This piece of coursework focuses on implementing and simulating a distributed prototype of Distance-vector Routing protocol with the Bellman-Ford algorithm in PeerSim.

Running PeerSim (in ./lib) is done using Java with the following configuration.

• Main class: peersim.Simulator (imports from ./lib)
• Program arguments: ./config/dv-random.txt (or another config)
• Working directory: ./

PeerSim is a tool to simulate Peer-to-Peer (P2P) networks. Due to it being incredibly scalable, it can be used to simulate networks of a very large scale (e.g. millions of nodes) [1]. It is also useful in this assignment as it allows to simulate a network using a cycle-driven approach. As a result, the protocol can have multiple stages – in this case, initialisation, broadcast and computation.

The Bellman-Ford algorithm is an algorithm that calculates the shortest paths from any single source vertex to all other vertices in a weighted digraph [2]. Compared to Dijkstra’s algorithm, the Bellman-Ford algorithm tends to be slower for the same problem. However, it is more versatile in the sense that edge weights (i.e. costs) can be negative numbers.

The Link-state protocol class from a previous lab was reused as a base for the new protocol. The main difference between the two protocols is refactoring and the compute() method.

The protocol was tested using different topologies supported by PeerSim. The resulting graph and table below are the minimum distances for a random network topology.

ND#  0->|   0,  1,  2,  3,  4, |
    cost|   0,  5,  4,  1,  3, |
     via|   0,  0,  3,  0,  3, |
--------------------------------
ND#  1->|   0,  1,  2,  3,  4, |
    cost|   5,  0,  7,  4,  2, |
     via|   1,  1,  3,  4,  1, |
--------------------------------
ND#  2->|   0,  1,  2,  3,  4, |
    cost|   4,  7,  0,  3,  5, |
     via|   3,  4,  2,  2,  3, |
--------------------------------
ND#  3->|   0,  1,  2,  3,  4, |
    cost|   1,  4,  3,  0,  2, |
     via|   3,  4,  3,  3,  3, |
--------------------------------
ND#  4->|   0,  1,  2,  3,  4, |
    cost|   3,  2,  5,  2,  0, |
     via|   3,  4,  3,  4,  4, |
--------------------------------

Further testing was done with larger networks as well as other topologies, such as tree and star. The resulting paths were identical to the previous protocol with Djikstra's algorithm.

Based on feedback, the protocol's broadcast() method should be modified to share calculated distances as opposed to neighbouring links.