Downstream Multiple Receiver Capabilities

This section describes the mechanism by which the CM communicates to the CMTS the constraints on receive channel assignment imposed by the CM's capabilities. The CMTS needs to be aware of the CM's capabilities when it assigns or changes the parameters of a downstream channel received by a CM. If the CM were reconfigured without regard to its capabilities, a disruption of downstream data and/or DOCSIS master clock synchronization could result. The CM reports its capabilities to the CMTS by sending its Receive Channel Profiles (RCP). In response, the CMTS configures the CM by sending a Receive Channel Configuration (RCC).

The CM MUST support all the capability it reports to the CMTS.

The CMTS MUST NOT command the CM to operate outside its advertised capabilities.

The [MULPI3.0] specification defines the detailed encodings by which Receive Channel Profiles and Receive Channel Configurations describe Receive Modules, Receive Channels, and the interconnections between them.

6.3.4.1 Receive Module Parameters

A Receive Module (RM) is a grouping of channels, together with parameters describing the constraints on those channels. Examples of RMs are:

• Tuner, with constraints on capture bandwidth and frequency range.

• Demodulator, with constraints on contiguous positioning of channels, frequency range, modulation order, and interleaver depth.

A Receive Channel Profile communicated from CM to CMTS defines the following attributes of each Receive Module:

• Adjacent Channels: The number of contiguous channels processed by the Receive Module.

• Channel Block Range: The minimum center frequency of the lowest-frequency channel in the block and the maximum center frequency of the highest-frequency channel in the block.

• Common Physical Layer Parameters: A list of physical layer parameters which are shared by all Receive Channels connected to the Receive Module. Examples may include modulation type and interleaver settings.

• Connection Capability: A list of the higher level (closer to RF port) Receive Modules to which this Receive Module can connect.

A Receive Channel Configuration (RCC), communicated from CMTS to CM, assigns one or more of the following attributes of a Receive Module:

• First Channel Center Frequency: Center frequency of the lowest-frequency channel of a block of adjacent channels.

• Connection Assignment: Specifies to which single higher-level Receive Module to connect.

6.3.4.2 Receive Channel Parameters

A Receive Channel (RC) is the packet stream output to the MAC layer originating from a single QAM channel. A Receive Channel Profile, communicated from CM to CMTS, defines the following attributes of each Receive Channel:

• Connection Capability: A list of the Receive Modules to which the Receive Channel can connect.

• Connected Offset: The offset of the Receive Channel within a block of adjacent channels.

• Primary Downstream Channel Capability: A flag indicating whether the Receive Channel is capable of providing the DOCSIS master clock reference to the CM.

A Receive Channel Configuration communicated from CMTS to CM assigns the following attributes to a Receive Channel:

• Center Frequency Assignment: The RF center frequency of the Receive Channel.

• Primary Downstream Channel Indicator: A flag indicating that the CMTS assigns this Receive Channel the responsibility to provide master clock reference timing to the CM.

• Connection Assignment: Specifies to which Receive Module the Receive Channel is to connect.

6.3.4.3 Standard Receive Channel Profile

In order to limit the complexity in the CMTS of configuring arbitrarily complicated Receive Channel Profiles, DOCSIS defines a set of "Standard" Receive Channel Profiles that describe a minimal set of constraints.

A CM reports to the CMTS at least one standard RCP as well as its "Manufacturer" RCP that gives more details of its capabilities and constraints. If the CMTS configures the CM with a Receive Channel Configuration based on a Standard RCP, some CM capabilities represented in the Manufacturer RCP but outside the Standard RCP may not be available.

The Standard Receive Channel Profile named "6-DOCSIS-01" is defined for 6 MHz operation as depicted in Figure 6–33. The RF input from the cable plant is connected to a Receive Module with a block of 10 adjacent channels. This Receive Module represents the constraints of a tuner with a 60 MHz capture bandwidth that can be placed at any point in the full DOCSIS frequency range. The demodulation of four channels anywhere within the capture bandwidth is represented by the four Receive Channels, each corresponding to the packet stream from a single QAM channel output to the MAC layer.

Tuner

Receive Module 1 [ Adjacent Channels Constraint: 10 ]

RC1 RC2 RC3 RC4 MAC Sublayer Receive Channels (each cor- responds to single QAM channel) Packets RF Port Diplexer Splitter RF Connection to HFC Plant

Figure 6–33 - 6 MHz DOCSIS Standard Receive Channel Profile 01

For this Standard Receive Channel Profile, the CMTS sends the following parameters to the CM in the Receive Channel Configuration:49

• Center frequency of the first channel in the 10-channel Receive Module.

• Center frequency of each Receive Channel within the capture bandwidth of the Receive Module.

6.3.4.4 Example Manufacturer Receive Channel Profile

A more complex example showing a Manufacturer Receive Channel Profile as reported by the CM to the CMTS is depicted in Figure 6–34. The RF input from the cable plant is distributed to three Receive Modules, corresponding to tuner modules with capture bandwidth constraints. A network connects the tuners to a group of four Receive

Modules, corresponding to demodulators with contiguous channel constraints. Each demodulator connects to four Receive Channels, each representing a single QAM channel output to the MAC layer.

In response, the CMTS configures each Receive Module and Receive Channel as follows:

• Frequency range of each analog tuner.

• Center frequency of first channel of each demodulator.

• Center frequency of each Receive Channel.

• Interconnection between Receive Modules.

• Interconnection between lower-level (demodulator) Receive Modules and Receive Channels.

RF Connection to HFC Plant

RF Port Diplexer Splitter

Tuner Receive Module 1 Tuner Receive Module 2 Tuner Receive Module 3 Demodulator Receive Module 4 Demodulator Receive Module 5 Demodulator Receive Module 6 Demodulator Receive Module 7 Interconnection Network RC1 RC2 RC3 RC4 RC5 RC6 RC7 RC8 RC9 RC10 RC11 RC12 RC13 RC14 RC15 RC16 MAC Sublayer Receive Channels (each corresponds to single QAM channel) Packets

Figure 6–34 - Example Manufacturer Receive Channel Profile

6.3.4.5 Reconfiguration of CM Receive Channels

Before the CMTS sends a DBC-REQ (dynamic bonding change request) asking the CM to change parameters of a receive channel, the CMTS can determine the constraints and connectivity of the CM based on the Receive Channel Profile and Receive Channel Configuration. From this information, the CMTS can determine whether the requested change can be implemented by the CM, and whether the change will interrupt other downstream channels. In this way, the CMTS can minimize and/or schedule the disruption of downstream traffic and any perturbations to DOCSIS master clock timing resulting from receive channel parameter changes.