1.1. Networking - The Open Systems Interconnection (OSI) model

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• published: 11 May 2015
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View Video Playlists Full Windows 8 Networking and Security https://www.youtube.com/playlist?list=PLSJUvA2v3Fs758eE5aNep3pkkWkWTTUeJ - Before we go into talking about configuring network connections with Windows Eight, we're going to do a quick overview of some network topics. The first one we want to look at is the Open System Interconnector, the OSI Model. So let's do a quick review of that for everybody. Now there are some standard mnemonics, or memory devices, to try to remember what the seven layers are, and I like to start at the bottom, because layer one, right here, is really the bottom one, and we work our way up towards layer seven. Layer one is the physical layer. With the physical layer, what we're really talking about is actual connectivity. So whether we're fiber connected, we're Ethernet wire connected, we're wireless connected, whatever that physical layer of connectivity is, we sit here at layer one. When we talk about layer one, we're talking about connecting devices using hubs. So we use a hub here at layer one. Our layer two is the data link layer. When we talk about data link layer, we're talking about the way that content, digital content, zeroes and ones, are put together inside of packets to be communicated across the internet. We have different methodologies for doing that. So for instance, when we talk about data link layer, and we're talking about Wi-Fi, we're talking about eight oh two dot 11, abgn, or we could be talking about Ethernet connections, or we could be talking about the way that we send or encapsulate packets by other standards. So that's the data link layer, layer number two. When we connect devices together at this layer, we talk about switches. A switch is a device that understands the different kinds of communication protocols that can occur between devices. So typically we can have any device talk to another device using common communication protocols at layer two. Layer three is the network layer. This is the layer where we introduce the concept of IP addressing. So IP addressing on the network here is layer two. We use routers typically to allow communication between devices using their IP addresses. I don't need a router if I'm just going to have all the devices speak to each other in a very small local network. We can use a switch to do that. Net BIOS, Net BOI protocols have been around for networking since the 80s supported by Microsoft operating systems, operate at layer two. The don't need IP addresses. Microsoft added IP addresses above and beyond that as the internet became available, and actually the first commercial use of internet protocols was in about 92 or 93, that's 1992 or 1993. So that's when we started using IP addressing for boxes to communicate with one another. Let's go beyond that to layer four. In layer four we're talking about the transport layer. The transport layer talks about how packages are transmitted back and forth. Now I'm going to go to another slide and go into all these layers more deeply, the upper layers, but the separation typically is, as we're talking right here between layers three and four typically, is where we're talking about our connectivity. The infrastructure's layers one, two, and three, when we get to layer four, five, six, and seven we're talking about what the operating system handles for us. The transport layer's going to be how we bundle actual data or information together. How we cut the pieces of the information up to send packets. We don't send all of the information at once. Because of the model, we are trying to send data in little packets. So let me stop for a second and just talk a little bit about the history and how the OSI model evolved to get a little better context for you. Well the internet evolved pretty much post World War Two as a means for different organizations, particularly military or country organizations, to talk to one another, with the concern that if there was a nuclear holocaust, all kinds of communications would drop. The goal was to get all data from one place somewhere in the world, or on a battlefield, to somewhere else, maybe headquarters or to another country that was an ally. If we dropped radio communications, we had to get the data there by carrier pigeon, wired, satellite when satellite came along, let's add all of those mechanisms together. So the goal was get the data there. Well if you had one carrier, one piece of information, the whole thing one way and it didn't get there, you'd be in trouble. So the whole goal was to take everything in small pieces and send it out to as many routes as you could to get it to the destination and allow it to be re-assembled once received.