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[802.3_4PPOE] Proposed wording for i-387 (follows comment and referred-to text)


Thompson, Geoffrey, Individual

Comment Type TR

P 205  51

Comment Status X

It is unclear whether this is a spec for the cabling or a load spec for the PSE. It needs to have a more complete requirement and be moved to the PSE or link segment clause. Expressing it in terms of the "PHY" and the "MDI" causes further confusion as which MDI is not specified nor is what to be done for a midspan system.


Clarify and place as appropriate.

Proposed Response



145.4 Additional electrical specifications

This clause defines additional electrical specifications for both the PSE and PD. The specifications apply for all PSE and PD operating conditions at the cabling side of the mated connection of the PI. The requirements apply during data transmission only when specified as an operating condition.

The requirements of 145.4 are consistent with the requirements of the 10BASE-T MAU and the 100BASE-TX, 1000BASE-T, 2.5GBASE-T, 5GBASE-T, and 10GBASE-T PHYs. 

145.4.7 Return loss 51 52 The differential impedance of the transmit and receive pairs at the PHY’s MDI shall be such that any reflection shall meet the return loss requirements as specified: 

  • —  in for a 10 Mb/s PHY,

  • —  in ANSI X3.263:1995 for a 100 Mb/s PHY,

  • —  in for a 1000 Mb/s PHY,

  • —  in for a 2.5 Gb/s or 5 Gb/s PHY, and

  • —  in for a 10 Gb/s PHY.

IEEE Draft P802.3bt/D3.0 20 July 2017

In addition, all pairs terminated at an MDI should maintain a nominal common-mode impedance of 75 Ohms.  The common-mode termination is affected by the presence of the power supply, and this should be considered to determine proper termination.


This clause defines additional electrical specifications for a fully connected PoE system (that is, PSE, cabling, PD and related PHYs) and therefore to each element of such a system.

Additionally, there should be a forward pointer to 145.4 at the end of 145.2 and 145.3, perhaps the following text.
"Additional electrical specifications that apply to the PSE/PD are in 145.4."