The TCP IP Model |Technical Support Fundamentals|Coursera| Google IT Support Professional
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To really understand networking,we need to understand all of the components involved.We're talking about everything from the cables that connect devices toeach other to the protocols that these devices use to communicate.There are a bunch of models that help explain how network devices communicate,but in this course, we will focus on a five-layer model.By the end of this lesson,you'll be able to identify and describe each layer and what purpose it serves.Let's start at the bottom of our stack,where we have what's known as the physical layer.The physical layer is a lot like what it sounds.It represents the physical devices that interconnect computers.This includes the specifications forthe networking cables and the connectors that join devicestogether along with specificationsdescribing how signals are sent over these connections.The second layer in our model is known as the data link layer.Some sources will call this layer the network interface or the network access layer.At this layer, we introduce our first protocols.While the physical layer is all about cabling,connectors and sending signals,the data link layer is responsible fordefining a common way of interpreting these signals,so network devices can communicate.Lots of protocols exist at the data link layer,but the most common is known as Ethernet,although wireless technologies are becoming more and more popular.Beyond specifying physical layer attributes,the Ethernet standards also define a protocol responsiblefor getting data to nodes on the same network or link.The third layer, the network layer is also sometimes called the Internet layer.It's this layer that allows different networks tocommunicate with each other through devices known as routers.A collection of networks connected together through routers is an internetwork,the most famous of these being the Internet.Hopefully you've heard of it.While the data link layer is responsible for getting data across a single link,the network layer is responsible for getting datadelivered across a collection of networks.Think of when a device on your home network connects with a server on the Internet.It's the network layer that helps gets the data between these two locations.The most common protocol used at this layer is known as IP or Internet Protocol.IP is the heart of the Internet and most small networks around the world.Network software is usually divided into client and server categories,with the client application initiating a request fordata and the server software answering the request across the network.A single node may be running multiple client or server applications.So, you might run an email program and a web browser, both client applications,on your PC at the same time,and your email and web server might both run on the same server.