A Network Connection Proxy to Enable Hosts to Sleep and Save Energy Miguel Jimeno and Ken Christensen Bruce Nordman Dept. of Computer Science and Engineering Environmental Energy Technologies Division University of South Florida Lawrence Berkeley National Laboratory Tampa, FL 33620 Berkeley, CA 94720 {mjimeno, christen}@cse.usf.edu [email protected] Abstract Much of the electricity consumed by network hosts is wasted. Being connected to the Internet requires some Billions of dollars of electricity are being used to keep active participation. When hosts fail to do this, they “fall idle or unused network hosts fully powered-on only to off the network” and applications fail. Billions of dollars maintain their network presence. We investigate how a worth of electricity every year are used to keep network Network Connectivity Proxy (NCP) could enable hosts fully powered on at all times only for the purpose of significant energy savings by allowing idle hosts to enter maintaining network connectivity or “presence” [18]. If a low-power sleep state and still maintain full network not for the need for network connectivity most of these presence. An NCP must handle ARP, ICMP, DHCP, and hosts could be asleep the majority of the time, with other low-level network presence tasks for a network significant energy savings resulting. Surveys have found host. An NCP must also be able to maintain TCP that about 60% of office desktop PCs are left on connections and UDP data flows and to respond to continuously [20], [27]. It is the need to maintain network application messages. The focus of this paper is on how connectivity that contributes to the disabling of existing TCP connections can be kept alive during periods of host power management features in many PCs. Saving this sleep by using a SOCKS-based approach called green wasted energy can be done by 1) redesigning network SOCKS (gSOCKS) as part of an NCP. The gSOCKS protocols and applications, or 2) encapsulating the includes awareness of the power state of a host. A intelligence for maintaining network presence in an entity prototype implementation of gSOCKS in a Linksys router other than the core of the networked devices. The second shows that TCP connections can be preserved. option we call Network Connectivity Proxying (NCP) where an NCP is an entity that maintains full network presence for a sleeping network host [18]. 1. Introduction The NCP concept has been previously defined by the authors [6], [7], [13], [18] and prototyped by Microsoft One of the most urgent challenges of the 21st century [1]. What has not been fully addressed is how to preserve is to engineer new technologies that can enable a existing TCP connections when a network host goes to transition towards a more sustainable society with a sleep. Our motivation is that applications such as SSH reduced CO2 footprint. Network hosts consume a large and IM (which maintain permanent TCP connections) can and growing amount of energy. Data centers and servers be proxied. The contributions of this paper are: consumed an estimated 1.5% of total US electricity • A formal definition of the requirements for a consumption in 2006 for a total cost of about $4.5 billion Network Connectivity Proxy (NCP). [21]. However, even greater is the electricity consumed • A design, implementation, and evaluation of a by network hosts not in data centers. The EPA estimates SOCKS-based approach to preserve TCP that PCs in the US consume 2% of all electricity connections and UDP flows for sleeping hosts. consumed [10]. It is estimated that 9% of the electricity The remainder of this paper is organized as follows. consumed by commercial buildings is from office Section 2 describes the network connectivity problem. equipment – much of this equipment being network Section 3 defines the requirements for the NCP. Section 4 connected PCs [22]. For a typical US household, the describes the architecture of the NCP focusing addition of a single 80 W PC powered-on 24/7 will add specifically on a “green SOCKS” (gSOCKS) component. about 6.5% to the utility bill [9]. Beyond PCs are the Section 5 describes the prototyping of gSOCKS. Section growing numbers of commercial and consumer devices – 6 describes the evaluation of the prototype. Section 7 such as set-top boxes and game consoles – that are describes related work. Finally, Section 8 contains a connected to the Internet and have become network hosts. summary and describes future work. 978-1-4244-3367-4/08/$25.00 ©2008 IEEE 101 2. The Network Connectivity Problem NCP to client packet flows Server to NCP packet flows Why are the majority of office and home PCs left Switch powered-on even when not in active use, such as over Client nights and during weekends? There are several major Server reasons for this with two most prominent: 1) the Network annoyance to a user of having to wait for a PC to wake-up NCP out of sleep state, and 2) the need to maintain network connectivity at all times to allow for remote access and/or Note: The NCP within the switch covers for the client host when it is sleeping to maintain full network presence. for network-centric applications to maintain their state. The first reason is becoming less significant as PCs Figure 1. System view of the NCP become able to wake-up faster, and the second reason is becoming more significant as more applications and If a host can remain reachable even when sleeping and protocols rely on persistent Internet connectivity. keep its NIC powered-up, it can then be woken-up from To maintain network connectivity a host must be able the network by “trigger” packets that the NIC recognizes. to support a number of application and protocol The Magic Packet was invented for this purpose in the primitives including: mid-1990s. Most NICs today support both Magic Packet • Maintain host-level reachability by responding to and the ability to pattern match for specific packets (such periodic ARP requests in order to not age-out of as a TCP SYN packet) to trigger a wake-up. Wake-up the last-hop router ARP cache. does not solve the problem of network connectivity. • Maintain its IP address by generating periodic Wake-up triggered on pattern matching can cause both DHCP lease requests in order to not lose its IP missed and unnecessary host wake-ups resulting in address (if using DHCP to obtain an IP address). applications that fail and/or reduced energy savings. • Maintain its manageability by responding to ICMP Estimating the exact cost of the network connectivity packets, such as ping. problem is difficult. There are about 170 million desktop • Support NetBIOS name resolution by responding PCs in the US (adapted from the data summarized in to NetBIOS name queries as appropriate (if [23]). Assuming an 80 W power consumption of an idle running NetBIOS protocol and applications). PC, 120 hours of idle overnight and weekend hours per • Maintain application-level reachability by week, and 60% of PCs not powered-down during these responding to TCP SYN packets sent to open hours results in about 50 TWh/yr of electricity wasted per (listening) ports. year in the US (this is $5 billion at $0.10 per kWh). • Maintain or preserve application state (for Further waste occurs from idle notebook PCs, set-top example, current user workspace and data) for any boxes, etc. left on. In [20] a similar calculation is made applications with open long-term TCP connections. resulting in an estimate of $1.72 billion wasted per year • Maintain or preserve application state by for office PCs alone. One reported study suggests that responding to any number of application-level half of all electricity consumed by PCs is wasted [17]. messages including heartbeat messages and Clearly, solving the network connectivity problem should specific requests for service. be of great interest to the research community. In addition, it is desirable in many cases that any packets sent to a host during the time it is sleeping not be lost. 3. Enabling Host Sleep with an NCP Since the above list is not complete, it is future work to better understand what packets are received by a sleeping Hosts connected to a network maintain their presence host and which of the received packets can be ignored, to other hosts by correctly generating and responding to which require an immediate reply, and which can be messages for both network protocols and applications. A buffered for later processing. Very important is the ability Network Connectivity Proxy (NCP) as proposed by the to respond to ARP packets even when sleeping. Ethernet authors in [18] is an entity that implements the key NICs that support DMTF’s Alert Standard Format (ASF) network presence capabilities of a network host in order Specification 2.0 [2] can respond to ARP packets for a to allow the host to sleep, yet it allows the host to appear sleeping host. This is done by keeping the NIC fully to other devices to be fully operational and connected to powered-up when the host is in a sleep state (with its the network. Thus, an NCP can enable a network host to CPU, display, memory, and storage powered-down). The sleep and save energy where without the NCP it could not powered-up NIC can also wake-up the host when specific sleep even if inactive or idle. packets pre-determined to trigger a wake-up are received. 102 Figure 1 shows a network with two network hosts flows, and network applications and higher-layer labeled as a client and server and an NCP located within a protocols.