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George , Allan and all, I agree with your conclusion George. Our "worst case data base" in which we are using it to calculate the worst case P2P Resistance Unbalance numbers are based on the following: Cable pair resistance unbalance is 2%. We assume it is the same for all temperature. Analytically we can show that this is pretty much the case. Channel pair resistance (4 connector model with the cables etc.) is 3%. Same conclusion over temperature. Regarding the new parameter, cable Pair to Pair resistance unbalance that we set it to 5%, is based on derivation of this parameter from other specified parameters
of the cable. Same conclusion over temperature. Regarding the Channel and end to end channel resistance unbalance: The number over temperature is about the same.
The rationale why over temperature is about the same is the fact that the resistance change due to temperature, is canceled over wires in the pairs and between
the pairs. Yair From: George Zimmerman [mailto:george@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx]
Alan – thank you. One has to be careful reading cabling specifications to make sure they are looking at the descriptions of the ‘channel’ or ‘permanent link’, or “CP link”, which
includes the connectors, as the specs you have sent are. Sometimes its confusing and you get just the ‘cable’ portion. The specs you sent specifically point out that channel specs, including resistance and resistance unbalance are met over the ALL temperatures,
therefore we can leave the temperature part out, at least for the cabling channel. I hope we’re not confused though, what Yair calls,
Channel Pair to Pair resistance unbalance is still an undefined parameter here, so it is not governed by the statement of compliance
– but I would expect that physics will imply that if the insertion loss and within-pair resistance and resistance unbalance, which are specified here are met, then pair-to-pair resistance unbalance will also be met. (note the resistance unbalance in Section
6.4.8 in your attachment is the ‘within-pair’ resistance unbalance, currently specified for PoE and PoE+ in IEEE Std. 802.3-2012, clause 33.1.4.2.) George Zimmerman Principal, CME Consulting Experts in Advanced PHYsical Communications Technology george@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx 310-920-3860 (PLEASE NOTE NEW EMAIL ADDRESS. THE OTHER WILL STILL WORK, BUT PLEASE USE THIS FOR CME BUSINESS) From: Alan Flatman [mailto:a_flatman@xxxxxxxxxxxxx]
Yair, The ISO/IEC 11801 channel DC loop resistance requirements are for the temperature the cabling is designed to be used. ISO/IEC SC25 WG3 did worst case calculations some time ago to verify that this was practical. I have copied the relevant DC loop resistance and DC resistance unbalance requirements from ISO/IEC 11801 for reference (these are attached). Best regards, Alan |