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In layers 3 and 4, we begin to see how data is routed between different networks and how transportation protocols function within these layers!

Layer 3 – Network

The Network layer describes how data packets are routed between wider networks such as the Internet. Whereas a data frame at the data link layer travels to local MAC addresses, a data packet at the network layer is routed from a source IP (Internet Protocol) address to a destination IP address.

Think of a data packet as an envelope. IP addresses are assigned to every computer or device connected to the Internet, and these addresses are formatted into four numbers each ranging from 0 to 255. Example:

192.168.0.1

At this layer, there are routing protocols designed to help packets (aka, our envelopes) get from point A to point B as quickly as possible over the Internet. Your nearest router is one of the many routers connected to the Internet that help packets find where they need to go!

Layer 4 – Transport

The Transport layer refers to how data is actually transferred. Let’s say you wanted to upload a photo from your phone onto social media. The transport layer handles how the image data from that photo is split (segmentation), the rate at which the packets are sent, and how errors are handled if data packets don’t make it to the site’s server.

The most common transport protocols on the Internet are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). We’ll go into these two protocols later in this lesson!

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