A helpful place to start is near the Very Beginning: You can pick up from where you left off the last time, or start at the beginning. Do you want to:.
What is the Internet? A Browser Madrigal Synchronizing the Browser Browsers and Privacy Malware, Phishing, and Security Risks Using Web Addresses to Stay Safe Validating Identities Online Evolving to a Faster Web In the internet, the network layer is special: When we send packets into the Internet, we must use the Internet Protocol. IP provides a deliberately simple service.
It is a simple, dumb, minimal service with four main features: It sends datagrams, hop-by-hop across the Internet. The service is unreliable and best-effort; there is no per-flow state making the protocol connectionless. TCP makes sure that data sent by an application at one end of the Internet is correctly delivered —in the right order -to the application at the other end of the Internet. Applications such as a web client, or an email client, find TCP very useful indeed. They can take advantage of the huge effort that developers put into correctly implementing TCP, and reuse it to deliver data correctly.
Reuse is another big advantage of layering. But not all applications need data to be delivered correctly. For example, if a video conference application is sending a snippet of video in a packet, there may be no point waiting for the packet to be retransmitted multiple times; better to just move on. UDP just bundles up application data and hands it to the Network Layer for delivery to the other end.
UDP offers no delivery guarantees. In other words, an Application has the choice of at least two different Transport Layer services: There are in fact many other choices too, but these are the most commonly used transport layer services.
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There are of course many thousands of applications that use the Internet. Applications typically want a bi-directional reliable byte stream between two end points. They can send whatever byte-stream they want, and Applications have a protocol of their own that defines the syntax and semantics of data flowing between the two end points. For example, when a web client requests a page from a web server, the web client sends a GET request.
This is one of the commands of the hypertext transfer protocol, or http.
As far as the Application Layer is concerned, the GET request is sent directly to its peer at the other end —the web server Application. It does this using the services of the Network layer, which in turn uses the services of the Link Layer. Network engineers find it convenient to arrange all the functions that make up the Internet into Layers. At the top is the Application, such as BitTorrent or Skype or the world wide web, which talks to its peer-layer at the destination.
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When the application has data to send, it hands the data to the Transport layer, which has the job of delivering the data reliably to the other end. The Transport Layer sends data to the other end by handing it to the Network Layer, which has the job of breaking the data into packets, each with the correct destination address. Finally, the packets are handed to the Link Layer, which has the responsibility of delivering the packet from one hop to the next along its path.
The data makes its way, hop by hop, from one router to the next. The Network Layer forwards it to the next router, one at a time, until it reaches the destination. There, the data is passed up the layers, until it reaches the Application.
Network engineers are responsible for implementing, maintaining, supporting, developing and, in some cases, designing communication networks within an organization or between organizations. Their goal is to ensure the integrity of high availability network infrastructure to provide maximum performance for their users. I highly recommend you taking the Stanford course if you want to learn more about computer networking.