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# Network Topologies
### Nodes and links
Nodes (computers) communicate with eachother over links (channels).
In graph theory, nodes are called vertices and links are called edges.
Nodes connected by a Link
### Fully Connected Network
A fully connected network has direct links from every node to every other node. This scales badly in networking as the number of links grows quadratically with the number of nodes.
The formula is `l = n x (n - 1) / 2`
In graph theory, this is called a complete graph.
### Star Network
Introducing a central node (**router / relaying node**) reduces the number of links between nodes.
In a star network, the number of links scales linearly with the number of nodes.
Non-relaying nodes act as communication endpoints.
**A star network is centralized**, with the central node exerting control over communication and being a single point of failure.
This topology **reduces availability** and may be undesirable for political and technical reasons.
Star network with central node (router) in blue
### Mesh Network
Increasing the number of routers (relaying nodes) avoids the drawbacks of centralization.
In a mesh network, communication remains possible even if some routers fail.
A partially connected network **balances redundancy and scalability.**
Mesh networks are typically **preferred for flexibility and reliability**.
Critical systems may connect to multiple routers for **increased availability, despite higher costs**.