DOCSIS Checklists
Headend (Downstream) CMTS or Upconverter Output
Test
performed

Parameter
CMTS downstream IF output
Digitally modulated carrier
amplitude at upconverter input
Digitally modulated carrier
amplitude at upconverter
output
Digitally modulated carrier
center frequency
Carrier-to-noise ratio
Modulation error ratio (MER)3
Pre-FEC BER4
Post FEC BER5
Amplitude ripple (in-channel
flatness)
Group delay ripple
Constellation evaluation
Parameter value
Measured
value/comments
+42 dBmV1
+25 to +35 dBmV2
+50 to +61 dBmV
91-857 MHz
Not less than 35 dB
64-QAM: 27 dB minimum
256-QAM: 31 dB minimum
N/A
Less than or equal to 10-8
3 dB6
75 ns maximum
Look for evidence of gain
compression; phase noise; I-Q
imbalance; coherent
interference; excessive noise;
and clipping
1. Check with your CMTS manufacturer to confirm correct downstream IF output level, typically
specified at a value similar to that shown here (+/- 2 dB).
2. Nominal average power level input range to most external upconverters. Check upconverter
manufacturer’s specifications to confirm recommended input level. Note that an in-line
attenuator (pad) between the CMTS IF output and upconverter input may be required.
3. Downstream MER is not a DOCSIS parameter. The values shown are minimum values that
represent good engineering practice. MER measured in the headend generally will be in the
34 to 36 dB or higher range. The upconverter’s input and output MER should be at or near
the same value. A change of more than 1~2 dB indicates a possible upconverter problem.
4. DOCSIS does not specify a minimum pre-FEC BER. Ideally there should be no pre-FEC bit
errors at the CMTS or upconverter output.
5. Ideally there should be no post-FEC bit errors at the CMTS or upconverter output.
6. DOCSIS 1.0 specifies 0.5 dB for this parameter, however, it was relaxed to 3 dB in DOCSIS
1.1.
DOCSIS Checklists
Headend (Downstream) Laser Transmitter or First
Amplifier Input, Node Output
Test
performed

Parameter
Parameter value
Measured
value/comments
Digitally modulated carrier
average power level relative to
-10 to -6 dBc
analog TV channel visual
carrier amplitude
Digitally modulated carrier
center frequency
91-857 MHz
Carrier-to-noise ratio
Not less than 35 dB
Modulation error ratio (MER)1
64-QAM: 27 dB minimum
256-QAM: 31 dB minimum
Pre-FEC BER2
N/A
Post FEC BER3
Less than or equal to 10-8
Amplitude ripple (in-channel
flatness)
3 dB4
Group delay ripple
75 ns maximum
Constellation evaluation
Look for evidence of gain
compression; phase noise; I-Q
imbalance; coherent
interference; excessive noise;
and clipping
1. Downstream MER is not a DOCSIS parameter. The values shown are minimum values that
represent good engineering practice. MER measured in the headend and node output
generally will be in the 34 to 36 dB or higher range.
2. DOCSIS does not specify a minimum pre-FEC BER. Ideally there should be no pre-FEC bit
errors at the downstream laser or first amplifier input.
3. Ideally there should be no post-FEC bit errors at the downstream laser or first amplifier
input.
4. DOCSIS 1.0 specifies 0.5 dB for this parameter, however, it was relaxed to 3 dB in DOCSIS
1.1.
DOCSIS Checklists
Input to Cable Modem
Test
performed

Parameter
Parameter value
Digitally modulated carrier
91-857 MHz
center frequency
Digitally modulated carrier
average power level relative to
-10 to -6 dBc
analog TV channel visual
carrier amplitude
Digitally modulated carrier
-15 to +15 dBmV
average power level1
Carrier-to-noise ratio
Not less than 35 dB
Total downstream RF input
power2
<+30 dBmV
Modulation error ratio (MER)3
64-QAM: 27 dB minimum
256-QAM: 31 dB minimum
Pre-FEC BER4
N/A
Post FEC BER
Less than or equal to 10-8
Look for evidence of gain
compression; phase noise; I-Q
imbalance; coherent
interference; excessive noise;
and clipping
Constellation evaluation
Amplitude ripple (in-channel
flatness)
3 dB5
Hum modulation
5% (-26 dBc)
Maximum analog TV channel
visual carrier level
+17 dBmV
Minimum analog TV channel
visual carrier level
-5 dBmV
Transit delay from CMTS to
most distant cable modem6
<=0.800 millisecond
Signal level slope, 50-750 MHz 16 dB
Group delay ripple7
75 ns
Measured
value/comments
1. While DOCSIS specifies –15 to +15 dBmV, good engineering practice suggests that
maintaining digitally modulated carrier levels in the –5 to +5 dBmV range will be less likely
to overload the modem.
2. Total power of all downstream signals in the 40-900 MHz frequency range.
3. Downstream MER is not a DOCSIS parameter. The values shown are minimum values that
represent good engineering practice, although in a properly operating cable network the
MER should be in the low- to mid-30s at the cable modem input.
4. DOCSIS does not specify a value for pre-FEC bit error rate.
5. DOCSIS 1.0 specifies 0.5 dB for this parameter, however, it was relaxed to 3 dB in DOCSIS
1.1 and 2.0.
6. Transit delay may be estimated.
7. In-channel group delay may be measured using Sunrise Telecom’s Avantron AT2000RQ
(must have latest firmware/software) or AT2500RQv. See
http://www.sunrisetelecom.com/broadband.
DOCSIS Checklists
CMTS Upstream Input
Test
performed

Parameter
Parameter value
Digitally modulated carrier
bandwidth
Digitally modulated carrier
symbol rate
Digitally modulated carrier
center frequency
Digitally modulated carrier
amplitude1
Total 5-42 MHz RF spectrum
power
200, 400, 800, 1,600 or 3,200
kHz
160, 320, 640, 1,280 or 2,560
ksym/sec
Must be within 5-42 MHz
spectrum
-16 to +26 dBmV depending on
symbol rate
Carrier-to-noise ratio
Not less than 25 dB2
Carrier-to-interference ratio
Not less than 25 dB2
Carrier-to-ingress power ratio
Not less than 25 dB2
Hum modulation
7% (-23 dBc)
Amplitude ripple
0.5 dB/MHz
Group delay ripple3
200 ns/MHz
Measured
value/comments
Must not exceed +35 dBmV
Transit delay from most distant
<=0.800 millisecond
cable modem to CMTS4
1. Default value for most CMTSs is 0 dBmV, although this may be set to other values.
2. Measured at CMTS upstream input port. The value shown is an in-channel value.
3. Upstream group delay may be measured with an instrument such as Holtzman, Inc.’s Cable
Scope™. See http://www.holtzmaninc.com/cscope.htm.
4. Transit delay may be estimated.