Distributed Computing -- Assignment 1

<body> <table> <tr> <td>  <p class="c1"><a href="http://www.gu.edu.au/" target="_top"><img src="images/gu.gif" width="89" height="74" alt="Griffith University" border="0" /></a></p> <p class="c1"><a href="http://www.gu.edu.au/school/cit/" target="_top">ICT Home</a></p> <hr /> <p class="c1"><a href="http://www.cit.gu.edu.au/teaching/3510CIT/index.shtml" target="_top">DC Home</a></p> <p class="c1"><a href="http://www.cit.gu.edu.au/teaching/3510CIT/news.shtml" target="_top">Notice Board</a></p> <p class="c1"><a href="http://www.cit.gu.edu.au/teaching/3510CIT/resources.shtml" target="_top">Resources</a><br /> <a href="http://www.cit.gu.edu.au/teaching/3510CIT/modules.shtml" target="_top">Modules</a></p>  <p class="c1"><a href="http://www.cit.gu.edu.au/teaching/3510CIT/virgil.shtml" target="_top">Virgil Main</a></p> <p class="c1"><a href="http://www.cit.gu.edu.au/teaching/3510CIT/forum.shtml" target="_top">Virgil Forum</a></p> <hr />  </td> <td> <h1>Assignment 1 for Semester 2, 2006 (Draft)</h1> <p>The aim of this assignment is to gain some experience in designing and implementing distributed computing applications on the Internet using the peer-to-peer computing and communication model and protocols. The programming language will be Java. Communication protocols in the distributed application will be based on sockets.</p> <p>Implementation of the protocol in a different programming language may be possible. If you prefer using a different language, please contact the course convenor first!</p> <h2>Virtual Photo Album</h2> <p>Your task in this assignment is to design, implement, test, and discuss a peer-to-peer distributed photo album. </p> <p> The system uses a protocol for distributed membership on the Internet. Although the actual downloading and viewing of a photo follows a client/server paradigm, the distinction of the system is its peer-to-peer decentralised computing and communication model. In this model, every client is a server, and vice versa. These so-called <em>servents</em> perform tasks normally associated with both clients and servers. They provide client-side interfaces through which users can issue queries and view search results, while at the same time they also accept queries from other servents, check for matches against their local data set, and respond with applicable results. Due to its special communication protocol, a network of servents is highly fault-tolerant, as operation of the network will not be interrupted if a subset of servents goes offline. </p> <p> Your program should implement the the two parts that make up the system, the <em>membership service</em> and the <em>photo viewing</em> system. In total, the following basic functionality should be implemented in each servent: </p> <ol> <li>A GUI user interface to accept input and display results. In particular, a user should be able to search for, add, delete, and view photos, as well as mangage network connectivity.</li> <li>The protocol to connect a servent to the network. See the protocol specification below for details.</li> <li>Four protocol messages <em>Ping</em>, <em>Pong</em>, <em>Query</em> and <em>QueryHit</em> and their routing rules (see the protocol specification for details).</li> <li>A simple download protocol to send a photo from one node to another one, where the photo gets displayed.</li> </ol> <p>Your program (a network of at least 4 servents) must be tested on both single and multiple machines. This means that either just one or multiple servents need to run on each machine (think multiple users on a single machine). To allow multiple servents on one machine, you need to be able to specify a <em>local port number</em> to use when the servent starts (either as a command line parameter or through the GUI). </p> <p> To enable a servent to know which hosts are active, you may supply each servent with an initial list of potential hosts (<em>IP addresses</em> and <em>port numbers</em>) to which it attempts to communicate. This list should be configurable at run time (e.g., through the command line or the GUI). </p> <h2>The Membership Service</h2> <p> The membership service is the primary way in which servents communicate over the network. It consists of a set of messages used for communication between servents and a set of rules governing the inter-servent exchange of messages. </p> <h3>Messages</h3> <p>The messages are defined as follows:</p> <h4>Message Header</h4> <p> Every message is prepended by a header, containing common information for all messages. This message header contains at least the following information: </p> <blockquote> <dl> <dt>Descriptor ID</dt> <dd>A value or string that uniquely identifies a message. No two messages sent may ever have the same descriptor ID!</dd> <dt>TTL</dt> <dd>Time To Live. The number of times the descriptor will be forwarded by servents before it is removed from the network. Each servent will decrement the TTL before passing it on to another servent. When the TTL reaches 0, the descriptor will no longer be forwarded.</dd> <dt>Hops</dt> <dd>The number of times the descriptor has been forwarded. As a descriptor is passed from servent to servent, the TTL and Hops fields of the header must satisfy the following condition: <blockquote>TTL(0) = TTL(i) + Hops(i)</blockquote> Where TTL(i) and Hops(i) are the value of the TTL and Hops fields of the header at the descriptor's i-th hop, for i >= 0. </dd> <dt>Payload Descriptor</dt> <dd>The message type. This identifies payload data for one of the following four message types. </dd> </dl> </blockquote> <p> Immediately after the header, a message is followed by one of the following four types of payload data. </p> <h4>Ping</h4> <p> This message is used to actively discover servents and users on the network. A servent receiving a Ping is expected to respond with one or more Pong descriptors. The Ping message does not contain any payload data. </p> <h4>Pong</h4> <p> The response to a Ping. Includes the IP address and port number of a connected servent and information regarding the number of users it is making available to the network. Individual assignments only need to be able to handle one user per servent (but multiple servents, and thus, multiple users per computer). If you are working on your assignment in a pair with another student, each servent needs to support multiple users at the same time (in addition to allowing muliple servents per computer). A Pong message contains at least the following data: </p> <blockquote> <dl> <dt>IP Address</dt> <dd>The IP Address of a servent within the network</dd> <dt>Port</dt> <dd>The port number on which that servent can be reached</dd> <dt>Number of Users</dt> <dd>The number of users on that host (optional for individual assignments)</dd> </dl> </blockquote> <h4>Query</h4> <p> The Query message is the primary mechanism for searching the distributed network for photos. A servent receiving a Query descriptor will respond with a QueryHit if a match is found against its local data set. The Query message only contains one element, a <em>photo name</em> search string. An empty string denotes that all users should be reported, otherwise all users whose name starts with the search string should be returned. </p> <h4>QueryHit</h4> <p> The response to a Query. This descriptor provides the recipient with enough information to download a photo matching the corresponding Query. Zero or more QueryHit messages will be sent in response to every Query. A QueryHit message contains the following data: </p> <blockquote> <dl> <dt>Photo Name</dt> <dd>The name of a photo logged stored on a servent</dd> <dt>IP Address</dt> <dd>The IP Address of a that servent</dd> <dt>Port</dt> <dd>The port on which the photo can be downloaded from the servent</dd> </dl> </blockquote> <h3>Routing</h3> <p> The peer-to-peer nature of the network requires servents to route network traffic (queries, query replies, etc.) appropriately. A well-behaved servent will route protocol descriptors according to the following rules: </p> <ol> <li>Pong descriptors may only be sent along the same path that carried the incoming Ping descriptor. This ensures that only those servents that routed the Ping descriptor will see the Pong descriptor in response. A servent that receives a Pong descriptor with Descriptor ID = n, but has not seen a Ping descriptor with Descriptor ID = n should remove the Pong descriptor from the network. </li> <li>QueryHit descriptors may only be sent along the same path that carried the incoming Query descriptor. This ensures that only those servents that routed the Query descriptor will see the QueryHit descriptor in response. A servent that receives a QueryHit descriptor with Descriptor ID = n, but has not seen a Query descriptor with Descriptor ID = n should remove the QueryHit descriptor from the network. </li> <li>A servent will forward incoming Ping and Query descriptors to all of its directly connected servents, except the one that delivered the incoming Ping or Query. </li> <li>A servent will decrement a descriptor header's TTL field, and increment its Hops field, before it forwards the descriptor to any directly connected servent. If, after decrementing the header's TTL field, the TTL field is found to be zero, the descriptor is not forwarded along any connection. </li> <li>A servent receiving a descriptor with the same Payload Descriptor and Descriptor ID as one it has received before, should discard the message (and not forward it on). </li> </ol> <h2>The Photo Viewing System</h2> <p> Add a simple mechanism of downloading photos from a remote servent. A viewer window should then display the first photo. The viewer window should have two buttons, one to display the next photo in sequence and one button to display the previous photo. Through these buttons, the user should be able to cycle through all the photos matched by a query (i.e. the list of all QueryHit responses to a Query message). A servent only needs to be able to have one photo viewing window open at a time. </p> <h2>Viewing Photos</h2> <p> The procedure, from the user's perspective, for viewing photos is as follows: </p> <ol> <li>A user sends an empty query string to find all the available photos, or searches for a particular (set of) photo(s) by specifying a non-empty query string. </li> <li>In response, the user will get a list of (zero or more) name/servent combinations that match that query. If the query string was empty, all the names and servents of all photos that are currently available online should be returned. </li> <li>When selecting a photo or a set of photos, these should be displayed in the viewer window.</li> </ol> <h2>General Suggestions</h2> <ol> <li>Read this document carefully.</li> <li>Attend all tutes and lab sessions for discussing the techniques related to this assignment.</li> <li>Read through the <a href="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/imageio_guideTOC.fm.html">Java Image-I/O API Guide</a> for an introduction on how to load and display photos (images).</lia> <li>It's not hard to find existing Java implementations of peer to peer programs, and you are welcome to inspect these as a source of ideas. But you can hardly submit one as your solution for a variety of obvious reasons. Remember, plagiarism is serious academic misconduct and will be penalised.</li> </ol> <h2>Assessment</h2> <p>This assignment is worth 30 marks (30% of the total maximum marks for the course).</p> <p>This is an individual assignment, group work is not permitted. </p> <p>Your project will be judged on its correctness, functionality, documentation, and general quality. 80% of the total marks will be allocated for the correctness, functionality, and quality of the implemented program, and 20% of the total marks for the quality of the accompanying documentation and demonstration.</p> <h2>Submission Procedure</h2> <p>You must submit your work (including your program and and documentation) electronically using <a href="Virgil/Virgil.cgi/dc?submit-assignment1">this web page</a>. </p> <p>You should submit your work in time. Penalties for late submissions are 10% per day late!</p> <h3>Due Date</h3> <p> This assignment is due on Friday, 8 September 2006 (End of week 7). </p> <h3>Electronic submission</h3> <p>Your electronic submission should consist of a <a href="cgi-bin/man.cgi?zip"><tt>ZIP</tt></a> file, including a .jar file capable of being executed, a well-presented, compilable listing of your source, and documentation (see below). You need to demonstrate your running program. in the week after the assignment is due (or the week thereafter, if you are submitting late).</p> <p><a href="Virgil/Virgil.cgi/dc?submit-assignment1">Use Virgil to electronically submit</a> your assignment <a href="Virgil/Virgil.cgi/dc?submit-assignment1">by following this link</a>.</p> <h3>Documentation Submission</h3> <p>Your documentation should be in electronic form. It should be included in the above <a href="cgi-bin/man.cgi?zip"><tt>ZIP</tt></a> file and comprise the following:</p> <ol> <li>A cover page, clearly showing the code and name of the course (3510CIT Distributed Computing), your name and student number.</li> <li>A report containing a brief description of your design, the reasons for your main design decisions, a summary of the program's functionality and limitations, a reflective analysis of your approach and achievements, a description of the testing performed, a discussion of how you could extend the program, and instructions for running the program. <li>A listing of Java source files (with sensible comments) which implement the program.</li> </ol> <hr /> <p>Last Changed: $Date: 2006/08/30 22:26:09 $</p> </td> </tr> </table>  <p><a href="http://validator.w3.org/check/referer"><img border="0" src="images/valid-xhtml10.png" alt="Valid XHTML 1.0!" height="31" width="88" /></a></p>  </body>