OSPF - The Dijkstra algorithm explained

At the heart of OSPF is the SPF calculation. See how the Dijkstra algorithm turns the network into a tree, then picks out best routes.

What you'll learn from this video:
The OSPF protocol passes around Router and Network LSAs to build up a so called "Topological Database", from which the magic of the Dijkstra algorithm can calculate IP routes. But, what does the Topological Database actually store? How can an algorithmic manipulation calculate routes from this database?

This animation presents an example of how a network can be represented as a set of "Jigsaw Pieces" that can be re-arranged into a least-cost tree, from which it is then easy to find the least-cost route to any subnet.

[yamabushi]

Good video presenting a simple yet sometimes confusing concept in a suitable concise manner. Many thanks.

[rn]

Why is the cost from the subnets to routers neglected? "..because the purpose of creating the tree ist to find the least-cost path from the root to any given destination" does not make sense to me.
E.g. if the cost from S1 to R1 was 100, the end result would be the same tree, but it would not be an optimum solution.