This section describes terminologies used while configuring SPAs:
Wideband Channel or Bonding Group
A wideband channel or bonding group is a logical grouping of one or more physical radio frequency (RF) channels over which wideband MPEG-TS packets are carried. By aggregating or “channel bonding” multiple RF channels, the wideband channel is capable of greater bandwidth capacity for downstream data traffic than a single narrowband channel. During Cisco Wideband SPA configuration, each wideband channel is associated with one or more RF channels. Each Cisco Wideband SPA supports 32 wideband channels.
A narrowband channel is a logical representation of a non-bonded channel that is a standard DOCSIS 1.x/2.0 protocol downstream channel that contains one RF channel.
A wideband-cable interface is a logical representation of the channels in the bonding group and is configured using the interface wideband-cable command.
A modular-cable interface is a logical representation of the downstream channel’s capability to carry non-bonded data traffic on the SPA downstream channels and is configured using the interface modular-cable command.
The Cisco DOCSIS 3.0 Downstream Channel Bonding feature can be deployed in parallel with DOCSIS 1.x/2.0 technology. The CMTS supports DOCSIS 1.x/ 2.0 modems on non-wideband interfaces while wideband cable modems deliver higher-speed throughput on the wideband ports.
For a fiber node to be in valid state, all wideband and modular cable interfaces that use the RF channels in the fiber node must belong to the same virtual bundle interface. You must assign virtual bundle numbers for wideband interfaces using CLI configuration. The bundle membership of the MAC domain, namely the line card host interface, is inherited by the modular-cable interface via the CGD configuration.
Wideband-Cable Interfaces Belonging to the Same Virtual Bundle
The example below shows wideband-cable interfaces that belong to the same virtual bundle. Fiber node 1 includes RF channels 0 to 3 of Cisco Wideband SPA 1/0/0 and these RF channels are used by two wideband interfaces.
The fiber node is in valid state because the two wideband channels share the same RF channel and the wideband interfaces are in the same virtual bundle.
This example shows the syntax supported prior to Cisco IOS Release 12.2(33)SCB.
no ip address
cable bundle 1
cable bonding-group-id 36
cable rf-channel 0 bandwidth-percent 90
cable rf-channel 1 bandwidth-percent 50
cable rf-channel 2
no ip address
cable bundle 1
cable bonding-group-id 37
cable rf-channel 1 bandwidth-percent 50
cable rf-channel 2
cable rf-channel 3
Modular-Cable Interfaces Belonging to the Same Virtual Bundle
In the example shown above, if RF channel 0 of the Cisco Wideband SPA 1/0/0 is configured as a primary-capable channel and is associated with the line card host interface 6/0/1, then the modular-cable interface 1/0/0:0 inherits the bundle membership of this host interface. This bundle number must be the same as the two wideband interfaces, interface Wideband-Cable 1/0/0:12 and interface Wideband-Cable 1/0/0:13. Otherwise, fiber node 1 that includes the RF channels 0 to 3 will be in invalid state.
The virtual bundle number of the wideband or modular-cable interfaces cannot be changed after the RF channels that belong to these interfaces are added to the fiber node. To change the virtual bundle number, you must remove the RF channel from the fiber node before making the change.
All wideband channels on a fiber node and all associated primary downstream channels must belong to the same virtual bundle interface. The tasks involved in configuring wideband channels and primary downstream channels as members of the same virtual bundle are as follows:
Define a virtual bundle interface.
Use the cable bundle command to add wideband channels as virtual bundle members.
For recent releases of Cisco IOS, a virtual bundle interface with virtual bundle members has replaced the master-slave model that was previously used for cable bundles. The virtual bundle model is used in Cisco IOS Release 12.3(21)BC and subsequent releases.
Primary-Capable Downstream Channel
A SPA downstream channel is made primary-capable via Channel Grouping Domain (CGD) configuration. A primary-capable downstream channel can carry narrowband traffic as well as wideband traffic. An RF channel is considered primary-capable when it has been associated with one or more upstream channels from a Cisco uBR10-MC5X20 cable interface and this RF channel can carry DOCSIS MAC management messages (MMM) including SYNC messages, Mini-slot Allocation Packet (MAP) messages, and Upstream Channel Descriptors (UCDs). Such an RF channel downstream is referred to as a primary-capable downstream channel. A DOCSIS Timing Interface (DTI) server that interfaces with the EQAM device and the Cisco DTCC card is used to synchronize DOCSIS MAC-layer messages. The interface represented by a single primary-capable downstream represents the narrowband portion of the RF channel.
A SPA downstream channel, whether primary-capable or not, can always be part of a bonded channel that carries bonded data traffic.
An RF channel can be shared by the associated modular-cable interface and by the wideband interfaces. The bandwidth of each RF channel can be configured to be statically divided between the modular-cable and wideband interfaces. Each RF channel’s bandwidth can be used for wideband channels or narrowband channels or for a combination of the two.
A primary downstream channel is a primary-capable channel that is being used as a narrowband channel or as part of a wideband channel. 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. A primary downstream channel of one MAC domain can serve as non-primary downstream channel of another MAC domain. The total available bandwidth of a primary downstream channel, which is 96 percent, is split between the primary-capable downstream and non-primary-capable downstream channels. The remaining 4 percent is reserved for DOCSIS MAP and SYNC bandwidth.
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 under a cable interface, where the downstream channels can be shared by one or more upstreams.. 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 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.
A CGD is created using the following:
Figure 1. MAC Domain Support via Channel Grouping Domain Configurations
Upstream channels 1 to 8 from a single line card
A single downstream from the line card (This downstream can optionally be disabled.)
Downstream channels 0 to 24 from one or more SPAs
In this example:
The Interface Cable 5/0/0 serves as the Channel Grouping Domain host downstream channel.
Upstream channels 0 to 3 from the line card are associated, by default, with the CGD host downstream channel.
Downstream RF channels 0 and 1 from the SPA residing in slot 1, subslot 0, and bay 0 are associated with the line card upstream channels 0 and 1.
Downstream RF channels 1 and 3 from the SPA residing in slot 1, subslot 0, and bay 0 are associated with the line card upstream channels 2 and 3.
The downstream channel from the line card can serve either as a MAC domain or as a primary downstream channel.
The CGD allows load balancing groups to be created across one or more CGDs and enables the load balancing groups by default within the CGDs.
Fiber Node Configuration
In a cable network, a fiber node is a point of interface between a fiber trunk and the coaxial portion of the cable plant. A cable modem is physically connected to only one fiber node. Fiber node software configuration mirrors the physical topology of the cable network and is needed to optimize the DOCSIS MAC-layer messages for channel bonding. When configuring fiber nodes with Cisco IOS CLI commands, a fiber node is a software mechanism to define the following:
The set of downstream RF channels that will flow into the fiber node
At least one primary downstream channel for the fiber node
The set of upstream channel ports on the cable interface line card that are connected to the fiber node and available as upstream channels
A fiber node will be associated with at least one primary downstream channel. A fiber node can be associated with more than one primary downstream channel though only one primary downstream channel is used at any given point in time. Each primary-capable downstream channel can be associated with up to 8 fiber nodes. All channels that belong to a fiber node are configured with different non-overlaying frequencies.
Fiber Nodes for Wideband
In a cable network, a fiber node is a point of interface between a fiber trunk and the coaxial distribution. A cable modem is physically connected to only one fiber node. Fiber node software configuration mirrors the physical topology of the cable network. When configuring wideband channels, a fiber node is a software mechanism to define a set of downstream and upstream channels that will flow into the physical fiber node.
Configuring cable fiber nodes with the cable fiber-node command is required for fiber nodes that are used for wideband channels. Cable fiber node configuration does not allow downstream interfaces to be combined into the same fiber node unless they are members of the same virtual bundle interface.
For a wideband channel to work correctly, each fiber node must be configured as follows:
Use the cable fiber-node command to create the fiber node and to enter cable fiber-node configuration mode.
Use the downstream cable command to associate the fiber node with one or more line card downstream channels. Each fiber node should have at least one primary downstream. This command is optional if the primary downstream channel for this fiber node is assigned from a SPA downstream.
Use the upstream command to specify the upstream channel ports that are connected to a fiber node.
Use the downstream modular-cable rf-channel command to associate one or more SPA RF channels or primary-capable RF channels from the SPA with the fiber node.
Optionally, use the description command to specify a description for the fiber node.
For each fiber node, a primary downstream channel is used to carry SYNCs, MAPs, and other MAC-layer management messages, and the associated upstream channel is used to carry MAC management messages. A DTI server that interfaces with the EQAM device and the Cisco DTCC card is used to synchronize DOCSIS MAC-layer messages.
In Cisco IOS Release 12.3(21)BC, the primary downstream channel, which is a traditional DOCSIS downstream channel on the cable interface line card, is used to carry MAC management and signaling messages, and the associated traditional DOCSIS upstream channel is used for return data traffic and signaling.
Beginning in Cisco IOS Releases 12.3(23)BC and 12.2(33)SCB, either an RF channel from the SPA or a line card downstream channel can serve as a primary channel in a fiber node. If the fiber node does not have a line card downstream channel, then make sure that at least one of the RF channels specified in the downstream modular-cable rf-channel command is a primary-capable downstream channel.
The maximum number of cable fiber nodes that can be configured is limited to 256 for each CMTS.
Load Balancing Groups
A Load Balancing Group (LBG) is an operator-configured managed object that controls how the CMTS assigns the service flows of registered cable modems among an identified set of upstream and downstream channels of the CMTS.
An operator configures a Load Balancing Group with the following attributes:
A Load Balancing Group Index unique within the CMTS
A set of downstream and upstream channels in the same MAC Domain cable modem Service Group (MD-CM-SG)
A boolean optionally configuring the LBG as a “Restricted” LBG
A policy that governs if and when the cable modem or its individual service flows can be moved
A priority value that can be used by the CMTS in order to select which cable modems and service flows to move
For more information on load balancing, see the Cisco DOCSIS 3.0 Downstream Solution Design and Implementation Guide.
Primary Downstream Channel Selection in a Fiber Node Configured with Downstreams from the Cable Interface Line Card and SPA Downstreams
If a fiber node is configured with a primary downstream from a cable interface line card as well as a primary downstream from the SPA that is part of a wideband channel, then the primary downstream channel selection depends on the downstream channel selection policies (that govern when the cable modem can be moved) implemented and enforced by the configuration. The fiber node can be configured to force a Scientific Atlanta DPC2505 (EPC2505 for EuroDOCSIS) to perform 3-channel bonding. But this will also depend on the implemented downstream channel selection policies that govern when the cable modem can be moved.
Wideband Cable Modems
The number of RF channels that can be aggregated into a wideband channel is determined by the capability of the wideband cable modem. The Cisco Cable Wideband Solution, Release 2.0 supports DOCSIS 3.0-compliant multichannel modems, including the following Linksys and Scientific Atlanta modems:
Linksys WCM300-NA, WCM300-EURO, and WCM300-JP Modems
For wideband channels, the Linksys WCM300-NA (WCM300-EURO for EuroDOCSIS and WCM300-JP for Japanese DOCSIS) wideband cable modem supports the receiving of a 50-MHz capture window of up to eight different downstream RF channels at 6 MHz per channel, or six different downstream RF channels at 8 MHz per channel. In addition to these eight RF channels, the Linksys WCM300 modem supports reception of one primary downstream channel (traditional DOCSIS channel).
The Linksys WCM300 wideband cable modem software supports the acquisition of up to eight wideband (bonded) downstream channels:
One primary bonded channel is the wideband channel on which the wideband cable modem receives all of its unicast data and some multicast data.
Up to two secondary bonded channels are the wideband channels on which the wideband cable modem receives common multicast data streams. Secondary bonded channels are intended to receive multicast data such as broadcast video that is not available on the primary bonded channel.
The DOCSIS configuration file and the cable bonding-group-id command define the primary and secondary bonded channels for the modem to select and acquire. The cable modem identifies the primary bonded channel and any secondary bonded channels to the CMTS at cable modem registration time.
For information on how the Linksys WCM300 modem selects primary and secondary bonded channels, see the Cisco DOCSIS 3.0 Downstream Solution Design and Implementation Guide, Release 2.0.
Scientific Atlanta DPC2505 and EPC2505 Modems
When used with the Cisco uBR10012 CMTS, the Scientific Atlanta DPC2505 and EPC2505 (for EuroDOCSIS) wideband cable modems support the receiving of one wideband channel, which consists of up to three bonded downstream RF channels from the SPA at 6 MHz per channel or at 8 MHz per channel. One of the RF channels from the Cisco Wideband SPA serves as the primary downstream channel.
The Scientific Atlanta DPC2505 is DOCSIS 3.0-compliant and can be used in this mode (for example, if the modem is connected to a non-wideband Cisco CMTS or to a non-Cisco CMTS). The modem is also backward compatible with existing DOCSIS 1.x networks.