How to Simulate Layer 3 Routed Protocol Using MATLAB

To simulate the Layer 3 Routed Protocols like RIP, OSPF, and BGP using MATLAB, it function at the network layer of the OSI model and are responsible for discovering the optimal routes for data packets to move among the networks. To replicate the Layer 3 routing protocols using MATLAB that includes making a network topology, executing a routing algorithm, and replicating data forwarding according to the routing tables are sustained by routers. Follow the below procedure on how to approach this simulation using MATLAB.

Steps to Simulate Layer 3 Routed Protocols in MATLAB

1. Define the Network Topology

• Describe a network topology, which encompasses routers and links amongst them. We will allocate the costs such as hop counts or link costs to the links between routers.

Example of defining a network topology:

numRouters = 6;  % Number of routers in the network

networkArea = 100;  % Area size (100×100 meters)

routerPositions = rand(numRouters, 2) * networkArea;  % Random positions for routers

adjacencyMatrix = inf(numRouters);  % Initialize adjacency matrix with infinite costs

% Define connections between routers (hop count or cost of the links)

adjacencyMatrix(1, 2) = 1; adjacencyMatrix(2, 1) = 1;

adjacencyMatrix(1, 3) = 2; adjacencyMatrix(3, 1) = 2;

adjacencyMatrix(2, 4) = 1; adjacencyMatrix(4, 2) = 1;

adjacencyMatrix(3, 4) = 3; adjacencyMatrix(4, 3) = 3;

adjacencyMatrix(3, 5) = 1; adjacencyMatrix(5, 3) = 1;

adjacencyMatrix(4, 6) = 2; adjacencyMatrix(6, 4) = 2;

adjacencyMatrix(5, 6) = 3; adjacencyMatrix(6, 5) = 3;

2. Routing Table Initialization

• A routing table comprising the distance (cost) and the next hop to attain each destination sustained by each router. At first, routers only understand the distance to its direct neighbors.

Example of initializing routing tables:

function routingTable = initializeRoutingTable(numRouters, adjacencyMatrix)

routingTable = inf(numRouters);  % Initialize with infinity (unknown routes)

for i = 1:numRouters

routingTable(i, i) = 0;  % Distance to itself is 0

neighbors = find(adjacencyMatrix(i,:) < inf);

for neighbor = neighbors

routingTable(i, neighbor) = adjacencyMatrix(i, neighbor);  % Distance to neighbors

end

end

end

routingTable = initializeRoutingTable(numRouters, adjacencyMatrix);

3. Implement Distance Vector or Link-State Routing Protocol

• Distance vector protocols like RIP utilize the Bellman-Ford algorithm to bring up-to-date routing tables, even though link-state protocols such as OSPF use the Dijkstra algorithm. Now, we will execute the Bellman-Ford algorithm for a distance vector routing protocol such as RIP.

Example of implementing Bellman-Ford for RIP:

function routingTable = updateRoutingTable(adjacencyMatrix, routingTable)

numRouters = size(routingTable, 1);

% Bellman-Ford update for each router

for src = 1:numRouters

for dest = 1:numRouters

for intermediate = 1:numRouters

if routingTable(src, dest) > routingTable(src, intermediate) + adjacencyMatrix(intermediate, dest)

routingTable(src, dest) = routingTable(src, intermediate) + adjacencyMatrix(intermediate, dest);

end

end

end

end

end

% Example of updating the routing table over multiple iterations

numIterations = 10;  % Number of iterations for the protocol to converge

for iteration = 1:numIterations

routingTable = updateRoutingTable(adjacencyMatrix, routingTable);

disp([‘Routing table after iteration ‘, num2str(iteration)]);

disp(routingTable);

end

4. Simulate Periodic Updates (RIP) or LSA (OSPF)

• In RIP, routing data is periodically swapped among the routers. In OSPF, routers flood link-state advertisements (LSAs) informing others of network changes.

Example of simulating periodic updates (for RIP):

function routingTable = ripPeriodicUpdate(adjacencyMatrix, routingTable)

routingTable = updateRoutingTable(adjacencyMatrix, routingTable);

end

% Simulate periodic updates

numPeriods = 10;  % Number of periodic updates

for period = 1:numPeriods

routingTable = ripPeriodicUpdate(adjacencyMatrix, routingTable);

disp([‘Routing table after period ‘, num2str(period)]);

disp(routingTable);

end

Example of Dijkstra’s algorithm for OSPF:

function [dist, prev] = dijkstra(adjacencyMatrix, src)

numRouters = size(adjacencyMatrix, 1);

dist = inf(1, numRouters);

prev = NaN(1, numRouters);

dist(src) = 0;

Q = 1:numRouters;  % Unvisited nodes

while ~isempty(Q)

[~, u] = min(dist(Q));  % Node with the smallest distance

u = Q(u);

Q(Q == u) = [];  % Remove u from Q

neighbors = find(adjacencyMatrix(u,:) < inf);

for v = neighbors

alt = dist(u) + adjacencyMatrix(u, v);

if alt < dist(v)

dist(v) = alt;

prev(v) = u;

end

end

end

end

% Example: Calculate shortest paths from router 1 using OSPF

srcRouter = 1;

[dist, prev] = dijkstra(adjacencyMatrix, srcRouter);

disp([‘Shortest distances from router ‘, num2str(srcRouter), ‘:’]);

disp(dist);

5. Simulate Data Transmission Based on Routing Table

• Replicate the transmission of data amongst routers by following the optimal path signified by the routing table, after the routing tables have been updated.

Example of simulating data transmission:

function transmitData(routingTable, src, dst)

if routingTable(src, dst) < inf

disp([‘Data transmitted from router ‘, num2str(src), ‘ to router ‘, num2str(dst), ‘ via hop count: ‘, num2str(routingTable(src, dst))]);

else

disp(‘No valid route found.’);

end

end

% Example: Transmit data from router 1 to router 5

srcRouter = 1;

dstRouter = 5;

transmitData(routingTable, srcRouter, dstRouter);

6. Evaluate Layer 3 Routing Protocol Performance

• Calculate the performance of the routing protocol by assessing parameters like convergence time, average hop count, routing overhead, and packet delivery ratio.

Example of calculating the average hop count:

totalHopCount = 0;

pathCount = 0;

for i = 1:numRouters

for j = i+1:numRouters

if routingTable(i, j) < inf

totalHopCount = totalHopCount + routingTable(i, j);

pathCount = pathCount + 1;

end

end

end

avgHopCount = totalHopCount / pathCount;

disp([‘Average hop count: ‘, num2str(avgHopCount)]);

7. Visualize the Network Topology

• Envision the network, routers, and the links among them with the help of MATLAB’s plotting functions.

Example of visualizing the network topology:

figure;

hold on;

plot(routerPositions(:,1), routerPositions(:,2), ‘bo’, ‘MarkerSize’, 10, ‘LineWidth’, 2);  % Plot router positions

for i = 1:numRouters

for j = i+1:numRouters

if adjacencyMatrix(i,j) < inf

plot([routerPositions(i,1), routerPositions(j,1)], …

[routerPositions(i,2), routerPositions(j,2)], ‘k-‘);

end

end

end

title(‘Network Topology with Routers’);

hold off;

Conclusion

To replicate the Layer 3 Routed Protocols within MATLAB:

1. Describe the network topology with routers and link costs (hop counts or weights).
2. Introduce the routing tables in which each router understands the distance to their direct neighbors.
3. Execute a routing algorithm, like Dijkstra’s algorithm for link-state protocols or the Bellman-Ford algorithm for distance vector protocols.
4. Mimic periodic updates in which routers swap routing data to update its routing tables.
5. Replicate data transmission by forwarding packets along the optimal paths based on the routing tables.
6. Estimate the performance by computing parameters such as convergence time, average hop count, and routing overhead.
7. Envision the network topology and routing paths utilizing the MATLAB’s plotting capabilities.

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