| Thread Links | Date Links | ||||
|---|---|---|---|---|---|
| Thread Prev | Thread Next | Thread Index | Date Prev | Date Next | Date Index |
Hi Steve,
The intent of the posted proposed objective is to indicate that the 25G Ethernet copper cable PHY is not to start from a blank slate, but rather is constrained to permit end users and suppliers to leverage technology developed for 100GBASE-CR4, e.g., transceivers.
The expressed concern with the posted proposed objective is that it might be interpreted to be too restrictive and may not allow any non-obvious deviations; e.g., must use the host loss budget as specified in 802.3bj. As an example, Vineet’s presentation yesterday proposed an additional host configuration restricted to around half the 802.3bj host budget with cable lengths up to 3 m that might allow no FEC or lower latency FEC (e.g., Clause 74) and meet BER/MTTFPA targets.
The intent is to find words that will not be interpreted as being that restrictive. Chris’s suggested wording is intended to clarify that the channel specifications referred to in the objective are the end to end (TP0 to TP5) parameters, not necessarily the partitioning of the budget. This would constrain the end to end channel to be compatible with 100GBASE-CR4 transceiver technology but would permit repartitioning of the channel budget between transceivers amongst other trade-offs.
From: Trowbridge, Stephen J (Steve) [mailto:steve.trowbridge@xxxxxxxxxxxxxxxxxx]
Hi David, Certainly fine to have that discussion to prepare for the task force, but no need to put any constraining details in the objective. If you think you might want to change stuff in this way, and a shorter reach meets the market need, you could back the objective off to “at least 3m” or “at least 4m” and leave yourself that flexibility. Even if you later decide to just copy what bj did, the bj solution meets “at least 3m” and “at least 4m”. Regards, Steve
From: Chalupsky, David [mailto:david.chalupsky@xxxxxxxxx]
Steve – we have been discussing repartitioning the end-to-end budget for CR… Maybe reduce the cable length & give some back to the host PCB channel segment… so if we are going to put a reach objective in for CR we need to finish that debate first. The other suggestions for CR objective wording kept things vague enough that we could work the partition later.
From: Trowbridge, Stephen J (Steve) [mailto:steve.trowbridge@xxxxxxxxxxxxxxxxxx]
Hi all, I think you guys are getting into the weeds here considering that this is the Study Group phase. I believe that the objectives can be much higher level than you are proposing and you can trust the task force to do the right thing, because this isn’t a waterfall thing where you are creating a set of objectives and throwing them over the fence to a totally disjoint group of engineers who you don’t trust to do the right thing unless you tie their hands: the task force will be YOU, and if you can’t trust yourself, who can you trust?
The only reason the later iteration of the P802.3bj objectives got into channel details was that they were trying to generate distinct identity for doing two backplane PHYs, otherwise they could just have left it as “up to 1m over a backplane”.
Assuming you are intending to specify a single backplane PHY rather than having KR and KP variants, I think you could leave it as: · Define a single lane 25 Gb/s PHY for operation over links consistent with copper traces (as specified by P802.3bj) with lengths up to at least 1m. · Define a single lane 25 Gb/s PHY for links consistent with copper twinaxial cables with lengths up to at least 5m. Regards, Steve
From: Vineet Salunke (vineets) [mailto:vineets@xxxxxxxxx]
Matt,
I agree, staying with CR4 specs would be best, but I am trying to understand the need for larger host loss.
The main volume would be “SFP” ports used on both switch and server, so we should optimize for that. QSFP switch ports will not be able to use the larger loss, but can still provide 4x25G CR breakout.
--vineet
From: Matt Brown (APM) [mailto:mbrown@xxxxxxx]
Hi Vineet,
I think it makes a lot of sense to retain the 802.3bj host loss. The case in point would be a switch with 4x25G connectors that may be used for either a signal 100G Ethernet port (100GBASE-CR4 per 802.3bj) or four 25G Ethernet ports (25GBASE-CR per new 25G project).
From: Vineet Salunke (vineets) [mailto:vineets@xxxxxxxxx]
Chris,
We heard on the call yesterday, at least 3 demands that do not exactly match Clause 92. · Need to reduce the host loss on the server side, to reduce total loss and avoid use of FEC. · Need to further optimize around 3m cables for above. · And I also heard need to allow larger host loss for the TOR switch side (when using RS-FEC).
So can we avoid the direct reference to Clause 92 specifications ?
--vineet
From: Christopher T. Diminico [mailto:00000025925d7602-dmarc-request@xxxxxxxx]
Rich,
Hopefully this addresses both you and George.
Given the intent is to operate over channels consistent with the channel (TP0-TP5) specified in IEEEStd802.3bj-2014 Clause92.
•Define a single-lane 25Gb/s PHY for operation over channels consistent with the channel specified in IEEEStd802.3bj-2014 Clause92 (Fig 92-2 - TP0-TP5) Regards, Chris DiMinico
-----Original Message----- Both suggestions allude to a specific host/module budget which I believe needs to re-evaluated in task force. Perhaps:
Define a single-lane 25Gb/s PHY for operation over copper twin-axial cables, host channels, and module channels consistent with channels (TP0-TP5) specified in IEEEStd802.3bj-2014 Clause93
This sort of reinforces a single silicon solution.
From: George Zimmerman [mailto:george@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx]
Chris – Clause 92 has a lot of non-channel stuff in it, and the parenthetical insert, while clarifying to those who know clause 92 intimately, isn’t perhaps as clear as you could be. Pointing to the correct subclause, a figure or a table would be a lot better.
The wording itself leads to confusion because it says “over copper twinaxial cables consistent with”, but TP0 to TP5 includes more than the twinax cables, as you know. We end up with a couple of choices: 1) Just identify the cables in clause 92, or 2) Say operate over the whole TP0 to TP5 channel in clause 92 (I apologize because I have another call which conflicted with yesterday’s meeting – I don’t have an opinion on whether using the whole channel from TP0 to TP5 is in fact the correct objective, or whether you want to do just the cables) If you just want to do (1) just the cables, the cable assembly is specified in 92.10 (and references elsewhere), I would suggest stating •Define a single-lane 25Gb/s PHY for operation over copper twin-axial cables consistent with cable assemblies specified in IEEEStd802.3bj-2014 Clause92.10
And, if you want to do the whole channel, including the PCB, as you stated, from TP0 to TP5, Clause 92.9 clearly specifies this (by referencing other subclauses)
•Define a single-lane 25Gb/s PHY for operation over copper twin-axial cables consistent with cable assemblies specified in IEEEStd802.3bj-2014 Clause92.9
Note I’m looking at draft 3.2 of the 802.3bj, and don’t have the final published version.
George Zimmerman Principal, CME Consulting Experts in Advanced PHYsical Communications Technology 310-920-3860
(PLEASE NOTE NEW EMAIL ADDRESS. THE OTHER WILL STILL WORK, BUT PLEASE USE THIS FOR CME BUSINESS)
From: Christopher T. Diminico [mailto:00000025925d7602-dmarc-request@xxxxxxxx]
Colleagues,
Based on the discussions of the objective given on slide 9 second bullet in http://www.ieee802.org/3/25GSG/public/adhoc/architecture/nowell_081214_25GE_adhoc.pdf during the ad-hoc yesterday, I suggest we explicitly identify 802.3bj channel by adding (TP0-TP5).
Change from •Define a single-lane 25Gb/s PHY for operation over copper twin-axial cables consistent with channels specified in IEEEStd802.3bj-2014 Clause92 To •Define a single-lane 25Gb/s PHY for operation over copper twin-axial cables consistent with channels (TP0-TP5) specified in IEEEStd802.3bj-2014 Clause92
Regards,
Chris DiMinico
-----Original Message----- Sorry everyone – calendar screw up on my side around the re-arranged architecture ad-hoc meeting. Will update soon with improved logistics.
Mark
On 8/19/14, 5:42 PM, "Mark Nowell (mnowell)" <mnowell@xxxxxxxxx> wrote:
Dear 25Gb/s Ethernet Study Group Members,
A few reminders and updates:
1) Optical Ad-hoc is tomorrow Wed 8/20 @ 9am PST. Dial in details are here: http://www.ieee802.org/3/25GSG/public/adhoc/index.html
2) Architecture ad-hoc meeting next week has moved to Wed 8/27 @ (am PST (shifted from Tues). Dial in details are here: http://www.ieee802.org/3/25GSG/public/adhoc/index.html
3) Reminders on Call for presentations and September Meeting planning. Presentation request deadline is Friday Aug 29th. Please see my original email for details on meeting logistics and travel planning (We meet all-day Thurs and Friday). http://www.ieee802.org/3/25GSG/email/msg00004.html
As a reminder, the September Study Group meeting has limited meeting time and the presentations will be focused on the Study Group work of building objectives, developing responses to the CSD (5 Criteria) and PAR. Presentations outside of the scope of those priorities will be given time on agenda as possible.
Regards…Mark |