From the course: Learning the Packet Delivery Process

Understand the data packet and TTL

From the course: Learning the Packet Delivery Process

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Understand the data packet and TTL

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- [Instructor] When a person, workstation, printer, server, or any other device needs to send data, that data must be divided up into pieces the computer and the network can understand. These pieces are called packets, or datagrams. You might also see them referred to as segments, data blocks, cells, or even frames. Whatever you call them, data packets are the generic units of data sent across a network during data transfers. There are a number of steps involved in creating packets, and the structure varies with the applications, and related protocols used. However, every packet has a header and a payload. A header can contain the source and destination addresses, the payload length and more. And the payload section contains the actual data. Each packet contains only a small piece of the data being sent, because each packet is only a few kilobytes each. Therefore, there could be hundreds of thousands of packets in a single data stream. Another reason for the size of the packet is to make it easier to retransmit data when a packet gets lost. With packets, the entire stream of data won't need to be resent, only the packets that are missing. Notice the Time to Live section in the header here. When data travels from its source to its destination over the internet, it hops from one router to another to get there. The TTL notation tells the packet how many routers it can pass through before it's considered lost, and needs to be resent. To understand this better, let's look at a packet delivery scenario in real terms. Here, a user sends data, in this case, over the internet. The data arrives at the local router. That's one hop. The router forwards the packet to a nearby router that it thinks knows the way to the packet's destination. This process repeats until the packet is delivered. That's a best case scenario. However, sometimes the packet runs out of permissible hops, and must be resent. It's important to note that the packets in a packet stream of data, don't all travel the same route to get to their destination, some packets might take 20 hops, while others only need 12. When they all do arrive though, the packets are pieced back together, and the data is delivered to the user. Let's explore the concept of hops in real life. Open a command prompt on your computer. I'll type CMD in the search bar, and select it in the results. Now type this word "tracert," followed by the name of the website you want to reach. I'll type tracert www.google.com. And I'll press Enter. Take a look at this list. Each of these entries shows a hop. Each hop is a router. You can see my first hop here is a Linksys, and that's the name of my router. My router sends it to 142.254.131.9. And if I were to look that up, I would suspect that's my ISP. You can see that the packets continue to move through the internet, hopping and hopping, until they get to where they need to be, and the trace is complete. You may see a few requests timed out here, or little stars that show something has gone awry, but don't worry about that. Some devices aren't configured to provide a reply. As long as tracert succeeds, everything is good. In upcoming videos, we will build on what you've learned here. There's a lot more to learn about how data packets are created and packaged for delivery, and what protocols and technologies are used in the process.

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