A cable modem sends a CM-STATUS event 16 message to the CMTS to indicate a downstream OFDM profile failure. CMTS would react
to CM-STATUS events by either downgrading the profile or changing the cable modem status to partial service.
When a cable modem reports a CM-STATUS event 16 message for profile 0, the profile is neither added to the unfit list, nor
any action is taken. As a result, the cable modem continues to send data on OFDM profile 0 which can lead to to packet loss.
This can result in FEC errors on profile 0 for the cable modem. Periodic RxMER measurements do not show the problem, which
leaves the cBR-8 still scheduling data on an OFDM channel using profile 0. This may cause downgraded performance for the cable
modem.
Downstream Resiliency Enhancements for Profile 0
Table 3. Feature History
Feature Name
|
Release Information
|
Feature Description
|
Downstream Resiliency Enhancements
|
Cisco IOS XE Dublin 17.12.1z
|
With this release, the CMTS response to a cable modem's CM-STATUS event 16 message is optimized for profile 0.
Profile 0 is processed in the same way as FEC Loss or MDD timeout and hence experiences the same benefits of better performance
and reduced packet loss.
Command introduced: ofdm-rf-change-trigger prof-zero-fail dampen-time seconds recovery-multiplier number .
|
When a cable modem sends a CM-STATUS event 16 message to the CMTS to indicate a downstream OFDM profile failure, CMTS does
not downgrade the profile or change the cable modem status to partial service. Instead, downstream resiliency rules are applied,
resulting in a better handling of Profile 0.
Handling CM-STATUS Event 16
When a CMTS handles a CM-STATUS event 16 on profile 0 as a downstream impairment:
-
Downstream resiliency moves the OFDM channel to the Down state after the configured dampen-time .
-
Cable modem enters a downstream partial-service (p-online) state.
-
Cable modem downstream service flows (SF) move to RBG or NB with existing downstream resiliency logic.
Handling CM-STATUS Event 24
When a CMTS handles a CM-STATUS event 24 on profile 0 as a as a downstream impairment recovery:
-
Downstream resiliency uses this event to indicate the recovery of event 16 impairment.
-
CMTS moves the OFDM channel to Up state after the configured duration (dampen time * recovery multiplier).
-
Cable modem moves back to wideband online (w-online) state.
-
Cable modem downstream service flows (SF) move to the original bonding group existing downstream resiliency logic.
See
Configuring Downstream Resiliency for Profile 0
Configuring downstream resiliency for profile 0 is disabled by default. This sample configuration shows how to configure Downstream
Resiliency for profile 0:
Router# configure terminal
Router(config)# cable ofdm-rf-change-trigger prof-zero-fail dampen-time 20 recovery-multiplier 2
-
Use the dampen-time seconds option to specify the time in seconds for a non-primary RF channel to remain in its current state before downstream resiliency
processes a CM-STATUS event.
-
Use the recovery-multiplier to set an event specific recovery delay that is equal to the dampen-time in seconds times the recovery-multiplier value.
The following example shows how to disable downstream resiliency for profile 0:
Router# configure terminal
Router(config)# no cable ofdm-rf-change-trigger
Disabling downstream resiliency for profile 0, resets dampen-time and recovery-multiplier values to 0. No resiliency action for CM-STATUS 16 and 24 is performed for profile 0 if this feature is disabled. The following
example shows a sample configuration to disable the feature.
Router# configure terminal
Router(config)# no cable ofdm-rf-change-trigger
Router(config)# end
Router# show run all | sec prof-zero-fail
cable ofdm-rf-change-trigger prof-zero-fail dampen-time 0 recovery-multiplier 0