Principles

1
Principles Testing of Digital Signaling
Associated Physical Interfaces
2
Making Voice Compatible
Voice Signals Complex Analog Waveforms
Digital (Computer) Data Already Compatible With
T1 Format 1110010 00100101 00011110 10111010
01110101 00101111
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Making Voice Data Compatible
Voice Signals (Complex Analog Waveforms) Must Be
Sampled Often Enough To Sound Like The Original
Conversation At The Receiving End. Pulse Code
Modulation (PCM) A Sampling Process That
Compresses A Conversation Into A 64Kbps Digital
Signal Level 0 (DS0). The Incoming Analog
(Voice) Signal Is Sampled At 8000 Times Per
Second Using Pulse Amplitude Modulation
(PAM) Each Pulse Is Assigned An 8-Bit Binary
Value Based On Its Amplitude Polarity 8-Bits
Per Pulse x 800 Samples Per Second 64 Kbps
(DS0) Once Digitized, Voice Data Can Be
Combined. Human Voice Range 300Hz -3300Hz.
A 4000Hz Bandwidth, As Defined By The Telco
Industry, Offers Optimum Voice Fidelity While
Minimizing Crosstalk. Nyquests Theorum States
That The Original Analog Signal Must Be Sampled
At A Minimum Of Twice Its Highest Frequency To Be
Recognized By The Receiving Party. Therefore,
Sampling Rate 8000
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Sampling Analog (Voice) Waveform
Voice Waveform
Enlarged View Of Voice Waveform Showing Sampling
At 8000 Times Per Second
5
Time Division Multiplexing
Time Division Multiplexing (TDM) Divides The T1
Frame Into Twenty-Four 64Kbps Time Slots
(DS0s). Each DS0 Contains A Single Digital Word
Made Up of 8 Data Bits (7 Data bits 1 LSB For
Signaling) 8 Data Bits x 24 Frames 192
Bits. An Additional Bit Is added For Framing
193 Bits Total Each T1 Is Transmitted At 800
time Per Second. 8000 x 193 Bits 1.54Mbps, A
Digital Signal Level-1 (DS1)
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Ti Frame
8-Bit Data Word
Frame Bit
DS0 Time Slots
T1 Frame (24 Time Slots, 8-Bits Each 1 Framing
Bit 193 Bits)
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DS0 gt T1 gt Tree
T1
T3
24 DS0s
24 DS0s
8
AMI Format
Alternate Mark Inversion Binary 1 Square
Wave (Pulse, Mark) Binary 0 Line (No Pulse,
Space) Each Pulse Alternates Between Positive
Negative Bipolar Signal Allows The Signal To
Travel Greater Distances Over A Copper
Pair. Also Provides A Limited Amount Of Error
Detection Since No Two Consecutive Can Have The
The Same Polarity. Consecutive Pulses With The
Same Polarity Bipolar Violation (BPV).
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Pulse Stuffing
All DS1 Signals MUST Have A Minimum Of 1s (Marks
or Pulses) Density. Required For Recovery Of
Clock Information Min 1 Pulse In Any 8-Bit
Sequence (12.5 1s). 3 Pulses In Any 24-Bits
Of Information AND No More Than 15
Consecutive 0s. Pulse Stuffing Overcomes These
Conventions Every 8th Bit Stuffed With A
1 Since The 8th Bit Can No Longer Represent
Data, The Data Word Length Becomes 7-Bits
Long. 7 Bits x 8000 Samples Per Second 56kbps
(DS0) Pulse Stuffing Reduces Data Rate To
56kbps (From 64kbps).
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Bipolar Data Waveform
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B8ZS (Bipolar with 8-Zero Substitution)
B8ZS Is used To Break Up Long Stings (8 Or More)
Of 0s Long Strings Of 0s Impair Clock
Information Recovery The CSU Detects A Long
String Of 0s And Substitutes A Fictitious 8-Bit
Byte. Receiving Equipment Detects The B8ZS
Pulses And Replaces Them With 0s.
12
Superframe Framing
A Superframe Consists Of 12 T1 Frames The 193rd
Bit Of Each Frame Forms A 12-Bit Word Used To
Control Frame Signaling Management. Robbed
Bit Signaling Takes (Robs) And Uses The Least
Significant Bit (LSB) Of The DS0s 6th 12th
Frames For Signaling. This Is Used To Signal
On-Hook Off Hook
13
ESF Fraoming (Extend SuperFraming)
ESF Contains Twenty-Four 193 Bit
Frames Three-Fourths Of the Control Bits Are
used For Evaluating Circuit Performance 6
Control Bits Are Used For Cyclic Redundancy Check
(CRC) 12 Bits Are Used As A Data Link For
Communicating Between Transmission and
Reception. 6 Bits Are Used To Manage
Signaling Framing.
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CRC (Cyclic Redundancy Check)
A 6-Bit Word Used To Detect Bit Errors 6-Bit
Word Calculation Sent By The Transmitting
Equipment. The Receiving Equipment Performs
The Same Calculation On The Received Data And
Then Compares Both 6-Bit Words. They Must Be
Identical. If Not, The Receiving Equipment
Requests The Data To Be Resent.
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Facility Data Link within ESF Framing
4 kbps Overhead Reserved For Facility Data Link
Communications A Synchronous Communications
Channel Standard Message Formats Performance
Data Report Specific Error Events Historical
Information Error Counts
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BERT Testing (Bit Error Rate Test)
Out-Of-Service Test! Used To Find Errors Not
Uncovered Via In-Service Monitoring Transmits
Unique Data Patterns To Stress Transmission
Path. Common Patterns 3-In-24 A 24 Bit
Pattern Which Contains Three 1s, Twenty-one
0s. Maximum Of 15 Consecutive 0s (Mark
Density Of 12.5) Used To Test Timing
Recovery Forces A B8ZS Code If Circuit Is
Provisioned Properly 17 (1 In 8) An 8-Bit
Pattern Which Contains One 1 (Mark). Used To
Test Timing Recovery Will Not Force A B8zs When
Transmitted Unframed Forces A B8zs When
Transmitted Framed If Circuit Is Provisioned
Properly
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BERT Testing (Bit Error Rate Test)
QRSS Used For Both Maintenance Installation
System Verification A Pseudorandom Pattern Of
High Low Density Sequences Based On A 20-Bit
Shift Register - Pattern Repeats Every 1,048,575
Bits! Never More Than 14 Consecutive
0s Stresses Timing Recovery Forces A B8SZ
When Transmitted Framed If Circuit Is Provisioned
Properly All 1s All Bits Set To 1s
(Marks) Maximum Power Consumption Verifies
Properly Regulated Power Employed During
Installation All 0s All Bits Set To 0s
(Spaces) Used Only On B8ZS Configured
Circuits Verifies All Call Circuit Elements Are
Provisioned Properly For B8ZS
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BERT Testing (Bit Error Rate Test)
T1-DALY 55 Octet Contains 55 8-Bit
Octets Of Rapidly Changing Data (Changes
Between High Low Density) 55 Octet Has 15
Consecutive 0s May Violate 1s Density
Requirements If Transmitted In A Framed
Mode. Both T1-DALY 55 Octet Will Force A
B8ZS In A Properly Provisioned Circuit 2-In
-8 An 8-Bit Pattern With two 1s And A Maximum Of
4 Consecutive 0s Will Not Force A
B8ZS Employed Primarily On AMI Circuits Will
Expose Improperly Provisioned Circuit Element(s)
Not AMI Configured
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BERT Testing (Bit Error Rate Test)
Channel Test Patterns Employed To Simulate
Customer Traffic For DS0 Testing 2047 A
Pseudorandom Sequence based On An 11-Bit Shift
Register 215-1 A Pseudorandom Sequence Based On
A 15-Bit Shift Register 220-1 A Pseudorandom
Sequence Based On A 20-Bit Shift
Register 223-1 A Pseudorandom Sequence Based On
A 23-Bit Shift Register
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T1 Testing
Choice Of In-Service Monitoring Out-Of-Service
Tests In-Service Monitoring Allows Data To Be
Monitored At Various Points Within The System
Without Interrupting Traffic Real Time
Analysis Not As Thorough As Out-Of-Testing,
May Not Detect/Identify All Errors
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T1 Testing
Out-Of-Service Testing Requires Taking
Over The T1, Interrupts All Live
Traffic/Revenue Typically Employed At
Turn-Up Or For Severely Degraded Traffic
Conditions Performed Head-To-Head Or By
Creating A Loopback Head-To-Head Requires
2 Test Sets (And 2 Technicians)
Simultaneously Sending Receiving Known
Test Patterns Loopback Utilizes A Single
Test Set. Test Set Must Transmit A Loopback
Code To The Far End Device.
Alternately, A Hard Loop May Be Manually
Placed At The Far End, Achieving The Same
Results. All Subsequent Data Is Then
Looped Back To The Test Set Accomplis
hed With A Single Technician
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Summary Of T1 Tests Measurements
Bit Error Performed In Out-Of-Service Testing
Only Provides Counts Of Logic errors In The Bit
Stream Permits Stress Testing Of All Circuit
Elements BPV Performed In Out-Of-Service
Testing Only Measures/Counts Consecutive Pulses
Of Same Polarity As Transmitted Across The
T1 Frame Errors Performed In-Service Or
Out-Of-Service Measures The Number Of Times An
Incorrect Value Appears In The Framing Bit
Position CRC Errors In-Service Test That
Detects Bit Errors In A Block Of Data. Requires
ESF Framing
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Summary Of T1 Tests Measurements
Rx Level (V) In or Out-Of-Service Bipolar
Peak-To-Peak Measurement. Nominal 6 Vdc
P-P Rx Level (dB) In or Out-Of-Service Received
Signal Power Measurement. Nominal 0
dB Rx Frequency In of Out-Of-Service Data
Communication Rate. Nominal 1.544
Mbps Clock Slips In of Out-Of-Service Comparison
Between Network And Equipment Timing.
Errored Free Secs In of Out-Of-Service Count
Of Error Free Seconds. Errored Secs In of
Out-Of-Service Count Of Errored Seconds.
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Loopback Connecting To A CSU
Loopback Connecting To A CSU
CSU
Red Test Set Rx Blue Test Set Tx