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Dear 25Gb/s Study Group members,
In today’s ad-hoc call we had a more discussion on language options for picking an objective for the twin-ax cable application. The previous Straw poll results and the slides from the discussion are posted here:
Per the discussion on today’s call, it appeared we were getting some convergence on suitable language for the twin-ax cable objective(s). I’ve established a 2nd SurveyMonkey to use for the straw poll. This 2nd Straw Poll will close on Friday evening.
The differences in this straw poll are:
The link for the new survey is here:
https://www.surveymonkey.com/s/VCFLQZW
Regards…Mark
Below are the explanations that were written up for the 1st straw poll. I’m copying them here again (with slight edits) for those that missed the call.
Three survey questions. One as Chicago Rules, one a regular straw poll (i.e. Pick one) and finally a negative variant, where you should pick all options that you would oppose (I.e. Actually vote “No”
if a motion was made for this option)
Background information
====================
Without the benefit of the discussion, the straw poll may need some explanation. The tension between the options revolves around the balance of reach and budget allocation that people want to be able to explore in task force. When thinking through this, please
remember, that the key decision we need to make is to find language for the objective that will give everyone confidence that when they get into Task Force they will be able to do the work they need to do and drive towards the outcomes they want.
Below I will give the options as they are set up in the Survey Monkey, I’ll also add my
personal commentary on what choosing this option mean. This commentary is intended to capture the intent of the discussion and the interpretation I shared on the call but it is obviously not the definitive view.
Straw poll options for Twin-Ax Objective wording:
1. Define a single lane 25 Gb/s PHY for operation over links consistent with copper twin axial cables, with lengths up to at least 3m
Commentary on #1: This is felt to be the simplest objective. Allows the TF to work on a 3m specification and it is felt that it also enable the TF to also include a mode of operation to support 5m. Concern raised that
this would not guarantee that a 5m specification would happen and budget allocation could cause interoperability issues for 4x25G breakout applications from a 100G CR4 port. Concern that 3m alone would impact Broad Market potential.
2. Define a single lane 25 Gb/s PHY for operation over links consistent with copper twin axial cables, with lengths up to at least 5m
Commentary on #2: Variant on #1, but explicitly calling out the 5M reach. It was felt the TF would be able to still define a mode of operation to support 3m. Similar concerns to above around whether that would occur in TF.
3. Create two objectives (from options above)
Define a single lane 25 Gb/s PHY for operation over links consistent with copper twin axial cables, with lengths up to at least 3m
And
Define a single lane 25 Gb/s PHY for operation over links consistent with copper twin axial cables, with lengths up to at least 5m
Commentary on #3: This approach would explicitly instruct the TF that it needed to work on specifications for a 3m reach and for a 5m reach. As it is framed this way as two separate objectives, this does not preclude the
TF from developing two different PHYs, one for each reach. However, I do not think that there is any industry interest in that happening so believe the TF will work to keep the PHYs converged. But two objectives could allow that divergence to happen.
4. Define a single lane 25 Gb/s PHY for operation over links consistent with copper twin axial cables, that re-uses the host silicon transmitter and receiver characteristics specified in IEEE Std 802.3bj-2014 Clause 93
Commentary on #4: a different approach to addressing the same problem. Rather than define reach, define that the TF will re-use the industry specified transmitter and receiver specs as outlined in Clause 93. This provides both FEC and no-FEC variants,
and defines an end-to-end channel with no partitioning. The downside of this approach is that no reach is indicated which isn’t usual and not very informative to the non-expert. TF could theoretically meet the objective with a 1m cable, but I would not expect
that, in reality, the TF would move forward without solving industry needs (of 3m and 5 m).
Final comment on all of the above: I believe that everyone participating in these discussions and previous ad-hocs are fully aware of the scope of the work that will be addressed in the TaskForce. I do not think that any of these options will
really preclude that work happening but everyone has their own interpretations. Challenge for the SG is picking one with 75% support.
Regards…Mark
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