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Folks- Dan is correct here. When we did 802.3af, we were very careful to pick a signature characteristic that wasn't within the specified or common behavior of UTP applications. What we didn't (and couldn't) do was pick something that was FORBIDDEN in each of those applications, especially 802.3 applications. The piece we missed was we didn't (as a part of 802.3af or .3at) put advisory or normative text in each of the twisted pair applications within our scope to advise implementers of those twisted pair applications to avoid anything within their implementations (with special emphasis on those NOT doing PoE) to not do anything that would be confused with the detection of a signature network as specified in clause 33. I am not as convinced as Dan that "this is a maintenance issue though, and not an 802.3at issue." This is all (admittedly arguably) a deficiency of the way we did the original standard, the enhanced standard has to less of an obligation to "protect its signaling space" for detection. I'm willing to cut a little slack here though as we are so late in the process. On that basis alone, I am willing to consider doing it in maintenance. I do feel that we should be able to quickly come up with advisory reference text to put into the UTP clauses that says something like: Note-and that the addition of such non-normative text should not slow down the progress of P802.3at. Best regards, Geoff On 7/7/09 2:36 PM, Dove, Daniel wrote: All, I agree with Hugh's general theme, but I still see a need to add language into the UTP clauses that directs an implementer to avoid a valid PD signature at the MDI if they are not building a PD. While Hugh is correct that an Ethernet designer should be aware of the exposure created by failing to pay attention to clause 33, such changes would eliminate the exposure completely. Its my opinion this is a maintenance issue though, and not an 802.3at issue. Dan -----Original Message----- From: owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx] On Behalf Of George Zimmerman Sent: Tuesday, July 07, 2009 1:45 PM To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx Subject: Re: [8023-POEP] Liaison letter from IEC TC65/SC65C/JWG10 - Power over Ethernet performance in industrial environments Hugh - I agree with your well-written response. -george -----Original Message----- From: owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx] On Behalf Of Hugh Barrass Sent: Tuesday, July 07, 2009 10:51 AM To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx Subject: Re: [8023-POEP] Liaison letter from IEC TC65/SC65C/JWG10 - Power over Ethernet performance in industrial environments David, I can see that the liaison from IEC has caused some interesting discussion amongst PoE experts (and myself), however I think that we are being asked to comment on what may well be design flaws in specific products and I do not think that is a healthy discussion within 802.3. I suggest that we should send a reply along the following lines: ========================================== The problems described in your liaison spurred some vigorous discussion amongst our task force members regarding possible causes for the damage that you describe. However the members are not aware of any similar reports that might indicate a systemic problem with 802.3 compliant equipment. It is the opinion of the members of IEEE P802.3at Task Force that the standard allows product manufacturers to build reliable and interoperable equipment that will meet the requirements for supplying power over Ethernet in many environments. However, the standard does not define how a manufacturer must build the product to ensure reliability or how an installer should ensure that the media is suitable for correct operation within the standard. We suggest that you should work with the equipment manufacturers involved to determine whether the failure is the result of a systemic problem with the standard and whether a specific amendment may be required. With respect to the bit error rate performance of 802.3 links when power is being supplied over the same link, the members of IEEE P802.3at Task Force believe that a compliant system supplying power over an 802.3 link will not perturb the channel sufficiently to degrade the performance of the underlying link. However, it is the responsibility of the product manufacturer to ensure that noise introduced by the load does not couple to the link and violate the power over Ethernet specifications or the channel specifications required for the link. Similarly it is the responsibility of the system installer that the channel characteristics are met in the presence of environmental noise. =========================================== Hugh. David Law wrote: |