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Hi Brad, Perhaps one practical implication of having a 40G and 100G break out from 400G objective is to require the 400G MAC/PCS to be based on 5G VLs. This has been a major topic of discussion in the logic track. A developing consensus has been to move to 25G VLs because it simplifies the logic. This enables direct 100G break-out from 400G. However 40G break out is not directly enabled but rather requires different specifications. This has not been viewed as a problem because MLG 1.0 and 2.0 specifications already exist to enable 10G and 40G break out from 100G, respectively. Additionally, simple PMA bit muxing based on .ba 10G VLs and reduced physical lane rate enables 40G break out. Chris From: Brad Booth [mailto:bbooth@xxxxxxxx] John, While I understand the intent of this objective (and agree implementation of this functionality would be good to have), I'm not sure how the task force satisfies this objective. To provide breakout functionality such as 40G operating as 4x10G, the device operating in 40G mode complies with the 40G standard and when the device operates in 4x10G mode, does each 10G portion comply with the 10G standard? As an example, 40GBASE-SR4 has a different reach requirement than a 4x10GBASE-SR. Which reach requirement is required for compliance? This is strictly an implementation decision. There is nothing within the 40G specification or the 10G specification that implies any requirement for 40G to breakout to 4x10G, which permits some flexibility in implementations. Considering there are already 40G MAC/PHY and 100G MAC/PHY drafts or specifications in 802.3, how does a 400G MAC/PHY standard create compliance with those specifications? Does the "provide appropriate support" give the task force the ability to create new 40G MAC/PHY or 100G MAC/PHY specifications that are derivatives of the 400G MAC/PHY specifications? For example, if the 400G SG has a 2 km SMF objective, does that mean that to provide appropriate support for breakout that there would be the ability to create a 100G 2km SMF PMD? Implementation of breakout functionality is a great way to provide a migration path and I believe the TF should take that into consideration when selecting PHY proposals; I'm just not sure how the study group defines it as objective the TF can show has been met. Your thoughts/feedback on this would be greatly appreciated. Thanks, Brad On Wed, Oct 16, 2013 at 6:15 AM, John D'Ambrosia <John_DAmbrosia@xxxxxxxx> wrote: All, Per our call last week, what are the thoughts on the wording of this as a proposed objective – Provide appropriate support for breakout functionality to 40G and / or 100G There was some concern about potential impact or unintended consequences that people wanted to see this wording to discuss further. Regards, John |