I like this topic as it does highlight one of the aspects previously mentioned in January about the need to have a low or zero FEC latency AUI.For the 25G-based interface (CAUI-4), the task force(s) wisely provided the ability for the interface to operate with and without FEC. This has permitted flexibility in implementations. For example, the ability to use a CAUI-4 without FEC between an Ethernet adapter's ASIC and FPGA will permit a low latency interface; whereas, between the adapter's FPGA and the switch's ASIC, FEC can be used to provide end-to-end error correction.It would be great if we continue to provide interfaces like CAUI-4 that can transport either FEC or non-FEC data. This would provide the greatest level of flexibility for various implementations that could occur.I've requested time to make a presentation in Macau to discuss these use cases in both the 50G and 100G market.Thanks,
BradOn Wed, Feb 24, 2016 at 10:31 AM, John D'Ambrosia <jdambrosia@xxxxxxxxx> wrote:Chris,
You are mistaken.
The FS FEC was developed and a 4 lane solution was developed but it was not CAUI-4. That was done in 802.3bm. There is no way I would ever try to steal that credit away from Dan Dove who had the fortitude of a saint with that effort.
I think the confusion is coming from FEC and non-FEC protected interfaces.
From what I see
802.3bj RS-FEC clause developed to support the cr4, -kr4, -kp4
802.3bm developed CAUI-4 and specified its operation to 10^-15 without FEC. However the architecture itself can be done in such a way that the CAUI-4 is carrying either non-FEC or FEC protected data. 802.3bm also developed -sr4 where FEC is mandatory.
So the AUI based on 25Gb/s signaling can be independent of whether there is FEC or not.
I think everyone is right, but it clearly points out we have to be very specific with language.
John
From: Chris Cole [mailto:chris.cole@xxxxxxxxxxx]
Sent: Wednesday, February 24, 2016 1:24 PM
To: John D'Ambrosia <jdambrosia@xxxxxxxxx>; STDS-802-3-50G@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_50G] CAUI-4 operating modes
CAUI-4 with KR4 RS-528 FEC was developed in the P802.3bj project you led to first support CR4. P802.3bm then defined SR4 with CAUI-4 with KR4 FEC. This enable subsequent efforts to quickly define optical PMDs that use KR4 FEC. P802.3bm also defined CAUI-4 with no FEC to support existing PMDs; LR4 and ER4.
So coming out of 802.3bm we had two CAUI-4 operating modes, one without FEC for backwards compatibility, and one with FEC for new PMDs.
Chris
From: John D'Ambrosia [mailto:jdambrosia@xxxxxxxxx]
Sent: Wednesday, February 24, 2016 10:04 AM
To: STDS-802-3-50G@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_50G] CAUI-4 operating modes
Reading the spec – it looks more like the specification of CAUI-4 is done not assuming FEC, but a port type may include FEC that could go over the CAUI-4.
From: Rick Rabinovich [mailto:rrabinovich@xxxxxxxxxxx]
Sent: Wednesday, February 24, 2016 12:20 PM
To: STDS-802-3-50G@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_50G] CAUI-4 operating modes
Correct, CAUI-4 does not include FEC.
Rick Rabinovich
Hardware Architect – Signal Integrity
Phone: +1 (818) 208-7328
26601 W. Agoura Rd.
Calabasas, CA 91302 US
visit: www.ixiacom.com
From: Gary Nicholl (gnicholl) [mailto:gnicholl@xxxxxxxxx]
Sent: Wednesday, February 24, 2016 9:18 AM
To: Rick Rabinovich <rrabinovich@xxxxxxxxxxx>
Cc: STDS-802-3-50G@xxxxxxxxxxxxxxxxx
Subject: Re: CAUI-4 operating modes
Perhaps, but 802.3bj did not define CAUI-4 and Chris’s comment was specifically on CAUI-4.
Gary
From: Rick Rabinovich <rrabinovich@xxxxxxxxxxx>
Date: Wednesday, February 24, 2016 at 12:15 PM
To: Gary Nicholl <gnicholl@xxxxxxxxx>
Cc: "STDS-802-3-50G@xxxxxxxxxxxxxxxxx" <STDS-802-3-50G@xxxxxxxxxxxxxxxxx>
Subject: RE: CAUI-4 operating modes
Hi Gary,
Thank you for bringing this up . CAUI-4 defined in IEEE802.3bm was specified without FEC to eliminate the latency incurred.
Perhaps Chris was also referring to 4x25G as defined in IEEE802.3bj which includes RS-FEC for 100GBASE-CR4.
Cordially,
Rick Rabinovich
Hardware Architect – Signal Integrity
Phone: +1 (818) 208-7328
26601 W. Agoura Rd.
Calabasas, CA 91302 US
visit: www.ixiacom.com
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
