302 lines
14 KiB
ReStructuredText
302 lines
14 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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PSE Power Interface (PSE PI) Documentation
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==========================================
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The Power Sourcing Equipment Power Interface (PSE PI) plays a pivotal role in
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the architecture of Power over Ethernet (PoE) systems. It is essentially a
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blueprint that outlines how one or multiple power sources are connected to the
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eight-pin modular jack, commonly known as the Ethernet RJ45 port. This
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connection scheme is crucial for enabling the delivery of power alongside data
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over Ethernet cables.
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Documentation and Standards
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---------------------------
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The IEEE 802.3 standard provides detailed documentation on the PSE PI.
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Specifically:
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- Section "33.2.3 PI pin assignments" covers the pin assignments for PoE
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systems that utilize two pairs for power delivery.
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- Section "145.2.4 PSE PI" addresses the configuration for PoE systems that
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deliver power over all four pairs of an Ethernet cable.
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PSE PI and Single Pair Ethernet
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-------------------------------
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Single Pair Ethernet (SPE) represents a different approach to Ethernet
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connectivity, utilizing just one pair of conductors for both data and power
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transmission. Unlike the configurations detailed in the PSE PI for standard
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Ethernet, which can involve multiple power sourcing arrangements across four or
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two pairs of wires, SPE operates on a simpler model due to its single-pair
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design. As a result, the complexities of choosing between alternative pin
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assignments for power delivery, as described in the PSE PI for multi-pair
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Ethernet, are not applicable to SPE.
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Understanding PSE PI
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--------------------
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The Power Sourcing Equipment Power Interface (PSE PI) is a framework defining
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how Power Sourcing Equipment (PSE) delivers power to Powered Devices (PDs) over
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Ethernet cables. It details two main configurations for power delivery, known
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as Alternative A and Alternative B, which are distinguished not only by their
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method of power transmission but also by the implications for polarity and data
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transmission direction.
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Alternative A and B Overview
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----------------------------
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- **Alternative A:** Utilizes RJ45 conductors 1, 2, 3 and 6. In either case of
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networks 10/100BaseT or 1G/2G/5G/10GBaseT, the pairs used are carrying data.
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The power delivery's polarity in this alternative can vary based on the MDI
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(Medium Dependent Interface) or MDI-X (Medium Dependent Interface Crossover)
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configuration.
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- **Alternative B:** Utilizes RJ45 conductors 4, 5, 7 and 8. In case of
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10/100BaseT network the pairs used are spare pairs without data and are less
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influenced by data transmission direction. This is not the case for
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1G/2G/5G/10GBaseT network. Alternative B includes two configurations with
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different polarities, known as variant X and variant S, to accommodate
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different network requirements and device specifications.
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Table 145-3 PSE Pinout Alternatives
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-----------------------------------
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The following table outlines the pin configurations for both Alternative A and
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Alternative B.
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+------------+-------------------+-----------------+-----------------+-----------------+
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| Conductor | Alternative A | Alternative A | Alternative B | Alternative B |
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| | (MDI-X) | (MDI) | (X) | (S) |
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+============+===================+=================+=================+=================+
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| 1 | Negative V | Positive V | - | - |
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+------------+-------------------+-----------------+-----------------+-----------------+
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| 2 | Negative V | Positive V | - | - |
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+------------+-------------------+-----------------+-----------------+-----------------+
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| 3 | Positive V | Negative V | - | - |
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+------------+-------------------+-----------------+-----------------+-----------------+
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| 4 | - | - | Negative V | Positive V |
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+------------+-------------------+-----------------+-----------------+-----------------+
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| 5 | - | - | Negative V | Positive V |
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+------------+-------------------+-----------------+-----------------+-----------------+
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| 6 | Positive V | Negative V | - | - |
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+------------+-------------------+-----------------+-----------------+-----------------+
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| 7 | - | - | Positive V | Negative V |
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+------------+-------------------+-----------------+-----------------+-----------------+
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| 8 | - | - | Positive V | Negative V |
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+------------+-------------------+-----------------+-----------------+-----------------+
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.. note::
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- "Positive V" and "Negative V" indicate the voltage polarity for each pin.
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- "-" indicates that the pin is not used for power delivery in that
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specific configuration.
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PSE PI compatibilities
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----------------------
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The following table outlines the compatibility between the pinout alternative
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and the 1000/2.5G/5G/10GBaseT in the PSE 2 pairs connection.
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+---------+---------------+---------------------+-----------------------+
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| Variant | Alternative | Power Feeding Type | Compatibility with |
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| | (A/B) | (Direct/Phantom) | 1000/2.5G/5G/10GBaseT |
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+=========+===============+=====================+=======================+
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| 1 | A | Phantom | Yes |
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+---------+---------------+---------------------+-----------------------+
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| 2 | B | Phantom | Yes |
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+---------+---------------+---------------------+-----------------------+
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| 3 | B | Direct | No |
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+---------+---------------+---------------------+-----------------------+
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.. note::
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- "Direct" indicate a variant where the power is injected directly to pairs
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without using magnetics in case of spare pairs.
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- "Phantom" indicate power path over coils/magnetics as it is done for
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Alternative A variant.
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In case of PSE 4 pairs, a PSE supporting only 10/100BaseT (which mean Direct
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Power on pinout Alternative B) is not compatible with a 4 pairs
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1000/2.5G/5G/10GBaseT.
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PSE Power Interface (PSE PI) Connection Diagram
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-----------------------------------------------
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The diagram below illustrates the connection architecture between the RJ45
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port, the Ethernet PHY (Physical Layer), and the PSE PI (Power Sourcing
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Equipment Power Interface), demonstrating how power and data are delivered
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simultaneously through an Ethernet cable. The RJ45 port serves as the physical
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interface for these connections, with each of its eight pins connected to both
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the Ethernet PHY for data transmission and the PSE PI for power delivery.
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.. code-block::
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+--------------------------+
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| RJ45 Port |
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+--+--+--+--+--+--+--+--+--+ +-------------+
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1| 2| 3| 4| 5| 6| 7| 8| | |
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| | | | | | | o-------------------+ |
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| | | | | | o--|-------------------+ +<--- PSE 1
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| | | | | o--|--|-------------------+ |
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| | | | o--|--|--|-------------------+ |
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| | | o--|--|--|--|-------------------+ PSE PI |
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| | o--|--|--|--|--|-------------------+ |
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| o--|--|--|--|--|--|-------------------+ +<--- PSE 2 (optional)
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o--|--|--|--|--|--|--|-------------------+ |
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| | | | | | | | | |
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+--+--+--+--+--+--+--+--+--+ +-------------+
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| Ethernet PHY |
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+--------------------------+
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Simple PSE PI Configuration for Alternative A
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---------------------------------------------
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The diagram below illustrates a straightforward PSE PI (Power Sourcing
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Equipment Power Interface) configuration designed to support the Alternative A
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setup for Power over Ethernet (PoE). This implementation is tailored to provide
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power delivery through the data-carrying pairs of an Ethernet cable, suitable
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for either MDI or MDI-X configurations, albeit supporting one variation at a
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time.
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.. code-block::
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+-------------+
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| PSE PI |
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8 -----+ +-------------+
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7 -----+ Rail 1 |
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6 -----+------+----------------------+
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5 -----+ | |
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4 -----+ | Rail 2 | PSE 1
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3 -----+------/ +------------+
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2 -----+--+-------------/ |
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1 -----+--/ +-------------+
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+-------------+
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In this configuration:
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- Pins 1 and 2, as well as pins 3 and 6, are utilized for power delivery in
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addition to data transmission. This aligns with the standard wiring for
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10/100BaseT Ethernet networks where these pairs are used for data.
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- Rail 1 and Rail 2 represent the positive and negative voltage rails, with
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Rail 1 connected to pins 1 and 2, and Rail 2 connected to pins 3 and 6.
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More advanced PSE PI configurations may include integrated or external
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switches to change the polarity of the voltage rails, allowing for
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compatibility with both MDI and MDI-X configurations.
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More complex PSE PI configurations may include additional components, to support
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Alternative B, or to provide additional features such as power management, or
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additional power delivery capabilities such as 2-pair or 4-pair power delivery.
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.. code-block::
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+-------------+
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| PSE PI |
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| +---+
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8 -----+--------+ | +-------------+
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7 -----+--------+ | Rail 1 |
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6 -----+--------+ +-----------------+
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5 -----+--------+ | |
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4 -----+--------+ | Rail 2 | PSE 1
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3 -----+--------+ +----------------+
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2 -----+--------+ | |
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1 -----+--------+ | +-------------+
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| +---+
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+-------------+
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Device Tree Configuration: Describing PSE PI Configurations
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-----------------------------------------------------------
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The necessity for a separate PSE PI node in the device tree is influenced by
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the intricacy of the Power over Ethernet (PoE) system's setup. Here are
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descriptions of both simple and complex PSE PI configurations to illustrate
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this decision-making process:
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**Simple PSE PI Configuration:**
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In a straightforward scenario, the PSE PI setup involves a direct, one-to-one
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connection between a single PSE controller and an Ethernet port. This setup
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typically supports basic PoE functionality without the need for dynamic
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configuration or management of multiple power delivery modes. For such simple
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configurations, detailing the PSE PI within the existing PSE controller's node
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may suffice, as the system does not encompass additional complexity that
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warrants a separate node. The primary focus here is on the clear and direct
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association of power delivery to a specific Ethernet port.
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**Complex PSE PI Configuration:**
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Contrastingly, a complex PSE PI setup may encompass multiple PSE controllers or
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auxiliary circuits that collectively manage power delivery to one Ethernet
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port. Such configurations might support a range of PoE standards and require
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the capability to dynamically configure power delivery based on the operational
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mode (e.g., PoE2 versus PoE4) or specific requirements of connected devices. In
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these instances, a dedicated PSE PI node becomes essential for accurately
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documenting the system architecture. This node would serve to detail the
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interactions between different PSE controllers, the support for various PoE
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modes, and any additional logic required to coordinate power delivery across
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the network infrastructure.
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**Guidance:**
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For simple PSE setups, including PSE PI information in the PSE controller node
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might suffice due to the straightforward nature of these systems. However,
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complex configurations, involving multiple components or advanced PoE features,
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benefit from a dedicated PSE PI node. This method adheres to IEEE 802.3
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specifications, improving documentation clarity and ensuring accurate
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representation of the PoE system's complexity.
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PSE PI Node: Essential Information
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----------------------------------
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The PSE PI (Power Sourcing Equipment Power Interface) node in a device tree can
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include several key pieces of information critical for defining the power
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delivery capabilities and configurations of a PoE (Power over Ethernet) system.
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Below is a list of such information, along with explanations for their
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necessity and reasons why they might not be found within a PSE controller node:
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1. **Powered Pairs Configuration**
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- *Description:* Identifies the pairs used for power delivery in the
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Ethernet cable.
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- *Necessity:* Essential to ensure the correct pairs are powered according
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to the board's design.
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- *PSE Controller Node:* Typically lacks details on physical pair usage,
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focusing on power regulation.
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2. **Polarity of Powered Pairs**
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- *Description:* Specifies the polarity (positive or negative) for each
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powered pair.
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- *Necessity:* Critical for safe and effective power transmission to PDs.
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- *PSE Controller Node:* Polarity management may exceed the standard
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functionalities of PSE controllers.
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3. **PSE Cells Association**
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- *Description:* Details the association of PSE cells with Ethernet ports or
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pairs in multi-cell configurations.
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- *Necessity:* Allows for optimized power resource allocation in complex
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systems.
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- *PSE Controller Node:* Controllers may not manage cell associations
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directly, focusing instead on power flow regulation.
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4. **Support for PoE Standards**
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- *Description:* Lists the PoE standards and configurations supported by the
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system.
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- *Necessity:* Ensures system compatibility with various PDs and adherence
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to industry standards.
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- *PSE Controller Node:* Specific capabilities may depend on the overall PSE
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PI design rather than the controller alone. Multiple PSE cells per PI
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do not necessarily imply support for multiple PoE standards.
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5. **Protection Mechanisms**
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- *Description:* Outlines additional protection mechanisms, such as
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overcurrent protection and thermal management.
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- *Necessity:* Provides extra safety and stability, complementing PSE
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controller protections.
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- *PSE Controller Node:* Some protections may be implemented via
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board-specific hardware or algorithms external to the controller.
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