Chapter 21: Integrated Upstream Agility
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
663
An improvement trigger causes a transition to another state when the operating conditions of the upstream channel
improve to a certain degree. The improvement threshold is defined by a unique metric derived from the uncorrectable FEC
error percentage, the errored (= uncorre correctable) FEC error percentage, and the average sampled SNR over a
period of time.
A degradation trigger causes a transition to another state when the operating conditions on the upstream channel
deteriorate past a certain threshold. Like the improvement trigger, the metric that defines the degree of degradation is
derived from the uncorrectable FEC error percentage, the errored (= uncorre correctable) FEC error percentage,
and the average sampled SNR over a period of time.
The Integrated Upstream Agility feature permits fine-tuning of channel parameters, such as a modification of the T or K
values for Forward Error Correction (FEC). It also permits substantial changes, such as a switch from 16 QAM to QPSK or
even a change in the channel width for a particular upstream channel. This is accomplished by assigning a different
Modulation Profile to the upstream channel or changing the channel width of the channel. Finally, the system operator can
use this feature to change the center frequency of the channel, if necessary, to avoid ingress noise in one part of the
spectrum. Using such changes in a carefully selected order, the MSO can maximize upstream throughputs.
Examples of Upstream Agility State Machines
In this example the MSO has selected two center frequencies for upstream transmission: 20 MHz and 28 MHz, two
modulation profiles: 16 QAM with FEC T=2 for low noise conditions and QPSK with FEC=10 for noisy conditions, and two
channel widths: 3.2 MHz for low noise conditions 1.6 MHz for noisy conditions.
What combination of these channel configurations should be used for operation by the upstream channel? If Integrated
Upstream Agility is enabled with an appropriate state machine, then the feature itself can determine which combination is
best at a given time. In this specific example Integrated Upstream Agility first tries the combination that offers the highest
throughput. If that combination provides acceptable performance, then Upstream Agility does not alter the channel
settings. If the performance becomes unacceptable, then Upstream Agility changes the channel settings to recover
acceptable performance. If the performance becomes unacceptable again, then the Integrated Upstream Agility feature
either reverts to the original channel configuration or tries other settings, depending on how the state machine is
configured, until acceptable performance is restored.
