802.3at PoE and Intel® Atom™ Processor Advance Embedded Devices

When combined with the Intel® Atom™ processor, the newly ratified IEEE 802.3at Power Over Ethernet standard enables developers to create richly featured, “no new wires” embedded devices that offer significant advantages in cost, reliability, and manageability.

By Steve Yates, ADI Engineering

Distributing power and data are two of the biggest challenges facing developers of sophisticated embedded systems. The costs of installing new cables—in terms of labor, material, and logistics—are growing as embedded systems become more complex. For next-generation embedded systems, which emphasize integration, cost, and energy management and conservation, the struggle is significant. While wireless approaches may replace data cables in certain applications, wired power distribution is commonly required due to the limitations of batteries in their capacity or tolerance for harsh environments.

IEEE 802.3af Power Over Ethernet (PoE) was ratified in 2003 to support networked devices needing 12.95 W or less and where running local AC power to each device was impossible, costly, or overly cumbersome. Examples include IP phones, enterprise-grade wireless access points, and IP cameras. By using standard Category 5/5e (Cat5) Ethernet cables to transmit both power and data, IEEE 802.3af PoE reduces system cost and complexity. PoE-enabled systems have been demonstrating their cost, reliability, and management advantages in real-world deployments. Such advantages are needed by many classes of embedded devices. But the 12.95-W limit of 802.3af precluded widespread embedded-systems usage.

Multiple factors are now converging to make PoE technology appealing for a much wider range of embedded applications. With the IEEE’s ratification of the next-generation 802.3at PoE+ standard this past September, the power capacity of the older 802.3af standard has been nearly doubled to 25 W. This new 25-W capacity allows PoE+ to support new classes of complex embedded systems incorporating multiple I/O devices, video displays, cameras, sensors, and other peripherals. In addition, low-power Intel® Atom™ processor technology now allows the creation of high-performance Intel® architecture (IA) -based embedded systems within the power budgets of PoE+ technology. Such systems include large, backlit HD video displays and other peripherals. Together, Intel Atom processors and 802.3at PoE+ are transforming Power Over Ethernet from a niche technology to one that sits squarely in the mainstream of embedded applications.

IEEE 802.3at PoE+ Overview

The ideas behind PoE aren’t new. A variety of techniques for distributing power and data with a common cable have been tried in the past. These approaches have included proprietary PoE implementations, power-line communications, and Universal Serial Bus (USB). IEEE 802.3at PoE+ has a number of noteworthy advantages over these approaches. Relative to proprietary PoE implementations, IEEE 802.3af and 802.3at allow for multi-vendor interoperability and assured levels of power and data performance. At the same time, they eliminate the possibility of damaging non-PoE devices connected to PoE-powered ports. USB only offers 2.5 W of capacity to bus-powered devices, which is insufficient for most embedded devices. Plus, USB and power line both have major topology and cable limitations. In contrast, PoE benefits from the flexibility of Ethernet’s purely distributed nature.

The IEEE 802.3at standard offers the following main features:

  • 802.3at power sourcing equipment (PSE) provides 50 to 57 VDC—an increased and tightened range compared to 44 to 57 VDC for 802.3af.
  • Current to 600 mA—up from the 350 mA under 802.3af—provides as much as 25 W at the powered device (PD) after allowing for cable voltage drops.
  • Support for 10Base-T, 100Base-T, 100Base-TX, and 1000Base-T (Gigabit Ethernet) data protocols and bandwidths
  • Two power modes determined by the PSE with Mode A providing power on pin pairs 2 and 3 and Mode B providing power on pin pairs 1 and 4
  • Non-intrusive signaling and detection of PDs for interoperability of 802.3af, 802.3at, and non-PoE devices on the same network—and to allow PDs to identify themselves and negotiate their power requirements with PSEs
  • New power-management functions have been added. 802.3at incorporates the Link Layer Discover Protocol (LLPD) from IEEE 802.1AB and Type, Length, Values (TLVs) from IEEE 802.3bc. These additions allow dynamic power allocation by the PSE to optimize power distribution and power-supply utilization, which leads to increased system efficiency and reduced costs.

PSEs are the brains of any PoE+ deployment. They detect and identify compliant PDs, dynamically allocate and apply power when it’s safe to do so, and implement remote powermanagement features. PSEs are of two types: endspans or midspans. PoE-enabled Ethernet switches are one example of an endspan, also known as an endpoint. They provide power to their Ethernet interfaces, allowing any connected PD to draw power. Midspans are essentially power supplies with two Ethernet connections and the conversion between PoE and non-PoE Ethernet. Midspans connect to standard non-PoE switches on one side and PoE-enabled PDs on the other side.

Advantages Of PoE+ For Embedded Applications

In embedded systems, PoE+ has many significant advantages over conventional power and data distribution approaches. Primary among these is the concept of “no new wires,” as PoE+ utilizes standard cabling and works with common Ethernet connector interfaces. The advantages of “no new wires” are major because existing network cabling infrastructures can be utilized without running high-voltage AC power or a separate power connection to each embedded device. Plus, the one connection that must be made—the PoE+-enabled network cable—is a low-voltage circuit. As a result, installation doesn’t require a licensed electrician and cables don’t have to be run through conduit. Because of their low-voltage classification, PoE+ cables and equipment normally can be installed in plenum spaces as well. The result is greatly simplified system installation with increased flexibility and significant cost savings.

A 2003 case study by Microsemi Corp. and Purdue University estimates that when replacing conventional power wiring, PoE saves between $350 and $1000 per device in upfront installation costs. To put this in perspective, assume that the incremental cost of adding PoE+ to an embedded device currently (including both the per-port cost of the PSE and PD functions) is on the order of $50. For a $50 investment, PoE+ yields a $350 to $1000 up-front cost savings as compared to conventional powering techniques. It yields a return on investment (ROI) of between 600% and 1900%. And as PoE+ volumes increase, equipment costs and ROI will improve even more.

Even if AC power is readily available at the embedded device, PoE+ still offers significant advantages over conventional power-distribution techniques. These advantages include the following:

  • The elimination of “wall wart” power supplies from each embedded device simplifies the overall system while reducing costs. In doing so, it eliminates multiple failure points and reduces cables and connections. Plus, wall-wart power supplies frequently are inexpensively made. They therefore offer limited robustness against power-line transients and lack remote-management capabilities.
  • PoE+ provides a uniform power interface to PDs without regard to country-specific power-line standards, plugs, or regulatory requirements.
  • With a consolidated network-based power infrastructure, PoE+ finally makes it practical to deploy robust AC surge protection and backup power in embedded applications—even in highly distributed systems or harsh environments.
  • Many PSEs offer smart power control and management that can be accessed over the network via SNMP or other means. Thus, they provide new remote power diagnostics, status reporting, and PD power management including remote power cycling of embedded devices. PoE+ adds significant new management capabilities to embedded systems that can improve fault diagnosis and speed repairs.

Intel® Atom™ Processor: The Ideal Solution For High-Performance PoE+ Embedded Devices

Offering high performance, low power consumption, and a highly integrated feature set including an on-chip HD video decoder, embedded Intel® Atom™ processors like the Z5xx and Z5xxP product lines are the ideal basis for next-generation PoE+-powered embedded devices. Using off-the-shelf Intel Atom processor Z5xx/Z5xxP-based single-board computers (SBCs) with PoE+ support, such as ADI Engineering’s Cinnamon Bay SBC line (see Figure 1), developers can quickly create no-new-wires products in a wide range of embedded applications. Examples include digital signage, interactive kiosks, panel PCs, human-machine interfaces, industrial controls, medical, and military.

Figure 1: Pictured is the Cinnamon Bay SBC with a PoE+ Option Module. Based on the Intel Intel® Atom™ processor Z5xxP, it offers extended temperature and low cost.

When running on 802.3at PoE+, the Cinnamon Bay SBC provides up to 20 W of spare power— enough for peripherals like backlit HD liquid-crystal displays (LCDs), touchscreens, audio power amplifiers, disk drives, wireless radios, cameras and motion sensors, and more. Table 1 shows some example PoE+ embedded applications enabled by the Intel Atom processor. But the possibilities are limited only by one’s imagination. In every case, PoE+ and Intel Atom processors combine to deliver substantial advantages in cost, reliability, manageability, and energy efficiency.

Table 1: Examples of PoE+-Powered Embedded Devices Enabled by the Intel® Atom™ processor


i http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?tp=&isnumber =5089344&arnumber=5089345&punumber=5089343 ii http://www.microsemi.com/PowerDsine/AboutUs/ SuccessStories/CaseStudy_Purdue_University.pdf iii For more information on ADI Engineering’s Bay SBC, please refer to http://www.adiengineering.com/php-bin/ ecomm4/productDisplay.php?category_id=25&product_ id=91

Steve Yates founded ADI in 1990 and has led the company to its position as a leading provider of embedded IA single-board computers, “Open IP” custom and semi-custom products, and customer-directed manufacturing. Prior to ADI, Yates worked as a hardware engineer for Intel Corp. and GE Fanuc. He graduated with a BS and MS in electrical engineering from the University of Virginia. Yates is a registered professional engineer in the Commonwealth of Virginia.