White Paper: Power over Ethernet A Technology Overview Roxane Rager, RCDD Application Engineer Leviton Network Solutions C/7 #1922
Table of Contents Introduction 3 Definitions 4 How PoE Works 5 Why Choose PoE? 7 PoE Midspan versus PoE Switch 8 A Powerful Future 9 Sources 10 2
Josie sucks Josie sucks Introduction IEEE 802.3af was approved in June of 2003 and is the first international standard to define specifications for delivering power over standard Ethernet cabling. Today, Power over Ethernet (PoE) is the solution for supplying both low voltage current and data over a common point-to-point Ethernet network cable to locations with applications that require both mediums. Among the advantages offered by Power over Ethernet technology: cost savings, flexibility, accessibility, and reliability. Technologies and applications that will benefit from PoE are: VoIP, IP cameras, WLAN, Wireless Access Points, Building Automation Systems (BAS), security, and access control. Power over Ethernet technology can be deployed in all category ratings, including CAT 6A/10G. Camera (Powered device) B B A A Wireless Access Point (Powered device) A A A B Server (Non-powered device) B B VoIP Phone (Powered device) Printer (Non-powered device) A = 90m from panels to outlets B = 5m from jack to powered device/ non-powered device 3
Definitions Powered Device (PD) Terminal device designed to receive power and data on the same UTP cable. Power Sourcing Equipment (PSE) Equipment supplying power over LAN infrastructure. Examples include: Midspan Device resembling patch panel installed between the Ethernet switch and the Powered Device over a single link section. Endspan Ethernet switch incorporating Power over Ethernet technology. Uninterruptible Power Supply (UPS) Also called an uninterruptible power source or battery backup, a UPS is a device that maintains a continuous supply of electrical power to connected equipment from a separate source when utility power is not available. Data Terminal Equipment (DTE) The connection the computer uses to exchange data with a serial device. 4
How PoE Works A PoE system has two primary components: Power Sourcing Equipment (PSE) and a Powered Device (PD). The PD receives its power from the PSE using standard Ethernet cabling. The process begins with Auto-Sensing. Auto-Sensing is a device probe built into all IEEE 802.3af compliant Power Sourcing Equipment that determines whether or not a Powered Device is PoE-enabled. It does so by applying two small current-limited voltage signals across the cable to check for the presence of a characteristic resistance. Power will not be transmitted if compatibility is not established, thus protecting equipment from voltage damage. PSEs also feature built in Safety Extra Low Voltage (SELV) to prevent outside voltage from entering the wiring plant. The PSE classifies each PD based on maximum power needs prior to transmission, see Table 1. Classes are based on all input voltages and operational modes the PD will draw. Class 0 is the default with a power range 0.44 to 12.95 Watts. Table 1 - Power Classification Class Usage Minimum Power Level Output at PSE Voltage Min/Max Current 0 Default 15.4 Watts 14.5-20.5 0-4 ma 1 Optional 4.0 Watts 14.5-20.5 9-12 ma 2 Optional 7.0 Watts 14.5-20.5 17-20 ma 3 Optional 15.4 Watts 14.5-20.5 26-30 ma 4 Reserved for Future Use Treat as Class 0 14.5-20.5 36-44 ma Differences in power levels between the PSE and PD are for power loss during transmission. Possible factors contributing to power line loss are cabling distances, quality of system/installation, or other unknown variables. Power is not sent if the maximum power level is not available. Power allocation information communication between PSEs is beyond the scope of the IEEE 802.3af standard. However, power allocation management is available that will manage power levels to all PDs using one or more PSEs. 5
Once compatibility is established, the Power Sourcing Equipment injects 15.4 Watts DC onto UTP cable without causing data degradation. Depending on the type of PSE deployed (Midspan or Endspan), power may travel on either the used or the unused cable pairs. Midspans provide power over pin pairs 4/5 and 7/8, while Endspans provide power over either used or unused pairs. PDs may use either A or B, but not both at the same time. Polarity of the power source is not a factor of the PD. See Table 2 below. Table 2 - PSE & PD Pinouts PSE Data Pairs PD Unused Pairs PIN # A B A B 1 + +/- 2 + +/- 3 - -/+ 4 + +/- 5 + +/- 6 - -/+ 7 - -/+ 8 - -/+ Optional management features include: Simple Network Management Protocol (SNMPv3) Enables web-based remote management of multi-site/multi-building centralized power control. PSE Port Control Deactivate ports when exceeding allotted power budget, port priority, and power maximum per port. Power Consumption on the Network Maintains necessary power levels to PDs. Remote Monitoring or Access of PDs Centralized location for troubleshooting or maintenance. It is important to note that Power over Ethernet works only in point-to-point connections. Multipoint cabling may result in unpredictable performance and damaged equipment. 6
Why Choose PoE? Cost Savings The cost to install an electrical outlet can range from $350 to $1K. PoE uses the same Ethernet cabling infrastructure already in place for data transmission. This eliminates the need for additional electrical wiring installations, saving on electrician s fees. Flexibility Midspan PoEs may be installed anywhere along the cabling path offering installation flexibility when equipment rooms are not the ideal location. Midspans are considered a consolidation point (CP) when installed as an interconnection between the floor distribution patch panels and telecommunication outlets. Convenience It is now easier to provide network access and power to far off building locations such as sales kiosks, warehouse transactions work areas, access controls areas, etc. Remote power feeding allows power to be consolidated into one central location. Power over Ethernet operates using legacy cabling infrastructures of 10 Mb/s, 100 Mb/s, 1000 Mb/s. Accessibility Switches still within their productive life cycles do not need to be replaced with PoE switches. Adding a Midspan into the cabling infrastructure will achieve the same purpose. Reliability Always on access and monitoring is achieved when Uninterruptible Power Source (UPS) and PoE are combined, creating an ideal combination for mission critical systems. Examples of Powered Devices IP Phones Security Cameras Wireless Access Points Access Control Pads 7
PoE Midspan vs. PoE Switch Equipment Cost A PoE Midspan will cost (on average) 30% less than a PoE Switch. Available in a Variety of Port Configurations Most PoE Switches are available in 24/48 port configurations often many more ports than PDs. Midspans are available in 24/48 ports, but may also be purchased with 6, or even just 1 port. A Midspan will allow a network planner greater flexibility to choose the appropriate equipment for their particular network needs. Ease of Installation A single patch cord is all that s needed to connect a Midspan to the existing network. In contrast, replacing a PoE Switch involves disconnection, rack space, removal, replacement, and reconnection, creating potential network downtime. Equipment Location PoE Switches are limited to active equipment environments, whereas a PoE Midspan may be located anywhere a consolidation point would be as part of the permanent link segment of the cabling system. Midspans deliver PoE on a port-by-port basis where PoE switches enable all ports, needed or not, with PoE. Greater Versatility An Endspan is an Ethernet switch incorporating PoE technology that is capable of 48 Volts and 15.4 Watts, whereas a Midspan may be used with various voltages and protocol types. Midspans may also be used in the interim of a planned updated system with PoE switches. Standards compliant, pre-standards, and enhanced versions of PoE products are available today. Reduced Downtime Midspans allow separate maintenance for power or data only one application needs to be disabled while performing maintenance or repair. Lower Operating Temperatures Less heat is generated by a Midspan. Midspan Versus Endspan Endspan Power Source Equipment Permanent Link PoE Switch Patch Panel Powered Device Midspan Power Source Equipment Permanent Link Patch Panel Switch PoE Midspan Powered Device 8
A Powerful Future The benefits of implementing PoE Technology are clear, but its low voltage current ouput limits the number of applications it can support. To address this, the PoEPlus Task Force is planning to increase the deliverable power to support software and hardware enhanced Powered Devices to 30 Watts. This standard will be IEEE 802.3at. The PoEPlus Task Force is quoted as follows: In 2005, VDC (Venture Development Corporation) market predictions claim that 45% of all Ethernet ports shipped will support 802.3af. There is a demonstrated need for more power to support Pan/Tilt/Zoom security cameras, IP videophones, POS terminals, thin client, 802 multiband wireless nodes and access points, laptop computers, and RFID readers. The proposed increase in the supplied power will result in a potential doubling or tripling of the PoE market. Increasing the inserted power over multiple cables bundled together and run through conduit does present some issues. To achieve increased power levels, two pair, four pair, or a combination of both are being tested. While not considered a fire hazard, heat dissipation is a potential issue and cable deformity and/or data degradation issues may result. To address the heat dissipation issue, the Task Force is planning to set limits on current, cable bundle size, ambient temperature, and cabling installation. The PoEPlus Task Force objectives for the upcoming 802.3at standard are as follows: 802.3at should operate on CAT5 and higher infrastructure, unlike 802.3af, that took into account the CAT3 limitations 802.3at should follow the power safety rules and limitations pertinent to 802.3af A 802.3at PSE must be backwards compatible with 802.3af, being able to power both 802.3af and 802.3at PDs 802.3at should provide the maximum power to PD's as allowed within practical limits, at least 30W 802.3at PDs, when connected to a legacy 802.3af PSE, will provide the user an indication that an 802.3at PSE is required Research the operation of Midspans for 1000BASE-T Research the operation of Midspans and Endspans for 10GBASE-T 9
Sources IEEE P802.3at DTE Power Enhancements Task Force PoEPlus Task Force IEEE 802.3af Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications Amendment: Data Terminal Equipment (DTE) Power via Media Dependent Interface (MDI) PowerDsine Leviton 2222-222nd St. S.E. Bothell, WA 98021-4422 USA Phone: (800) 722-2082 Fax: (425) 483-5270 Email: info@leviton.com Website: www.leviton.com Leviton Canada 165 Hymus Blvd. Point-Claire, Quebec Canada H9R-1G2 Phone: (514) 954-1840 Fax: (514) 954-1853 International Customers Call Leviton Network Solutions International Sales Department Phone: (425) 486-2222 Fax: (425) 485-9170 Email: intl@leviton.com 10