| .. 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. |
