Suddenly by Allstar Weekend free essay sample

Get ready to Dance Forever! Because Cameron, Zach, Nathan, and Michael have whipped up an amazing track list for their first studio album, â€Å"Suddenly†. With their two hit singles, â€Å"Dance Forever† and â€Å"A Different Side of Me†, this band will undoubtedly blow your socks off! Also making guest appearances on the album are â€Å"Journey to the End of My Life†, â€Å"Amy†, and the crowd pleaser â€Å"Hey, Princess.† The band got their start on Radio Disney’s Next Big Thing, and, although they didn’t win, they got picked up by Hollywood Records soon after, and produced their first music video for â€Å"A Different Side of Me.† This video then debuted on the Disney Channel, and the band was an instant hit. Since then, the band has also released another music video for their song â€Å"Dance Forever†, and they have started their first tour, with thousands of waiting fans. Allstar Weekend’s songs have a different sound to them, and they will make you really want to dance forever! And the boys themselves aren’t that bad either! So, go check out and pick up your copy and listen to the latest hot band of 2010!

The Good, the Bad and College Application Essay Samples Biology

The Good, the Bad and College Application Essay Samples Biology Being in college might be a tiny struggle for some. People today tell you things that could help you when you truly listen. Details of College Application Essay Samples Biology To stick out from a substantial number of applicants, your college application essay has to be strong, distinctive and creative. On our site, you can receive the very best scholarship application essay in a couple of clicks. It's easy to locate students not understanding how to write college application essays. A student doesn't write admission essay to have a high grade. So many students believe that they know what colleges want from an applicant, and this may have a big influence above their essays. The majority of the colleges utilize the typical application essay prompts. Given that the absolute most competitive colleges in the nation generally ask you to compose multiple supplemental essays and short answer questions past the most important Common Application essay, it's more important than ever to acquire the top-of-the-line assistance that can produce a difference in the approach. Your college counselor can offer valuable insight into how to boost your college application essays, so make sure to find feedback on your drafts whenever possible. By doing that the student stays true to the very first paragraph in supplying a crystal clear direction throughout the full essay. In any case, college community may locate a valuable input given by my essay. Thus, it's important to have a look at excellent application essay examples. As you are interested in getting the essay to communicate the very best information about you, you have to do thorough preparation for the sample college admission essays to attain its purposes. Thus, the essay is supposed to coincide with the applicant's qualities and interests in order for it to boost the probabilities of admission. Our admission essay examples can prove that we're here in order to provide simply the very best assistance to assure you which you submit an application essay you can be confident in. College Application Essay Samples Biology for Dummies School-based counselors have lots of students to advise and are extremely busy, so seek out guidance early and often. Furthermore, there's an allowance to use the exact same funny approach utilized by the college. It features information about oneself that proves to the council a person deserves the chance for additional studies in a spe cific area. Since there's a pool of applicants competing for limited chances in a specific college or school, it's important for a student to use every opportunity they must compose the very best essay. Top College Application Essay Samples Biology Choices An application essay is a kind of intellectual property. It's very valuable to take writing apart as a way to see just the way that it accomplishes its objectives. This section gives the applicant a chance to create a last statement to the reader. Listed here are the guarantees we offer to anybody who is prepared for professional support. The purpose of the introduction is to provide a glimpse of the aim of the essay. If you wish to secure far better idea about what the peculiarities of writing inside this subject field are, feel free to seek advice from our Natural sciences section. The topics are simple, but expert help won't ever be odd. For a beginning, the typical application essay topics need you to use language th at's totally free from language flaws and grammatical mistakes. The only factor to consider is how long the paper is. There are lots of experts online who might not understand how essays are written. As a consequence, spending money to deal with your essays could possibly be challenging. When you have prejudice knowledge about the kind of question would be asked during the admission procedure, then your essay writing can be simple, but if you don't then it would be an intimidating undertaking.

Easy Essay Topics For Class

Easy Essay Topics For ClassYou may find it hard to decide on what easy essay topics for class should you use. Well, in this article I will be discussing that topic is the best for your students. So let's take a look at some of the different choices that you have.Special Event - Have the students write about an event that they are attending in class. You could also have them write about something they are doing while they are in class. It could be something as simple as having a meeting with their friends or going out to eat. If they happen to run into the instructor then that would be even better.Forum Topic - As the name suggests, this is one of the easiest ways to put a topic on your paper. The forum is used as a discussion group that meets regularly. So, instead of giving the students a specific class they could use this forum to discuss anything related to the class. It could be a case where someone had a question, but no answers were given, or if they wanted to find out how they can succeed in the class.Student Stories - These are one of the most popular essay topics for class. You will need to have each student write a short story related to the subject of the class. The professor will read through all of the stories and give his or her opinion on each one.Picture Based Essay Topics - The next category of essay topics is pictures. You will need to take pictures of people doing something in class. It could be a picture of a person looking at a clock or just a picture of the class talking.Activities - Make sure that you include some activities in the class. For example the students could do some word find. You could do a quiz on the meaning of words for instance. Just be sure that you don't ask them to write an essay on the word.Summary - Now the last tip would be to include some type of summary at the end of the essay. Usually this is done by using the format of an introduction. Then the summary at the end is usually something like a conclusion. Whatever y ou do make sure that you include the summary at the end of the essay.There are so many easy essay topics for the class that you could choose from. However you want to make sure that you are picking the right one. You could use this article as a way to get ideas on which one is the best for your class.

Life After Applied Reliability Research Papers to Nanotechnology

Life After Applied Reliability Research Papers to Nanotechnology The most important difficulty is that topic is the most significant element of the entire research paper. By taking a look at a well-written case of research proposal paper, you will learn that topics which are too broad can be challenging to manage as you will probably have different, and frequently conflicting, ideas on how best to tackle the issue. A vague topic will be difficult to comprehend also stop you from having a consistent research paper. When you are confronted with choosing healthcare research paper topics, all the choices may be intimidating for you. Regarding experience, working with a person who has worked on similar papers means they understand the requirements and rules. In the event you doubt that it is possible to handle the job, ensure you search for skilled support. Just after the title there's an introduction part that permits the speaker draw the interest of the listeners to his favor such that they're keen to what he is saying. Applied research is thought to be non-systematic inquiry and it is generally launched by an organization, agency or an individual as a way to deal with a particular issue. What You Should Do to Find Out About Applied Reliability Research Papers to Nanotechnology Before You're Left Behind The subject of well-being and well-being covers such a wide number of academic disciplines, odds are you will come face to face with selecting health research paper topics sooner or later in your college career. Primary and secondary sources may be used. For instance, researching a wide topic like business management'' is difficult since there can be hundreds of sources on all facets of business administration. As an advertising student, you most likely have access to a plethora of resources like your college library and naturally, the net, to produce good research paper topics. Where to Find Applied Reliability Research Papers to Nanotechnology Y our admission appears to be secured. For example, a master level research paper demands an expert with no less than a master or Ph.D. degree. It's possible to find out more regarding students' term papers here. Informative speech papers have an outline that has a brief title at the start of the speech. Now you have a great idea of the way to hunt for college research paper topics, you are prepared for some suggestions. Much like any research paper essay, the most essential thing is to construct your topic and paper with the robust evidence. The very first step in writing a research paper will need to be choosing your topic. A research paper that concerns scientific issues isn't only a free-style essay where you are able to tell readers whatever you desire. Attempting to compose a research paper on a topic that doesn't have a lot of research on it's incredibly hard, so before you choose a topic, do a little bit of preliminary searching and make certain you are going to have all the info you must compose your paper. Our objective is to be the research paper assistance, the initial one which you will recall in case of writing emergency. To be able to compose a paper, you are needed to compose a research question. If you still feel you need help, even if you've managed to decide on a topic, you may always seek the services of a custom writing service to assist you produce a fabulous research paper of which you'll be proud and will guarantee you a nice mark. What Does Applied Reliability Research Papers to Nanotechnology Mean? There are various sets of rules that are applied based on the specifics of the area of study. The research ideas will help determine the general presentation of the project dependent on the data you will find. Next step would need to be data gathering. Nanotechnology has started to play a major role in the energy industry through solar cells and fuels. Microelectronics Reliability is devoted to disseminating the most rece nt research results and relevant information regarding the reliability of microelectronic devices, circuits and systems. Tracking the cells need many images. Nanotechnology materials may be used to elongate the life span of ploughs in addition to fuel efficiency at farmlands, he argues and the users of the materials don't actually have to be aware of the science. Hearsay, Deception and Applied Reliability Research Papers to Nanotechnology Creating a careful decision helps to ensure that the research procedure is not merely informative but also rewarding. The research procedure takes a string of steps as listed below. The process of selecting fantastic research paper topics is a big commitment. Research and talk about the benefits of Catalonia receiving independence. Without a suitable content, excellent research paper topics are not going to make sense. After you have that narrowed down, you can concentrate your research and compose a remarkable paper. So, first of all, a college research paper has to be informative. Significantly, an analysis research paper supplies you with an insight on how best to do a specific experiment. The success of a research paper mostly is dependent upon the topic, which is why a number of time is spent searching for the best research paper topics for college students. A research topic ought to be interesting to the audience along with the writer. When you're worried about writing research paper, it can cause you to be stressed and not to have the ability to perform in the simplest way throughout different regions of your life. A research paper is a rather significant type of academic writing. What follows is an extensive collection of the most intriguing research topics to have you started. As a result of its practical focus, applied research information will be discovered in the literature connected with individual disciplines. In a conclusion, it's time to extend a review of the findings, restate thesis, stres s the worth of the research, and share suggestions for future experiments. Strive to add fresh info to the study area by means of your research. The Hidden Gem of Applied Reliability Research Papers to Nanotechnology If people talk about nanotechnology, the very first thing which most people think about is extremely futuristic science. So studying business can be unbelievably interesting, because you may choose literally anything and earn a business research paper of it. Make the reader believe the given paper comprises the beneficial details on the appropriate problem and matters for the growth of science. You may choose to look at how your tips for research may eventually influence your creation of the analysis.

Essay Topics That building on the Parable of the Sower

Essay Topics That building on the Parable of the SowerEssay topics that build on one parable of the sower can become classic essays. This is because the parable helps us to see the relevance of basic themes to our lives. In other words, it helps us put a face to a concept and this makes it more real to us. We begin to think in terms of how these concepts impact our lives and begin to understand why this particular concept is so important to us.Consider that the parable of the sower, while having some religious overtones, is a profound spiritual concept. It is about the importance of sowing one's seed. The parable also tells us how a farmer must be very cautious and careful when he begins to sow his seed. When we listen to the parable of the sower, we begin to recognize the need for wisdom and sensitivity in all our interactions with others.Why then do I recommend essay topics that build on this theme as the first essay topic? First, this particular parable is often the perfect starti ng point for beginning a discussion about issues of compassion. As I said earlier, this parable gives us the opportunity to learn about the value of sowing one's seed in life. We can learn how we can be sensitive to the needs of others and how we can cultivate the ability to be compassionate. We learn from the parable that we should always put our desires above others.The parable of the sower is also a wonderful starting point for turning toward greater topics in life. As we begin to reflect on the values we hold dear, we can begin to ask ourselves if these values are really necessary for our own happiness. Are we really willing to live according to those values or are they just something we have picked up along the way? By reflecting on the parable of the sower, we can begin to explore the issues of living according to our own best interests and values.The parable of the sower is also the perfect starting point for developing a compassionate outlook on life. In addition, it reminds us that we should never forget that our role as teachers is not just limited to teaching others but also to train ourselves to care for others. We are teachers for those who come to us.In order to apply the lesson learned from the parable of the sower, you must apply it. You must be willing to be sensitive to those around you and show compassion to those who need it. You must be sensitive to the needs of others and want to take that opportunity to nurture yourself and create positive change in your own life. You must find your own voice and begin to talk about what you value.While it may be easy to dismiss the parable of the sower as just another story from the Bible, the truth is that the parable is full of relevance to our lives. It teaches us how we should treat others and how we should live. It teaches us that we should be compassionate and that we should value kindness and forgiveness above all else.You may find that the topic of essay topics that build on the parable of the s ower is very appealing. If so, you might want to look into these topics because you will never regret doing so.

Response about Landscape and Narrative by Barry Lopez

As the title illustrates, ‘Landscape and Narrative’ by Barry Lopez illustrates the relationship between the landscape and a narrative.   The author illustrates that a narrative serves its purpose if it manages to illustrate the relationship between the interior and the exterior landscape effectively and in an orderly manner.Advertising We will write a custom critical writing sample on Response about Landscape and Narrative by Barry Lopez specifically for you for only $16.05 $11/page Learn More The exterior landscape represents the earth and the ecosystem while the interior landscape represents the mind, thoughts and everything that happens in a person’s mind.   Therefore,  it is clear that Lopez uses the issue of landscape to illustrate the role of a narrative as well as the points that ought to be considered to come up with an effective narrative. Lopez illustrates that a narrator should have knowledge on the interior and exter ior landscape to come up with an effective narrative. Since the exterior landscape represents the land, a narrator is supposed to have a lot of knowledge on the   Ã‚  same to be in a position to effectively provide the relationship between the two landscapes. However, since it is not possible to have full knowledge on the land or the exterior landscape, observing the relationship between different elements can be very helpful. Most importantly, the author illustrates that full knowledge can only be realized if all the elements are studied together not separately. For instance, in an organization, there are different departments and the importance of each department can only be understood if someone studies how the whole system works. By so doing, the narrator is able to represent the exterior environment in such a way that the reader can identify with it and believe the narrator. Apart from that, the way it is presented is also a consideration as well as the phrases used since it is important to ensure that all readers at all levels can be in a position to grasp the main idea and understand the content. In that case, Lopez has succeeded in illustrating how a story can be informative since it is a main prerequisite of an effective narrative. The role of a narrative is also a major idea that is brought out throughout the whole story.   Lopez   illustrates   that a well organized story that  unites the two landscapes is able to result to a state   of well being   since it is stated that â€Å" The  Ã‚   listener who takes the   story to heart will feel pervasive sense of congruence within   himself and   also in the world â€Å"(Lopez pp. 44). Therefore, according to Lopez, a well written story has got the power of healing and even  nurturing the spirit  of human beings after uniting the interior and the exterior landscape. Moreover, it provides individuals with knowledge concerning various elements in the land through studying their r elationship as illustrated by the narrator.Advertising Looking for critical writing on american literature? Let's see if we can help you! Get your first paper with 15% OFF Learn More Lopez uses the example of a narrative to illustrate the constituents of an effective narrative as well as the eventual roles played by the same. Use of the wolverine stories is very effective since by so doing, the reader grasps the intent of the author without major difficulties. Moreover, the  story also illustrates the power of presenting information of the exterior environment in an orderly manner and in a way that the reader can identify with the elements of the land. As a result, the author is able to believe the narrator and to take the information as truth. As an example, Lopez explains that after sending the information about the wolverine to a friend, she got a positive response though the friend had never seen the creatures. Therefore, although Lopez does not concentrate so mu ch on presentation, she has made a major contribution in illustrating not only the role, but also the constituents of `the story. In conclusion, Lopez states that â€Å"As long as the  storyteller carefully  describes the  order before him, and uses his story telling skill to heighten and emphasize certain relationships, it is even possible for the story to be more successful  than the story teller himself is able to imagine† (Lopez pp. 146). Work Cited Lopez, Barry. Landscape and Narrative . 1970. Web. This critical writing on Response about Landscape and Narrative by Barry Lopez was written and submitted by user K0hen to help you with your own studies. You are free to use it for research and reference purposes in order to write your own paper; however, you must cite it accordingly. You can donate your paper here.

Smart socket Essays

Smart socket Essays Smart socket Essay Smart socket Essay Although ad-hoc solutions exist for some of these problems, it is usually up to the applications user to discover the cause of the connectivity problems and find a solution. In this paper we describe Smokestacks, a communication library that lifts this burden by automatically discovering the connectivity problems and solving them with as little support from the user as possible. Categories and Subject Descriptors: C. 2. 4 [Distributed Systems]: Distributed applications General Terms: Algorithms, Design, Reliability Keywords: Connectivity Problems, Grids, Networking, Parallel Applications 1 . Parallel applications are increasingly run in Grid environments. Unfortunately, on many Grid sites the ability of machines to create or accept network connections is severely limited by network address translation (NAT) [14, 26] or firewalls [15]. There are even sites that completely disallow any direct communication between the compute nodes and the rest of the world (e. G. , the French Grinding system [3]). In addition, multi homing (machines with multiple network addresses) can further complicate connection setup. For parallel applications that require direct communication between their components, these limitations have hampered the transition from traditional multi receptors or cluster systems to Grids. When a combination of Grid sites is used, serious connectivity problems are often encountered. Smokestacks is part of the Ibis project, and can be found at CSS. Vi. Ml/ibis Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or the full citation on the first page. Many problems, however, can only be solved by adapting the application or the communication library it uses. To make matters worse, as soon as the set of Grid systems being used changes, large part of this process needs to be repeated. As a result, running a parallel application on multiple Grid sites can be a strenuous task [34]. In this paper we will describe a solution to this problem: the Smokestacks communication library. The primary focus of Smokestacks is on ease of use. It automatically discovers a wide range of connectivity problems and attempts to solve them with little or no support from the user. Smokestacks combines many known solutions, such as port forwarding, TCP splicing and SSH tunneling, and introduces several new ones that resolve problems with multi homing and machine identification. In 30 connection setup experiments, using 6 different sites worldwide, Smokestacks was always able to establish a connection, while conventional sockets only worked in 6 experiments. Using heuristics and caching, Smokestacks is able to significantly improve the connection setup performance. Smokestacks offers a single integrated solution that hides the complexity of connection setup in Grids behind a simple interface that closely resembles sockets. We will show that it is relatively straightforward to port an existing application to Smokestacks, provided that certain programming guidelines are followed. Smokestacks is not specifically intended for use in parallel applications or Grids. It can also be applied to other distributed applications, such as visualization, cooperative environments, or even consumer applications such as instant messaging, file sharing, or online gaming. However, many of these applications only require a very limited degree of connectivity. Often, clients simply connect to a server in a well-known location, making it relatively easy to apply an ad-hoc solution when a connectivity problem occurs. Parallel applications, however, can be much more challenging. They often require a large number of connections between the participating machines, and each machine must such applications in a Grid environment with limited connectivity is difficult. Therefore, this paper will focus on this domain. N Section 2 we describe the connectivity related problems encountered while running applications on multiple Grid sites. Section 3 describes how these problems are solved in Smokestacks and briefly looks at the programming interface. Section 4 evaluates the performance of Smokestacks, Section 5 describes related work, and Section 6 concludes. 2. CONNECTIVITY PROBLEMS In this section we will give a description of the network related problems that can occur when running a single parallel or distributed application on multiple Grid sites. . 1 Firewalls As described in [1 5], A firewall is an agent which screens network traffic in some way, blocking traffic it believes to be inappropriate, dangerous, or both. . Many sites use firewalls to protect their network from unauthorized access. Firewalls usually allow outbound connections, but block incoming connections, often with the exception of a few welkin ports (e. G. , port 22 for SSH). It is obvious that this inactivity restriction can cause severe problems when running a parallel application on multiple sites. When only a single participating site uses firewall, the connectivity problems can sometimes be solved by ensuring that the connections setups are in the right direction, I. E. , that all required connections between open and firewall machines are initiated at the firewall site. This solution may require changes to the applications or communication libraries, however. Also, if both sites use a firewall, this approach can no longer be used. In this case, a firewall will always be encountered regardless of he connection setup direction. One way to solve the problems is to request an open port range in the firewall. Connectivity can then be restored by adapting the application to only use ports in this range. Besides requiring reconfiguration of the firewall, open ports are also seen as a threat to site security. When both machines are behind a firewall it may still be possible to establish a direct connection using a mechanism called TCP splicing [6, 10, 13, 20]. Simply put, this mechanism works by simultaneously performing a connection setup from both sides. Since this approach requires explicit cooperation teens the machines, some alternative communication channel must be available. . 2 Network Address Translation As described in [21], Network Address Translation is a method by which IP addresses are mapped from one address realm to another, providing transparent routing to end hosts. . NAT was introduced in [12] as a temporary solution to the problem of IPPP address depletion. Although the intended solution for this problem, IPPP, has been available for some time, NAT is still widely used to day. Frequently used [21, 29]. This type of NAT allows outbound connections from sites using riveter addresses, but does not allow incoming connections. Both the IP address (and related fields) and the transport identifier (e. G. , TCP and JODI port numbers) of packets are translated, thereby preventing port number collisions when a set of hosts share a single external address. As mentioned above, NAT only allows outbound network connections. Incoming connections are rejected, since the connection request does not contain enough information to find the destination machine (I. E. , only the external IP address is provided, but that may be shared by many machines). This restriction leads to connectivity problems hat are very similar to those caused by firewalls. Therefore, the solution described in Section 2. 1 (connecting in the right direction) also applies too NAT setup, and fails in a similar way when multiple NAT sites try to interconnect. Although the TCP splicing mechanism can also be used to connect two NAT sites, a more complex algorithm is required to compensate for the port translation performed by NAT [6, 20]. Some NAT implementations have support for port forwarding, where all incoming connections on a certain port can be automatically forwarded to a certain host inside the NAT site. Using mechanisms such as Upon [5], DIF [28], or MEDICO [30], applications can contact the NAT implementation and change the port forwarding rules on demand. Port forwarding lifts many of the restrictions on incoming connections. Unfortunately, Upon is mostly found in consumer devices, MEDICO is still under development, and DIF only supports NAT (and firewall) implementations based on Interfile [1]. As a result, these mechanisms are not (yet) generally usable in Grid applications. Currently, Smokestacks only supports Upon. In addition to causing connection setup problems, NAT also complicates machine identification. Machines in a NAT tit generally use IP addresses in the private range [26]. These addresses are only usable within a local network and are not globally unique. Unfortunately, parallel applications often use a machines IP address to create a unique identifier for that machine. When multiple NAT sites participate in a single parallel run, however, this approach can not be used, since the machine addresses are no longer guaranteed to be unique. 2. 3 Non-routed networks On some sites no direct communication between the compute nodes and the outside world is possible due to a strict separation between the internal and external networks. No aching is accessible, and the connectivity of this machine may be limited by a firewall or NAT. Two of the sites used in Section 4 use such a setup. It is clear that this is a major limitation when the site is used in a parallel application. The only possibility for the compute nodes to communicate with other sites is to use front-end machine as a bridge to the outside world, using, for example, an SSH tunnel or a SOCKS [24] proxy. These are non-trivial to set up, however. 2. 4 Multi Homing When multi-homed machines (I. E. , machines with multiple network addresses) participate in a parallel application, another interesting problem occurs. When creating a connection to such a machine, a choice must be made on which of the possible target addresses to use. The outcome of this choice may depend on the location of the machine that initiates the connection. For example, the front-end machine of a site has two addresses, a public one, reachable over the internet, and a private one used to communicate with the sites compute nodes. As a result, a different address must be used to reach teachings depending on whether the connection originates inside or outside of the site. In [34] we called this the Reverse Routing Problem. Normally, when a multi-homed machine is trying to connect to a single IP address, a routing table on the machine decides which network is used for the outgoing connection. In the example described above the reverse problem is encountered. Instead of having to decide how to exit a multi-homed machine, we must decide on how to enter it. This problem is non-trivial, since the source machine generally does not have enough information available to select the correct target address. As a result, several connection attempts to different addresses of the target may be necessary before a connection can be established. In Section 3. 2 we will describe heuristics that can be used to speed up this process. Multi homing can have a major effect on the implementation of parallel programming libraries. The example above shows that it is not sufficient to use a single address to represent a multi-homed machine. Instead, all addresses must be made available to the other participants of the parallel application. In addition, some of the addresses may be in a private range and refer to a different machine when used in a different site. Therefore, it is also essential to check if a connection was established to the correct machine. 3. SMOKESTACKS In this section we will give an overview of the design, implementation and programming interface of the Smokestacks library, and describe how it solves the problems described in the previous section. 3. 1 Overview Currently, Smokestacks offers four different connection setup mechanisms, Direct, Reverse, Splicing, and Routed. An overview of how these mechanisms solve the connectivity problems described in Section 2. As the table shows, each problem is solved by at least one mechanism. Table 1 : Overview of connectivity problems and their solutions. Connection Setup Mechanism Problems Direct Reverse Splicing Routed Identification X Multi Homing X Single FEW/NAT pox xx Dual MINOT (X) XX No Routing X The machine identification and multi-homing problems are solved by the direct connection setup. As will be explained below, this approach also has limited firewall traversal capabilities (using SSH tunneling), so in certain situations it may succeed in establishing a connection in a single or even a dual firewall setting. In the table these entries are shown between brackets. A reverse connection setup is only capable of creating a connection when a single firewall or NAT limits the connectivity. Splicing is capable of middling both single and dual firewall/NAT configurations. However, this approach is significantly more complex than a reverse connection setup (especially with dual NAT) and may not always succeed. Therefore, reverse connection setup is preferred for single firewall/NAT configurations. A routed connection setup can be used in any situation where the connectivity is limited. Unlike the previous two approaches it does not result in a direct connection. Instead all network traffic is routed via external processes called hubs (explained in Section 3. 3), which may degrade both latency and throughput of the connection. Therefore, the previous mechanisms are preferred. When connecting to or from a machine on a non-routed network, however, a routed connection is the only choice. The Smokestacks implementation is divided into two layers, a low-level Direct Connection Layer, responsible for all actions that can be initiated on a single machine, and a high-level Virtual Connection Layer that uses side-channel communication to implement actions that require cooperation of multiple machines. The direct connection layer is implemented using the standard socket library. The virtual connection layer is implemented using the direct connection layer. Both layers will be explained in more detail below. Currently, Smokestacks is implemented using Java [2]. 3. 2 Direct Connection Layer do not require explicit cooperation between machines, such as determining the local addresses or creating a direct connection. It also supports a limited form of SSH tunneling. 3. 2. 1 Machine Identification During initialization, the direct connection layer starts by scanning all available network interfaces to determine which IP addresses are available to the machine. It then generates a unique machine identifier that contains these addresses, and that can be used to contact the machine. This identifier will automatically be unique if it contains at least one public address. If all addresses are private, however, additional work must be done. A machine that only has private addresses is either in a NAT site or uses a non-routed network. In the first case, a unique identifier can still be generated for the machine by acquiring the external address of the NAT. Provided that this address is public, the combination of external and machine addresses should also be unique, since other machines in the same NAT site should have a different set of private addresses, and all other NAT sites should have different external address. The Smokestacks library will use Upon to discover the external address of the NAT site. If this discovery fails, or if the returned address is not public, a Universally Unique Identifier (JUDI) [23], will be generated and included in the machine identifier, thereby making it unique. 3. 2. 2 Connection Setup Once initialized, the direct connection layer can be used to set up connections to other machines. The identifier of the target machine may contain multiple network addresses, some of which may not be reachable from the current location. The private dresses in the identifier may even refer to a completely different machine, so it is important that the identity of the machine is checked during connection setup. As a result, several connection attempts may be necessary before the correct connection can be established. When multiple target addresses are available, a choice must be made in which order the connection attempts will be performed. Although simply using the addresses in an arbitrary order should always result in a connection (pro-vided that a direct connection is possible), this may not be the most efficient approach. Many Grid sites offer historiographer networks such as Merriment [7] or Infinite [4] in addition to a regular Ethernet network. Using such a network for inter-site communication may significantly improve the applications performance. In general, these fast networks are not routed and use addresses in the private range, while the regular Ethernet networks (often) use public addresses. Therefore, by sorting the target addresses and trying all private ones first, the fast local networks will automatically be selected in sites with such a setup. The drawback of if the connection originates on a different site. This may cause a significant overhead. Therefore, Smokestacks uses a heuristic that sorts the target addresses in relation to the addresses that are available locally. For example, if only a public address is available on the local machine, it is unlikely that it will be able to create a direct connection to a private address of a target. As a result, the connection order public before private is used. This order is also used if both machines have public and private addresses, but the private addresses refer to a different network (e. G. , 10. 0. 0. 10 vs 192. 168. 1. 20). The order private before public is only used if both machines have private addresses in the same range. Section 4 will illustrate the performance benefits of this heuristic. Unfortunately, it is impossible to make a distinction between addresses of the same class. For example, if a target has multiple private addresses, we can not automatically determine which address is best. Therefore, if a certain network is preferred, the user must specify this explicitly. Without this explicit configuration, Smokestacks will still create a direct connection (if possible), and the parallel application will run, but its performance may be suboptimal. When a connection has been established, an identity check s performed to ensure that the correct machine has been reached. This would be a simple comparison if the complete identifier of the target is available, but unfortunately this is not always the case. User provided addresses are often used to bootstrap a parallel application. These addresses are often limited to a single hosannas or IP address, which may only be part of the addresses available to the target machine. Therefore, the identity check used by Smokestacks also allows the use of partial identifiers. Whenever a connection is created, the target machine provides its complete identity o the machine initiating the connection. This machine then checks if both the public and private addresses in the partial identity are a subset of the ones in the complete identity. If so, the partial identity is accepted as a subset of the complete identity, and the connection is established. Note that although the connection is created to a machine that matches the address specified by the user, it is not necessarily the correct machine from the viewpoint of the parallel application. Unfortunately, in such cases it is up to the user to provide an address that contains enough information to reach the correct machine. . 2. 3 Open Port Ranges and Port Forwarding When a firewall has an open port range available, Smokestacks can ensure that all sockets used for incoming connections are bound to a port in this range. There is no way of discovering this range automatically, however, so it must be specified explicitly by the user. In addition, Smokestacks can use the Upon protocol to configure a NAT to do port forwarding, I. E. Automatically forward all incoming connections on a certain external port to a specified internal address. However, as explained before, this protocol is mainly used in consumer devices. In addition to regular network connections, the direct connection layer also has limited support for SSH tunneling. This feature is useful for connecting to machines behind a firewall that allows SSH connections to pass through. It does, however, require a suitabl e SSH setup (I. E. , public key authentication must be enabled). Creating an SSH tunnel is similar to a regular connection setup. The target addresses are sorted and tried consecutively. Instead of using the port specified in the connection setup, however, the default SSH port (I. E. , 22) is used. When a connection is established and the authentication is successful, the receiving SSH daemon is instructed to forward all traffic to the original destination port on the same machine. If this succeeds, the regular identity check will be performed to ensure that the right machine has been reached. Although this approach is useful, it can only be used to set up a tunnel to a different process on the target machine. Using this approach to forward traffic to different machines requires extra information. For example, setting up an SSH tunnel to a compute node of a site through the sites fronted, can only be done if it is clear that the fronted must be contacted in order to reach the target machine. Although this approach is used in some projects [8], the necessary information cannot be obtained automatically and must be provided by the user. Therefore, Smokestacks uses a different approach which will be described in detail in Section 3. 3. 3. 2. Limitations The direct connection layer offers several types of connection setup which have in common that they can be initiated by a single machine. No explicit cooperation between machines is necessary to establish the connection. There are many cases, however, where connectivity is too limited and the direct connection layer cannot be used. In general, direct connections to sites that use NAT or a firewall are not possible. Although SSH tunneling and o pen port ranges alleviate the firewall problems, they require a suitable SSH setup or extra information from the user. Port forwarding reduces the problems with NAT, but is rarely supported in Grid systems. Therefore, these features are of limited use. In the next section we will give a detailed description of the virtual connection layer, which solves these problems. 3. 3 Virtual Connection Layer Like the direct connection layer, the virtual connection layer implements several types of connection setup. It offers a simple, socket-like API and has a modular design, making it easy to extend. Besides a direct module that uses the direct connection layer described above, it contains several modules that offer more advanced types of connection setup. These modules have in common that they cooperation (and thus communication) between the source and target machines in order to establish a connection. As a result, side-channel communication is required to implement these modules. 3. 3. 1 Side-Channel Communication In Smokestacks, side-channel communication is implemented by creating a network f interconnected processes called hubs. These hubs are typically started on the fronted machines of each participating site, so their number is usually small. When a hub is started, the location of one or more other hubs must be provided. Each hub will attempt to setup a connection to the others using the direct connection layer. Although many of these connections may fail to be established, this is not a problem as long as a spanning tree is created that connects all hubs. The hubs use a gossiping protocol to exchange information about themselves and the hubs they know, with the hubs that they are connected to. This way information about each hub quickly spreads to all hubs in the network. Whenever a hub receives information about a hub it has not seen before, it will attempt to set up a connection to this hub. This way, new connections will be discovered automatically. All gossiped information contains a state number indicating the state of the originating machine when the information was sent. Since information from a hub may reach another hub through multiple paths, the state number allows the receiver to decide which information is most recent. By recording the length of the path traversed thus far in he gossiped information, hubs can determine the distance to the sites that they can not reach directly. Whenever a hub receives a piece of information about another hub containing a shorter distance than it has seen so far, it will remember both the distance and the hub from which the information was obtained. This way, we automatically create a distributed routing table with the shortest paths between each pair of hubs. This table is later used to forward application information (as will be described below). When an application is started, the virtual layer on each machine creates a single connection to the hub local to its tit. The location of this hub can either be explicitly species- fled or discovered automatically using JODI multicast. 3. 3. 2 Virtual Addresses The connection to the hub can now be used as a side channel to forward requests to otherwise unreachable machines. To ensure that the target machines can be found, addresses are used, consisting of the machine identifier (see Section 3. 2), a port number, and the identifier of the hub the machine is connected to. All requests for the target machine can then be sent to the local hub, which forwards it in the direction of the target