Layer 1, Layer 2, Layer 3 and Layer 4. Physical, Link Layer/MAC Layer, Network Layer, Transport Layer.
Physical is Physics which is improving allowing more bandwidth limits.
Layer 2 sitting atop physical involves Links/Mediums access control mechanisms between devices. It provides bits data transfer over the physical connectivity and involves payloads/addresses.
Layer 3 involves connecting multiple networks and forming an internetwork which further provides network level end-to-end connectivity.
Layer 4 involves end to end host level connectivity.
Within Layer 2 we have software enabled Virtual LANs, we have loop avoidance via Spanning Tree, we have Link aggregation via LACP etc.
Within Layer 3 we have IGP,EGP,VPN,SP,DC,WAN,TE, QoS and what not.
Within Layer 4 we have TCP,UDP; Connection-oriented/Connection-less; Flow-control, windowing; Reliability, acknowledgements, sequencing; Error control, checksum; Port numbers, etc.
Layer 2 and Layer 4 are relatively ‘localized’. Layer 2 due to its physical/link level vicinity and layer 4 due to its in-host & between-host proximity. While there is science in these layers it is somewhat local.
Layer 3 involves much geography. It is the domain which deals with providing end-to-end connectivity spanning much space and area. With this comes much management. It entails reachability across multiplexed systems via addressing, reliability via multi-pathing, reachability status communication, path preferencing in multipath options, path avoidance, virtual privacy and isolation across multiplexed systems, time management for timely fault tolerance and fault bypass. geolocation based path selection and load balancing. etc. etc.
Hence the birth of large-scale Internetworking Protocols.
Protocols which are engineered to have some have mechanisms built-in & agreed upon while some options require configurations.
Autonomous Networks which have all the mechanisms built-in and require no configurations are not present at the moment, except perhaps somewhere inside Google et al.
For now we have to sift and select between options and configurations for making data flow.