Dear Colleagues,
I have received several private emails correcting errors and making suggestions for clarifications, to my previous email.
Below is the corrected text, with the addition of IEEE Public Review Comments that have just been submitted on the IEEE Standards site. The deadline for comments is today, so if you have any, now is the time to submit them.
The following is an explanation of Chromatic Dispersion Penalty (CDP) scaling with reach and Baud rate, and interplay with transmitter chirp characteristics.
CDP is proportional to CD coefficient, link length, and Baud rate squared.
CDP ∝
CD * L * B2
Calculating the exact penalty is complex, however the CD * L * B2
term can be used for direct, relative comparisons, by defining it as a CDP Figure of Merit (CDP FM).
For convenience, 10km and 25Gbaud are used for normalization.
CDP FM = CD * (L/10) * (B/25)2
Table 1 below lists key transmitters specs. and CDP FM for various codes, with red highlighting concerns. The take away points are:
- 400GBASE-LR4 10km reach proposal had excessive CDP FM.
- 400GBASE-LR4 6km reach baseline has reasonable CDP FM.
- 400GBASE-ER8 40km reach baseline has excessive CDP FM for CD (min).
(Qualitative statement that 50G PAM4 “is a lot easier” than 100G PAM4 is not true at 40km. In fact the opposite it true; 400G ER8 40km (50G PAM4) is harder than 400G LR4 6km and 100G LR1 10km (both 100G PAM4).
)
- 400GBASE-ER8 30km reach proposal will have reasonable CDP FM.
- 200GBASE-ER4, 400GBASE-ER8 40km baselines have excessive TX OMA (min). 50GBASE-ER 40km baseline may have an excessive TX OMA (min).
(This is higher than previous TX OMA values (0.3 and 0.1 dBm for 40G ER4 and 100G ER4, respectively), and is higher than other codes in Table 1. It will significantly drive transmitter cost up by likely requiring
a TX amplifier. This undermines the Broad Market Potential, and is counter to the expressed need for low cost by Network Operators.)
- 200GBASE-ER4, 400GBASE-ER8 30km proposals will have reasonable TX OMA (min).
- 50GBASE-LR, 50GBASE-ER have not changed their suffixes to LR1 and ER1 to align with 802.3 convention established this year.
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TABLE 1
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~Baud Rate
|
Reach
|
TX OMA
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TX OMA – TDECQ
|
TDECQ
|
~CD
|
CDP FM
|
~CD
|
CDP FM
|
|
Codes
|
each lane
|
(max)
|
each lane (min)
|
each lane (min)
|
(max)
|
(min)
|
for CD (min)
|
(max)
|
for CD (max)
|
|
Gbaud
|
km
|
dBm
|
dBm
|
dB
|
ps/nm-km
|
normalized
|
ps/nm-km
|
normalized
|
|
4WDM-40 (100G ER4f) (TDP not TDECQ)
|
25
|
40
|
0.5
|
-0.5
|
3
|
-3
|
12
|
1
|
4
|
|
50GBASE-LR
|
25
|
10
|
-1.5
|
-2.9
|
3.2
|
-2
|
2
|
1.5
|
2
|
|
50GBASE-ER
|
25
|
40
|
3.4
|
2
|
3.2
|
-2
|
8
|
1.5
|
6
|
|
100GBASE-LR1
|
50
|
10
|
0.7
|
-0.6
|
3.4
|
-2
|
8
|
1.5
|
6
|
|
200GBASE-LR4
|
25
|
10
|
-0.4
|
-1.7
|
3.4
|
-3
|
3
|
1
|
1
|
|
200GBASE-ER4
|
25
|
40
|
3.4
|
2
|
3.2
|
-3
|
12
|
1
|
4
|
|
400GBASE-LR8
|
25
|
10
|
0.2
|
-1.1
|
3.1
|
-5
|
5
|
1
|
1
|
|
400GBASE-ER8
|
25
|
30
|
0.2
|
-1.2
|
3.4
|
-5
|
15
|
1
|
3
|
|
400GBASE-ER8
|
25
|
40
|
2.4
|
1
|
3.4
|
-5
|
20
|
1
|
4
|
|
400GBASE-LR4
|
50
|
6
|
0.2
|
-1.1
|
3.5
|
-6
|
14
|
3
|
7
|
|
400GBASE-LR4
|
50
|
10
|
0.2
|
-1.1
|
3.5
|
-6
|
24
|
3
|
12
|
Table 2 and 3 below explains the dynamics of the review process that happened in 802.3cu and 802.3cn.
In 802.3cu the proponents showed favorable data for 400GBASE-LR4 10km using TX favorable to the proposal. The opponents showed unfavorable data using TX unfavorable to the proposal. Therefore, the Task Force had a complete data set for
its review of Technical Feasibility.
In 802.3cn the proponents showed favorable data for 400GBASE-ER8 40km using TX favorable to the proposal. No unfavorable data was shown because no other type of TX was used. Therefore, the Task Force had an incomplete data set for its review
of Technical Feasibility. And the missing data is exactly in the area of concern as identified by Chromatic Dispersion Penalty Figure of Merit analysis. Further, the data presented in 802.3cu for 400GBASE-LR4 10km, which has similar CDP FM for CD (min) to
400GBASE-ER8 40km was determined by the 802.3cu to have insufficient margin to be considered Technically Feasible. Therefore, 802.3cn has not established Technical Feasibility.
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TABLE 2
|
EML TX
|
EML TX
|
SiPIC TX
|
|
802.3cu area of concern
|
high positive chirp
|
moderate positive chirp
|
no chirp
|
|
CDP effect
for CD (max)
|
big detriment
|
moderately detriment
|
no detriment
|
|
Proponent data brought in
|
No
|
Yes
|
Yes
|
|
Opponent data brought in
|
Yes
|
No
|
No
|
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TABLE 3
|
EML TX
|
EML TX
|
SiPIC TX
|
|
802.3cn area of concern
|
high positive chirp
|
moderate positive chirp
|
no chirp
|
|
CDP effect for
CD (min)
|
big help
|
moderate help
|
no help
|
|
Proponent data brought in
|
Yes
|
No
|
No
|
|
Opponent data brought in
|
No
|
No
|
No
|
802.3cn needs to go back and take more measurements to establish a complete data set to be in a position to determine Technical Feasibility.
Thank you
Chris
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Category
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Page
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Sub-clause
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Line #
|
Comment
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Suggested Change
|
|
General
|
22
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45
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1
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50GBASE-FR, 50GBASE-LR, 50GBASE-ER need 1 suffix to be consistent with 802.3 convention, pages 22 to 27, lines 1 to 54 pn each page
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Change to 50GBASE-FR1, 50GBASE-LR1, 50GBASE-ER1 everywhere in the document
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Technical
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45
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122
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16
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400G ER8 can only support 30km, lines 16 to 18
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Keep 200GBASE-ER4 2 m to 30 km || 2 m to 40 kma, Change 400GBASE-ER8 to 2 m to 30 km only, make same changes everywhere else in the entire document
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Technical
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46
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122
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21
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Outer Optical Modulation Amplitude (OMAouter), each lane (min)b for 200GBASE-ER4 of 3.4 dBm it too high, lines 21 to 22
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Change Outer Optical Modulation Amplitude (OMAouter), each lane (min)b for 200GBASE-ER4 to 1.2 dBm
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Technical
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46
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122
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27
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Launch power in OMAouter minus TDECQ, each lane (min): for extinction ratio
> 4.5 dB for 200GBASE-ER4 of 2 dBm is too high, lines 27 to 28
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Change Launch power in OMAouter minus TDECQ, each lane (min): for extinction ratio
> 4.5 dB for 200GBASE-ER4 to -0.2 dBm, Change all other limits in this table consistent with the OAM (min) reduction by 2.2dB.
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|
Technical
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48
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122
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18
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TX OAM (min) reduced by 2.2dB in Table 122-9, lines 18 to 54
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Change all limits in this table consistent with the TX OAM (min) reduction by 2.2dB in Table 122-9
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|
Technical
|
47
|
122
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26
|
Outer Optical Modulation Amplitude (OMAouter), each lane (min)b for 400GBASE-ER8 of 2.4 dBm is too high, lines 26 to 27
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Change Outer Optical Modulation Amplitude (OMAouter), each lane (min)b for 400GBASE-ER5 to 0.2 dBm
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Technical
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47
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122
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32
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Launch power in OMAouter minus TDECQ, each lane (min): for extinction ratio > 4.5 dB for 200GBASE-ER4 of 1 dBm is to high, lines 32 to 33
|
Change Launch power in OMAouter minus TDECQ, each lane (min): for extinction ratio
> 4.5 dB for 200GBASE-ER4 to -1.2 dBm, Change all other limits in this table consistent with the OAM (min) reduction by 2.2dB.
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|
Technical
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49
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122
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10
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TX OAM (min) reduced by 2.2dB in Table 122-10, lines 10 to 54
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Change all limits in this table consistent with the TX OAM (min) reduction by 2.2dB in Table 122-10
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|
General
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73
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139
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1
|
50GBASE-FR, 50GBASE-LR, 50GBASE-ER need 1 suffix to be consistent with 802.3 convention, pages 73 to 87, lines 1 to 54 on each page
|
Change to 50GBASE-FR1, 50GBASE-LR1, 50GBASE-ER1 everywhere in the document
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