So in the last few videos we've been covering a lot of different networking technologies, and I thought we could quickly look at how they fit into the OSI model. So this is a seven-layer model developed by the International Standards Organization in the early 1980s, and OSI stands for Open Systems Interconnection Model. And it's not a perfect model, it's been around for a while, but it is ubiquitous in any sort of detailed conversation that you might have about networking.
And it's still a pretty useful conceptual model, I think, to reason about how... different technologies fit together. So, you know, we'll refer to it from time to time just to kind of see how things fit in.
So, so far we haven't talked too much about layers 3 through 7 yet, but we have been talking quite a bit about layer 1 and layer 2 in the last few videos. And so layer 1 is the physical layer. So some of the things that we've talked about at this layer include the sort of physical means of...
encoding information, so whether that's over copper or fiber or radio waves. And we've specifically been talking about Manchester code as one way of encoding data. There are a couple others that we haven't really touched on, NRZ, which is non-return zero, and QAM, which is the quadrature amplitude modulation.
We may cover in some later videos on some more advanced things. But just wanted to show you that there are some other things here. And then layer two is the data link layer, which has to do primarily with framing and frame formats.
And so we've talked about Ethernet framing, using the preamble and the inner frame gap to denote frames. We've also talked about HDLC and using those flag bites to denote frames. And then we've also talked about the frame format. So the Ethernet logical link control, which is the Ethernet frame format that we just looked at, or the PPP logical link control. And so, Those are basically all of the layer one and layer two technologies that we'll talk about for now.
But then as we start to cover more of the layers in this model, I think it'll help more to kind of see how things fit together. We'll check back in here just to kind of see how things fit and how each layer sort of depends on the layers below it.