Cisco Cisco IOS Software Release 12.1(3)EC
Cisco uBR7200 Series Dynamic Upstream Modulation
Feature Overview
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Cisco IOS Release 12.1(3a)EC1
Feature Overview
Noise in the upstream line from the consumer to the service provider degrades data transmission from
the subscriber home. If the noise impairment is of substantial duration, it may cause the cable modem
to temporarily lose communication with the headend facility altogether. As a contingency plan,
Multiple Service Operators (MSOs) can reserve multiple upstream frequencies or channels for their
subscribers so that if one channel suffers too much interference, the Cable Modem Termination System
(CMTS) requests that the cable modems hop to another channel. This method of ingress avoidance is
called frequency agility. The Dynamic Upstream Modulation feature in
Cisco IOS Release 12.1(3a)EC1 checks that the upstream signal can support the configured modulation
scheme, and adjusts to a more robust modulation scheme if necessary. When return path conditions
improve, this feature returns the upstream channel to the higher modulation scheme.
the subscriber home. If the noise impairment is of substantial duration, it may cause the cable modem
to temporarily lose communication with the headend facility altogether. As a contingency plan,
Multiple Service Operators (MSOs) can reserve multiple upstream frequencies or channels for their
subscribers so that if one channel suffers too much interference, the Cable Modem Termination System
(CMTS) requests that the cable modems hop to another channel. This method of ingress avoidance is
called frequency agility. The Dynamic Upstream Modulation feature in
Cisco IOS Release 12.1(3a)EC1 checks that the upstream signal can support the configured modulation
scheme, and adjusts to a more robust modulation scheme if necessary. When return path conditions
improve, this feature returns the upstream channel to the higher modulation scheme.
The upstream channel is characterized by many cable modems transmitting to the CMTS. These signals
operate in a burst mode of transmission. Time in the upstream channel is slotted. The CMTS provides
time slots and controls the usage for each upstream interval.
operate in a burst mode of transmission. Time in the upstream channel is slotted. The CMTS provides
time slots and controls the usage for each upstream interval.
The Cisco uBR7200 series equipment periodically broadcasts Upstream Channel Descriptor (UCD)
messages to all cable modems. These messages define upstream channel characteristics including
upstream frequencies, symbol rates and modulation schemes, FEC parameters, and other physical layer
values.
messages to all cable modems. These messages define upstream channel characteristics including
upstream frequencies, symbol rates and modulation schemes, FEC parameters, and other physical layer
values.
Cisco supports all DOCSIS error correction encoding and modulation types and formats. Upstream
signals are demodulated using Quadrature Phase Shift Keying (QPSK) or Quadrature Amplitude
Modulation (16QAM). QPSK carries information in the phase of the signal carrier, but 16QAM uses
both phase and amplitude to carry information.
signals are demodulated using Quadrature Phase Shift Keying (QPSK) or Quadrature Amplitude
Modulation (16QAM). QPSK carries information in the phase of the signal carrier, but 16QAM uses
both phase and amplitude to carry information.
Sending data reliably in the upstream direction is an issue because upstream spectrum varies greatly
between cable plants. Select upstream parameters based on your cable plant’s return paths.
between cable plants. Select upstream parameters based on your cable plant’s return paths.
Tips
Customize upstream profiles for maximum trade-offs between bandwidth, efficiency, and
upstream channel robustness. For example, 16QAM requires approximately 7dB higher
carrier-to-noise ratio (CNR) to achieve the same bit error rate (BER) as QPSK, but
transfers information at twice the rate of QPSK.
upstream channel robustness. For example, 16QAM requires approximately 7dB higher
carrier-to-noise ratio (CNR) to achieve the same bit error rate (BER) as QPSK, but
transfers information at twice the rate of QPSK.
Caution
You can assign upstream modulation profiles to specific upstream ports based on the Cisco
cable modem card used. But, only those familiar with Data Over Cable Service Interface
Specification (DOCSIS) who have received the proper training should create upstream
modulation profiles.
cable modem card used. But, only those familiar with Data Over Cable Service Interface
Specification (DOCSIS) who have received the proper training should create upstream
modulation profiles.
Dynamic Upstream Modulation adjusts the modulation profiles of an upstream channel based on
upstream signal quality. A modulation profile is a collection of six burst profiles that are sent out in a
UCD message to configure modem transmit parameters for the upstream message types: request,
request/data, initial maintenance, station maintenance, short grant, and long grant.
upstream signal quality. A modulation profile is a collection of six burst profiles that are sent out in a
UCD message to configure modem transmit parameters for the upstream message types: request,
request/data, initial maintenance, station maintenance, short grant, and long grant.
The return path of several fiber nodes can be combined together at a single point to form a single RF
frequency domain called a combiner group. The frequency hop table associated with a combiner group
is called a spectrum group. Dynamic Upstream Modulation can be configured on interfaces with fixed
upstream frequencies or on interfaces with assigned spectrum groups.
frequency domain called a combiner group. The frequency hop table associated with a combiner group
is called a spectrum group. Dynamic Upstream Modulation can be configured on interfaces with fixed
upstream frequencies or on interfaces with assigned spectrum groups.