There has been a lot of researches lately regarding the wasted energy consumed especially by the IT environment, [11], [3], [6], [1]. One of the most frequent cases is that of office machines left on despite of user activity on them.
The focus of this paper is exactly enterprise's PCs, the power management of which would save up significant energy.
The main reason PC users and IT administrators want to leave PCs on all the time is they want to access them whenever they want to, or whenever it is planned a broadcasting update or process. Among many ideas, lately the focus is back to Sleep Proxy concept, which was first introduced in 1998 [9] and later researched. A Sleep Proxy allows a PC to pass into a Sleep state, meanwhile it preserves PC's network presence and awakens it if necessary. The architecture of this Sleep Proxy system is composed by a client which periodically updates the server with information it needs to represent this client while it is asleep, and the server (Sleep Proxy) that based on a designed policy on how to manage network traffic protocols, will eventually ignore some packets, answer to some requests, and awake the sleeping computer for other packets.
The aim of developing a Sleep Proxy system is to encourage users to enable power management features, assuring them that they can have access to their computers even when they are asleep. So, in our work we emphasize this by testing a real system in an office environment, showing and highlighting the differences between non-proxy system and proxy system network regarding their energy consumption.
In Section 2, we mention related articles, papers and publications regarding this area. In Section 3 we will give a preview of the design and implementation of Sleep Proxy server, how are all the components related to each other in Hardware and Software level. Section 4 describes the experimental environment, also the tests regarding the power consumption without and with Proxy server implemented in the experiment, in order to get an idea of energy savings this system can provide. The results of the experiments and their interpretation are given in section 5, where we emphasize the need of synchronization between IT staff and the Proxy system in order to get the best results. At last we come with our conclusions.
The Sleep Proxy idea was first introduced in 1998 by Kenneth Christensen in an International Journal [9]. Although there were some technologies such as "Wake on LAN" and "Advanced Configuration and Power Interface Specification" in 90's regarding saving energy issue, due to some of their disadvantages, there are no more researches in the area. Instead, attention was back to Sleep Proxy in 2004 by Bruce Nordman [8]. An interesting paper comes in 2007 for an implemented Proxy specifically designed for Universal Plug and Play Protocol (UPnp) [12]. Later in 2007, Bruce Nordman and Keneth Christensen came with another work where they propose solution [10] for a Sleep Proxy which can manage protocols such as ARP, DHCP, ICMP. Another scheme similiar to Sleep Proxy comes in 2008 called Somniloquy [13]. It offers a hardware implementation of Sleep Proxy in a so-called "gumstix", thought as a predecessor of future NIC. We can also mention [4]: Sleep Proxy as a standard of European Computer Manufacturers Association in November 2009. Researches go on and another paper of 2010' [7], illustrates designing, implementing and testing of a Sleep Proxy in Microsoft Offices.
In this section we show some design and implementation issues based on previous known architecture of Sleep Proxy Server, expressed in papers such as [2], [8] and [9]. The Sleep Proxy system is based on a client/server architecture where every client can fall asleep, being represented on the network by the Sleep Proxy server. prevent any network traffic to wake the sleeping computer in vain by ignoring or answering to these kind of packets • wake up the sleeping computer by sending a WoL packet whenever there is a network traffic too important not to be answered by the client itself
Based on the survey of [11] regarding network chattering, we decide to implement this reaction policy for the Proxy server:
• it will answer back to ARP requests, will send ARP probes broadcasts on the network when necessary • wake up sleeping computer by sending WoL packet in case of TCP requests toward that computer • ignore all the others Programming this system will need: • Java RMI for building the client / server applications (as a programming environment is chosen "Eclipse IDE for Java Developers", Version 3.5.2 "Helios Service Release"),
Jpcap library (Java packet capturing) which serves for capturing, analyzing and processing network packets.
The experiment environment is composed by 6 computers clients and one server. 6 computers have these parameters: In every client is installed Java JDK and executes the client.jar application, which is the client Proxy application. Meanwhile the server executes the Server Proxy application. The network topology is Bus.
There will be held these experiments to test the Sleep Proxy system. The first testing: we will measure the consumed energy and the network traffic (number of packets) passing to them during the time 16:00 to 8:00 of the next day, for three continuous days, providing so 3 samples for each computer, without "sleep proxy" implemented. The second testing, will include the 7-th computer, the server Sleep Proxy, and we will measure the same parameters for 16 hours, in three days. So we will have 3 other samples for each of 6 client computers. Based on the results of the experiments we will compare the energy consumed and network traffic, also the time of each computer passed on sleeping state with Sleep Proxy system implemented, which is automatically translated into energy savings.
The power consumption is measured by a specific tool produced by Microsoft called Joulemeter. We will measure the power consumption for 16 hours, for 3 days.
Wireshark is the program from which we will get information about the network traffic in the experimental client machine, in terms of number of packets, saved in generated .pcap files.
The first testing results regarding the power consumption and total number of packets are shown in Table 1 below.
As we can see from the table, Computer C1 and C6 have higher power consumption and this happens because of the CRT screen that consumes more power. The same data of Table 1 are shown in a graphical form in Figure 1. The results about the second testing, when Sleep Proxy is implemented on the network, regarding power consumption and total number of packets are shown in Table 2, also in a graphical form in Figure 2: During the 16 experimenting hours, using a Sleep Proxy server, it was provided a percentage of sleeping time in a range of 44% to 65%, with an average sleeping time of 8.71 hours, illustrated in Table 3 and Figure 3.
The results of this paper highlights the importance of power management features application and encourage this by evaluating a Sleep Proxy system, making a comparison of energy consumed between two situations: without Sleep Proxy implemented, and with Sleep Proxy implemented on the network.
The system we implemented can provide significant energy savings, assuring computers's availability on the network and a high level of transparency for other computers of the network. Due to our experiments, we calculate that in our system of 6 computers, daily average energy consumption in a Sleep Proxy system is 0.92 kWh per each computer. Compared to the daily average energy consumption value without implemented Sleep Proxy, of 1.97 kW, the energy savings results up to 53%, so computers in a Sleep Proxy environment consume 53% less energy than the same computers in a Non-Sleep Proxy environment. These values belong to only one computer on the network, but as the size of the company grows the energy saving becomes more and more significant in an annual period, up to hundreds of MWh. The energy savings is achieved by longer sleeping time in the presence of a Sleep Proxy Server. In a non-Sleep Proxy environment, sleeping time is almost 0 hours. Meanwhile the results of the experiments with Sleep Proxy implemented, show that during 16 hours of experimental time, the 6 computers stayed in sleeping time from 44% to 65% of the time, translated in 7.2 to 10.4 sleeping hours, from a total of 16 hours. Knowing that Sleep proxy is a system which is closely related to other Software components, brings to the need for some Software policies that would help in a better performance of the Sleep Proxy system. We can mention here procedures and routines such as backup, patches, automatic updates, scheduled by the IT department. Of course, IT department policies and schedules regarding these fields play a non-trivial role in Sleep Proxy performance. Sleep Proxy is active during non-official time (16-8 of the next day) so it would be much helpful from the IT department to be synchronized with this system in order to get the best results from Sleep Proxy.