few examples: 2 DS x1 US,
2 DS x 2 US, 3 DS x1 US, 3 DS x 2 US and 4 DS x1 US. The operator can also control the association of upstreams to primary-capable downstreams to ensure that MAPs for a given upstreams are sent on the right set of downstreams instead of being flooded to all downstreams in the CGD and using bandwidth on all downstreams.Figure 3-5 provides an example of how the flexible upstream/downstream association may facilitate the distribution of channel frequencies to different fiber nodes. This illustration only represents the upstream/downstream associations of primary-capable downstream channels.
Figure 3-5 Flexible Upstream/Downstream Associations
Figure 3-5 shows the fiber nodes served by the frequencies of the upstream and downstream associations listed in Table 3-1.
Table 3-1 US/DS Association to FibreNodes
Fiber Node 1
US0 and SPA DS0
Fiber Node 2
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Fiber Node 3
US2 and uBR10-5x20 DS0
Fiber Node 4
US3 and uBR10-5x20 DS0
Therefore, in this example, SPA DS0 needs to be associated only with US0 and US1, and Cisco uBR10-MC5x20 DS0 needs to be associated only with US2 and US3.
Virtual bundle support for modular cable interfaces
The CMTS does not allow the user to explicitly configure virtual bundles on the MC interfaces. When a CGD configuration within a MAC domain designates a SPA DS channel as a primary-capable channel, the corresponding MC interface is exclusively associated with the MAC domain and this MAC domain is referred to as the "hosting MAC domain" of the MC interface. As a result, the MC interface automatically inherits the bundle membership of its hosting MAC domain, that is, if a Layer 3 virtual bundle includes a particular MAC domain (the traditional Cisco uBR10-MC5x20 interface) as its member, it also includes all of the MC interfaces hosted by the same MAC domain.
CMTS Interfaces Associated with a Cable Modem
Previously, the Cisco uBR10-MC5X20 cable interfaces were used to manage both the upstream and downstream traffic to cable modems, but with the introduction of the M-CMTS architecture, there is a need to separate this functionality. While the Cisco uBR10-MC5X20 line card DS interfaces are used to manage upstream traffic, the Cisco uBR10-MC5X20 line card interfaces as well as the SPA DS channel wideband cable interfaces and modular-cable interfaces can be used to manage downstream traffic. Therefore, interfaces from the Cisco uBR10-MC5X20 line card as well as the SPA DS wideband and modular-cable interfaces can be simultaneously involved in the communication with a cable modem.
Here are possible scenarios where interfaces from the Cisco uBR10-MC5x20 line card as well as the SPA DS can be involved in the communication with a cable modem:
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The Cisco uBR10-MC5X20 cable interface is used for both upstream and downstream traffic.
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The Cisco uBR10-MC5X20 cable interface, which is the modular-cable interface's hosting MAC domain via CGD, is used for its upstream traffic only, and the modular-cable interface is used for its downstream traffic.
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The Cisco uBR10-MC5X20 cable interface is used for its upstream traffic and its downstream DOCSIS MAC management messages (MMM). A wideband interface consisting of the SPA DS channels is used for its downstream bonded data traffic.
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The Cisco uBR10-MC5X20 interface, which is the MC interface's hosting MAC domain via CGD, is used for its upstream traffic only. The primary-capable SPA DS channel is used for its DOCSIS MAC management messages, and a wideband interface is used for its downstream bonded data traffic.
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Fiber node
The fiber node configuration on the CMTS is used to construct the MAC domain service groups, or more specifically, the MAC domain downstream service group (MD-DS-SG) as defined in DOCSIS 3.0 in this release. This information is used only by DOCSIS 3.0 modems. DOCSIS 1.x/2.0 modems do not require fiber node configuration.
In hybrid fiber coaxial (HFC) networks, all cable modems connected to the same coaxial segment of a fiber node reach the same set of downstream and upstream channels on one or more CMTSs located at the headend.
A cable modem is physically connected to only one fiber node. On the CMTS, the fiber node software configuration defines the set of channels reaching the fiber node, and this configuration mirrors the physical topology of the cable network.
The fiber node must include at least one primary-capable channel for the modems connected to the fiber node to be operational.The fiber node can include one or more primary-capable channels either from the uBR10-5x20 line card, or from the primary-capable SPA downstream channels or both.
A fiber node configuration must be valid to be able to construct the MD-DS-SG. For a fiber node to be valid, it must satisfy the following conditions:
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Enhanced SPA downstream channel support
This section discusses the enhancements for SPA downstream channels.
L2TPv3 Encapsulation Support on Downstream External PHY Interface
The Cisco DOCSIS 3.0 Downstream Solution supports DEPI data plane MPEG Transport Stream (D-MPT) within the L2TPv3 encapsulation. The parameters required by L2TPv3 should be statically configured for each SPA DS channel and must be consistent between CMTS and EQAM.
A SPA DS channel that is configured to be primary-capable requires sync insertion in the SPA and SYNC restamping by the EQAM. Because this SYNC message handling is not standardized for legacy MPEG over User Datagram Protocol (UDP) format, configuring DEPI D-MPT/L2TPv3 transport for any SPA DS channel that is primary capable is required.
If a SPA DS channel is not used as a primary-capable channel, the legacy MPEG over UDP format is supported for backward compatibility.
The DEPI control plane—protocol negotiation, DLM, Session keepalive, and so on, is not supported in this release.
Flexible Connection of SPA DS Channels to EQAM Channels
Beginning in Cisco IOS Release 12.3(21)BC, the physical layer parameters including annex, modulation, and interleave depth are configurable for each individual SPA DS channel. This allows the SPA DS channels in the same SPA to be tunneled via DEPI to an EQAM where RF channels from the EQAM are configured differently or to different EQAMs.
The following types of connectivity are supported between the SPA and the EQAM:
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Load balancing support for DOCSIS 1.x/2.0 modems on SPA RF channels
Load balancing (LB) is the ability to assign a cable modem to a specific channel in order to utilize the downstream and upstream bandwidth effectively. Downstream load balancing on SPA DS channels is restricted to DOCSIS1.x/2.0 modems. Downstream-only bonding-enabled modems are eligible for upstream load balancing without downstream channel changes. The modular-cable interfaces inherit downstream load balancing group membership from the hosting MAC domain. If the upstream must be changed due to downstream load balancing, the target upstream channel must be associated to the target downstream channel in the CGD configuration, and belong to the same load balancing group as the modem's current upstream channel with a lower load.
The load on an upstream or downstream channel can be measured by one of the following:
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The balanced load can be accomplished by one of the following means:
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For Dynamic Load Balancing, Dynamic Channel Change (DCC) is used for changing a modem's downstream channel, Upstream Channel Change (UCC) is used for changing a modem's upstream channel. Advanced DCC initialization techniques (DCC initialization technique 1 and above, which keeps modem online during the DCC transaction) can be used for channel changes among the DS channels within a CGD or between the CGDs if the CGD hosting interfaces reside on the same
Cisco uBR10-MC5X20 line card. If DCC initialization technique 2 and above, which assumes the timing difference between the source and target channel pairs can be compensated by station maintenance ranging, is desired for channel change between a modular cable interface and a local Cisco uBR10-MC 5X20 DS interface, the EQAM timing delay must be calibrated such that the downstream PHY processing delay at EQAM is consistent with the DS PHY processing delay on a Cisco uBR10-MC5X20 line card.For DS channel changes hosted by different Cisco uBR10-MC5x20 line card, DCC initialization technique 0 will be enforced regardless of DCC initialization configuration in the load balancing group, in which case, the modem will drop offline on the source DS interface and reregister on the target DS interface.
Legacy feature support
The Cisco DOCSIS 3.0 Downstream Solution supports the following legacy features:
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The Cisco DOCSIS 3.0 Downstream Solution supports full DOCSIS QoS, including Committed Information Rate (CIR) support. Downstream low latency service flows for voice are configurable only on wideband interfaces.
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Cisco DOCSIS 3.0 Downstream Solution supports bonded multicast for Linksys cable modems that are capable of 8-channel bonding.
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Cisco DOCSIS 3.0 Downstream Solution introduces support for DSG on DOCSIS 1.x/2.0 modems. DSG tunnel configuration is performed on the host interface and the modular cable interface inherits all DSG configurations of the host interface.The IP Media Gateway (IPMG) static group is enabled at the physical level of the modular cable interface. After the DSG configurations are added to the host interface, the DC Directories (DCD) are replicated on all modular cable interfaces that are part of the CGD.
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Cisco DOCSIS 3.0 Downstream Solution introduces support for SAMIS for service flows on SPA DS channels.
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Cisco DOCSIS 3.0 Downstream Solution introduces support for encryption of unicast packets for narrowband modems using SPA DS channels. The encryption keys are either generated or renewed in the Cisco uBR10-MC5x20 line card MAC domain and then forwarded to the SPA.
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Cisco DOCSIS 3.0 Downstream Solution introduces support for static multicast with BPI on modular-cable interfaces.
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Cisco DOCSIS 3.0 Downstream Solution supports dynamic multicast BPI. The encryption keys for dynamic multicast BPI are generated when an IGMP join is received from the CPE.
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Cisco DOCSIS 3.0 Downstream Solution supports static multicast QoS. The modular-cable interface inherits the QoS parameters from the Cisco uBR10-MC5x20 line card host interface and the cable bundle interface. Service flows are created once the multicast data is received. For modular-cable interfaces, the CMTS assigns unique service flow IDs ranging from 12to16K.
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Cisco DOCSIS 3.0 Downstream Solution supports dynamic multicast QoS. The CMTS adds a service flow only to the DS interface of the cablem modem from which the IGMP join originated and the multicast data is only forwarded to that interface which has the service flow.
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Cisco DOCSIS 3.0 Downstream Solution introduces support for PHS for narrowband modems using SPA DS channels.
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Cisco DOCSIS 3.0 Downstream Solution introduces support for PCMM on wideband and is compliant with PCMM version IO3.
Primary-capable downstream channel selection
This section describes the primary downstream channel selection for wideband, narrowband and voice-enabled modems.
Primary-Capable Downstream Channel Selection for Downstream Bonding Capable Cable Modems
In order to fully utilize downstream bonding capacity, it is desired to force downstream bonding (wideband) capable modems to register on a primary-capable channel that is part of an operational downstream bonding group.
A downstream bonding capable modem is identified upon cable modem registration. A modem is downstream bonding capable if the modem reports a multiple-tuner receive capacity and a Remote Copy Protocol (RCP) known by the CMTS in REG-REQ. A wideband media terminal adapter (MTA) will be treated also as DS bonding-capable modems, therefore subject to the same primary channel selection policy.
In order to select a bonded primary channel (a primary channel that is part of a downstream bonding group), the CMTS needs to know the modem's downstream service group information. If the modem has resolved its MD-DS-SG, the CMTS will select a primary channel that is part of an operational bonding group, which in turn is part of the QAM set corresponding to the MD-DS-SG determined by the modem. The bonded primary channel has to be hosted by an interface on the same Cisco uBR10-MC5X20 line card. A target DS channel will be selected randomly among channels that match the above criteria. If the modem has not resolved the MD-DS-SG, an enforce option is provided through configuration to allow CMTS to select a bonded primary channel based on the MAP group associated to the modem's upstream channel. It is assumed that in many deployed topologies, an upstream channel is configured into a single fiber node, so the CMTS can infer the topology information based on the DS channels associated to the upstream. If no target primary channel can be found, the modem will be allowed to register on its current primary channel.
The primary channel selection for bonding capable modems can be enabled through the global DS channel selection configuration. By default, if such configuration is not present, downstream bonding capable modems will be allowed to operate on a primary channel even it is not included in any load balancing group.
At any time after the system is up, enabling the primary channel selection for bonding capable modems will not affect existing modems in the system. The operator has to manually reset the bonding capable modems through the clear cable modem command either globally or at the per-MAC domain level.
Primary-Capable Downstream Channel Selection for Narrowband Cable Modems
The primary downstream channel selection for narrowband modems is intended to provide the operator the flexibility to segregate non-bonding capable modems to specific types of DS channels with the following two options:
Redirecting Modems that Access a CMTS with Legacy DOCSIS INIT-RNG-REQ at Initialization
This option allows the operator to prevent potential non-bonding capable modems. The modems initialize with legacy initial ranging request message type, INIT-RNG-REQ, by registering to a CMTS that is loaded with bonding capable modems. Although a DOCSIS 3.0 modem may also send INIT-RNG-REQ if it fails to receive the MAC Domain Descriptor (MDD), this option allows the operator to filter out and redirect all potential pre-DOCSICS 3.0 non-bonding capable modems at the modem's initial ranging time without waiting for modem registrations. The target frequency is specified using downstream frequency in Hertz. If the target frequency matches one or multiple downstream channels on the local CMTS, load balancing will be disabled on these downstream channels to prevent modems being moved away from the target channel for load balancing purposes.
Moving Non-Bonding Capable Modems to Bonding-Disabled Primary Channels
This option allows the operator to restrict non-bonding capable modems to non-bonded primary channels on the CMTS. A more stringent method is applied for this option to identify the non-bonding capable modems, by decoding the modem's Multiple Receive Channel Support capability (type-length-value (TLV) 5.29) and RCP ID (TLV 48.1) in the registration request. A modem is non-bonding capable if it reports value 1 for TLV5.29 or RCP IDs unknown to the CMTS. With this option, a non-bonding capable modem, identified at registration, will be moved to a non-bonded primary channel through downstream frequency override, if its current primary channel is part of a bonding group. The target non-bonded primary channel will be selected among primary capable channels that are associated to the modem's current upstream channel, however not included in any bonding groups associated to any host interfaces on the local line card. Once this option is enabled, the bonded primary channels will be taken out of the load balancing group to prevent non-bonding capable modems from being moved back to bonded primary channels for load balancing purposes.
The above two options can be enabled through the global DS channel selection configuration. By default, if the configuration is not present, the modem will be allowed to continue the ranging process on its current primary channel. At any time after the system is up, enabling DS channel selection to segregating non-bonding capable modems will not affect existing modems in the system. Additionally, if the frequency specified for the target DS channel is changed, the new frequency setting will only affect new modems trying to initialize after the frequency change. In order to enforce the DS selection policy on existing modems, the operator mustmanually reset the non-bonding capable modems through the clear cable modem command.
Downstream Channel Selection for Voice-Enabled Cable Modems
This downstream channel selection option provides the operator the ability to provide high-availability for voice services by restricting voice-enabled modems to Cisco uBR10-MC5X20 downstream channels.
A voice-enabled cable modem is identified either at registration by decoding Dynamic Host Control Protocol (DHCP) TLV 122 in the modem's DHCP-ACK, or at its first voice call if DHCP TLV 122 is not exchanged. If a voice-enabled modem is detected at registration on a SPA DS channel, it will be moved to the Cisco uBR10-MC5X20 DS channel in the CGD via downstream frequency override. If the voice-enabled modem is detected at its first voice call after registration, it will be moved after the call is over to the Cisco uBR10-MC5X20 DS channel in the CGD via DCC using DCC initialization technique 1. If the voice-enabled modem fails to come up on the target Cisco uBR10-MC5X20 DS channel, the CMTS will continue to move the modem until the maximum number of retries (3) has been reached, when the modem will be allowed to stay on the SPA DS channel until another set of retries is attempted by the CMTS every 24 hours. A voice-enabled modem on the Cisco uBR10-MC5X20 DS channel will be excluded from being load balanced to a SPA downstream channel.
The downstream channel selection option to support high availability for voice-enabled modems can be enabled via global downstream channel selection configuration. By default, if such configuration is not present, voice-enabled modems are allowed to operate on both the Cisco uBR10-MC5X20 downstream channel and SPA downstream channels in the CGD. If this option is enabled at any time after the system is up, voice-enabled modems that have been identified on the SPA dowsntream channel without active voice calls will be gradually moved to the Cisco uBR10-MC5X20 DS channel in the CGD at the rate of one modem per five seconds.
High availability support for cable modems on SPA DS channels
Cisco High Availability is technology delivered in Cisco IOS Software that enables network-wide resilience to increase IP network availability. This feature is supported for PRE redundancy, N+1 redundancy for the Cisco uBR10-MC 5X20 line cards, and N+1 failover of the modular host line card. A Wideband SPA does not support DOCSIS 3.0 Downstream Solution operations by itself and uses a modular host line card for these high-availability operations. The higher system availability feature is implemented using the HCCP and high availability infrastructure for N+1 redundancy and PRE redundancy allowing the cable modems to stay online in certain failure scenarios.
When a narrowband cable modem uses a SPA RF downstream channel and a Cisco uBR10-MC5X20 MAC domain host, and if the Cisco uBR10-MC5X20 MAC domain host to which the SPA RF channel belongs fails, the modem stays online because of N+1 redundancy of the Cisco uBR10-MC5X20 line card.
In a scenario in which a wideband cable modem's SPA uses a Cisco uBR10-MC5X20 line card as a modular host, which is different from the modem's MAC domain, which is defined by the CGD, if the modular host Cisco uBR10-MC 5X20 line-card fails, the modem stays online because of the N+1 redundancy support for the modular host on the Cisco uBR10-MC 5X20 line-card. However, N+1 redundancy for MAC domains is not supported for wideband cable modems. If a wideband cable modem's MAC domain interface fails, the modems go offline.
For more information on the modular host line card, refer to the modular-host subslot command in the Cisco Broadband Cable Command Reference.
Table 3-1 summarizes the scenarios in which the modems are functional during specific component failures.
High Availability for Voice Modems
The Cisco DOCSIS 3.0 Downstream Solution, Release 2.0 provides higher system availability for voice services by providing the ability to restrict voice services only to Cisco uBR10-MC5X20 line cards. This allows the CMTS to make an attempt to move the voice modems to the hosting Cisco uBR10-MC5X20 line cards of Cisco uBR10-MC5X20 downstream channels in the same load balancing group.
DOCSIS 3.0 Support on a Wideband SPA
The Cisco DOCSIS 3.0 Downstream Solution is an industry-standard DOCSIS 3.0 implementation of channel bonding. With channel bonding, bandwidth is increased by combining or bonding multiple RF channels to create a wideband channel. The Cisco DOCSIS 3.0 Downstream Solution extensions affect the CMTS and the cable modem as well as the provisioning and network management systems. A 3-channel cable modem that performs 3-channel bonding must be able to access three SPA RF channels of which at least one RF channel must be a primary-capable channel that is used for modem registration.
The core of the Downstream 3.0 downstream solution is the sending of DOCSIS packets for a given service flow across multiple RF channels, offering significant increases in the peak downstream data rate that can be provided to a single cable modem. The transmit framer in the Cisco Wideband SPA "stripes" the DOCSIS packets for a given flow and transmits them across the multiple RF channels of the wideband channel. When the packets are received at the wideband cable modem, the modem's receiver framer uses a sequence number embedded in each DOCSIS packet to reassemble the packets into the original flow.
The Cisco DOCSIS 3.0 Downstream Solution defines a wideband channel as a unique combination of downstream RF channels from the same SPA. The wideband CMTS manages up to 64 wideband channels (32 wideband channels per Wideband SPA). A wideband cable modem uses a wideband channel. Many wideband cable modems can share the same wideband channel.
The Cisco Wideband SPA on the Cisco uBR10012 router provides DOCSIS 3.0 channel bonding for DOCSIS Network processing. In the Cisco DOCSIS 3.0 Downstream Solution, Release 2.0, for the wideband downstream channel, the Wideband SPA uses its Gigabit Ethernet port to send data traffic to the EQAM device. This EQAM device uses one or more QAM output channels, depending on how the wideband channel is configured, to send striped packets to the wideband cable modem. In Cisco DOCSIS 3.0 Downstream Solution, channel bonding is used for downstream wideband channels only. A downstream wideband channel can combine up to three RF channels for a total bandwidth of over hundreds of megabits to gigabits per second with bonded modems supporting data rates of up to 292 Mbps.
In Release 2.0, channel bonding is used for downstream wideband channels only.
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Figure 3-6 shows a wideband channel consisting of three bonded RF channels on the EQAM device. These RF channels are asynchronous and carry only bonded traffic.
Figure 3-6 Channel Bonding to Create a Wideband Channel
For information on configuring wideband channels, see the Cisco uBR10012 Universal Broadband Router SIP and SPA Software Configuration Guide.
Security
A wideband channel uses Baseline Privacy Plus (BPI+) for its link level encryption. BPI+ provides cable modem users with data privacy across the cable network by encrypting traffic flows between the wideband cable modem and the wideband CMTS. BPI+ also provides MSOs with protection against theft of service.
The wideband cable modem uses the same BPI+ keys on its wideband channels as it does on its DOCSIS 1.x/2.0 channels. The wideband cable modem uses the BPI+ keys negotiated on the primary service flow of the DOCSIS 1.x/2.0 downstream channel for the service flows on the wideband channel.
Quality of Service
For a modem that uses a wideband interface or MC interface as its downstream data forwarding interface, its service flows will be associated with the Wideband or MC interface. The bandwidth for the WB or MC interfaces may vary due to configured bandwidth partitioning. The traditional support for cable QoS is otherwise unchanged.
Support for Cisco SIP-600 and Gigabit Ethernet SPAs
The Cisco 10000 Series SPA Interface Processor-600 (referred to as the Cisco SIP-600) is a high-performance, feature-rich SPA interface processor (SIP) that functions as a carrier card for shared port adapters (SPAs) on the Cisco uBR10012 router. The SIP is compatible with the following platform-independent SPAs in Cisco IOS Release 12.2(33)SCB:
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The Cisco SIP-600 is supported on both PRE2 and PRE4 configurations. With a PRE2 configuration, the Cisco SIP-600 can support up to four Cisco Wideband SPAs, and with a PRE4 configuration, the SIP can support up to six Cisco Wideband SPAs.
The Cisco SIP-600 is a full-height line card that occupies two physical slots in a Cisco uBR10012 router. Each chassis supports a maximum of two SIPs that can be inserted in the following slots:
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The Cisco SIP-600 supports four bays (subslots) for the installation of SPAs. The SPA bays are numbered from 0 to 3 on a Cisco uBR10012 router. The number for each SPA bay is indicated by a small numeric label on the SIP faceplate.
SPAs on a Cisco uBR10012 router use an addressing format that specifies the physical location of the SIP, SPA, and interface in the format slot/bay/port, where:
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For more information about the Cisco SIP-600 and supported SPAs, see the Cisco uBR10012 Universal Broadband Router SIP and SPA Hardware Installation Guide and Cisco uBR10012 Universal Broadband Router SIP and SPA Software Configuration Guide.
Wideband Modem Resiliency
In the Cisco IOS Release 12.2(33)SCB, the Wideband Modem Resiliency feature enables the Cisco uBR10012 router to interact with DOCSIS 3.0-compliant cable modems in order to provide the best possible service in the event of non-primary radio frequency channel disruptions such as loss of quadrature amplitude modulation (QAM), forward error correction (FEC) locks, and MAC Domain Descriptor (MDD) time-outs. If a CM loses connectivity to the CMTS on one or all of its non-primary RF channels, the CMTS does not force the CM to perform a MAC reset and enables the CM to remain operational.
A DOCSIS 3.0-qualified CMTS transmits data to one or more DOCSIS 3.0-compliant cable modems using multiple RF channels. For a CM, one of the RF channels is used as the primary RF channel, and the rest of the channels are considered non-primary channels. The primary RF channel is defined to be the downstream (DS) RF channel on which the CM receives DOCSIS MAC messages needed for upstream timing and synchronization.
This feature enables the CMTS to collect and analyze data related to RF channel disruptions per cable modem and identify the impairment.
For more information on how the Wideband Modem Resiliency feature enables the Cisco uBR10012 router to interact with DOCSIS 3.0-compliant cable modems, see the Wideband Modem Resiliency feature guide.
Dynamic Bandwidth Sharing
Dynamic bandwidth sharing (DBS) is the dynamic allocation of bandwidth for wideband (WB) and modular cable (MC) interfaces sharing the same downstream channel. The bandwidth available to each WB, MC, or narrowband channel is not a fixed value-it depends on the configuration and the traffic load on the WB or MC.
DBS is achieved using a new type of modality called a link queue. Link queues represent a specific share of bandwidth on a particular channel. Link queues are only used to calculate the effective bandwidth of a channel, and such link queues are activated and deactivated according to the state of activity on a specific channel. DBS and static bandwidth allocations are configured at the WB or MC interface level. By default, bandwidth for a WB or MC channel is statically allocated. When DBS is enabled on an interface, the static bandwidth percentage is converted to a committed information rate (CIR) value for the corresponding link queue. The interface CIR value represents the guaranteed portion of the interface bandwidth and is used for admission control of the service flows with minimum reserved rate. When DBS is enabled, you can also specify the remaining ratio value of the excess bandwidth for the link queue. If DBS is enabled and no bandwidth percentage is specified, no bandwidth is reserved for the WB or MC interface and the interface is effectively in protocol down state where link queues are not created.
Dynamic bandwidth sharing does not preclude static bandwidth configuration. If a static portion of bandwidth is configured on any radio frequency (RF) channel that one or more DBS-enabled channel utilizes, that portion is subtracted from the RF link's CIR. Therefore, such a portion is always reserved and is not available to dynamic WB or MC interfaces. The DBS feature continues working across line card and performance routing engine (PRE) switchovers with no loss of functionality.
For more information on dynamic allocation of bandwith for WB modems and MC interfaces, see the Dynamic Bandwidth Sharing on the Cisco CMTS Router feature guide.
DOCSIS WQF Scheduler
The Data-over-Cable Service Interface Specifications (DOCSIS) Weighted Fair Queuing (WFQ) Scheduler is an output packet scheduler that provides output scheduling services on both WAN uplink interfaces and DOCSIS downstream interfaces.
In Cisco IOS Release 12.2(33)SCB, 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.
For more details on the DOCSIS WQF Scheduler, see the DOCSIS WFQ Scheduler on the Cisco CMTS Routers feature guide.
Voice Support on Wideband Modems
CMTS supports voice services on voice-enabled wideband (WB) cable modems. Committed information rate (CIR) downstream service flows on WB interfaces are supported. You can reserve up to 90% of the wideband interface bandwidth. If multiple MAC domains (MDs) are sharing a WB interface, the available link rate is distributed evenly between all MDs that share the WB interface. If the MDs that share the WB interface are on the same line card, they share the CIR pool.
To display the reserved and available bandwidth, you can use the show-module bay all association wideband command. To display the reserved and available bandwidth for wideband interfaces, you can use the show interface wideband-cable command. For more information, see the Cisco IOS CMTS Cable Command Reference Guide.
Note
DOCSIS 3.0 Downstream Bonding for Bronze Certification
The DOCSIS 3.0 Downstream Bonding for Bronze Certification feature enables high-speed broadband access (100 Mbps) and helps cable operators offer more bandwidth-intensive services by adding one or more additional downstream quadrature amplitude modulation channels to the standard broadband DOCSIS system. This new set of downstream channels is grouped into one larger channel, known as a bonded channel.
For more information on the DOCSIS 3.0 Downstream Bonding for Bronze Certification, see the DOCSIS 3.0 Downstream Bonding for Bronze Certification feature guide.
