Kenneth J. Christensen

Reducing the Energy Consumption of Ethernet with Adaptive Link Rate (ALR)

The rapidly increasing energy consumption by computing and communications equipment is a significant economic and environmental problem that needs to be addressed. Ethernet network interface controllers (NICs) in the US alone consume hundreds of millions of US dollars in electricity per year. Most Ethernet links are underutilized and link energy consumption can be reduced by operating at a lower data rate. In this paper, we investigate adaptive link rate (ALR) as a means of reducing the energy consumption of a typical Ethernet link by adaptively varying the link data rate in response to utilization. Policies to determine when to change the link data rate are studied. Simple policies that use output buffer queue length thresholds and fine-grain utilization monitoring are shown to be effective. A Markov model of a state-dependent service rate queue with rate transitions only at service completion is used to evaluate the performance of ALR with respect to the mean packet delay, the time spent in an energy-saving low link data rate, and the oscillation of link data rates. Simulation experiments using actual and synthetic traffic traces show that an Ethernet link with ALR can operate at a lower data rate for over 80 percent of the time, yielding significant energy savings with only a very small increase in packet delay.

IEEE 802.3az: the road to energy efficient ethernet

Ethernet is the dominant wireline communications technology for LANs with over 1 billion interfaces installed in the U.S. and over 3 billion worldwide. In 2006 the IEEE 802.3 Working Group started an effort to improve the energy efficiency of Ethernet. This effort became IEEE P802.3az Energy Efficient Ethernet (EEE) resulting in IEEE Std 802.3az-2010, which was approved September 30, 2010. EEE uses a Low Power Idle mode to reduce the energy consumption of a link when no packets are being sent. In this article, we describe the development of the EEE standard and how energy savings resulting from the adoption of EEE may exceed

The potential impact of green technologies in next-generation wireline networks: Is there room for energy saving optimization?

400 million per year in the U.S. alone (and over

Measuring building occupancy using existing network infrastructure

1 billion worldwide). We also present results from a simulation-based performance evaluation showing how packet coalescing can be used to improve the energy efficiency of EEE. Our results show that packet coalescing can significantly improve energy efficiency while keeping absolute packet delays to tolerable bounds. We are aware that coalescing may cause packet loss in downstream buffers, especially when using TCP/IP. We explore the effects of coalescing on TCP/IP flows with an ns-2 simulation, note that coalescing is already used to reduce packet processing load on the system CPU, and suggest open questions for future work. This article will help clarify what can be expected when EEE is deployed.

An Initial Evaluation of Energy Efficient Ethernet

Recently, network operators around the world reported statistics of network energy requirements and the related carbon footprint, showing an alarming and growing trend. Such high energy consumption can be mainly ascribed to networking equipment designed to work at maximum capacity with high and almost constant dissipation, independent of the traffic load. However, recent developments of green network technologies suggest the chance to build future devices capable of adapting their performance and energy absorption to meet actual workload and operational requirements. In such a scenario, this contribution aims at evaluating the potential impact on next-generation wireline networks of green technologies in economic and environmental terms. We based our impact analysis on the real network energy-efficiency targets of an ongoing European project, and applied them to the expected deployment of Telecom Italia infrastructure by 2015-2020.

A parallel-polled virtual output queued switch with a buffered crossbar

The primary focus of Green IT has been on reducing energy use of the IT infrastructure itself. Additional significant energy savings can be achieved by using the IT infrastructure to enable energy savings in both the IT and non-IT infrastructure. Our premise is that energy can be saved by driving building operation on information gleaned from existing IT infrastructure already installed for non-energy purposes. We call our idea implicit occupancy sensing where existing IT infrastructure can be used to replace and/or supplement traditional dedicated sensors to determine building occupancy. Our implicit sensing methods are largely based on monitoring MAC and IP addresses in routers and wireless access points, and then correlating these addresses to the occupancy of a building, zone, and/or room. Occupancy data can be used to control lighting, HVAC, and other building functions to improve building functionality and reduce energy use. We experimentally evaluate the feasibility of this dual-use of IT infrastructure and assess the accuracy of implicit sensing. Our findings, based on data collected from two facilities, show that there is significant promise in implicit sensing using the existing IT infrastructure present in most modern non-residential buildings.

A Network Connection Proxy to Enable Hosts to Sleep and Save Energy

In September 2010, the Energy Efficient Ethernet (IEEE 802.3az) standard was officially approved. This new standard introduces a low power mode for the most common Ethernet physical layer standards and is expected to provide large energy savings. In this letter, for the first time, Network Interface Cards (NICs) that implement Energy Efficient Ethernet (EEE) are used to measure energy savings with real traffic. The data presented will be useful to better estimate the energy savings that can be achieved when EEE is deployed. Existing analysis of EEE based on simulations predict a large overhead due to mode transitions between active and low power modes. The experimental results confirm that transition overheads can be significant, leading to almost full energy consumption even at low utilization levels. Therefore traffic patterns will play a key role in the energy savings achieved by EEE as it becomes deployed in the field.

The next frontier for communications networks: power management

Input buffered switches with virtual output queues (VOQ) are scalable to very high speeds, but require switch matrix scheduling algorithms to achieve high throughput. Existing scheduling algorithms based on parallel request grant-accept cycles cannot natively support variable length Ethernet packets. A parallel-polled VOQ (PP-VOQ) architecture is proposed that natively supports variable length packets. Small amounts of FIFO buffering within a crossbar are used. Using simulation, the PP-VOQ with buffered crossbar switch is shown to have lower switch delay at high offered loads than an iSLIP switch for both cell and variable-length packet traffic. The PP-VOQ switch does not require internal speed-up or complex reassembly mechanisms. The priority mechanism implemented in both the iSLIP and PP-VOQ switches are demonstrated to provide guaranteed rate and bounded delay for schedulable traffic.

An evolution to crossbar switches with virtual output queuing and buffered cross points

Billions of dollars of electricity are being used to keep idle or unused network hosts fully powered-on only to maintain their network presence. We investigate how a network connectivity proxy (NCP) could enable significant energy savings by allowing idle hosts to enter a low-power sleep state and still maintain full network presence. An NCP must handle ARP, ICMP, DHCP, and other low-level network presence tasks for a network host. An NCP must also be able to maintain TCP connections and UDP data flows and to respond to application messages. The focus of this paper is on how TCP connections can be kept alive during periods of host sleep by using a SOCKS-based approach called green SOCKS (gSOCKS) as part of an NCP. The gSOCKS includes awareness of the power state of a host. A prototype implementation of gSOCKS in a Linksys router shows that TCP connections can be preserved.

A Simulation Study of a New Green BitTorrent

Performance evaluation is used to gain an understanding of how to make the best use of scarce resources. Storage, memory, processing, and communications bandwidth are all relatively plentiful and inexpensive. What is the next frontier for communications networks and performance evaluation? I will argue that it is power management to achieve cost-effective operation. In the past few years, entirely new network protocols have been developed for battery-hungry sensor networks. But, what about the existing Internet? Estimates place the Internet as consuming from 2% to 8% of the total electricity produced in the USA - much of this power consumption is unnecessary. Do our “always on” desktop computers really need to be fully powered-up all the time? What can be done to achieve power-savings in these computers? The goal is to eliminate unnecessary energy usage by desktop computers in the near future and by networked embedded systems in the longer term. Traffic characterization is the first step towards this goal. Traffic characterization at inter-flow, intra-flow, and protocol levels is being done to investigate power management. The resulting savings achievable from relatively simple power management schemes are measured in TWh per year - or roughly equivalent to the electricity generated by one nuclear power plant. This is cost-effectiveness on a large scale!