The Network and Transport Layers

Above the local-only data link layer sit two layers that make wider communication possible. Layer 3 is the network layer and Layer 4 is the transport layer. The network layer moves data between separate networks using logical addresses, while the transport layer manages the conversation between applications, including reliability. Together they carry data across the internet and deliver it to the right program.

The network layer handles logical addressing and routing, choosing paths so data can travel across multiple networks. Its star is the IP address (Internet Protocol), a logical address that identifies a device anywhere on the internet, unlike a local MAC address. The network layer is where the journey from one network to a distant one is planned and directed.