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