Ethernet standard a sign of network greening

July 1, 2009
The 802.3az project could impact an installed base of more than a billion ports, and will change more clauses in the existing 802.3 standard than any project in history.

The 802.3az project could impact an installed base of more than a billion ports, and will change more clauses in the existing 802.3 standard than any project in history.

National and international bodies worldwide have been increasing pressure to reduce energy use and greenhouse-gas emissions. Standards and legislation have addressed the biggest usage areas first, and are gradually moving into smaller energy-usage sectors. Inevitably, network equipment is coming under the energy- efficiency spotlight, and many organizations are looking to produce network energy-effi- ciency guidelines or standards.

Networks have increased significantly in utility and capacity, and are now a critical feature of most businesses. The energy consumed by networks, however, has also increased, and now takes about 10% of all information-technology (IT) energy usage in data centers, according to the Environmental Protection Agency’s “Report to Congress on Server and Data Center Energy Efficiency” (August 2, 2007). Note: this figure excludes equipment in telecommunications networks, enterprise wiring closets, or home networks.

The active/idle concept detailed in IEEE 802.3az works on the principle that energy is consumed only when there is work to be done; i.e., data to transmit or receive. When not transmitting or receiving data, network devices will operate in low-power idle mode.
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Network users are looking for ways to reduce or limit the growth of network energy use without compromising critical network functionality. The nature of networking dictates that energy-efficient operation will require some measure of cooperation between communicating devices. It can be anticipated that network energy-efficiency standards will require equipment to comply with energy-saving protocols.

The role of IEEE 802

IEEE 802 defines the behavior of physical layer (PHY) and link layer devices. The PHY is the key component connecting network devices together, and IEEE 802.3 defines many of the most popular PHYs. Even though the PHY device may be only a small part of a networking system, the interface standard covers the most basic interaction between systems and makes an ideal starting point for end-to-end energy-efficiency savings. There was a clear requirement for a project that could reduce the power used by these network PHYs, and the systems using them, without impacting the network’s performance. The IEEE 802.3az Energy Efficient Ethernet draft standard has already been recognized as an important feature for future energy-efficiency standards by bodies such as the EPA in the Energy Star program.

In November 2006, IEEE 802 hosted a call for interest (CFI) that led to the formation of the Energy Efficient Ethernet project, although work had been in progress in various places before then. The Energy Efficient Ethernet Study Group worked for a year to define the purpose and scope of the IEEE P802.3az project that was authorized in December 2007.

The project task force is working on the draft standard, and is hoping to enter the next phase by submitting the amendment for 802.3 Working Group ballot this month (July). If the project stays on course, it should lead to a published standard in the fall of 2010. The changes defined in the standard will require most manufacturers to develop new hardware in order to comply, so it is unlikely that new products will be available until 2011 or later. As with any major change, it should be expected that multiple generations of development will be needed before the benefits are widely seen.

The main principle behind Energy Efficient Ethernet is that you should only consume energy when there is work to do–a principle for all of us to use. To this end, the standard defines a “low-power idle” operation that can significantly reduce the power consumed in the interface when there is no data to send. This works in a similar way to a porch light on a motion detector; it comes on when someone approaches the door and goes off again when no one is nearby. When there is no traffic to send, the PHY enters a low-power state that involves very little electrical activity; it also signals to its link partner so that the other end of the link can do the same.

As data arrives to be sent, the PHY wakes up its own circuits and notifies the link partner. After a short delay–typically, a few microseconds–the link returns to normal operation. This works independently in each direction, so sometimes a PHY may be asleep in one direction and fully active in the other.

Practical impact

To get this low-power idle function in the standard, changes are being made to the coding and state machines for all the main copper PHYs, including 100Base-TX, 1000Base-T, 10GBase-T, 1000Base-KX, 10GBase-KX4, and 10GBase-KR. This project will change more clauses in the existing IEEE 802.3 standard than any project in history, and could impact an installed base numbering more than one billion links. For this reason, the project will include many cycles of careful review by many people with a vested interest in Ethernet technology.

Alongside the changes to the PHY specifications, the project includes definitions for managing these new functions and for extending the benefits of low-power idle to the systems that contain the PHYs. Oftentimes, the PHY may be able to awaken quickly (when there is data to be sent), but the system itself has gone into a deeper sleep. To cater to these situations, the standard includes a means to negotiate deeper-sleep modes that require longer wake times, and potentially deeper buffers to absorb data during wakeup.

Another innovation in the new standard takes advantage of the improvements in twisted-pair cabling over the last 20 years. The original definition for 10Base-T used large voltage-swings to cope with the losses of Category 3 or similar cable. The new standard defines 10Base-Te with a smaller transmission voltage that is, in all respects, compatible with legacy 10Base-T on any cable that has Category 5 (or better) characteristics. This new standard will allow manufacturers to use the latest high-density processes that will save power on multi-speed devices.

The principle being applied in Energy Efficient Ethernet–that energy should be conserved when there is no work to do–will inevitably be applied to the products that use Ethernet interfaces. Some efficiency-testing metrics are already assessing Ethernet products on the basis of energy consumption at low usage.

Impact on cabling design

Although the changes may take many technology generations to have their fullest impact, we should expect that Ethernet products in the future will show significantly different power consumption for periods of high utilization than for periods of low utilization. This will then influence the infrastructure design as it must cope with the peak power supply and cooling demands, but must also be able to operate efficiently at much lower power levels. This infrastructure scala- bility requirement is reflected in such metrics as The Green Grid’s ( Data Center Infrastructure Effi- ciency (DCiE), or Power Utilization Efficiency (PUE) scalability and analysis.

It is unclear how these trends will influence cabling design. As the principle of scalability is applied to Ethernet interfaces, Ethernet products, and building-infrastructure designs, it may lead to innovations in network architecture that cannot be foreseen.

The evolution of these architectures will require focus on both the network-equipment design and the interconnect design to deliver the most-efficient implementations from a holistic standpoint.

This ARTICLE was written on behalf of The Ethernet Alliance ( by: Hugh Barrass of Cisco Systems; Mike Bennett and Bruce Nordman of Lawrence Berkeley National Laboratory; Manoj Wadekar of Intel; and Richard Mei of CommScope, who contributed the sidebar. Lawrence Berkeley National Laboratory research is supported by the United States Department of Energy under Contract Number DE-AC02-05CH11231.

802.3az’s impact on cabling, and vice versa

For both installed and new structured cabling systems, there is no impact from an application standpoint in implementing IEEE P802.3az Energy Efficient Ethernet. All applications that are supported currently by a particular performance category of structured cabling will be supported as IEEE P802.3az-compliant products are deployed. For all cabling systems with Category 5 performance or better, the energy-saving benefits of IEEE P802.3az products will be realized. Category 3 networks will not fully benefit from the complete suite of energy savings represented by IEEE P802.3az. Specifically, Category 3 networks will not support 10Base-Te and its smaller transmission-voltage benefits. Category 3 networks will, however, benefit from other energy- efficiency advantages of IEEE P802.3az.

The reality that existing structured cabling systems will be able to support a new protocol, such as IEEE P802.3az and its positive impact on the environment, is a result of the focused effort of the Energy Efficient Ethernet Task Force to ensure that the new standard will work on existing cabling systems. The coordination of the IEEE 802.3 Ethernet working group with the TIA TR-42 and ISO WG3 structured cabling standards groups ensures that users’ investments in structured cabling systems are protected for Ethernet applications that bring tangible benefits to the customer.

In fact, the investment in structured cabling allows customers to maximize the benefits of IEEE P802.3az. The full benefit of Energy Efficient Ethernet is realized when IEEE P802.3az-compliant products are at both ends of a link. Cabling standards recommend up to four connection points in a channel to accommodate various networking topologies.

The structured cabling is particularly important in a retrofit or expansion project, in which there will be a mix of legacy and IEEE P802.3az-enabled equipment. The distribution fields, such as interconnect and crossconnect areas, provide organized administration points to ensure that newer IEEE P802.3az electronics are always grouped and deployed in the most energy-efficient and optimal configuration.

Over time, as new IEEE P802.3az hardware is deployed, Ethernet links with lower energy needs will be realized. These low-power Ethernet links will make converged Internet Protocol networks more cost-effective from an operating-cost perspective, which, in turn, will make a wide variety of IP-based intelligent infrastructure (e.g., intelligent buildings) more viable and more widely accepted–further enabling energy-efficient products and systems. The coordinated work of application standards such as IEEE 802.3 and structured cabling standards will ensure maximum benefit to the industry, to the customer, and to the planet.–Richard Mei, CommScope

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