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Re: [802.3_B400G] WDM Transceiver functionality

Hi JJ,

I agree that a Reference Receiver is not a PMD Receive Function. However, just like with the PMD Receive Function, it is understood that Reference Receiver has appropriate wavelength selectivity. You are correct, that putting an optical filter in front of the single lane (DR) Reference receiver repurposes it for WDM testing. However, this type of helpful advice of how not to misuse test equipment does not belong in a standard. We could provide hundreds of other similarly helpful suggestions for how not shoot oneself in the foot. 

I also agree with you that test engineers select the correct wavelength selectivity for the Reference Receiver because it's blatantly obvious. After the meeting, I checked with multiple transceiver engineers, and everyone does the correct thing. 

If it's common understanding, it's blatantly obvious, and no problem exists with the existing draft why is this an issue requiring a change? If it ain't broke, don't fix it.

Chris

From: John Johnson <jejohnson@xxxxxxxx>
Sent: Monday, May 18, 2026 7:35 AM
To: STDS-802-3-B400G@xxxxxxxxxxxxxxxxx <STDS-802-3-B400G@xxxxxxxxxxxxxxxxx>
Subject: [EXTERNAL]: Re: [802.3_B400G] WDM Transceiver functionality
 
Chris,

I agree with you that it's unnecessary and said as much in the CRG.  No test engineer worth his salt is going to omit an optical filter in front of the Reference RX used for TX testing when all TX lanes are active, but given that this is a new requirement for 200G/L optics it might surprise some that their repurposed single-lane 100G/L test setup doesn't work initially.  That said, I don't agree with making an equivalence between 180.5 and 180.9.  A Reference Receiver is not a PMD Receive Function, it's a piece of test hardware.  For that reason, even though it ought to be blatantly obvious, showing an optical filter in front of the Reference Receiver in 181 and 183 isn't technically incorrect.

Regards,
John


On Fri, May 15, 2026 at 1:59 AM Chris Cole <chris.cole@xxxxxxxxxxxx> wrote:
Dear 802.3dj TF Pariticipants,
During Thursday's comment #95 resolution, there was some confusion about WDM transceiver (transmitter and receiver) functionality, so clarification may be helpful.
Common usage of a datacom WDM transceiver includes appropriate wavelength selective functionality. All 802.3 WDM optics are implemented as transceiver modules, and those contain WDM Mux and DeMux functionality in the transmitter and receiver portion, including block diagrams.
A widespread example is mobile devices. Their RF transceivers, including 802.11 ones, are understood to contain frequency selective functionality. This functionality cannot even be separated from the rest of the transmit and receive functionality, including in block diagrams.
This has always been the usage in 802.3 WDM optics. Most recently, 181.5.3 and 183.5.3 state “the PMD Receive function shall demultiplex the composite optical signal received from the MDI into four separate optical signals. The four optical signals shall then be converted into four symbol streams for delivery to the PMD service interface.” In contrast, 180.5.3 and 182.5.3 state "The PMD Receive function shall convert the n parallel optical signals received from the MDI into separate symbol streams for delivery to the PMD service interface."
Therefore, in Table 190-9, TDECQ conformance test diagram, the Reference receiver block contains the appropriate wavelength selective functionality. For 181 and 183 that’s WDM DeMuxing, and for 180 and 182 that’s none. Adding an optical filter block before the Reference receiver block in 181 and 183 is unnecessary and technically incorrect.

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