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Chapter 3
Cisco CMTS Show Commands
Table 3-27 Descriptions for the show cable modem phy Fields (continued)
Field
USPwr (dBmV)
USSNR (dBmV)
Timing Offset
Microreflec (dBc)
DSPwr (dBmV)
DSSNR (dBmV)
Note
Mode
OL-1581-08
Description
Displays the CM transmit level in dBmV, as measured by the CMTS.
Upstream signal-to-noise ratio (SNR) or carrier-to-noise ratio (CNR), in dB,
as measured by the CMTS. This field shows the CNR value for cable
interfaces that support onboard hardware-based spectrum management, such
as the Cisco uBR-MC16S card, and shows the SNR value for other cable
interfaces.
Although the field name shows the value as being given in dBmV, the
Note
actual value should be interpreted in dB.
The timing offset for the CM, in ticks, as recognized on the CMTS. (A tick,
as used here, is 6.25/64 microseconds.) This is the delay between when a
particular cable modem is scheduled to make a transmission and when the
CMTS actually receives it.
An exclamation point (!) in the Timing Offset column indicates that
Note
the CM has exceeded the maximum delay and timing offset specified
by the
The timing offset shown here is typically smaller than the TX Time
Note
Offset value shown by the
command, because the latter value is the offset as recognized on the
CM (which will include any internal delay between when the CM
software begins the transmission and when the bits actually appear on
the local cable interface).
The approximate value of microreflections on the downstream, measured in
dBc below the signal level, as seen by the CM. Microreflections are a type of
impairment that is caused by impedance mismatches between amplifiers,
couples, cables, and other equipment in the cable plant. Microreflections
create copies of a signal that arrive at the receiver with different amounts of
delay and attenuation, generating intersymbol interference (ISI) that can
cause the receiver to improperly detect the amplitude and phase of the
incoming signal.
Note
This value is not exact but provides an approximate indication of the
microreflections that have been received.
Downstream receive power level, in dBmV, as reported by the CM.
Downstream signal-to-noise ratio (SNR), in dB, as reported by the CM.
This command displays values for the downstream power and SNR values only if you have
configured the
cable modem remote-query
providing those options.
DOCSIS operating mode for the CM:
•
tdma=DOCSIS 1.X, TDMA-only mode
•
atdma=DOCSIS 2.0 A-TDMA mode
A hyphen (-) indicates the mode is unknown or the CM has not yet registered.
This field is the same as that returned by the
Note
docsIfCmtsCmStatusModulationType object in the DOCS-IF-MIB.
cable map-advance
command.
show cable modem remote-query
command on the CMTS, and if the CM supports
Cisco Broadband Cable Command Reference Guide
show cable modem phy
3-103
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