The Power Sourcing Equipment Power Interface (PSE PI) plays a pivotal role inthe architecture of Power over Ethernet (PoE) systems. It is essentially ablueprint that outlines how one or multiple power sources are connected to theeight-pin modular jack, commonly known as the Ethernet RJ45 port. Thisconnection scheme is crucial for enabling the delivery of power alongside dataover 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 PoEsystems that utilize two pairs for power delivery.
Section “145.2.4 PSE PI” addresses the configuration for PoE systems thatdeliver power over all four pairs of an Ethernet cable.
PSE PI and Single Pair Ethernet¶
Single Pair Ethernet (SPE) represents a different approach to Ethernetconnectivity, utilizing just one pair of conductors for both data and powertransmission. Unlike the configurations detailed in the PSE PI for standardEthernet, which can involve multiple power sourcing arrangements across four ortwo pairs of wires, SPE operates on a simpler model due to its single-pairdesign. As a result, the complexities of choosing between alternative pinassignments for power delivery, as described in the PSE PI for multi-pairEthernet, are not applicable to SPE.
Understanding PSE PI¶
The Power Sourcing Equipment Power Interface (PSE PI) is a framework defininghow Power Sourcing Equipment (PSE) delivers power to Powered Devices (PDs) overEthernet cables. It details two main configurations for power delivery, knownas Alternative A and Alternative B, which are distinguished not only by theirmethod of power transmission but also by the implications for polarity and datatransmission direction.
Alternative A and B Overview¶
Alternative A: Utilizes RJ45 conductors 1, 2, 3 and 6. In either case ofnetworks 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 of10/100BaseT network the pairs used are spare pairs without data and are lessinfluenced by data transmission direction. This is not the case for1G/2G/5G/10GBaseT network. Alternative B includes two configurations withdifferent polarities, known as variant X and variant S, to accommodatedifferent network requirements and device specifications.
Table 145-3 PSE Pinout Alternatives¶
The following table outlines the pin configurations for both Alternative A andAlternative B.
Conductor |
|
|
|
|
|---|---|---|---|---|
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 thatspecific configuration.
PSE PI compatibilities¶
The following table outlines the compatibility between the pinout alternativeand the 1000/2.5G/5G/10GBaseT in the PSE 2 pairs connection.
Variant | Alternative(A/B) | Power Feeding Type(Direct/Phantom) | Compatibility with1000/2.5G/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 DirectPower on pinout Alternative B) is not compatible with a 4 pairs1000/2.5G/5G/10GBaseT.
PSE Power Interface (PSE PI) Connection Diagram¶
The diagram below illustrates the connection architecture between the RJ45port, the Ethernet PHY (Physical Layer), and the PSE PI (Power SourcingEquipment Power Interface), demonstrating how power and data are deliveredsimultaneously through an Ethernet cable. The RJ45 port serves as the physicalinterface for these connections, with each of its eight pins connected to boththe Ethernet PHY for data transmission and the PSE PI for power delivery.
+--------------------------+| || 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 SourcingEquipment Power Interface) configuration designed to support the Alternative Asetup for Power over Ethernet (PoE). This implementation is tailored to providepower delivery through the data-carrying pairs of an Ethernet cable, suitablefor either MDI or MDI-X configurations, albeit supporting one variation at atime.
+-------------+ | PSE PI |8 -----+ +-------------+7 -----+ Rail 1 |6 -----+------+----------------------+5 -----+ | |4 -----+ | Rail 2 | PSE 13 -----+------/ +------------+2 -----+--+-------------/ |1 -----+--/ +-------------+ | +-------------+
In this configuration:
Pins 1 and 2, as well as pins 3 and 6, are utilized for power delivery inaddition to data transmission. This aligns with the standard wiring for10/100BaseT Ethernet networks where these pairs are used for data.
Rail 1 and Rail 2 represent the positive and negative voltage rails, withRail 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 externalswitches to change the polarity of the voltage rails, allowing forcompatibility with both MDI and MDI-X configurations.
More complex PSE PI configurations may include additional components, to supportAlternative B, or to provide additional features such as power management, oradditional power delivery capabilities such as 2-pair or 4-pair power delivery.
+-------------+ | PSE PI | | +---+8 -----+--------+ | +-------------+7 -----+--------+ | Rail 1 |6 -----+--------+ +-----------------+5 -----+--------+ | |4 -----+--------+ | Rail 2 | PSE 13 -----+--------+ +----------------+2 -----+--------+ | |1 -----+--------+ | +-------------+ | +---+ +-------------+
Device Tree Configuration: Describing PSE PI Configurations¶
The necessity for a separate PSE PI node in the device tree is influenced bythe intricacy of the Power over Ethernet (PoE) system’s setup. Here aredescriptions of both simple and complex PSE PI configurations to illustratethis decision-making process:
Simple PSE PI Configuration:In a straightforward scenario, the PSE PI setup involves a direct, one-to-oneconnection between a single PSE controller and an Ethernet port. This setuptypically supports basic PoE functionality without the need for dynamicconfiguration or management of multiple power delivery modes. For such simpleconfigurations, detailing the PSE PI within the existing PSE controller’s nodemay suffice, as the system does not encompass additional complexity thatwarrants a separate node. The primary focus here is on the clear and directassociation of power delivery to a specific Ethernet port.
Complex PSE PI Configuration:Contrastingly, a complex PSE PI setup may encompass multiple PSE controllers orauxiliary circuits that collectively manage power delivery to one Ethernetport. Such configurations might support a range of PoE standards and requirethe capability to dynamically configure power delivery based on the operationalmode (e.g., PoE2 versus PoE4) or specific requirements of connected devices. Inthese instances, a dedicated PSE PI node becomes essential for accuratelydocumenting the system architecture. This node would serve to detail theinteractions between different PSE controllers, the support for various PoEmodes, and any additional logic required to coordinate power delivery acrossthe network infrastructure.
Guidance:
For simple PSE setups, including PSE PI information in the PSE controller nodemight 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 802.3specifications, improving documentation clarity and ensuring accuraterepresentation of the PoE system’s complexity.
PSE PI Node: Essential Information¶
The PSE PI (Power Sourcing Equipment Power Interface) node in a device tree caninclude several key pieces of information critical for defining the powerdelivery capabilities and configurations of a PoE (Power over Ethernet) system.Below is a list of such information, along with explanations for theirnecessity and reasons why they might not be found within a PSE controller node:
Powered Pairs Configuration
Description: Identifies the pairs used for power delivery in theEthernet cable.
Necessity: Essential to ensure the correct pairs are powered accordingto the board’s design.
PSE Controller Node: Typically lacks details on physical pair usage,focusing on power regulation.
Polarity of Powered Pairs
Description: Specifies the polarity (positive or negative) for eachpowered pair.
Necessity: Critical for safe and effective power transmission to PDs.
PSE Controller Node: Polarity management may exceed the standardfunctionalities of PSE controllers.
PSE Cells Association
Description: Details the association of PSE cells with Ethernet ports orpairs in multi-cell configurations.
Necessity: Allows for optimized power resource allocation in complexsystems.
PSE Controller Node: Controllers may not manage cell associationsdirectly, focusing instead on power flow regulation.
Support for PoE Standards
Description: Lists the PoE standards and configurations supported by thesystem.
Necessity: Ensures system compatibility with various PDs and adherenceto industry standards.
PSE Controller Node: Specific capabilities may depend on the overall PSEPI design rather than the controller alone. Multiple PSE cells per PIdo not necessarily imply support for multiple PoE standards.
Protection Mechanisms
Description: Outlines additional protection mechanisms, such asovercurrent protection and thermal management.
Necessity: Provides extra safety and stability, complementing PSEcontroller protections.
PSE Controller Node: Some protections may be implemented viaboard-specific hardware or algorithms external to the controller.
