For those that were not on today’s Joint P802.3by 25G Ethernet TF and 50G Ethernet & NGOATH SG Conference Call, the discussion Gary is referring to was about
the definition of 50G, 100G, and 200G C2M interfaces.
Presentations on this topic by Wang, Gustlin, Stone and Ghiasi from previous calls and today’s call can be found on the adhoc page:
http://www.ieee802.org/3/50G/public/adhoc/archive/index.html
The CAUI-4 discussion was started by the suggestion that we should look at prior work to see if it offers guidance.
As Gary documents, P802.3bm defined CAUI-4 to have two modes: 1) no FEC mode to support 100G PMD that were defined prior to P802.3bm (LR4, ER4,) and 2) KR4
RS-528 FEC mode to support new interfaces (CR4, SR4.) P802.3bm specification of KR4 FEC for CAUI-4 did not require the definition of all PMDs that would use it. P802.3bm did the heavy lifting, which then enabled MSAs that followed to quickly write PSM4, CWDM4,
and CLR4 4x25G NRZ SMF specifications. Other PMD specifications using CAUI-4 with KR4 FEC interfaces are expected.
Deployed CAUI-4 interfaces now support two modes depending on what type of module is plugged in. For example, if a LR4 module is plugged in, CAUI-4 operates
with no FEC, and if SR4 is plugged in, CAUI-4 operates with KR4 FEC.
As second precedent is in P802.3bs which defined CDAUI-16 only with RS-544 KP4 FEC for compatibility with CDAUI-8. Even though KR4 FEC would be sufficient for
25G NRZ based interface, it was not specified because there was no backwards compatibility requirement.
50G and 100G C2M are like the CAUI-4 case because there is an existing C2M specification with which we would like backwards interoperability (CAUI-4 with KR4
FEC), and a new C2M specification for best performance going forward (KP4 FEC).
So the precedent suggested C2M interfaces for 50G are:
·
LAUI and LAUI-2 with KR4 RS-528 FEC (for backwards compatibility)
·
LAUI with KP4 RS-544 FEC
The precedent suggested C2M interfaces for 100G are:
·
CAUI-2 with KR4 RS-528 FEC (for backwards compatibility)
·
CAUI-2 with KP4 RS-544 FEC
On the other hand, 200G is more like CAUI-16 case because there is no existing C2M specification.
So the precedent suggested C2M interface for 200G is:
·
CCAUI-4 with KP4 RS-544 FEC (only)
A separate question is whether we need two sets of 50G single lane PMDs and 100G two lane PMDs, one for each FEC. Again, P802.3bm offers precedence, where it
did not define all PMDs that use CAUI-4.
So one approach is to specify the following PMDs in the current project:
·
50G single lane with KP4 RS-544 FEC
·
100G two lane with KP4 RS-544 FEC
·
200G two lane with KP4 RS-544 FEC
50G single lane and 100G two lane with KR4 FEC don’t have to be specified in the project. However, if the SG decides to specify KR4 FEC variants, then as pointed
out by Mark, it will require separate objectives.
Chris
From: Gary Nicholl (gnicholl) [mailto:gnicholl@xxxxxxxxx]
Sent: Wednesday, February 24, 2016 9:08 AM
To: STDS-802-3-50G@xxxxxxxxxxxxxxxxx
Subject: [802.3_50G] CAUI-4 operating modes
Following on from the discussion this morning I checked 802.3bm and there is only a single operating mode for CAUI-4.
CAUI-4 C2M is defined in Annex 83E. There is only one operating mode and that assumes no FEC.
There is no separate FEC operating mode, where some of the FEC gain is used to relax the CAUI-4 electrical specifications.
In 802.3bm if RS-FEC is being used, it is carried completely transparently over the CAUI-4 interface, and all of the FEC gain is used for the PMD (i.e. 100GBASE-SR4). The CAUI-4
specification is completely independent of whether FEC is being used on the link or not. Perhaps this is what Chris meant by “two CAUI-4 operating modes” on the call this morning, even though from a CAUI-4 perspective there is only a single operating mode?
Another way to state this is that the FEC requirements for the host are defined by the PMDs to be supported and not the CAUI.
Gary