In distributed computing, a peer is both a client and a server at the same time, being able to request services from other peers or providing services to other peers. For the general knowledge about peer, you can read the following academic article.
Rodrigues, R., Druschel, P., 2010. Peer-to-Peer Systems, Communications of the ACM. 53(10), 72-82. (available at http://zoo.cs.yale.edu/classes/cs426/2012/bib/rodrigues10peer-to-peer.pdf on 23rd Dec 2017).
In this assignment, you are to develop programming skills of peer via a particular Peer-to-Peer (P2P) application - content distribution and distributed query. The application allows peers to form an overlay and share information from the entire peer overlay. In this assignment, you will need to upgrade a client and a server into a peer. The peers are to form an overlay by IP multicast and the information stored in a peer can be shared by any other peers. When a peer queries a question, it will multicast a request including the question to the peer overlay and the peer that has the answer to the question to respond to the requester peer. To query a question, a UDP datagram via IP multicast is used. Once the answer is found, replying the answer is to use another separate UDP communication between the requester and the replier. To complete this assignment, you need to complete the following 2 parts.
In this part, you are to develop the simplified system of content distribution and distributed query. The assumptions on the system are specified as follows.
1. Each peer has a unique ID.
2. Peers form a networking overlay by IP multicast (reference to Chapter 4.4 of the textbook, Week 5 lecture slides, Week 6 lab projects, and search for other academic articles about IP multicast if necessary).
3. Each peer has a number of answers to some questions that can be shared by other peers.
4. Once a peer has a question, it needs to compose a request, including the question and communication information such as the reply IP address and port number.
5. Each peer can multicast a query request to all other peers in the overlay. After that, the peer is waiting on the port for answers.
6. To simplify the problem, we assume that the answer to a queried question can always be found from at least one peer.
7. Once the answer to the question is found, the replier peer (the one who has the answer) will use a UDP datagram to send the answer to the requester peer (the one who asks the question).
8. A peer needs to ignore the requests from itself because by default IP multicast sends a message to every peer on the overlay.
The following screenshots show an implementation of the system of content distribution and distributed query.
1. The 3 peers (with ID of PPP1, PPP2 and PPP3) join the same IP multicast group. Note: 228.5.6.7 and 8888 are the IP multicast address and port number that were used in this example.
PPP1 joins (using port 7896 as the UDP port to receive answers): see image.
In the above example, clicking the Set button will bring PPP1 into full function by joining the multicast group and initialising the service threads for querying questions and receiving answers.
PPP2 and PPP3 start and join the peer overlay in the same way as shown by the following screenshots.
Figure: see image.
Figure: see image.
2. The following screenshots show the single-answer examples:
PPP1 queries Question 2, only PPP2 has the answer and replies. Note: entering a question on PPP1's Question text field and clicking the Query button will multicast the question to the peer overlay and query to all the peers.
PPP2 queries Question 3, only PPP3 has the answer and replies.
PPP3 queries Question 1, only PPP1 has the answer and replies.
Figure: see image.
Figure: see image.
3. The following screenshots show the multiple-answers examples. Note the multiple-answer function is required by this assignment.
PPP1 queries Question 5, PPP2 and PPP3 have answers and reply. see image.
PPP2 queries Question 6, PPP1 and PPP3 have answers and reply. see image.
PPP3 queries Question 4, PPP1 and PPP2 have answers and reply. see image.
The aforementioned examples have shown the equity between peers, that is, every peer is both a client and a server to share contents by distributed processing. Your implementation must satisfy all the aforementioned requirements in order to get the full mark.
On completion of the implementation of the framework, prepare a document to include:
1. An end user' instruction about how to compile, run and test your system.
2. The key issues about upgrading a client and a server to a peer and overlay forming.