Re: [802.3_25GSMF] Parameter changes for MPI penalty

["Dudek, Mike" <Mike.Dudek@xxxxxxxxxx>]

See David Lewis’s email.   My calculation shows that there was 0.6dB margin included in the 10GBASE-LR specification for Tx/Rx reflections.  I think this would have covered most of these MPI penalties.

 

From: Matt Traverso (mattrave) [mailto:mattrave@xxxxxxxxx]
Sent: Tuesday, June 20, 2017 7:24 AM
To: STDS-802-3-25GSMF@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_25GSMF] Parameter changes for MPI penalty

 

Gary,

See king_01_25gsmf_061417.

 

As Jonathan shows, running the spreadsheet for NRZ (PAM2) still results in appreciable penalties.  By the way, this also occurs in the case of 10GE.  Since we as an industry have deployed a lot of 10GE, and we have not seen this issue arise. 

 

I believe the conclusions are some mix of:

-          Return loss of deployed transceivers is much less than the minimum specified in 10GE SMF PMD’s

-          Return loss of deployed SMF connectors for 10GE is more benign than specified

-          MPI penalty method is still overestimating penalty values (laser linewidths? Other?)

 

Regards

--matt

 

Matt Traverso PRINCIPAL ENGINEER.ENGINEERING mattrave@xxxxxxxxx	Cisco Systems, Inc. 3700 Cisco Way SAN JOSE 95134 United States cisco.com

 

 

 

 

 

From: Gary Nicholl (gnicholl)
Sent: Tuesday, June 20, 2017 6:19 AM
To: STDS-802-3-25GSMF@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_25GSMF] Parameter changes for MPI penalty

 

Correcting the typo (I guess I haven’t  woken up yet!)..

 

I haven’t been following this discussion carefully, but how can there be a 0.7dB MPI penalty for 25GBASE-ER ?  I thought this PMD was based on NRZ, and for NRZ the MPI penalty was minimal (compared to PAM4). I don’t believe we have accounted for 0.7dB MPI penalty in the existing 40GE and 100GE budgets in 802.3ba (or 10GE in 802.3ae for that matter).

 

Gary

 

 

 

 

From: Gary Nicholl <gnicholl@xxxxxxxxx>
Reply-To: Gary Nicholl <gnicholl@xxxxxxxxx>
Date: Tuesday, June 20, 2017 at 9:16 AM
To: "STDS-802-3-25GSMF@xxxxxxxxxxxxxxxxx" <STDS-802-3-25GSMF@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_25GSMF] Parameter changes for MPI penalty

 

Dave,

 

I haven’t been falling this discussion carefully, but how can there be a 0.7dB MPI penalty for 25GBASE-ER ?  I thought this PMD was based on NRZ, and for NRZ the MPI penalty was minimal (compared to PAM4). I don’t believe we have accounted for 0.7dB MPI penalty in the existing 40GE and 100GE budgets in 802.3ba (or 10GE in 802.3ae for that matter).

 

Gary

 

From: David Lewis <David.Lewis@xxxxxxxxxxxx>
Reply-To: David Lewis <David.Lewis@xxxxxxxxxxxx>
Date: Monday, June 19, 2017 at 4:47 AM
To: "STDS-802-3-25GSMF@xxxxxxxxxxxxxxxxx" <STDS-802-3-25GSMF@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_25GSMF] Parameter changes for MPI penalty

 

Pete,

Thank you.  I think this will be the way to do it for 25GBASE-ER.

 

What do people think about 25GBASE-LR?  Should we tighten sensitivity and SRS by 0.7 dB or tradeoff channel insertion loss versus MPI?  I think the consensus from the ad hoc call was to keep the same 6.3 dB budget currently used at 10G and 100G-LR4.

 

David

 

From: Anslow, Peter [mailto:panslow@xxxxxxxxx]
Sent: Monday, June 19, 2017 10:30 AM
To: David Lewis <David.Lewis@xxxxxxxxxxxx>; STDS-802-3-25GSMF@xxxxxxxxxxxxxxxxx
Subject: RE: Parameter changes for MPI penalty

 

David,

 

I think that if you want to adopt the principle of trading MPI penalty against channel insertion loss, then you should follow what was done for 100GBASE-DR in the P802.3cd draft:

 

 

 

Regards,

Pete Anslow | Senior Standards Advisor
43-51 Worship Street | London, EC2A 2DX, UK
Direct +44 2070 125535 |

 

From: David Lewis [mailto:David.Lewis@xxxxxxxxxxxx]
Sent: 19 June 2017 08:19
To: STDS-802-3-25GSMF@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_25GSMF] Parameter changes for MPI penalty

 

Hi Kohichi,

I agree with what you say. 

 

Thinking about it, we have 2 columns for 25GBASE-ER:  the 30km column that has 3 dB of unallocated margin, and the 40km column that has 0 dB margin but is an “engineered link”.

 

Would you support the following:

1. Add a note to the 3 dB margin in the 30km column that says the margin is to include allowance for an MPI penalty of up to 0.7 dB.
2. Add a note to the 18 dB channel insertion loss in the 40 km column that says the 18 dB includes an allowance of up to 0.7 dB for MPI penalty.

 

I think that we need a comment that will not draw opposition in the recirculation ballot.   I would like to know whether the above will be supported or opposed.

 

Regards,

David Lewis

 

 

From: 田村公一 Kohichi Tamura [mailto:Kohichi.Tamura@xxxxxxxxxx]
Sent: Monday, June 19, 2017 1:46 AM
To: STDS-802-3-25GSMF@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_25GSMF] Parameter changes for MPI penalty

 

Hi David,

For 25GBASE-ER, my feeling is that we’ve already put the sensitivity as low as it ought to be for APD receivers. The transmitter OMA is also on the high side. So, to budget for MPI, I’d prefer to trade off a small amount of channel loss, leaving the powers as they are. One would expect use cases requiring the full loss budget to be rare, so it doesn’t seem necessary to burden the transmitter or receiver specifications further, unless justification is provided from channel data.

Regards,

Kohichi

 

From: David Lewis [mailto:David.Lewis@xxxxxxxxxxxx]
Sent: Sunday, June 18, 2017 8:14 PM
To: STDS-802-3-25GSMF@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_25GSMF] Parameter changes for MPI penalty

 

Mike,

That’s my initial proposal.  However if enough people object to the 0.7 dB reduction in sensitivity & SRS, we’ll need to introduce a loss table similar to the one in 100GBASE-DR.

 

During the ad hoc call there was opposition to the idea of giving users a tradeoff table for insertion loss for the 10km application.  The point was that some users would want to operate over existing cable plant currently operating at 10 Gb/s.  If we were to accept what I proposed, then those users would still need to check on how many connectors and the RL of each one, before knowing they could use it for 25 Gb/s.  At least they would not need to measure channel loss before knowing they could re-use a 10 Gb/s cable.

 

David Lewis

 

From: Dudek, Mike [mailto:Mike.Dudek@xxxxxxxxxx]
Sent: Saturday, June 17, 2017 3:14 AM
To: David Lewis <David.Lewis@xxxxxxxxxxxx>; STDS-802-3-25GSMF@xxxxxxxxxxxxxxxxx
Subject: RE: Parameter changes for MPI penalty

 

Is your proposal to not make any allowed trade offs between number of connectors and link loss?   If so I think the numbers in the table on slide 6 would be replaced by ticks.   I do wonder with such a large difference between TDP and the allowance for penalties whether we should give people a clue what that is for.   Maybe split the row into two.   One that says “Allocation for TDP” (value of 2.7dB) and the other says “Allocation for other penalties including Multi Path Interference” (value of 0.7dB).

 

From: David Lewis [mailto:David.Lewis@xxxxxxxxxxxx]
Sent: Friday, June 16, 2017 5:17 PM
To: STDS-802-3-25GSMF@xxxxxxxxxxxxxxxxx
Subject: [802.3_25GSMF] Parameter changes for MPI penalty

 

All,

 

At the ad hoc on Wednesday I took an action to provide the changes that would be needed in the optical link parameter tables for an MPI penalty of 0.7 dB.  See the attached presentation for what I think is needed.

 

The approach is to tighten Rx sensitivity and SRS by 0.7 dB for both the -LR and -ER variants.  In addition this proposal tightens the Transmitter reflectance from a maximum of -12 dB to a maximum of -26 dB.

 

Please use the reflector for discussion of this topic.  Our next ad hoc is on Wed June 28^th and will be the only one between now and when the sponsor recirculation ballot ends.

 

Regards,

David Lewis

P802.3cc Task Force Chair