Sunrise Telecom Presents:
Cable 101
Sales Training – CATV Products
D’strea
m
Upstrea
m
Shift
On-Line
Link
Ethern
et
ESC
CM200
0
By: Jerry Green
March 2010
Proprietary & Confidential
1
Agenda
In the beginning……
System Architectures
Signal on the Network
Channel Allocations
Analog Channels
Digital Channels
System Sweep
DOCSIS
Future
March 2010
Proprietary & Confidential
2
It all began…..
1948 – John Walson of Pennsylvania installs an antenna on the
mountain and runs twin-lead wires to his appliance store. TV
sales soared. John began to connect customers to his antenna
& changes the wire to coaxial cable to improve picture quality.
1948 - Ed Parson, of Astoria, Oregon built a CATV system
consisting of twin-lead strung from housetop to house top.
1950 – Bob Tarlton, of Lansford Pennsylvania used coaxial cable
on utility polls under a franchise from the city.
Community Antenna Television (CATV) was born.
March 2010
Proprietary & Confidential
3
First Network Architecture
System components:
–
Preamp installed at antenna
–
Maybe a ‘booster’ in the tree
–
300 ohm ‘Railroad Track’ wire
Number of channels:
–
1 to 10
Performance:
–
OK to poor
March 2010
Proprietary & Confidential
4
Test Equipment of the 1950’s & 60’s
Jerrold 704
•Developed 1951
•Manufactured from 1952 to 1967
Jerrold 727
•Developed 1966
•Manufactured from 1967 to mid 70’s
Portable TV
•Measure levels with modified unit
•See distortions
March 2010
Proprietary & Confidential
5
Tapped Trunk Architecture
antennas
Distrib.
Amp.
Signal
Combining
tap
Coax. cable
drop
Headend
March 2010
Proprietary & Confidential
6
Trunk/Bridger Architecture
Antenna Tower
Headend
TV Transmitter
Typical amplifier cascades:
35+ amplifiers.
March 2010
Proprietary & Confidential
7
Trunk/Bridger Architecture with Return
March 2010
Proprietary & Confidential
8
Microwave Transport
March 2010
Proprietary & Confidential
9
Hybrid Fiber Coax (HFC) Architecture
Fiber Link
Fiber Link reduces the
number of amplifiers in
cascade
March 2010
Proprietary & Confidential
10
Broadband networks HFC architectures
Hybrid Fiber-Coaxial Network Infrastructure
Remote
Site
Optical Fiber
Primary
Hub 3
Node
Node
Node
Coax. cable
Secondary
Hub 3
Antennas
Main
HeadEnd
Earth station
Primary
Hub 1
Optical
Fiber
Ring
Secondary
Hub 1
Secondary
Hub 2
Node
Node
Node
Node
Node
Primary
Hub 2
March 2010
Proprietary & Confidential
11
What is the Forward Path of the System
Forward Signal Path
H
R
R
L
Return Equip.
Each amplifier compensates for
the loss in the wire before the
amplifier under test.
Signal flow in the forward
path is from the headend to
the customers home as
indicated by the blue arrows.
March 2010
Proprietary & Confidential
12
Sample Amplifier
Forward Path
Forward Amplifier
Slope
Control
-20 dB
Response
Equalizer
-20 dB
T.P.
T.P.
H
L
H
L
AGC / ASC
H
L
T.P.
Return Amplifier
March 2010
Bridger Amplifier
Proprietary & Confidential
-20 dB
13
What is the Return Path
Return Signal Path
H
R
R
L
Return Equip.
Each amplifier compensates for
the loss in the wire after the
amplifier under test.
Signal flow in the return
path is from the customers
home to the headend as
shown by the blue arrows.
March 2010
Proprietary & Confidential
14
Sample Amplifier
Return Path
Forward Amplifier
Slope
Control
-20 dB
Response
Equalizer
-20 dB
T.P.
T.P.
H
L
H
L
AGC / ASC
H
L
T.P.
Return Amplifier
March 2010
Bridger Amplifier
Proprietary & Confidential
-20 dB
15
Signals on the Network
March 2010
Proprietary & Confidential
16
Channel Types & Terms
Analog
– NTSC, PAL, SECAM
Digital
– 64QAM, 256QAM, 8VSB
– Annex A, Annex B, Annex C
– DOCSIS, EuroDOCSIS
March 2010
Proprietary & Confidential
17
Digital Channel Penetration
–
Evolution of digital signals penetration in HFC
transport architecture
C
2000
90 % analog TV
10% digital TV
March 2010
2005
60 % analog TV
40% digital TV
2008
25 % analog TV
75% digital TV
Proprietary & Confidential
2012
0 % analog TV
100% digital TV
18
Why change to Digital?
Bandwidth efficiency allows more program channels
Picture quality improvement
Better conditional access system
Supports HDTV
Not content dependent
March 2010
Proprietary & Confidential
19
PAL Cable Frequency Allocation
March 2010
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20
Channel Plan
March 2010
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21
Analog TV Standard Spectrum
March 2010
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22
Analog TV, NTSC / PAL / Secam / HDTV
Lines/Image
Images/second
Horizontal
Frequency
Vertical Frequency
–
HDTV
SDTV
March 2010
NTSC
PAL
SECAM
525
625
625
30
15.734
kHz
59.94 Hz
25
15.625
kHz
50 Hz
25
15.625
kHz
50 Hz
High Definition Television (HDTV)
•
16:9 Format (widescreen)
Format
Horizontal
lines
Horizontal
Pixels
Image
Format
1080p
1080p
1080i
720p
720p
720p
480p
480p
480p
480i
480i
480i
1080
1080
1080
720
720
720
480
480
480
480
480
480
1920
1920
1920
1280
1280
1280
640
640
640
704
704
640
16:9
16:9
16:9
16:9
16:9
16:9
4:3
4:3
4:3
16:9
4:3
4:3
Proprietary & Confidential
Display
Images per
scanning
second
format
Progressive
24
Progressive
30
Interlaced
30
Progressive
24
Progressive
30
Progressive
60
Progressive
24
Progressive
30
Progressive
60
Interlaced
30
Interlaced
30
Interlaced
30
23
Spectrum Analysis
Ch. 3 Spectrum Analysis
Ch. Allocation
6 MHz
V/A
4.5 MHz
V/Color
3.58 MHz
Lower Band
Edge
60.00 MHz
March 2010
Video
Carrier
61.25 MHz
Audio
Carrier
65.75 MHz
Proprietary & Confidential
Lower Band
Edge
60.00 MHz
24
VITS Signals
Horizontal Blanking
525
LINES
485
LINES
Receiver Frame
SCAN MOTION
Vertical Blanking
(Raster)
Vertical Sync
March 2010
Proprietary & Confidential
25
Analog Channel in Time
March 2010
Proprietary & Confidential
26
Analog TV, TV Signal Modulation
March 2010
Proprietary & Confidential
27
Analog TV, test signal
• Basic video reference points,
- Sync tip amplitude,
- Depth of modulation
- Color Burst
• Test signals are added to measure signal quality
- Vertical synchronisation
- Lines 7 to 21 are part of the non-visible image
March 2010
Proprietary & Confidential
28
Analog TV Chroma
–
Chroma (or Color)
March 2010
•
Subcarrier 3.58MHz
•
Suppressed carrier,
AM modulation
Proprietary & Confidential
29
Analog TV
–
–
–
audio transmissions
Frequency modulated audio sub-carrier
• 4.5 MHz to 5.5 MHz, ± 25 kHz
Pre-emphasis
• Reduces high frequency transmission noise
• Amplification of high frequencies before modulation
• An inverse filter is applied after demodulation
Encoding similar to FM stereo receivers
• L+R base signal
• L-R differential signal
March 2010
Proprietary & Confidential
30
Analog Measurements
Levels
Carrier Frequency
Carrier to Noise (CCN)
Coherent Disturbances (CCN, CSO & CTB)
HUM
In-Channel Response
Color Measurements
March 2010
Proprietary & Confidential
31
Analog Measurements
Carrier Levels
March 2010
Proprietary & Confidential
32
Absolute and Relative
Absolute
Frequency, Hz
Relative
Amplitude
in dB
Absolute
Amplitude,
dBmV


Absolute levels and frequency
only on visual carrier
All other amplitudes and
frequencies are relative to the
visual carrier
Relative
Frequency, Hz
March 2010
Proprietary & Confidential
33
CM2000/2800 SLM Mode
March 2010
Proprietary & Confidential
34
Multi-Channel Modes
Mini Scan
Scan
March 2010
Proprietary & Confidential
35
AT2500 Channel Level Display
March 2010
Proprietary & Confidential
36
CATV Measurements
Carrier to Noise (CCN)
March 2010
Proprietary & Confidential
37
Carrier to Noise Ratio
Overload (TP)
Dynamic Range
CCN
S.A. Noise Floor
March 2010
Proprietary & Confidential
38
CCN Measurement Algorithm
Measure Carrier Level
Measure Noise in a 30KHz Bandwidth
Correct for:
– Bandwidth of noise to 4 MHz (add 21.25 dB)
– Log Detection (add 2.5 dB)
– Bandpass Filter Shape (subtract .5 dB)
Correct for Noise to near Noise
Correct for pre-amplifier if used
Subtract corrected noise from carrier level
March 2010
Proprietary & Confidential
39
Out of Band CCN Measurement
Carrier Level
NOTE:
Noise measurement
most be corrected for
video bandwidth &
instrument measurement
errors.
Noise
Measurement
March 2010
Proprietary & Confidential
40
Setup Out-of-Band CCN Measurement

Center frequency = Video carrier frequency
==>
SINGLE
OR
==>
COMBINED
==> IN-CH
GATED
Noise Meas set
to clear area
Press F5 to setup
Measurement parameters.

March 2010
Proprietary & Confidential
41
Out-of-Band CCN Measurement
March 2010
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42
Out-of-Band CCN Measurement
CCN Result
Noise near Noise Correction
Measurement Point
March 2010
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43
Out-of-Band CCN Measurement
March 2010
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44
Instrument Noise Measurement
March 2010
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45
In Band CCN Measurement
NOTE:
CNR
Noise measurement
most be corrected for
video bandwidth &
instrument measurement
errors.
Measurement Range
March 2010
Proprietary & Confidential
46
Gated CCN Measurement
Quiet Line of Video
March 2010
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47
Setup CCN Measurement

Center frequency = Video carrier frequency
==>
SINGLE
OR
==>
COMBINED
IN-CH
==> GATED
Noise Meas set
2 MHz
Press F5 to setup
Measurement parameters.

March 2010
Proprietary & Confidential
48
CCN Measurement
CCN Result
Noise near Noise Correction
Measurement Point
March 2010
Proprietary & Confidential
49
CATV Measurements
Coherent Disturbances (CSO & CTB)
March 2010
Proprietary & Confidential
50
Second Order Inter-modulation
2IM = f1 ± f2
61.25 MHz
211.25 MHz
271.25 MHz
CSO
272.50 MHz
March 2010
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51
Third Order Inter-modulation
3IM = ± f1 ± f2 ± f3
61.25 MHz
211.25 MHz
271.25 MHz
CTB
272.50 MHz
121.25 MHz
March 2010
Proprietary & Confidential
52
Where do the beats fall?
Visual Carrier
Composite Distortions are
measured as a ratio in terms
of dB down from the carrier.
Lower
Adjacent
Aural
Aural Carrier
CTB
CSO
0.75 MHz
.25 MHz
March 2010
Proprietary & Confidential
53
Digital Beat Products
Add pix of digital channels beating together.
March 2010
Proprietary & Confidential
54
Manual Measurement Procedures
Measure carrier peak
Turn off carrier
Set 30 kHz resolution bandwidth
Narrow video bandwidth to 10 KHz
Composite level using marker
CSO or CTB = visual carrier - distortion level
Automatic cable analyzers can makes CSO measurement without interrupting the subscriber
March 2010
Proprietary & Confidential
55
Setup CCN/CTB/CSO

Center frequency = Video carrier frequency
SINGLE
==> COMBINED
IN-CH
==> GATED
Press F5 to setup
Measurement parameters.

March 2010
Proprietary & Confidential
56
Initiate Measurement
Set Frequency to
Video Carrier

Press F6 to
MEASURE

User is prompted to
remove test carrier at
the headend once test
has been initiated
March 2010
Proprietary & Confidential
57
CCN/CSO/CTB Results
CTB
CSO
CNR
March 2010
Proprietary & Confidential
58
CATV Measurements
Low Frequency Disturbances
or Hum
March 2010
Proprietary & Confidential
59
Hum Definition
Hum is ANY low frequency disturbance of the RF carrier
Program modulation sometimes interferes with hum
measurements causing the measurement to look worse
than it actually is.
Hum looks like AM modulation of the carrier
HUM problems reduce MER and increase BER
March 2010
Proprietary & Confidential
60
How is Hum Measured?
Demodulated Carrier Voltage
Peak-to-Peak
Peak
0
Time
Peak-to-Peak
% Hum = 100 X
Peak
March 2010
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61
Hum Results
March 2010
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62
Digital HUM
March 2010
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63
CATV Measurements
In Channel Frequency Response
March 2010
Proprietary & Confidential
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Response Specification
6 MHz
4.25 MHz
 2 dB Measurement Area
0.75 MHz
Visual Carrier
1.25 MHz
Lower
Channel
Boundary
March 2010
1 MHz
Aural Carrier
(Off or Suppressed)
Upper
Channel
Boundary
Proprietary & Confidential
65
VITS Signals
Horizontal Blanking
525
LINES
485
LINES
Receiver Frame
SCAN MOTION
Vertical Blanking
(Raster)
Vertical Sync
March 2010
Proprietary & Confidential
66
Multi-Burst
March 2010
Proprietary & Confidential
67
Ghost Cancelation Reference
March 2010
Proprietary & Confidential
68
In-Channel Frequency Response
Results Using GCR VITS
March 2010
Proprietary & Confidential
69
Digital Channels
March 2010
Proprietary & Confidential
70
Digital Measurements
Levels
Constellation
MER, EVM
BER
Frequency Response
Group Delay
March 2010
Proprietary & Confidential
71
Basic Components
Consistent Wave Carrier (CW Carrier)
Content
– MPEG stream
• Multiplexed video/audio streams
• HD video/audio
• Audio content
• Modem traffic
• VOIP traffic
March 2010
Proprietary & Confidential
72
CW Carrier
Consistent Wave Carrier
Sine wave shape
At one consistent rate
At one frequency
Used to carry content over the network
March 2010
Proprietary & Confidential
73
CW Carrier
Time Domain
Time
Frequency Domain
March 2010
Proprietary & Confidential
74
Multiple CW Carriers
Frequency Domain
F1
F2
Time Domain
F1
F2
Time
March 2010
Time
Proprietary & Confidential
75
Purpose of CW Carrier
It’s the BUS
Modulation is putting content on the Bus
Demodulation is taking content off the Bus
March 2010
Proprietary & Confidential
76
Describing a sine wave
Phase
90°
Rate (Frequency):
• Time to complete a cycle
• Unit of measure = Hertz
Amplitude
• 1 cycle/sec = 1Hz
0°
Ref. Point
Time
March 2010
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Putting Content on the BUS
0
AM
1
0
1
0
0
1
0
FM
ASK
1
0
1
0
0
1
FSK
Frequency Modulation
Amplitude Modulation
FM
0
1
0
1
0
0
1
PSK
Phase Modulation
March 2010
Proprietary & Confidential
78
Phase Relationships
0º 90º 180º
Time
March 2010
Proprietary & Confidential
79
Bi-Phase Shift Keying (BPSK)
Simplest method of digital transmission.
Data transmitted by reversing the phase of the carrier.
Carrier amplitude & frequency remains constant.
1 bit transmitted at a time
Advantage - Very robust method
Disadvantage - Consumes significant bandwidth (1 bit per hertz)
180º
0º
1
0
March 2010
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80
Amplitude and Phase Modulation
Higher data rates are achieved by
adding amplitude modulation to the
carriers
180º
0º
00 01
10
11
By having multiple levels of
amplitude and phase more
symbols can be transmitted in the
same time period.
Two Levels of Amplitude Modulation and
Bi-Phase Modulation Makes Four Possible
Symbols
March 2010
Proprietary & Confidential
81
QPSK
Two carriers at the same frequency, 90º out-of-phase, transmitted at the
same time
One carrier is at 0º or at 180º, called the In Phase carrier – one carrier is at
90º or 270º, called the Quadrature carrier
The resultant vector of these two carriers designates the symbol to be
transmitted.
A symbol is a digital word that is a combination of several bits.
In this case the symbol contains two bits
Using this method twice as much data can be transmitted in the same
amount of bandwidth.
March 2010
Proprietary & Confidential
82
How QPSK symbols are transmitted
10|11|01|00|11
10
11
01
00
11
1011010011
The digital receiver analyzes both the phase and the
amplitude of the incoming signal and produces a bit stream
that corresponds to that signal.
March 2010
Proprietary & Confidential
83
Symbols, Symbol Rate, Bit Rate
The Digital Language
– If bits are the letters, then symbols are the words in the
language of digital modulation.
The bit rate is the number of bits sent per second
Symbols transmit one or more bits of digital information.
Symbol Rate is the number of symbols sent per second.
The transmission bandwidth is the symbol rate.
Symbol Rate = Bit Rate / Number of bits per Symbol
H
March 2010
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84
Describing a sine wave
Phase
90°
Rate (Frequency):
• Time to complete a cycle
• Unit of measure = Hertz
Amplitude
• 1 cycle/sec = 1Hz
0°
Ref. Point
Time
March 2010
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QPSK
Example: I carrier
transmitted at 0º, Q carrier
transmitted at 90º.
90º
11
45º
10
135º
180º
0º
I Carrier
01
315º
00
225º
270º
Q Carrier
March 2010
Resultant vector at 45º
represents a symbol of 11.
If we needed to transmit a
01, then the I carrier would
be at 0º and the Q carrier
would be at 270º.
Proprietary & Confidential
86
Quadrature Amplitude Modulation (QAM)
Analog color subcarrier similar to QAM modulation
Two signals carried at the same frequency out of
phase
Two carriers called the I and Q, each carrying onehalf of the data.
Each I & Q carrier transmits 8 levels of data for 64
QAM
Hence 82 equals 64 combinations or 64 QAM
March 2010
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87
In-Phase and Quadrature
180 Deg Shift
I Channel
Carrier
Phase
+
Q Channel
Carrier
Phase 90°
Shifted
March 2010
t
=
I
Carrier
Amplitude
t
Q
Carrier Phase Shift over time
Proprietary & Confidential
88
Creating a QAM signal
I & Q carriers, same frequency, but phase shifted by 90°
AM modulated
Combined make up the QAM signal.
8 Level AM
Modulator
I Component
Bit Stream
101 010
Local Osc
Combiner
64 QAM
Signal
Oscillator
Shifted 90°
8 Level AM
Modulator
March 2010
Proprietary & Confidential
Q Component
89
QAM
QAM is Quadrature Amplitude Modulation
Two carriers at the same frequency, 90º out-ofphase, transmitted at the same time
Uses multiple levels of amplitude & phase
modulation
Each carrier is a representation of half of the
transmitted symbol.
March 2010
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90
QAM (Cont.)
If each of the I and Q channels transmits 4 levels of data
16 symbols transmitted in one clock cycle
Each symbol contains 4 bits
Known as 16QAM
8 levels per carrier
64 symbols transmitted
Symbol contains 6 bits
64QAM
16 levels per carrier
256 symbols transmitted
Symbol contains 8 bits
Known as 256QAM
March 2010
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91
Vectors and 16 QAM
Q 90°
1011
11
1011
1111
10
1010
1110
I 180°
I 0°
00
01
10
11
01
March 2010
0001
0101
0000
0100
00
Q 270°
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Vectors and 16 QAM
Q 90°
1011
11
1011
1111
10
1010
1110
I 180°
I 0°
00
01
10
11
01
March 2010
0001
0101
0000
0100
00
Q 270°
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64 QAM Constellation
6 Bits per Symbol
March 2010
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256 QAM
8 Bits per Symbol
March 2010
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Digital Measurements
Digital Channel Power
MER, ENM, and EVM
Constellation Impairments
Pre and Post FEC BER
Adaptive Equalizer
QIA Measurements
March 2010
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Analog vs. Digital Power Measurements
6 MHZ
300 KHz
6 MHZ
March 2010
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97
Digital Power Measurement
H
March 2010
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Balancing System Levels
March 2010
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99
Modulation Error Ratio
MER is used as a single figure of merit for quality for RF
digital carriers
It includes distortions such as CCN, CSO, CTB, laser
compression, etc…. The sum of all evils.
A 256 QAM picture tiles at 28dB MER
A minimally good MER is 31 dB for 256 QAM at the back
of the customer’s set.
H
March 2010
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100
Vectors and 16 QAM
Q 90°
1011
11
1011
1111
10
1010
1110
I 180°
I 0°
00
01
10
11
01
March 2010
0001
0101
0000
0100
00
Q 270°
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101
MER and a Constellation
H
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MER and a Constellation
H
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Acceptable MER
Output of QAM Modulator – 40 dB
Input to Lasers – 39 dB
Output of Nodes – 37 dB
Output of Subscriber Taps – 35 dB
At the input to the subscriber’s receiver – 34 dB
The absolute minimum is 31db.
March 2010
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Constellation Analysis
March 2010
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105
Noise Impairments
March 2010
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106
Phase Impairments
Looks good
here in
the
Headend!
March 2010
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107
Coherent Interference Constellation
March 2010
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108
Coherent Interference in Freq Spectrum
Ingress from UHF
off-air channels
Headend beats
CSO & CTB
March 2010
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109
Phase Impairments
March 2010
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110
Gain Compression
H
March 2010
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I/Q Gain Imbalance
H
March 2010
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Laser Compression
March 2010
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113
CM2000/2800 Constellation
March 2010
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114
BER Measurement
March 2010
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115
What is BER?
BER is defined as the ratio of the number of wrong bits over the
number of total bits.
Sent Bits
1101101101
Received Bits
1100101101
error
# of Wrong Bits =
BER =
# of Total Bits
March 2010
1
=
0.1
10
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116
BER Display
BER is normally displayed in Scientific Notation.
The more negative the exponent, the better the BER.
Better than 1.0E-6 is needed after the FEC for the system to
operate.
Fraction
Decimal
Scientific Notation
Lower
1/1
1
1.0E+00
and
1/10
0.1
1.0E-01
Better
1/100
0.01
1.0E-02
BER
1/1,000
0.001
1.0E-03
1/10,000
0.0001
1.0E-04
1/100,000
0.00001
1.0E-05
1/1,000.000
0.000001
1.0E-06
1/10,000,000
0.0000001
1.0E-07
1/100,000,000 0.00000001
1.0E-08
1/1,000,000,000 0.000000001
1.0E-09
2/1,000
0.002
2.0E-03
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Calculated Bit Error Rate
Using the amount of FEC overhead required to reproduce a
bit string, the bit error rate can be calculated.
Using the FEC to determine the BER allows BER to be
measured without removing the service which is usually
required for most BER testing.
March 2010
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118
Forward Error Correction Decoder
Forward error correction (FEC) is a digital transmission
system that sends redundant information along with the
payload, so that the receiver can repair damaged data and
eliminate the need to retransmit.
March 2010
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119
Pre and Post FEC errors
Pre FEC errors
– Errors that have occurred before the FEC has had an
opportunity to correct any of the errors.
Post FEC errors
– Errors that could not be corrected
A cable modem will tolerate pre-FEC errors and the FEC will
continue to correct pre-FEC errors up until 1E-06 or one error
in one million bits. After that the FEC can do no more.
Post-FEC errors will cause retransmissions requests and
slowdowns in a DOCSIS systems.
March 2010
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Pre and Post FEC BER
To get an accurate idea of the BER performance you need to
know both the pre and post FEC bit error rate.
The FEC decoder needs a BER of better than 1 E-6 in order to
operate.
Post FEC Bit errors are not acceptable.
You should look at both the Pre and Post FEC BER to determine
if the FEC is working to correct errors and if so how hard.
Pre FEC
BER
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FEC
Decoder
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Post FEC
BER
121
Parity
By adding an additional bit to a group of bits, errors can be
detected within the group. This is known as a parity bit.
Even parity means that when the parity bit is added the
group of bits including the parity always has an even number
of ones. Odd parity means the group would have an odd
number of ones.
If after transmission the number of ones is no longer even
(for even parity), then there must be an error.
101110001 1
010111011 0
Error
Always Even
Number of Ones
(Even Parity)
101100001 1
010111011 0
Odd Number
of Ones
Indicates
Error
Parity Bit
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How Reed Solomon FEC Works
FEC works by addition additional data bits to the data
stream to determine if errors exist and to try and correct
them.
Video Data
Stream
1011100010110100
1011
1000
1011
0100
1
1
1
1
1100
0
1=odd
0=Even
Stream With FEC
1011100010110100 1111 1100 0
Added
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How Reed Solomon Works
Once you know a bit is wrong, correcting it is easy, if you
know its wrong and its a zero, then it has to be a one.
1011
1000
1011
0100
1
1
1
1
1100
0
Before
Transmission
March 2010
Error
1011
1000
1001
0100
1
1
1
1
1100
0
1=odd
0=Even
After Transmission
the Bit in Error is
Detected and
Corrected
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BER and a Constellation
H
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125
CM2000/2800 Constellation
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126
Statistical Mode
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Statistical Mode
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Adaptive Equalizer
Every Digital Receiver has an Adaptive Equalizer
It performs 3 functions
– Compensates for amplitude imperfections of the
digital signal
– Compensates for group delay
– Rings at the symbol rate to only allow one
symbol at a time into the digital receiver
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Equalizer Mode
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130
Equalizer Mode
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131
Digital Video – EQ Control
Standard EQ
– Used in current equipment
– More taps
– Improved correction
Min EQ
– Less taps
– Mirrors performance of old
equipment
– Disables Auto Diagnosis
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Frequency Response
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–
Effective span
equal to symbol
rate
–
Measurement
calculated
using Equalizer
data
133
Amplitude Ripple
An in-service spectrum analyzer measurement
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134
Group Delay
Definition:
–Group delay is a measure of how long it takes a signal to
traverse a network, or its transit time. It is a strong function of the
length of the network, and usually a weak function of frequency. It
is expressed in units of time, pico-seconds for short distances or
nanoseconds for longer distances.
Measured in units of time,
–Typically nanoseconds (ns) over frequency
–Or, Delay per MHz.
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Group Delay (Cont.)
In an ideal system all frequencies are transmitted through the
system, network or component with equal time delay
Frequency response problems cause group delay problems
Group delay is worse near band edges and diplex filter roll-off areas
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Group Delay (cont’d)
Excessive group delay increases bit error rate due to
inter-symbol interference
DOCSIS spec.
– no greater than 200nSecs per MHZ
– Spec should be less than 100 nSecs per MHz
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Group Delay Measurement
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138
QIA Screen
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139
QAM Impairment Analysis (QIA)
I/Q Gain and Phase
– The phase and gain of both the I and Q carrier must be
equal in order for the constellation to be correct.
– This impairment is caused by the QAM modulators.
– The gain difference between the 2 carriers should be less
than 1.8% and the phase difference should be less than 1
degree.
Echo Margin
– A measurement in dB of how far the taps are from the
template with the time equalizer measurement.
– Caused by impedance mismatches in the system.
– Should be at least 6 dB.
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QIA Continued
Carrier Offset
– Carrier frequency test.
– Should be no more than +/- 25KHz
Estimated Noise Margin
– Difference in dB between MER and the digital cliff
– Depends on if the signal is 64 or 256 QAM
– Minimum depends on where the measurement is taken
– Example if the Minimum MER for 256 QAM is 28 and the
measurement is 34, than the ENM is 6
Frequency Response
– Frequency response of the digital carrier
– Should be less than 3 dB pk-to-pk
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QIA Continued
Hum
– Low frequency disturbances of the digital carrier
– Same as hum on analog carriers, if the level is the same,
it’s the system, if higher on the digitals then it’s probably the
QAM modulator
Symbol Rate Error
– Should be less than +/- 5 ppm
Phase Noise
– Jitter (changes in phase) of the oscillators, most likely
the up-converter
– The phase shift or jitter should be less than .5 degrees
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QIA Continued
Group Delay
– Different frequencies travel through the same medium at
different speeds. So the lower the lower frequencies of
the same carrier arrive at the receiver at different timing
than the higher frequencies.
– Should be less than 50 nSec pk-to-pk
Compression
– Caused by overdriving lasers or amplifiers
– Shows up as corners pulling in at the outer corners of
the constellation
– Should less than 1%
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System Sweep
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144
What does sweep do for the technician?
Measures the Frequency Response
of the network
Confirms Unity Gain
View impedance mismatches
– Bad connectors & cable
– Bad devices
Checks both Forward and Return
paths
Concept:
If the system is flat and levels are
correct, distortion will be minimal
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Why Sweep?
Insures proper headroom
Preventative Maintenance
Non-obtrusive measurement
Look at network with a microscope
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CM2800 Sweep
Compatible with 3010H/R
Forward Sweep
– New 3 Dwell definition
– Simultaneous Pilot &
Forward Sweep Results
Return Sweep
– Switch Control (Phase
2)
– Return Spectrum
(Phase 2)
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Sweep System Facts
CM2800 compatible with 3010 version 5.53 firmware only
3010R & 3010H, same measurement hardware
3010H ships fully loaded
– Basic unit support Return Path Monitor mode (both R&H)
– Option 052 – Forward Sweep TX & Dual Path Mode
– Option 061 – Switch control
3010 upgrade to ver. 5.53
– Version 4.x & above included with Calibration
– Version 3.x available for an additional charge
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Sweep Application
Node
Laser
Combiner
(20)
Spliter
Downstream
Channels
Fiber
Optical
Reciever
Downstream
To Neighborhoods
CMTS
US-1
Upstream 1
Upstream 2
Upstream 3
Upstream 4
US-2
AT1602
Switch
Forward &
Reverse
Sweep
US-3
AT2500
Upstream
3010H
Downstream
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US-4
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Forward Sweep
Node
Laser
Combiner
(20)
Fiber
Spliter
Downstream
Channels
Optical
Reciever
Downstream
To Neighborhoods
CMTS
US-1
Upstream 1
Upstream 2
Upstream 3
Upstream 4
US-2
AT1602
Switch
US-3
AT2500
Upstream
3010H
Downstream
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US-4
Forward Sweep Path
3010 Output Combined with Downstream
Signals
Sweep Level 16dB to 20dB below analog
levels
Sweep tilt = channel tilt
Normalized sweep is a relative meas.
Change in response between meas. Point
and reference point
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Reverse Sweep
Node
Laser
Combiner
(20)
Fiber
Spliter
Downstream
Channels
Optical
Reciever
Downstream
To Neighborhoods
CMTS
US-1
Upstream 1
Upstream 2
Upstream 3
Upstream 4
US-2
AT1602
Switch
US-3
AT2500
Upstream
3010H
Downstream
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US-4
Reverse Sweep Path
DS Comms Combined with
Downstream Signals (Comms only)
Test signal inserted in field,
measured by 3010H, meas. sent to
field instrument on DS Comms
Must know your reference points &
design levels
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Network basics
Unity Gain Network
Input – Cable Loss + Amp Gain = Output
Design Pilots”
Low = 32
High = 36
Sweep In
Low Pilot
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sertion L
Unity Gain Concept
–
Total System Gain equals Total Loss
–
Gain = Loss or Gain/Loss = 1
–
Forward Path:
•
Constant Output Levels
•
Amp compensates for cable before
device
–
Return Path:
•
Constant Input Levels
•
Amp compensates for cable after
device
•
Same cable forward amp is
compensating for.
e ve l
High Pilot
Sweep Insertion
–
~ 17 dB Below Channels
–
System Level to Sweep Delta will
Remain Consistent
–
Matches Design Level Tilt
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152
Combiner
(20)
Reality of Frequency Response
Node
10
40
40
40
40
45
0
35
35
35
35
40
-10
30
100
300
500
700
30
100
300
500
700
30
100
300
500
700
30
100
300
500
700
35
100
300
500
700
100
300
500
700
Output Levels and Slopes are customized to provide the
best performance
Highest Carrier to noise Ratio (CC/N & MER)
Highest Carrier to Distortion Ratio (CSO, CTB, ect.)
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How Sweep Works with no Sweep Table
400 measurement points
Transmitter output with
a blank sweep table.
1 MHz
50
Sweep Resolution =
(Stop freq... - Start freq...)
400 points
450
=
(450MHz - 50MHz)
400 points
= 1MHz/point
The sweep frequency resolution is determined by the start and
stop frequencies in areas of the spectrum where no frequencies are
in the sweep table.
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154
Components of the Sweep Table
61.25MHz
Start freq... = 50MHz
Stop freq... = 450MHz
57.20MHz
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63.20MHz
155
What is the Forward Path of the Cable System
Forward Signal Path
H
R
R
L
Return Equip.
Each amplifier compensates for
the loss in the wire before the
amplifier under test.
Signal flow in the forward
path is from the headend to
the customers home as
indicated by the blue arrows.
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Lash-Up for Forward Sweep Set Up
To Forward
Lasers
RF In
RF Out
Forward
Combiner
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Forward Sweep Setup Flow
Setup Channel plan
Connect the input of the 3010 to a port containing all the channels on
the network
Set Forward Sweep mode to Fast
In the Sweep Parameters screen set the following:
– Start Freq. to your start frequency
– Stop Freq. to your stop frequency
– Comm’s Pilot Freq. to a clear area of network spectrum
– Scan Type to Phantom
– Channel Plan to the Channel Plan you created
– Sweep Table to None
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Forward Sweep Parameters Screen
3010H
Start Frequency
Scan Type
Frequency Plan
Created for
system
under test
Stop Frequency
Communications
Pilot Frequency
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Sweep Table
(Set to None
to create a
new table.)
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159
Forward Sweep Setup Flow
Scan the network and the instrument creates the basic Sweep
table for you
Add system pilots and edit table
Save the table
Set the level & slope
Your done!!!!
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Table Entries for other type signals
Digital Signal
–
(Places sweep point between Digital Channels)
–
Frequency = Channel Center Freq..
–
Guard band = 1/2 Channel bandwidth
–
Dwell = 0
Digital Signal
–
(Measures Digital channel, no sweep point)
–
Frequency = Channel Center Freq.
–
Guard band = ½ Channel bandwidth + 0.1 MHz
–
Dwell = 3
Phantom Carrier Setup
–
(Sweep point in Vestiges Sideband)
–
Frequency = Center Freq. + 200 kHz
–
Guard band = ½ Channel bandwidth – 0.1 MHz
–
Dwell = 0
System AGC or Setup Pilot Channels
–
Frequency = Video carrier frequency
–
Guard band = 1MHz
–
Dwell = 0
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Forward Sweep Level
Sweep points between Digital Channels
– Sweep points must be at least 17dB or greater below analog
video level
No sweep points around Digital Channels
– Sweep points should be at the same level as the measured
digital channels
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Sweep Setup
Go to SETUP / SWEEP
–
Enter / Select the Low and High System
Pilot
–
Enter the Forward Sweep
Communications Pilot Frequency (per
3010 setting)
–
Enter the Reverse Sweep
Communications Pilot Frequency (per
3010 setting)
–
–
March 2010
Check “Get New Table” to force
download of new Forward Sweep
SAVE & EXIT
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163
Sweep Setup
Go to SETUP/LIMITS and SWEEP tab
–
Select the Location from the Pull Down
Menu
–
Set the Downstream Sweep Limits for
• Low System Pilot min & max
• High System Pilot min & max
• Tilt max (we will add min)
• Peak-to-valley max
–
Set the Upstream Sweep Limits for
• Tilt max (we are adding min)
• Peak-to-valley max
–
SAVE & EXIT
Sweep Limits Screen
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Sweep Tools
View Sweep
Table
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165
Screen Annotations – Forward Sweep
Freq. & dB/Div Control
Save Ref. File
View Sweep Table
Trace control
–
(only active when
reference is selected)
Site File
Select Reference
Attenuator
–
Sets Dynamic range
P/V freq.
range set by
Vert. Marker
Position
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System Pilot
Freq. & Level
166
Forward Sweep
Lock Symbol
First Connection
–
Communication Icon (lock symbol) will flash
yellow, Markers & start stop will update.
–
If Comms Icon not flashing - Adjust Attenuation
•
If test point system levels are > 10 dBmV,
increase the attenuator setting. If < 0 dBmV,
decrease attenuator setting.
–
Wait for sweep table download (or press F4 on
3010)
Note the sweep trace and the pilot graphs. Pilots
should be 10 to 15 dB above sweep.
–
–
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Note markers
•
Use Touch Screen or Arrows
•
Tilt & Peak-to-valley Calculated on Markers
•
Click on the SAVE icon at top tool bar and enter
a name for a
reference file.
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Sweep Reference
Sweep File are used
as a Reference
Select a Reference
File
–
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Sweep Display will be
the difference between
Ref and current results
168
168
Referenced Forward Sweep
–
–
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Click REFERENCE, select saved file.
RED trace = Live Trace – Reference
Trace
–
Automatically adjusts to 2 dB/Div
–
Click A, B, A&B, A-B to toggle Trace
(Live, Reference, Both or Difference
Traces)
–
Low & High Pilot Frequency & Levels
are Displayed
–
Tilt & Peak to Valley calculations based
on Vertical Marker Position
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Return Sweep Configuration
Return Signal Path
H
R
R
L
Return Equip.
Each amplifier compensates for
the loss in the wire after the
amplifier under test.
Signal flow in the return
path is from the customers
home to the headend as
shown by the blue arrows.
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Alignment Issues & the Return Path
The monitor point is some distance from the adjustment point.
The communications between the 3010R and 3010H is
through the system under test.
Interference on the return or forward path can affect the
communication between the instruments.
The Ingress detection system is used to troubleshoot
interference on the return path.
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Reverse Sweep Communications
Node
Laser
Combiner
(20)
Fiber
Spliter
Downstream
Channels
Optical
Reciever
Downstream
To Neighborhoods
CMTS
US-1
Upstream 1
Upstream 2
Upstream 3
Upstream 4
US-2
AT1602
Switch
US-3
AT2500
Upstream
3010H
Downstream
March 2010
US-4
Reverse Sweep Path
DS Comms Combined with
Downstream Signals (Comms only)
Test signal inserted in field,
measured by 3010H, meas. sent to
field instrument on DS Comms
Must know your reference points &
design levels
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172
3010H Polling Sequence
3010H services any field units
on line switching ports as
required
3010H Sends New User Poll
message on Forward Pilot
3010H sets switch string to
next polling set
3010H monitors return pilot
listening for field units
Receives data
No
Yes
Good Data is received
No
3010H Broadcast
spectrum measurement
on forward pilot
Yes
New field unit is placed on the
user list displayed on 3010H
3010H services new user
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Return Sweep Headend Lash-Up
F
o
r
w
ar
d
C
o
m
bi
n
er
To Forward
Lasers
RF out
Return Receivers
RF in
To Return Processing
Equipment
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Connecting the 3010R to the 3010H back to back
Output
Input
Output
3010H
Input
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Return Sweep Setup
Set dynamic range for measurement
Full Scale (FS) setting in Spectrum Scan
If < 5 return paths connected to 3010 or using AT1600 Switch
– Set FS for modem traffic to upper division of display
If > 5 return paths
– Set FS for noise floor below second division of display
Remember the setting!
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Return Sweep Setup (Cont.)
Set Switch driver if connected to a switch
Set Return Sweep mode to Fast
In Return Sweep Parameters screen set the following:
– Start Freq. to your start frequency
– Stop Freq. to your stop frequency
– Forward Pilot to a clear area Forward Path spectrum
– Return Pilot to a clear area Return Path spectrum
– Ret Swp Table to None (to create new table)
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Return Sweep Setup (Cont.)
To Speed up sweep
– Enter frequency every 1 MHz
– Guard band = 0.5 MHz
– Dwell = 0
Save Table
Set Forward Pilot level 10 dB below the analog channels
You are done!
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Screen Annotations
Save Ref. File
Freq. & dB/Div Control
View Sweep Table
Trace control
–
(only active when reference
is selected)
Site File
Select Reference
Attenuator
–
Sets Forward Pilot
Dynamic range
P/V freq.
range set by
Vert. Marker
Position
March 2010
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Source
Level/Slope
Controls
179
Reverse Sweep
–
Upstream sweep table is automatically
Downloaded
–
Communication Icon (lock symbol) will
flash yellow, Marker Freqs. & start / stop
will update
–
•
If test point system levels are above 10
dBmV, increase the attenuator setting. If
below 0 dBmV, decrease attenuator
setting.
–
–
Set the Transmitter Level for the
appropriate Injection Level
•
–
March 2010
Peak reference level limited by 3010H
setting
Note Markers
•
Tilt & P/V Calculated on Vertical Marker
Position
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Referenced Return Sweep
–
–
March 2010
Click REFERENCE, select saved file.
RED trace = Live Trace – Reference
Trace
–
Automatically adjusts to 2 dB/Div
–
Click A, B, A&B, A-B to toggle Trace
(Live, Reference, Both or Difference
Traces)
–
Tilt & Peak to Valley calculations based
on Vertical Marker Position
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Bi-directional Test Point
Typical Amp diagrams
How to connect
Splitter
Set the Test Point Loss to 3 dB to compensate for the Splitter or for
the Splitter and Test Point loss.
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Directional Test Points
Forward Pad
Forward EQ
Forward Input
Test Point
Forward Output
Test Point
RF In
Reverse Output
Test Point
RF Out
ReversePad
EQ
Reverse
Reverse PAD
Reverse EQ
Reverse Input
Test Point
Amp Configurations are Tailored for the Span they serve
Diplexers Separate the Upstream & Downstream Path
Pads adjust the Flat Gain of Amplifiers
Equalizers Compensate for Cable Loss
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Connecting the 3010R to the 3010H in the System
3010R
Forward Path
Fiber Laser
Fiber Node
RF out
Return Path
Fiber Receiver
3010H
RF in
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What is Ingress?
3010R
Return Path with Ingress
Ingress refers to interference typically
found on the Return Path. Most times
it is caused by signals entering the system
from the customer drop.
Return Path without Ingress
When ingress is detected by the 3010H, the
it makes a spectrum scan measurement
and broadcasts the display data to the field
on the forward Pilot.
When a 3010R receives the Broadcast
Ingress message, it is displayed over F3.
Pressing F3 with the message display
will allow you to view the spectrum scan
measurement from the 3010H
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When Ingress is a Problem.
3010R
F3
Indicates
Ingress
detection
at the 3010H
Pressing F3 will activate the
Broadcast Ingress
Measurement
F3
A flashing Square
Indicates loss of
Return
Communications
A flashing symbol indicate
the Forward pilot is received
from the 3010H
A solid symbol indicates no
Forward Pilot communications
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The Typical Return
To CMTS Receive Port
Spare Splitter Leg
Optical
Receiver
H
L
Fiber
Node
Optical
Receiver
H
L
Optical
Receiver
Fiber
Node
Coax
Dist.Network
H
L
Fiber
Node
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The Funnel
Noise from every nook & cranny in the system ends
up at the CMTS receive port.
H
L
Optical
Receiver
Fiber
Node
Optical
Receiver
H
L
Optical
Receiver
Fiber
Node
Coax
Dist.Network
H
L
Fiber
Node
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You can’t get there from here
The problem
could be here …
To CMTS Receive Port
Spare Splitter Leg
H
L
Optical
Receiver
Fiber
Node
Optical
Receiver
Optical
Receiver
or here …
H
L
The actual Call
might be here
H
L
March 2010
Coax
Dist.Network
or here …
or the problem could
be anywhere in these
three nodes.
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Upstream Impairments
Common Path
Distortion
Fast transient noise
Ingress
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Upstream Ingress
Return Path without Ingress
Ingress refers to interference
typically found on (but not
limited to) the return path.
Most ingress comes from the
drops.
Return Path with Ingress
March 2010
Some sweep systems detect
ingress on their return sweep
data frequency and
broadcast the display data to
the field on the forward data
carrier for display.
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Corrosion & Diode Effect
Crystallization
occurs and the
corrosion creates
thousands of small
diodes between
the two metals
Diodes are nonlinear devices that
can act as
frequency “mixers”
in a CATV plant
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Frequency Mixing
Mixing two frequencies (F1 & F2)
will yield four results:
F1
F2
F1 + F2
F2 – F1
March 2010
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55.25 MHz
61.25 MHz
116.50 MHz
6.00 MHz
193
Common Path Distortion
Corroded Connection
27
Downstream Signals
(~6, 12, 18, 24…)
March 2010
A corroded connection
causes mixing
The resulting impedance
mismatch also causes
reflections
The mixing products are
reflected right back into the
return amplifier.
The diplex filter takes out
everything above 42 MHz.
Difference frequencies
reflected upstream
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CPD in 6 MHz Intervals
Because the channels in the forward system are 6 MHz apart,
the sum & difference frequencies occur at 6 MHz intervals as
well.
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Other Non-Linear devices
Other non-linear devices can create return path
problems
Splitters utilizing toroid wound coils can also be nonlinear and create mixing problems.
A cable modem transmitting at high levels can saturate
the toroids forcing them to become non-linear.
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Spectrum Display Limitations
Scanning Spectrum Analyzers measure only one
band of frequencies at any given instant.
Frequency
Range Where
Measurement is
Being Made at
That Instant
Frequencies
Stored From
Last Pass of
Filter
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Fast Intermittents
If the spectrum analyzer is at another frequency
when the transient appears it will not be displayed.
A transient happening at this time
will be missed by the filter unless it
is still there when the filter comes
by again
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3010
Switch Control Feature
Setup and Operation
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Switch Control Description
3010H
–
Adds switch driver for AT160x & RPS switches
3010R
–
–
Adds remote switch control
Single node return sweep
Requirements
–
–
Firmware version 5.53 or greater
Option 061 turned on (Shown on opening screen)
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Features
Auto node polling
Two switch drivers
–
–
AT1601 or AT1602
RPS switch
Remote switch control
Backwards compatible
Single node sweep
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201
AT160x Configuration
3010H
3010 Cloning Cable
AT1601
RS232 IN
RF Out
TEST POINT -20dB
RF INPUT
SUNRISE TELECOM
B R O A D B A N D
RF OUT
STATUS
LOCAL
REMOTE
AT-1601M Broadband 16 X 1 Multiplexer
RESET
AT1601
TEST POINT -20dB
RF INPUT
SUNRISE TELECOM
B R O A D B A N D
RF OUT
STATUS
LOCAL
REMOTE
AT-1601M Broadband 16 X 1 Multiplexer
RESET
All RS232 cables are
straight-through type
unless otherwise noted.
AT1601
Combiner*
RS232 OUT
*Combining Ratio will depend on
the number of switches used.
TEST POINT -20dB
RF INPUT
SUNRISE TELECOM
B R O A D B A N D
LOCAL
RF OUT
STATUS
REMOTE
Maximum of 8 switches per 3010H
AT-1601M Broadband 16 X 1 Multiplexer
RESET
RF Inputs (Returns and Forward Feeds)
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Cabling & Equipment
Cable - 3010H to Switch string
– Cloning Cable
– Male 9-pin to Male 9-pin Null Modem
Cable - Switch to Switch
– Straight Through cable
– Female 9-pin to Male 9-pin Straight Through
Combiner
– Number of ports equals number of switches
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AT160x Programming the Considerations
Each Switch in the string requires a unique address
–
Switch address is used to identify the ports. If you have
multiple 3010H/switch configurations in your system you may
want to consider using different addresses for every switch in
the system.
Use the Short Protocol (P1)
Use 38,4k baud rate (b2)
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Programming the AT160x
Press Reset then Local/Remote button
– Status light will turn yellow
Set Switch address, then press Local/Remote button
Set Protocol to P1 (Short Protocol), then press
Local/Remote button
Set Band Rate to b2 (38,4k band), then press Local/Remote
button
Programming Complete
– Status light will turn green
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3010H
3010H Programming
F3
F3
Switch
Driver
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Port
Control
206
Switch Drivers
‘AT160x’ Driver
– AT1601
– AT1602
‘Alt SW1’ Driver
– RPS Switch
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RPS Limitations
Only one switch port in a string can be closed at a
time.
Special switch lash-up required to minimize
connection time.
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RPS Configuration 1
Configuration using 1 communications port per switch
DC
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
16-way
RS232 to
other
switches
Switch
Connect
through
DC to
Splitter
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Comm Node = 15
RS232
Output
3010H
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RPS Configuration 2
Comm Node = 7
Connect
through
DC to
Splitter
1
2
3
4
5
6
7
8
Connect
through
DC to
Splitter
RS232 to
other
switches
Switch
DC
8-way
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
DC
Configuration using 2 communications port per switch
RS232
1
2
3
4
5
6
7
8
8-way
Output
3010H
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RPS Configuration 3
DC
Comm Node = 4
2
3
4
DC
Connect
through
DC to
Splitter
Connect
through
DC to
Splitter
1
2
3
4
1
2
3
4
4-way
RS232 to
other
switches
Switch
4-way
1
4-way
Connect
through
DC to
Splitter
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
DC
Configuration using 3 communications port per switch
RS232
Output
Connect to
other
switches.
1
2
3
4
3010H
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3010H Programming
AT160x Driver
AT Driver
Set to Last
Polled port
Alt SW1 Driver
RPS Driver
Set to
4, 7 or 15
Select switch driver first, then Comm Node
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3010H Operation
F3
F3
Communication Status
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ADD REALWORX SLIDES
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Troubleshooting DOCSIS
Systems
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History of DOCSIS
DOCSIS 1.0
– Open standard for high-speed data over cable
– Best-effort
st
– 1 products certified 1999
DOCSIS 1.1
– Quality-of-Service (QoS) service flows
– BPI+ with Certificates
– Improved privacy with key distribution & encryption processes
– SNMP for network management security
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History of DOCSIS (Cont.)
DOCSIS 2.0
– Goal: greater throughput & robustness on Return Channel
• Adds 64 & 128 QAM modulation to Return Channels
• Higher symbol rate up to 5.12 Msps (BW 6.4)
• Adds Forward Error correction, Trellis coding &
programmable interleaving to Return channel
• Adds multiple modulation & access schemes
DOCSIS 3.0
– Channel bonding (Increase capacity)
– Enhanced network security
– Expanded addressability (IPv6)
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DOCSIS 1.0, 1.1 & 2.0 Reference Architecture
Courtesy of SCTE™
March 2010
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DOCSIS 3.0 Reference Architecture
Courtesy of Cable Labs®
March 2010
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219
Basic DOCSIS Setup
CMTS
ISP
TOD
DNS
Network
44 MHz
Upstream
In
Modem
Up-converter
Optical
Receiver
System
signals
Out
Combine
r
TFTP
10/100 Mb Ethernet
DHCP
Downstream
Signal to add’l
Laser inputs
LASER
Fiber
Node
Coax
Dist.Network
H
L
HTTP
Fiber Distribution
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Drop &
Home
Wiring
220
Basic DOCSIS Setup
CMTS
ISP
TOD
DNS
IP Network
44 MHz
Upstream
In
Modem &
Cust. Equip.
Up-converter
Optical
Receiver
System
signals
Out
Combine
r
TFTP
10/100 Mb Ethernet
DHCP
Downstream
Signal to add’l
Laser inputs
LASER
Fiber
Node
Coax
Dist.Network
H
L
HTTP
Fiber Distribution
March 2010
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Drop &
Home
Wiring
221
Cable Modem Registration
Physical layer (RF plant) - signal transport
DOCSIS and IP protocol layers - communicate messaging for
modems to come online
The next slides illustrate the interaction of these layers in the
registration process
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DS Freq. Acquisition
cable modem
CMTS
Sync Broadcast
(Minimum one per 200 msec)
Scan DS Frequency
for a QAM signal
Next
Frequency
No
Yes
No
Wait for Sync
Yes
UCD Broadcast (every 2 sec)
Wait for UCD
MAP Broadcast (every 2 ms)
Wait for MAP
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No
223
CM Ranging
CMTS
cable modem
RNG-RSP
Ranging Response Contains:
•Timing offset
•Power offset
•Temp SID
RNG-REQ
Initial Ranging Request
Sent in Initial Maintenance time Slot
Starting at 8 dBmV
Using an initial SID = 0
Wait for
RNG-RSP
NO
Increment by
3 dB
YES
Adjust Timing Offset and Power Offset
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DHCP Overview
CMTS
cable modem
MAP Broadcasts
Bandwidth Request
Use Temp SID (Service ID)
DHCP Reply (Offer)
DHCP offers an IP address
DHCP Discover
DHCP Ack (Response)
Contains IP Addr, plus
additional information
ToD Response
Contains Time of Day per
RFC 868 (Not NTP)
March 2010
DHCP Request
Acks Initial lP Address and
requests Default GW, ToD Server,
TOD offset, TFTP Server Addr
and TFTP Boot Config File Name
ToD Request
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225
TFTP & Registration
CMTS
cable modem
TFTP Boot File Transfer
DOCSIS config file which contains
Classifiers for QoS and schedule,
Baseline Privacy (BPI), etc.
TFTP Boot Request
For ‘Boot File name’
Validate file MD5 Checksum
Implement Config
Registration Request
Send QoS Parameters
Registration Response
Contains Assigned SID
Modem registered
Registration Acknowledge
Send QoS Parameters
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BPI+
Added in DOCSIS 1.1
If BPI+ is turned on, the modem will verify it’s authentication
Two Certificate types
– Factory installed
• Higher level of security
• Encrypted Certificate obtained by VeriSign and installed
by manufacturer
– Self signed
• MAC address referenced in Certificate server for
authentication
BPI+ eliminates MAC address spoofing
March 2010
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CM Registration Summary
Downstream channel search
Ranging
DHCP
ToD
TFTP
Registration
Optional BPI Encryption (DOCSIS 1.1 or higher)
If modem contains eMTA, the next slide shows a table of the
remaining 25 steps in the eMTA registration process
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eMTA Registration
CM
MTA
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Troubleshooting the Registration Process
Downstream
Downstream
Downstream
– First step in the process
– Make sure you are connected to the correct DOCSIS
channel
• One channel may be fine and another in trouble
– Check performance
• Levels (Remember adjacent channels)
• MER, BER
• Linear performance (Freq. response, Group Delay)
– If the Downstream is fine, Check the Upstream
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Troubleshooting the Registration Process
Upstream
Upstream
Upstream
– Check Transmit Level
• High or Low could indicate a problem
– Check Frequency & Modulation type
• May work using QPSK & not 16 or 64 QAM
– BKER
• Should be little or no errors
• Check for Lost or Discarded Packets
– Lost Packets indicate ingress
– Discarded Packets indicate congestion
– May be deceiving
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Troubleshooting the Registration Process
IP Network
Network
Network
– Check IP addresses
• A CPE, or Emulator IP address is required to pass data through
the network. Cable IP address is not enough
• Check Bootfile
– If default file, you are not provisioned
– Test ability to pass data through the network
• Ping – Test connectivity to another device
• Tracert (Trace route) – Test IP route with transmit times through
the network.
• Throughput – Test the ability to pass data through the network.
• Browser – Test the ability to connect to a known site through the
modem
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Troubleshooting the Registration Process
Modem & Customer Equipment
Modem
– Test ability to pass data through the customer modem
• Ping – Test connectivity to another device
• Tracert (Trace route) – Test IP route with transmit times through
the network.
• Throughput – Test the ability to pass data through the network.
• Browser – Test the ability to connect to a known site
– If your test equipment is fine, it is probably the customer equipment
Customer Equipment
– Connect customer PC to test instrument
Modem
• May have to reboot PC
• If not working, maybe bad Net card
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CM Network Analyzers
Cable Modem Network Analyzer are continually
being developed & improved to troubleshoot
DOCSIS systems
These powerful tools are designed around the
premise that if you can quickly determine the
source of the problems in a DOCSIS system, you
will also save valuable time and un-necessary truck
rolls while trying to troubleshoot and repair these
problems.
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Digital Network Analyzers
Connect to the CMTS
Obtain an IP from the DHCP server
Provide Downstream QAM information
Provide Lost Packets and BKER information in the upstream
Can do Ping, Trace Route and Throughput testing from the Cable
Modem or PC emulator
Provide the ability to emulate another modem and then step you
through the connection process using the customer equipment’s MAC
address if BPI+ is turned off.
Provide special measurements for extended services such as VoIP
and IPTV
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Connecting to the Network
Select the
Downstream
DOCSIS channel
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Connecting to the Network
Select UCD
(upstream channel
descriptor)
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Connecting Process
Screen updates
as the process is
completed &
displays the
status
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Instrument connected
Completed Range
& Register Process
Modem On-line
Win CE Emulator
IP
MTA IP
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Downstream/Upstream Info
Analyzer view
of Downstream
& Upstream
parameters.
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Key IP Detail Parameters
IP Address
Gateway
TFTP Server
DHCP server
TFTP File name
& more
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Key Downstream Details
Channel Displayed
Measurements
– MER
– Pre & Post FEC
BER
– Errored Sec
Click on a Quadrant
to Zoom In
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Upstream Detail
Upstream transmit
level
Lost Packets
Upstream Block Error
Rate
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Network Testing
Network
Downstream
Upstream
March 2010
Modem
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The Gateway
CMTS
TFTP
TOD
DNS
44 MHz
In
Up-converter
Optical
Receiver
System
signals
Out
Combiner
DHCP
10/100 Mb Ethernet
ISP
CMTS converts
DOCSIS to Ethernet
or some other
protocol.
Signal to add’l
Laser inputs
LASER
Fiber
Node
Coax
Dist.Network
H
L
HTTP
Fiber Distribution
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Drop &
Home
Wiring
245
Network Side of the Gateway
ISP – Internet Service Provider(s)
DHCP – Dynamic Host Control Protocol
Server hands out the IP addresses
ISP
DHCP
TFTP
DNS
HTTP
TOD
March 2010
10/100 Mb Ethernet
TFTP – Trivial File Transfer Protocol
Server sends the tftp file sometimes
called bootp file or bootfile.
DNS –
Domain Name Server
Resolves domain names/IP addresses
HTTP – Hypertext Transmission Protocol
Server used for download testing
TOD – Time of Day Server
CMTS
Connection to HFC Network
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Testing the Network
Ping Tests
Trace Route Tests
Throughput Tests
Protocol Analysis
Digital(DOCSIS) Network
Analysis
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How Pings Can Get Lost
A CMTS (or any router) will discard
any ping packet received in error
(upstream errors)
A CMTS will discard ping packets when
the upstream bandwidth allocation of
the originating modem is exceeded
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DISCARDED
PACKETS
248
A Simple DOS ping
C:\ping 10.0.0.10
Pinging 10.0.0.10 with 32 bytes of data:
Reply from 10.0.0.10: bytes=32 time<10ms TTL=128
Reply from 10.0.0.10: bytes=32 time<10ms TTL=128
Reply from 10.0.0.10: bytes=32 time<10ms TTL=128
Reply from 10.0.0.10: bytes=32 time<10ms TTL=128
Ping statistics for 10.0.0.10:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms
(TTL A set maximum amount of time a packet is allowed to propagate
through the network before it is discarded.)
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A Simple DOS Tracert
C:/tracert 38.211.178.2
Tracing route to SR-INTRA [38.211.178.2] over a
maximum of 30 hops:
1 <10 ms <10 ms <10 ms 10.0.0.254
2
82 ms
82 ms
83 ms 172.16.1.1
3
82 ms
82 ms
82 ms SR-INTRA [38.211.178.2]
Trace complete.
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Throughput Testing
HTTP
Server
Network PC
Any file
Care needs to be taken when making
throughput comparisons.
Processing time of the servers comes into
play as well as the type of networks and
routers that are involved.
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Network Summary
Ping – A packet sent to a specific IP address and
returned for test purposes.
Trace Route – An offshoot of the Ping test, but
provides a trace of the packet through the IP network
Throughput – Downloading files to a PC to determine
how much average data per second is being
transferred
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Downstream Testing
Downstream
Network
Upstream
March 2010
Modem
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Upstream Testing
Downstream
Network
Modem
Upstream
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Getting A BKER
NE
Ping Packets are
numbered
consecutively and
accounted for as
they are received.
PING#1
NE
PING#2
PING#3
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Serial Pings & Lost Packets
PING #1 Sent  PING #1
PING #2 Sent  PING #2
PING #3 Sent  PING #3
PING #4 Sent PING #8
Received
Received
Received
Received
4 PACKETS LOST
(#4, 5, 6 & 7)
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BLOCK ERROR RATE
# Lost Packets
Block Error Rate = ---------------------------------------Total # of Transmitted Packets
Block Errors (Lost Packets are used to
characterize return path performance)
It is possible to “Load Test” the
Upstream DOCSIS system using
BKER
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Why Test Loading ?
Confirm that the customer is actually getting the
upstream BW he is paying for
Confirm that the BW restrictions are working
properly
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258
Loading Calculation
50 bytes
Ping Packet
Header &
Overhead
Load =
(kb/sec)
0 - 1024 Bytes
P A Y L O A D (Packet Size)
(50 Bytes + Bytes in Payload) X (8 bits/Byte)
(delay in msec) X 1000 msec/sec
The upstream “load” is a function of the packet size and
the packet delay.
Packet size = Header + Payload
Packet Delay – How often the packets are transmitted.
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Approximate Loading
Delay
Size
Pkts/min
(mSec) (Bytes)
Upstream Load
(approximate)
20
1024
3000
430 kb/sec
40
1024
1500
215 kb/sec
60
768
1000
109 kb/sec
*Based on a 50 Byte ping packet in addition to the
size of the payload.
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Upstream Fly in the Ointment
In three out of the four
possible problem
areas, the trouble can
be solved by the
service tech handling
the call.
Downstream
Network
Modem
Upstream
The Upstream piece of
the puzzle is a different
story.
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You can’t get there from here
The problem
could be here …
To CMTS Receive Port
Spare Splitter Leg
H
L
Optical
Receiver
Fiber
Node
Optical
Receiver
Optical
Receiver
or here …
H
L
The actual Call
might be here
H
L
March 2010
Coax
Dist.Network
or here …
or the problem could
be anywhere in these
three nodes.
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Diplex Filter
CMTS
44 MHz
In
Up-converter
Out
Optical
Receiver
Optical
Receiver
Low
High
Common
H
L
March 2010
DOCSIS Network
Analyzer
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Amplitude
Zero Span/Time Domain Mode
Frequency
In the Spectrum Mode the
horizontal access of the
analyzer displays
frequency.
March 2010
TIME
In the Time Domain mode the
analyzer remains on one
specified frequency and the
horizontal access represents
TIME.
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264
Upstream Power Measurement
Because upstream Cable Modems transmit in
very short bursts, it is difficult to measure their
levels.
Putting the analyzer in Max Hold will allow you
to get an approximation of the CM return levels.
Using the Time Domain Mode on the analyzer
will allow you to get a very accurate power
measurement of your cable modem signals.
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Max Hold
Using Max Hold
will allow you to
get a relative
reading on the
Cable Modems in
the return.
This Method is
not very accurate,
but does provide
a good
approximation.
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Measuring Power in TDM mode
Measuring power of cable modems in the
return system is a two step process.
Step One – Calculate the half-channel bandwidth
of the Upstream signal in order to properly setup
the analyzer.
Step Two – Measure the power using the analyzer
average detector and make a bandwidth correction.
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Calculating Analyzer Center Freq
1. Half Channel Width = Symbol Rate / 2
2. Offset the Center Frequency by 80% of the Half Channel
Width:
New CF = Original CF - (half Channel Width X 80%)
3. Calculating New CF setting for a 1.6 MHz QPSK signal:
Half Channel Width = 1.6MHz (.80)/2
Half Channel Width = .64 MHz = 640 KHz
4. Analyzer CF = 11.98 MHz – 0.64 MHz
5. Analyzer CF = 11.34 MHz
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Measuring the Level
Set the SPAN to 50-100 mSec
and the Resolution Bandwidth to
1 MHz.
Set the trigger level near the top
of the signal and adjust to
where the preamble is clearly
displayed.
Use the average detector and
place a marker on the preamble
Make the bandwidth correction
for the measurement.
March 2010
Note: Making the measurement
with a noise marker will give
you the ability to automatically
have the analyzer give you the
BW correction. This summary
was derived from a detailed
Cisco procedure. More
detailed information can be
found on the Cisco website.
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Measurement at Preamble
The Measurement
Bandwidth is the
symbol rate. In this
case 1.6 MHz.
Adjust for B/W
difference between
RBW of 1 MHz and the
1.6 MHz measurement
BW.
Some analyzers will
calculate this
automatically.
BW adjustment= 10 log BW1/BW2
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Characterizing the Upstream
Return Path
Verification, Test
& Troubleshooting
Test signal injected in field
& measured on analyzer
Measure MER, BER,
Constellation, Freq.
Response, Group Delay
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Modem & Customer Equip. Testing
Downstream
Network
Upstream
Testing the
modem, it’s
provisioning and
the PC connection
is the last piece of
the troubleshooting
puzzle.
Modem
March 2010
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Network Analyzer as a CM
Customer
PC
Digital
Network
Analyzer
CMTS
ISP
In this case the Network Analyzer is taking the place of the
customer’s cable modem.
With some units, it is actually possible to “borrow” the MAC
address of the customer’s modem and actually emulate that
specific modem during the testing process
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PC Emulator
PC
Emulator
Digital
Network
Analyzer
CMTS
ISP
Using a PC emulation mode, the network analyzer is able
to do Ping, Trace Route and Throughput testing from the
customer’s premise to any location on the internet.
The PC emulation also allows analysis of IP details
related to the customers own MAC address
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Key to CM Troubleshooting
Downstream
Upstream
Network
Modem
The key to good DOCSIS
troubleshooting is to identify
which of the four areas need to
be worked on.
Then as Kenny Rogers said
“know when to hold ‘em and
know when to fold ‘em”.
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Architecture of the Future
????????
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Thank You
QUESTIONS??
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Group Delay
As different frequencies pass through a
Cable System, some will move faster than
others
5 MHz
5 MHz
10 MHz
10 MHz
15 MHz
20 MHz
25 MHz
30 MHz
35 MHz
40 MHz
SYSTEM
Filters &
Traps
15 MHz
20 MHz
25 MHz
t
5 MHz
10 MHz
SYSTEM
Filters &
Traps
15 MHz
20 MHz
25 MHz
30 MHz
35 MHz
40 MHz
30 MHz
35 MHz
40 MHz
T I M E
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Equalizer Taps
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What does sweep do?
Checks the Frequency response
of the network
Checks both forward and return
paths
Confirms unity gain
If the system is flat and levels are
correct, distortion will be minimal
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Setting the Dynamic Range in the 3010H
3010H
Press
ENTER
F3
F4
to save change
SCALE
F1
March 2010
F2
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