Geoff Thompson	P802.3bt/D3.0

There is no clear statement of the top level model of a PoE system in clause 145.1.  such a statement is essential for someone reading the standard for the first time in order for the reader to figure out how to structure his thinking and to parse the problem.

There should be a statement similar to the following:
A PoE system consists of 3 separately specified major elements.  They are the power supply, a non-data entity which is called the Power Sourcing Equipment (PSE), the powered load, another non-data entity which is called the Powered Device (PD) and the standards based balanced twisted pair cabling connecting the two. The cabling portion of the system is defined as the Link Section.  The interface between each of the elements is called the Power Interface (PI). The PD is an element of the powered DTE and the link section shares use of the cabling with the link segment used for data transmission.  The PSE is normally an element of the powering DTE but may, instead, be located within the cabling portion of the system.

I suggest that it be folded into a revised version of the current text like this:

145.1 Overview

This clause defines the functional and electrical characteristics for providing an enhancement of the Power over Ethernet (PoE) system defined in Clause 33. This clause includes the capability to provide power over 4 pairs while maintaining compatibility with equipment designed in accordance with Clause 33. 

A PoE system consists of 3 separately specified major elements.  They are the power supply, a non-data entity which is called the Power Sourcing Equipment (PSE), the powered load, another non-data entity which is called the Powered Device (PD) and the standards based, balanced, twisted-pair cabling connecting the two. The cabling portion of the system is defined as the Link Section.  The interface between each of the elements is called the Power Interface (PI). The PD is an element of the powered DTE. The link section shares use of the cabling with the link segment used for data transmission.  The PSE is normally an element of the powering DTE but may, instead, be located within the cabling portion of the system.

The system specified here is for use with IEEE 802.3 MAUs connected by 4-pair twisted pair cabling that have been qualified as being compatible with this clause.  Those MAUs are defined in clauses 14, 25, 40, 55, and 126.  Use in other environments is outside the scope of this standard.  The PSE and PD allow devices to supply/use power using the same generic cabling as is used for data transmission.

PSEs and PDs are categorized by Type. This clause specifies Type 3 and Type 4 devices as well as their interaction with Type 1 and Type 2 devices. References in this clause to PSEs and PDs without a Type qualifier refer exclusively to Type 3 and Type 4 devices. See Clause 33 for the specification of Type 1 and Type 2 devices.

Power over Ethernet is intended to provide a 10BASE-T, 100BASE-TX, 1000BASE-T, 2.5GBASE-T, 5GBASE-T, or 10GBASE-T device with a single cabling interface for both the data and power.