DOCSIS 3.1 Downstream Profile Selection

First Published: July 13, 2016

DOCSIS 3.1 introduces the concept of downstream profiles for OFDM channels.

Contents

Hardware Compatibility Matrix for the Cisco cBR Series Routers


Note
The hardware components that are introduced in a given Cisco IOS-XE Release are supported in all subsequent releases unless otherwise specified.
Table 1. Hardware Compatibility Matrix for the Cisco cBR Series Routers

Cisco CMTS Platform

Processor Engine

Interface Cards

Cisco cBR-8 Converged Broadband Router

Cisco IOS-XE Release 16.5.1 and Later Releases

Cisco cBR-8 Supervisor:

  • PID—CBR-SUP-250G

  • PID—CBR-CCAP-SUP-160G

  • PID—CBR-CCAP-SUP-60G

Cisco IOS-XE Release 16.5.1 and Later Releases

Cisco cBR-8 CCAP Line Cards:

  • PID—CBR-LC-8D30-16U30

  • PID—CBR-LC-8D31-16U30

  • PID—CBR-RF-PIC

  • PID—CBR-RF-PROT-PIC

  • PID—CBR-CCAP-LC-40G

  • PID—CBR-CCAP-LC-40G-R

  • PID—CBR-CCAP-LC-G2-R

  • PID—CBR-SUP-8X10G-PIC

  • PID—CBR-2X100G-PIC

Digital PICs:

  • PID—CBR-DPIC-8X10G

  • PID—CBR-DPIC-2X100G

Cisco cBR-8 Downstream PHY Module:

  • PID—CBR-D31-DS-MOD

Cisco cBR-8 Upstream PHY Modules:

  • PID—CBR-D31-US-MOD

Information about Downstream Profiles

A profile is a list of modulation orders that are defined for each of the subcarriers within an OFDM channel. The CMTS can define multiple profiles for use in an OFDM channel, where the profiles differ in the modulation orders assigned to each subcarrier. The CMTS can assign different profiles for different groups of CMs.

Default Data Profile

The first time a CM registers, it is assigned a default data profile. The default data profile is "profile-data 1". If "profile-data 1" is not configured, "profile-control" is assigned to the CM.

Note

Profile A, with profile ID 0, is also referred to as the control profile.

Recommended Profile

Based on the Receive Modulation Error Ratio (RxMER) values collected from a modem, the CMTS finds among the existing profiles the one that may provide the highest speed, and yet at the same time may have sufficient Signal to Noise Ratio (SNR) margin for the modem to receive code words with acceptable error. This profile is called the recommended profile for that CM. The show cable modem phy ofdm-profile command displays the recommended profile for each CM. Recommended Profile will take effect when the CM is reset by the operator. When the CM comes back online, recommended profile is assigned to it.

Internal PMA is enabled by default on the cBR-8. If external PMA is enabled, internal PMA is disabled and can be enabled by running the following config command on the cBR-8: 

no cable downstream ofdm-prof-mgmt prof-upgrade-pma

In external PMA, the cBR-8 does not automatically upgrade a CM's profile to the recommended profile. In internal PMA, the profile can be upgraded to the recommended profile in the next OFDM Profile Test (OPT) cycle.

A user configurable age is associated with each recommended profile, which can be configured as follows: 
Router (config)#cable downstream ofdm-prof-mgmt recommend-profile-age age-in-minutes
If the recommended profile exceeds this age, it is no longer valid for that CM.

Unfit Profile

When the CMTS receives CM-STATUS Event 16 (DS OFDM Profile Failure), the profile indicated in the CM-STATUS message is marked as 'unfit profile' for this modem.

A user configurable maximum age is associated with each unfit profile, which can be configured as follows: 
Router (config)#cable downstream ofdm-prof-mgmt unfit-profile-age age-in-minutes
If the unfit profile for a modem exceeds this age, it is no longer valid.

How to Configure Profiles

Configuring Profile Downgrade

A CM sends a CM-STATUS Event 16 message to indicate a DS OFDM profile failure. When this indication is received by the CMTS, it takes immediate action to downgrade the modem to a lower profile, as per the profile ordering displayed by the following command: 
Router# show controllers integrated-Cable 2/0/3 rf-channel 158 prof-order
The following table, extracted from [DOCSIS 3.1 MULPI], lists the CM-Status events that will trigger a profile downgrade:
Table 2. Table: CM-Status Events for Profile Downgrade

Event Type

Event Condition

Status Report Events

Parameters reported by CM

Trigger event to "on"

Trigger event to "off"

DCID

Profile ID

16

DS OFDM profile failure

Loss of FEC lock on one of the assigned downstream OFDM profiles of a channel

Re-establishment of FEC lock for that OFDM profile;

OR

Removal of the channel from the active channel list in the primary channel MDD;

OR

Removal of the channel from the CM's Receive Channel set via DBC-REQ

Yes

Yes

To disable the automatic profile downgrade, use the following command in global configuration mode: 
Router (config)#no cable downstream ofdm-prof-mgmt prof-dwngrd-auto

Configuring RxMER to Bit Loading Mapping

There are many ways to map the RxMER values to bit loading values. We use the following mapping recommended in [DOCSIS 3.1 OSSI], as our baseline mapping:

RxMER (in ¼ DB)

QAM

Bit Loading

60

16

4

84

64

6

96

128

7

108

256

8

122

512

9

136

1024

10

148

2048

11

164

4096

12

184

8192

13

208

16384

14

  • To configure a margin to adjust the RxMER to bit loading mapping, use the following command: 
    Router(config)# cable downstream ofdm-prof-mgmt mer-margin-qdb quarter-DB
    This configured value (quarter-DB) is added to the RxMER values collected by CMTS before using the above mapping table, thus giving a user more control in selecting the recommended profiles.
  • To specify the percentage of subcarriers that can be ignored in the recommended profile calculation, use the following command: 
    Router(config)# cable downstream ofdm-prof-mgmt exempt-sc-pct percent
    This provides a way to specify the extent that the outliers can be ignored.

Configuring Hitless OFDM Profile Changes

The recommended Pofile Management & Application (PMA) tool operation is as follows:

  1. PMA determines that the modulation order of a data profile in an OFDM channel can be upgraded or downgraded, based on the MER data received from cable modems that uses the profile.

  2. Poll cBR for all modems with active profiles to identify inactive ones.

  3. Move modems to temporary data profile (not control profile) if all are in use.

  4. Delete any unused OFDM profile. The PMA repeats step 2 and step 3 to avoid race conditions.

  5. Add (or Delete/Add) a new OFDM profile with the desired modulation order to the OFDM channel.

  6. Define the new profile list for the modems (DBC sent to modems by cBR).

  7. Move modems to new profile.

Configuring Ephemeral Profile to Cable Modem Assignment

If the modem is not listening to the desired profile, you can submit up to 4 data profiles. The Profile Management & Application (PMA) wants to be active for that cable modem before issuing the profile assignment command. The control profile zero (0) is always assumed to be included.

The following commands are supported:

  • cable modem <mac> ofdm-set-profiles chan <n> profiles <profile list>

    This command will initiate a DBC to the cable modem with the specified profile list. The profile list order defines the downgrade profile in case of cm-status 16.

  • cable downstream ofdm-flow-to-profile interface <integrated-Cable x/y/z:n> profile-data <n> mac- address <mac>

    This command enables the CMTS to start forwarding all traffic to the cable modem using the specified profile. Ensure that you use the accompanying cable modem mac-address mac opt0 command for the changes to take effect immediately.

    Move the cable modems traffic to one of the profiles it is listening to. DBC is not necessary. If the profile is not active on the cable modem then CLI will report error. If the CMTS receives a CM-STATUS 16 for that profile, the CMTS downgrades the profile automatically.

    Note that the does not reset when moving to another profile.

Additional References

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Feature Information for Downstream Profile Selection

Use Cisco Feature Navigator to find information about the platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to the https://cfnng.cisco.com/ link. An account on the Cisco.com page is not required.


Note

The following table lists the software release in which a given feature is introduced. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Table 3. Feature Information for Downstream Profile Selection

Feature Name

Releases

Feature Information

Downstream Profile Selection

Cisco IOS XE Everest 16.6.1

This feature was integrated into Cisco IOS XE Everest 16.6.1 on the Cisco cBR Series Converged Broadband Routers.

Hitless OFDM Profile Changes

Cisco IOS XE Everest 16.12.1x

This feature was integrated into Cisco IOS XE Everest 16.12.1x on the Cisco cBR Series Converged Broadband Routers.

Ephemeral Profile to Cable Modem Assignment

Cisco IOS XE Everest 16.12.1x

This feature was integrated into Cisco IOS XE Everest 16.12.1x on the Cisco cBR Series Converged Broadband Routers.