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Chris, I haven’t heard of much interest in 2X50G 100GbE, but IEEE could consider a future project that includes 1X50, 2X50 and 4X50. I’d be glad to hear if others are interested in 2X50G 100GbE. 200GbE, based on 4X50G,
has been added to the Ethernet Alliance roadmap that can be viewed at: http://www.ethernetalliance.org/subcommittees/roadmap-subcommittee/ My claim is that there is more crosstalk in a QSFP28 than an SFP28. I think this is backed up in all simulations that have been submitted to this group. In the case of 32GFC vs 128GFC, Avago has proposed that
there is a 2.5dB electrical crosstalk penalty for using QSFP28 vs an SFP28. Others, like John Petrilla and Jonathan King, are more versed in these crosstalk simulations and I hope that they can comment on the differences. Molex or TE should also be able
to discuss the differences in the crosstalk between the two connectors. I didn’t think this assumption that crosstalk is worse in a QSFP28 was really up for debate, the question is how much worse it is.
I’ll try and get some data that shows that electrical channels from the same SERDES in an ASIC support different lengths of traces depending on if they channels are routed through a QSFP28 or an SFP28. The SFP28
should support longer channels with the same BER than a QSFP28 on a similar board.
My second claim is that the crosstalk penalties between 1X50G in SFP56 and 8X50G in CFP2 will be even larger than 2.5dB. I don’t have data to back this assumption up yet and would like to hear if anyone has
such data. I agree that the standard should specify loss and not distance.
Kind regards, Scott From: Chris Cole [mailto:chris.cole@xxxxxxxxxxx]
Hi Scott, Thank you for bringing into the discussion the perspective that we should be cognizant of future 1x50G and 4x50G I/O when developing 8x50G CDAUI-8 specifications. 2x50G should also be included as this will double
ASIC and front panel 100G port density. However, the conclusion that 1x50G I/O will have lower cross-talk penalty than 8x50G is not supported by our experience with 1x10G and 1x25G I/O. 10G I/O is now used in break-out configurations, like 4x10G QSFP+
and 10x10G CFP2. 25G I/O is now used in break-out configurations like 4x25G CFP4 followed by QSFP28, and may be used in 16x25G CDFP. This strongly suggests that we are likely to see 50G I/O break-out configurations like 4x50G CFP4 followed by QSFP28, and 8x50G
CFP2. Therefore the same cross-talk penalty is appropriate for 1x50G, 2x50G, 4x50G and 8x50G specifications.
With respect to material loss, the normative specification should specify loss, allowing the designer to trade-off material quality (and cost) against reach. This means we should write the 8x50G specification
so that it can be used for a variety of applications. Precluding 8x50G I/O Switch applications until 4x100G I/O becomes available seems too restrictive.
Chris From: Scott Kipp [mailto:skipp@xxxxxxxxxxx]
400G Task Force, In the electrical ad hoc yesterday, I objected to using the materials loss tool because I thought it could be misused. After Beth explained how people should use the tool, I could not retract my objection before the conversation went out
of control. I agree to use the tool to predict losses, but would like for people to use the tool appropriately. I would like to build consensus to what kinds of electrical channels this project should support. The question that arises is: Should we define the same electrical channels for 1X50G, 4X50G and 8X50G when they are serving different markets and volumes? I propose that 8X50G (CDAUI-8) electrical channels should be different than channels that will eventually be defined for 1X50GbE (LAUI) because: 1.
Crosstalk - Crosstalk will impact the channel by more than 3dB. I base this off some excellent work that Avago presented to T11 earlier this month. In 14-409v0, Avago showed how going from 1X28G (32GFC) to 4X28G (128GFC) caused a 2.5dB
decrease in the channel mainly due to crosstalk in the QSFP28 connector. I would expect more crosstalk than 2.5dB when the speed and number of channels are doubled. 2.
Small market - The 400GbE market based on 802.3bs standards will be small compared to single lane 50GbE channels that won’t be standardized for a few years. 802.3bs needs to recognize that this project is targeting a very small market
for high-end router interconnects. The complete router market was less than 2M ports/year according to leading analyst firms and not growing much. 16X25G and 8X50G will never be deployed in millions of ports/year because it will be made obsolete by a future
4X100G 400GbE project. 50GbE will go after a larger market and be designed into high-volume, server interconnects by the end of the decade while 4X100G technology will be in the next decade. 3.
High cost – Because of the low volume of 8X50G and the high quality required by the router market, the cost will be high for 400GbE. Because of the premium nature of the router market, electrical channels will be made of high quality,
high cost materials that can be absorbed in high end router products. 4.
Better Materials – The group should model channels based on the better materials supported by the high-end router market in 2018. As others said, the materials being targeted in 802.3bs should be different than the materials targeted
for high volume servers in 802.3bj and a future 50GbE project. Based on these 4 factors that are related, we need to agree on a distance that needs to be supported and consider crosstalk and the loss/inch of better materials. Based on these difference, I bet that CDAUI-8 electrical channels will be
5dB different than the eventual LAUI-1 electrical channels. We should make sure that CDAUI-8 is optimized for our application, not for LAUI-1 that might be optimized for server and switches. I’d like to hear if you disagree with these claims. Kind regards, Scott Kipp |