What is a routing algorithm for?

Finding the path of least total cost between two nodes of the network.

Name an algorithm used to find a lowest-cost route.

Dijkstra's shortest path algorithm.

State the first step of Dijkstra's algorithm.

Set the start node's distance to zero and every other node's to infinity, and mark all nodes unvisited.

State the step Dijkstra's algorithm repeats.

Take the unvisited node with the smallest distance, and for each of its neighbours replace that neighbour's distance if going via the current node is shorter.

WJEC A-Level Computer Science 601-5345-3

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Communication Networks and File Organisation

Lowest-cost routing

3 things to know
A2 Unit 4

Overview

Network represented as, for the purposes of routing, algorithm used to find a lowest-cost route and first step of Dijkstra's algorithm.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

What can the weights on a network graph represent, and what are the opening steps of finding a lowest-cost route?

Key term

What is a network represented as, for the purposes of routing?

Key term

What can the weight on an edge represent?

Questions from this subtopic

Each one with the model answer underneath.

1
What is a network represented as, for the purposes of routing?
Model answer
A graph whose nodes are the routers or sites and whose weighted edges are the links between them.
2
What can the weight on an edge represent?
Model answer
Any cost being minimised — distance, monetary cost, delay, or the reciprocal of bandwidth.
3
What is a routing algorithm for?
Model answer
Finding the path of least total cost between two nodes of the network.
4
Name an algorithm used to find a lowest-cost route.
Model answer
Dijkstra's shortest path algorithm.
5
State the first step of Dijkstra's algorithm.
Model answer
Set the start node's distance to zero and every other node's to infinity, and mark all nodes unvisited.
6
State the step Dijkstra's algorithm repeats.
Model answer
Take the unvisited node with the smallest distance, and for each of its neighbours replace that neighbour's distance if going via the current node is shorter.

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