10gbase-r test patternsieee 802.3ae 3/12/2001 10gbase-r test patterns ibm test pattern • want to...
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10GBASE-R Test Patterns
John [email protected]
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Test Pattern• Want to evaluate “pathological” events that occur on
average once per day• At 10Gb/s “once per day” is equivalent to a
probability of 1.1×10–15 ~ 1/250
– Equivalent to 7.9σ for a Gaussian distribution• 231 – 1 PRBS repeats ~ 200ms
– Sufficient to meet worst case criteria of once per day?• 258 – 1 PRBS repeats in ~ 1 year
– Too long for practical testing
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
PCS
Test Pattern Function
16:66 Gearbox
Descrambler
Decoder
Sync Detect
66:16 Gearbox
Scrambler
Block Gen.
Coder
PMA
PMD
1616
Insert patterns at gearbox
Insert patterns at scrambler
Test here (or wrap only)?
BER Rx BER Tx
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Proposed Test Sequence• Use existing 1 + x39 + x58 scrambler
– Seed register with defined value– Run for N bits (propose N= 216)
• Allow non-zero scrambler data inputs for additional flexibility– Reset scrambler & repeat
• Can use scrambler data input to reset its state (pseudo-seed)• Seed can be set via management registers
• Seed chosen to stress:– Maximum run-length– Minimum transition density– Maximum baseline wander
• N arbitrary, but …– Choose power of 2 for easy implementation– Choose N < memory depth of typical BERT
• Periodically resetting the scrambler implies the pattern is no longer “random”
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Test Pattern Structure• Select a subset of the 258–1 PRBS using appropriate seed• Map the test pattern into the payload of the 66-bit blocks• Repeat the test pattern
N-bit Test Pattern (« 1017)
64b data0 1 64b data0 1 64b data0 1…
66b blocks
1 + x39 + X58 PRBS
3x1017 bits
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Test Pattern Generation• Seed the scrambler• Apply, short, repetitive data pattern (e.g. all zero’s)• Apply pseudo-seed after N bits to transition to pattern beginning• Repeat
Seed …
Time
InputData Data p-Seed Data Data … p-Seed Data Data
S0 S1 S2 S38 S39 S56 S57
++Input
Output
Seed …Output
Test Pattern Test pattern … Test pattern
N-bit test pattern
« N bits
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Example• Choose 1 + x6 + x7 PRBS,
– N= 16-bits– Pattern = 0 1 1 1 1 1 1 1 0 0 0 0 0 0 1 0 (longest run-length)
• Initial Seed = 1 0 1 0 1 0 0• To force scrambler to repeat the 16-bit pattern:
– “Data” = 0 1 1 1 0 0 1 0 0 0 0 0 0 0 0 0
• ∴∴∴∴Seed= 1010100, Pseudo-seed= 0111001• For Mth-order scrambler, need M-bits to reset the
scrambler
7bits reset the scrambler All zeros otherwise
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Error Detection• Only using a subset of the full 258–1 sequence• Self-synchronous descrambler will generate “errors”
at pattern boundary– “Errors” are deterministic due to pattern mismatch
• The “error” pattern at the descrambler equals the “data” pattern used to reset the scrambler to generate the test pattern
– Can be taken into account to compute real error rate– Increases somewhat the complexity at the error detector
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Pattern Characteristics• Compare proposed pattern with a 216 –1 PRBS
– PRBS choice is arbitrary– Want “random” pattern of ~216 length for comparison– 1+ x + x3 + x12 + x16 is convenient choice
• Evaluate– Running disparity– Transition density– Autocorrelation– Power spectral density– Baseline wander
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Running DisparityNomenclature• “216–1 PRBS”:
– 216 bits long (one cycle + 1 bit)
– 1 + x + x3 + x12 + x16
• “258–1 PRBS”:– 216 bits long
(« one cycle)– 1 + x39 + x58
– Seed chosen for max run-length ~8kb from pattern beginning
0 1 2 3 4 5 6 7x 104
-150
-100
-50
0
50
100
150
200
250
300
350
Time (UI)
Run
ning
Dis
parit
y
258-1 PRBS216-1 PRBS
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Transition Density• Transition density
averaged over 200 UI• 216–1
– 16 UI max run-length– 50% average density– 38% minimum density
• 258–1– 58 UI max run-length– 44% average density– 3% minimum density
0 1 2 3 4 5 6 7x 104
0.3
0.4
0.5
0.6
0.7
Tran
sitio
n D
ensi
ty 216-1 PRBS
0 1 2 3 4 5 6 7x 104
0
0.2
0.4
0.6
0.8
Tran
sitio
n D
ensi
ty
Time (UI)
258-1 PRBS
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Autocorrelation
• Random data = delta function
• Full PRBS closely approximates random data
• Partial PRBS more correlated than random data
0 1 2 3 4 5 6x 10
4
-0.1
-0.050
0.050.1
Aut
ocor
rela
tion
216 - 1 PRBS
0 1 2 3 4 5 6x 10
4
-0.05
0
0.05
0.1
0.15258 - 1 PRBS
Time (UI)
Aut
ocor
rela
tion
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Power Spectral Density• Increased low
frequency content in partial PRBS pattern
• Tones due to correlation in sequence
0 0.05 0.1 0.15 0.2-10
-5
0
5
Pow
er S
pect
ral D
ensi
ty (d
B/H
z)
0 0.5 1 1.5 2-30
-20
-10
0
Relative Frequency
258-1216-1
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Baseline Wander
0 0.5 1 1.5-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Time (UI)
Am
plitu
de
216-1 PRBS
DJσσσσ= 0.004,DJ-pp= 0.026Total ISI= -0.33 dB, Penalty= -0.03 dB, BLWσσσσ= 0.02442
0 0.5 1 1.5
-1
-0.5
0
0.5
1
Time (UI)
Am
plitu
de
258-1 PRBS
DJσσσσ= 0.007,DJ-pp= 0.089, Min. PW= 0.911Total ISI= -0.88 dB, Penalty= -0.62 dB, BLWσσσσ= 0.04551
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
|Amplitude| Histogram (216–1 PRBS)
0.9 1 1.1 1.20
500
1000
1500
2000
2500
3000
3500
Relative Amplitude0.95 1 1.05
0.0010.0030.01 0.02 0.05 0.10 0.25 0.50 0.75 0.90 0.95 0.98 0.99
0.9970.999
Relative Amplitude
Prob
abili
ty
Normal Probability Plot
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
|Amplitude| Histogram (258–1 PRBS)
0.6 0.8 1 1.2 1.40
1000
2000
3000
4000
5000
6000
7000
8000
Relative Amplitude0.8 0.9 1 1.1 1.2
0.0010.0030.01 0.02 0.05 0.10 0.25 0.50 0.75 0.90 0.95 0.98 0.99
0.9970.999
Relative Amplitude
Prob
abili
ty
Normal Probability Plot
“tails” in distribution
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Alternate 258–1 PRBS Segments
• “258–1 PRBS”:– 216 bits long
(« one cycle)– 1 + x39 + x58
– Seed chosen for run-length of 58 ~8kb from pattern start
• “258–1 Alternate”– 216 bits long
(« one cycle)– 1 + x39 + x58
– Seed chosen for run-length of 50 ~8kb from pattern start
0 1 2 3 4 5 6x 104
-200
0
200
400
600
Run
ning
Dis
parit
y
Time (UI)
0 0.5 1 1.5 2 2.5 3x 104
0
0.2
0.4
0.6
Tran
sist
ion
Den
sity
Time (UI)
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Baseline Wander
0 0.5 1 1.5
-1
-0.5
0
0.5
1
Time (UI)
Am
plitu
de
258-1 PRBS
DJσσσσ= 0.007,DJ-pp = 0.089, Min. PW = 0.911Total ISI = -0.88 dB, Penalty = -0.62 dBBLWσσσσ = 0.0455, BLWpp = 0.365
0 0.5 1 1.5-1
-0.5
0
0.5
1
Time (UI)
Am
plitu
de
258-1 PRBS (Alternate)
DJσσσσ= 0.005,DJ-pp = 0.036, Min. PW = 0.964Total ISI = -0.39 dB, Penalty = -0.05 dBBLWσσσσ = 0.0255, BLWpp = 0.17
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Baseline Wander
0.8 0.9 1 1.1 1.2
0.0010.0030.01 0.02 0.05 0.10 0.25 0.50 0.75 0.90 0.95 0.98 0.99
0.9970.999
|Amplitude|
Prob
abili
ty
258-1 PRBS
0.9 0.95 1 1.05 1.1
0.0010.0030.01 0.02 0.05 0.10 0.25 0.50 0.75 0.90 0.95 0.98 0.99
0.9970.999
|Amplitude|
Prob
abili
ty
258-1 PRBS (Alternate)
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Alternate “Data” Inputs
• “0000… data”– Seed chosen for
max run-length ~8kb from pattern start
– Data input to scrambler all zeros
• “1000… data”– Seed chosen for
max run-length – Data input to
scrambler = 1 + 63 zeros
– 64-bit data pattern repeats
0 2 4 6 8x 104
-200
0
200
400
Run
ning
Dis
parit
y 0000... data1000... data
0 2 4 6 8x 104
0
0.2
0.4
0.6
0.8
Time (UI)
Tran
sitio
n D
ensi
ty
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Summary• Use existing scrambler / descrambler to generate and
check test patterns• Wide variety of pattern characteristics available
– Select long PRBS segments using short seed values• Pattern can be set via management registers
– New patterns can be defined in the future without modifying hardware
• Cost: increased complexity in the pattern checker
Backup Material
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Stressed Eye
0 0.5 1 1.5-1
-0.5
0
0.5
1
Time (UI)
Am
plitu
de
K28.5 + Random 8B/10B Data
DJσσσσ= 0.030,DJ-pp = 0.084, Min. PW = 0.986Total ISI = 3.01 dB, Penalty = -2.84 dB
0 0.5 1 1.5-1
-0.5
0
0.5
1
Time (UI)
Am
plitu
de
258-1 PRBS
DJσσσσ= 0.028,DJ-pp = 0.089, Min. PW = 0.981Total ISI = -2.99 dB, Penalty = -2.76 dB
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
0 1 2 3 4 5 6 7 8x 104
-200
-100
0
100
200
300
400
500
600
700
800
Time (UI)
Run
ning
Dis
parit
y
OC-192 CID Pattern
16kb PRBS32kb PRBS
72 1’s72 0’s
16kb PRBS
A1/A2
OC-192 “CID” Pattern• 192 bytes A1• 192 bytes A2• 64 bytes C1• 128 bytes of “stuff”
(return disparity to 0 with 50% transition density)
• 16kb PRBS(x10+ x7+1)
• 72 zeros• 32kb PRBS
(x15+ x14+1)• 72 ones• 16kb PRBS
(x10+ x7+1)
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Running Disparity
0 1 2 3 4 5 6 7 8x 104
-200
-100
0
100
200
300
400
500
600
700
800
Time (UI)
Run
ning
Dis
parit
yOC-192 CID
258 - 1 PRBS
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
0 1 2 3 4 5 6 7x 104
0
0.2
0.4
0.6
0.8258 - 1 PRBS
Time (UI)
Tran
sist
ion
Den
sity
0 1 2 3 4 5 6 7 8x 104
0.2
0.3
0.4
0.5
0.6
0.7OC-192 CID Pattern
Tran
sist
ion
Den
sity
Transition Density• Transition density
averaged over 200 UI• OC-192 CID
– 72 UI max run-length– 50% average density– 21% minimum density
• 258–1– 58 UI max run-length– 44% average density– 3% minimum density
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Baseline Wander
0 0.5 1 1.5
-1
-0.5
0
0.5
1
Time (UI)
Am
plitu
de
OC-192 CID Pattern
DJσσσσ= 0.013,DJ-pp= 0.162Total ISI= -2.25 dB, Penalty= -1.76 dB, BLWσσσσ= 0.06953
0 0.5 1 1.5
-1
-0.5
0
0.5
1
Time (UI)
Am
plitu
de
258-1 PRBS
DJσσσσ= 0.007,DJ-pp= 0.089, Min. PW= 0.911Total ISI= -0.88 dB, Penalty= -0.62 dB, BLWσσσσ= 0.04551
IEEE 802.3ae 3/12/2001
10GBASE-R Test Patterns IBM
Baseline Wander (OC-192 CID)
0.5 1 1.50
0.5
1
1.5
2
2.5
3x 104
Relative Amplitude0.6 0.8 1 1.2 1.4
0.0010.0030.01 0.02 0.05 0.10 0.25 0.50 0.75 0.90 0.95 0.98 0.99
0.9970.999
Relative Amplitude
Prob
abili
ty
Normal Probability Plot