Objective:

The goal of this assignment is to build a Decentralized File Service using Python.

Description:

The Decentralized File Service (DFS) is a peer-to-peer network of nodes, which can be connected to by different clients. Each node in the system is capable of storing file fragments, splitting files into fragments, distributing the fragments among a set of neighbors, and responding to any download request by sending the appropriate file fragments. The DFS has three main stages:

1. Setup
• This is the stage where the system is configured. You have to start with a graph of nodes. Each node may have 0 or more neighbors. The graph doesn't necessarily need to be completely connected. In other words, the service should work whether the peers are fully connected or not.
2. Uploading
• When a client wants to upload a file into the system. It sends an Upload  request with the given file to any node. If the node has n neighbors, it splits the file into n+1 fragments. The target node stores one fragment and sends the remaining fragments to neighbor nodes.
• The messages used here are:
• Upload Request: a message sent from the client to a node to upload a given file.
• Put Request: a message sent from the targeted node to one of its neighbors to store a fragment that belongs to a given file.
3. Downloading
• A client wanting to download a specific file, sends a Download request with the name of the file and a Number-of-Hops (NOH) value. If the target node does not have the complete file, so it propagates the Download request across the network. As the request is propagated from one node to the other, its NOH is decremented by one at each hop. A request that has a NOH value of 0 cannot be propagated any further. Replies with fragments should be sent directly to the client.
• Upon reception of all the fragments, the client should reconstitute the file and save it.
• The messages used here are:
• Download Request: a message sent from the client to a node to download a given file. This is the same message that is propagated across the network to get the missing file fragments.
• Download Reply: a message sent from the nodes with fragments to the client.

Your DFS system should handle at least the following errors:

• Partial file received
• Redundant file fragments received
• Non existing file
• Time-outs

Extensions:

 Completion of one of these extensions will result in a better grade; however, groups of more than one person MUST complete one extension to receive a full grade. It should also be noted that, if you have an idea for a different extension, ask the instructor for approval.

 Enhance the DFS system to support the one of the following functionalities:

 
1. Dynamic load balancing
2. Replication of fragments
3. Evaluate the impact of a few peer topologies in file accesibility and retrieval times

Grading will be split in the following way:

• 60% correctness (Does it do what it's supposed to?)
• 20% error handling (Can it easily be crashed?)
• 20% documentation (Is it easy to read and understand the code?)

The due date for this project is March 5th, 2006, 11:55pm EST. You should use the assignments drop-off box located at the course's WebCT page. Upload a ZIP file containing all the relevant documented Python files, along with a README file describing the project and its usage.

Late submissions:

• 10% penalty for a one-day late submission.
• 25% penalty for up to a three-day late submission.
• Submissions more than 3 days late will not be accepted.