1 .. SPDX-License-Identifier: GPL-2.0 2 3 PSE Power Interface (PSE PI) Documentation 4 ========================================== 5 6 The Power Sourcing Equipment Power Interface (PSE PI) plays a pivotal role in 7 the architecture of Power over Ethernet (PoE) systems. It is essentially a 8 blueprint that outlines how one or multiple power sources are connected to the 9 eight-pin modular jack, commonly known as the Ethernet RJ45 port. This 10 connection scheme is crucial for enabling the delivery of power alongside data 11 over Ethernet cables. 12 13 Documentation and Standards 14 --------------------------- 15 16 The IEEE 802.3 standard provides detailed documentation on the PSE PI. 17 Specifically: 18 19 - Section "33.2.3 PI pin assignments" covers the pin assignments for PoE 20 systems that utilize two pairs for power delivery. 21 - Section "145.2.4 PSE PI" addresses the configuration for PoE systems that 22 deliver power over all four pairs of an Ethernet cable. 23 24 PSE PI and Single Pair Ethernet 25 ------------------------------- 26 27 Single Pair Ethernet (SPE) represents a different approach to Ethernet 28 connectivity, utilizing just one pair of conductors for both data and power 29 transmission. Unlike the configurations detailed in the PSE PI for standard 30 Ethernet, which can involve multiple power sourcing arrangements across four or 31 two pairs of wires, SPE operates on a simpler model due to its single-pair 32 design. As a result, the complexities of choosing between alternative pin 33 assignments for power delivery, as described in the PSE PI for multi-pair 34 Ethernet, are not applicable to SPE. 35 36 Understanding PSE PI 37 -------------------- 38 39 The Power Sourcing Equipment Power Interface (PSE PI) is a framework defining 40 how Power Sourcing Equipment (PSE) delivers power to Powered Devices (PDs) over 41 Ethernet cables. It details two main configurations for power delivery, known 42 as Alternative A and Alternative B, which are distinguished not only by their 43 method of power transmission but also by the implications for polarity and data 44 transmission direction. 45 46 Alternative A and B Overview 47 ---------------------------- 48 49 - **Alternative A:** Utilizes RJ45 conductors 1, 2, 3 and 6. In either case of 50 networks 10/100BaseT or 1G/2G/5G/10GBaseT, the pairs used are carrying data. 51 The power delivery's polarity in this alternative can vary based on the MDI 52 (Medium Dependent Interface) or MDI-X (Medium Dependent Interface Crossover) 53 configuration. 54 55 - **Alternative B:** Utilizes RJ45 conductors 4, 5, 7 and 8. In case of 56 10/100BaseT network the pairs used are spare pairs without data and are less 57 influenced by data transmission direction. This is not the case for 58 1G/2G/5G/10GBaseT network. Alternative B includes two configurations with 59 different polarities, known as variant X and variant S, to accommodate 60 different network requirements and device specifications. 61 62 Table 145-3 PSE Pinout Alternatives 63 ----------------------------------- 64 65 The following table outlines the pin configurations for both Alternative A and 66 Alternative B. 67 68 +------------+-------------------+-----------------+-----------------+-----------------+ 69 | Conductor | Alternative A | Alternative A | Alternative B | Alternative B | 70 | | (MDI-X) | (MDI) | (X) | (S) | 71 +============+===================+=================+=================+=================+ 72 | 1 | Negative V | Positive V | - | - | 73 +------------+-------------------+-----------------+-----------------+-----------------+ 74 | 2 | Negative V | Positive V | - | - | 75 +------------+-------------------+-----------------+-----------------+-----------------+ 76 | 3 | Positive V | Negative V | - | - | 77 +------------+-------------------+-----------------+-----------------+-----------------+ 78 | 4 | - | - | Negative V | Positive V | 79 +------------+-------------------+-----------------+-----------------+-----------------+ 80 | 5 | - | - | Negative V | Positive V | 81 +------------+-------------------+-----------------+-----------------+-----------------+ 82 | 6 | Positive V | Negative V | - | - | 83 +------------+-------------------+-----------------+-----------------+-----------------+ 84 | 7 | - | - | Positive V | Negative V | 85 +------------+-------------------+-----------------+-----------------+-----------------+ 86 | 8 | - | - | Positive V | Negative V | 87 +------------+-------------------+-----------------+-----------------+-----------------+ 88 89 .. note:: 90 - "Positive V" and "Negative V" indicate the voltage polarity for each pin. 91 - "-" indicates that the pin is not used for power delivery in that 92 specific configuration. 93 94 PSE PI compatibilities 95 ---------------------- 96 97 The following table outlines the compatibility between the pinout alternative 98 and the 1000/2.5G/5G/10GBaseT in the PSE 2 pairs connection. 99 100 +---------+---------------+---------------------+-----------------------+ 101 | Variant | Alternative | Power Feeding Type | Compatibility with | 102 | | (A/B) | (Direct/Phantom) | 1000/2.5G/5G/10GBaseT | 103 +=========+===============+=====================+=======================+ 104 | 1 | A | Phantom | Yes | 105 +---------+---------------+---------------------+-----------------------+ 106 | 2 | B | Phantom | Yes | 107 +---------+---------------+---------------------+-----------------------+ 108 | 3 | B | Direct | No | 109 +---------+---------------+---------------------+-----------------------+ 110 111 .. note:: 112 - "Direct" indicate a variant where the power is injected directly to pairs 113 without using magnetics in case of spare pairs. 114 - "Phantom" indicate power path over coils/magnetics as it is done for 115 Alternative A variant. 116 117 In case of PSE 4 pairs, a PSE supporting only 10/100BaseT (which mean Direct 118 Power on pinout Alternative B) is not compatible with a 4 pairs 119 1000/2.5G/5G/10GBaseT. 120 121 PSE Power Interface (PSE PI) Connection Diagram 122 ----------------------------------------------- 123 124 The diagram below illustrates the connection architecture between the RJ45 125 port, the Ethernet PHY (Physical Layer), and the PSE PI (Power Sourcing 126 Equipment Power Interface), demonstrating how power and data are delivered 127 simultaneously through an Ethernet cable. The RJ45 port serves as the physical 128 interface for these connections, with each of its eight pins connected to both 129 the Ethernet PHY for data transmission and the PSE PI for power delivery. 130 131 .. code-block:: 132 133 +--------------------------+ 134 | | 135 | RJ45 Port | 136 | | 137 +--+--+--+--+--+--+--+--+--+ +-------------+ 138 1| 2| 3| 4| 5| 6| 7| 8| | | 139 | | | | | | | o-------------------+ | 140 | | | | | | o--|-------------------+ +<--- PSE 1 141 | | | | | o--|--|-------------------+ | 142 | | | | o--|--|--|-------------------+ | 143 | | | o--|--|--|--|-------------------+ PSE PI | 144 | | o--|--|--|--|--|-------------------+ | 145 | o--|--|--|--|--|--|-------------------+ +<--- PSE 2 (optional) 146 o--|--|--|--|--|--|--|-------------------+ | 147 | | | | | | | | | | 148 +--+--+--+--+--+--+--+--+--+ +-------------+ 149 | | 150 | Ethernet PHY | 151 | | 152 +--------------------------+ 153 154 Simple PSE PI Configuration for Alternative A 155 --------------------------------------------- 156 157 The diagram below illustrates a straightforward PSE PI (Power Sourcing 158 Equipment Power Interface) configuration designed to support the Alternative A 159 setup for Power over Ethernet (PoE). This implementation is tailored to provide 160 power delivery through the data-carrying pairs of an Ethernet cable, suitable 161 for either MDI or MDI-X configurations, albeit supporting one variation at a 162 time. 163 164 .. code-block:: 165 166 +-------------+ 167 | PSE PI | 168 8 -----+ +-------------+ 169 7 -----+ Rail 1 | 170 6 -----+------+----------------------+ 171 5 -----+ | | 172 4 -----+ | Rail 2 | PSE 1 173 3 -----+------/ +------------+ 174 2 -----+--+-------------/ | 175 1 -----+--/ +-------------+ 176 | 177 +-------------+ 178 179 In this configuration: 180 181 - Pins 1 and 2, as well as pins 3 and 6, are utilized for power delivery in 182 addition to data transmission. This aligns with the standard wiring for 183 10/100BaseT Ethernet networks where these pairs are used for data. 184 - Rail 1 and Rail 2 represent the positive and negative voltage rails, with 185 Rail 1 connected to pins 1 and 2, and Rail 2 connected to pins 3 and 6. 186 More advanced PSE PI configurations may include integrated or external 187 switches to change the polarity of the voltage rails, allowing for 188 compatibility with both MDI and MDI-X configurations. 189 190 More complex PSE PI configurations may include additional components, to support 191 Alternative B, or to provide additional features such as power management, or 192 additional power delivery capabilities such as 2-pair or 4-pair power delivery. 193 194 .. code-block:: 195 196 +-------------+ 197 | PSE PI | 198 | +---+ 199 8 -----+--------+ | +-------------+ 200 7 -----+--------+ | Rail 1 | 201 6 -----+--------+ +-----------------+ 202 5 -----+--------+ | | 203 4 -----+--------+ | Rail 2 | PSE 1 204 3 -----+--------+ +----------------+ 205 2 -----+--------+ | | 206 1 -----+--------+ | +-------------+ 207 | +---+ 208 +-------------+ 209 210 Device Tree Configuration: Describing PSE PI Configurations 211 ----------------------------------------------------------- 212 213 The necessity for a separate PSE PI node in the device tree is influenced by 214 the intricacy of the Power over Ethernet (PoE) system's setup. Here are 215 descriptions of both simple and complex PSE PI configurations to illustrate 216 this decision-making process: 217 218 **Simple PSE PI Configuration:** 219 In a straightforward scenario, the PSE PI setup involves a direct, one-to-one 220 connection between a single PSE controller and an Ethernet port. This setup 221 typically supports basic PoE functionality without the need for dynamic 222 configuration or management of multiple power delivery modes. For such simple 223 configurations, detailing the PSE PI within the existing PSE controller's node 224 may suffice, as the system does not encompass additional complexity that 225 warrants a separate node. The primary focus here is on the clear and direct 226 association of power delivery to a specific Ethernet port. 227 228 **Complex PSE PI Configuration:** 229 Contrastingly, a complex PSE PI setup may encompass multiple PSE controllers or 230 auxiliary circuits that collectively manage power delivery to one Ethernet 231 port. Such configurations might support a range of PoE standards and require 232 the capability to dynamically configure power delivery based on the operational 233 mode (e.g., PoE2 versus PoE4) or specific requirements of connected devices. In 234 these instances, a dedicated PSE PI node becomes essential for accurately 235 documenting the system architecture. This node would serve to detail the 236 interactions between different PSE controllers, the support for various PoE 237 modes, and any additional logic required to coordinate power delivery across 238 the network infrastructure. 239 240 **Guidance:** 241 242 For simple PSE setups, including PSE PI information in the PSE controller node 243 might suffice due to the straightforward nature of these systems. However, 244 complex configurations, involving multiple components or advanced PoE features, 245 benefit from a dedicated PSE PI node. This method adheres to IEEE 802.3 246 specifications, improving documentation clarity and ensuring accurate 247 representation of the PoE system's complexity. 248 249 PSE PI Node: Essential Information 250 ---------------------------------- 251 252 The PSE PI (Power Sourcing Equipment Power Interface) node in a device tree can 253 include several key pieces of information critical for defining the power 254 delivery capabilities and configurations of a PoE (Power over Ethernet) system. 255 Below is a list of such information, along with explanations for their 256 necessity and reasons why they might not be found within a PSE controller node: 257 258 1. **Powered Pairs Configuration** 259 260 - *Description:* Identifies the pairs used for power delivery in the 261 Ethernet cable. 262 - *Necessity:* Essential to ensure the correct pairs are powered according 263 to the board's design. 264 - *PSE Controller Node:* Typically lacks details on physical pair usage, 265 focusing on power regulation. 266 267 2. **Polarity of Powered Pairs** 268 269 - *Description:* Specifies the polarity (positive or negative) for each 270 powered pair. 271 - *Necessity:* Critical for safe and effective power transmission to PDs. 272 - *PSE Controller Node:* Polarity management may exceed the standard 273 functionalities of PSE controllers. 274 275 3. **PSE Cells Association** 276 277 - *Description:* Details the association of PSE cells with Ethernet ports or 278 pairs in multi-cell configurations. 279 - *Necessity:* Allows for optimized power resource allocation in complex 280 systems. 281 - *PSE Controller Node:* Controllers may not manage cell associations 282 directly, focusing instead on power flow regulation. 283 284 4. **Support for PoE Standards** 285 286 - *Description:* Lists the PoE standards and configurations supported by the 287 system. 288 - *Necessity:* Ensures system compatibility with various PDs and adherence 289 to industry standards. 290 - *PSE Controller Node:* Specific capabilities may depend on the overall PSE 291 PI design rather than the controller alone. Multiple PSE cells per PI 292 do not necessarily imply support for multiple PoE standards. 293 294 5. **Protection Mechanisms** 295 296 - *Description:* Outlines additional protection mechanisms, such as 297 overcurrent protection and thermal management. 298 - *Necessity:* Provides extra safety and stability, complementing PSE 299 controller protections. 300 - *PSE Controller Node:* Some protections may be implemented via 301 board-specific hardware or algorithms external to the controller.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.