Welcome back to digital forensic concepts. In this course, course 10, we're going to talk about network basics. In overview of this course, we're going to define what a network is. We're going to talk about how a network functions. How does the data get across our network? We're going to talk about IP and MAC addresses and what they are, and how they're used in network protocols, and how they're used throughout the network to complete transmissions of data. We're also going to talk about Internet protocols and the OSI model. In Module 1, we're going to define the network and we're going to talk about the functions of the network. What is a computer network? Well, a computer network is defined as a collection of computers linked together for communication and sharing of data and other resources. You might have a network in your home where you share a printer and you could share data between the computers. If you work in a business environment, you might have a larger scale network that you use at work. A LAN, or a local area network, is a group of computers linked together in a small area, generally, it's one geographical location. It could be in one building or a small home office, whereas a WAN, a wide area network, is a group of computers linked together over a large geographical area. This can span city, states, and even countries. The data is transferred across this network in things called packets. These packets have a header, a footer, and a payload. The header, much like a file header, tells computers what type of service they are, are they TCP, UDP. They tell us the source, where these packets came from, the destination, where the packets are going, and each packet has a sequence number and flags. Now, the footer tells the receiving device that it has reached the end of the transmission. The footer also has error checking and usually that's in a CRC format which stands for cyclical redundancy check. Of course, the payload is the actual data contained within the packet. We're going to talk about the parts of a network. What are the hardware parts that make up our network? Well we have routers. A router is something you would have in your house, and you would also have that in a larger network. Routers provide Internet connection to a local area network. A router operates at layer 3 of the OSI model. That is the network layer. We're going to cover the OSI model in a later course. A router connects devices within a network by forwarding data packets between them. This data can be sent between devices or to the Internet. The router assigns a local IP address to the device on the network. Hub. Now, a hub, unlike a router, broadcasts out to everybody that is on that network. Hubs operate at the physical layer of OSI Layer 1 of a network. They are used to connect multiple devices in a network. Now, it can have multiple connections and they pass on anything they receive on one connection to all the other connections. There is no filtering by IP or MAC addresses. With the router, we had the filtering by IP, but with the hub, we do not. Switches are also part of a network. A switch operates at OSI layer 6, which is the data link layer. This connects the device to the network. It also does its filtering by MAC address. It uses MAC addresses to route the packets to where they need to go, unlike the router which uses the IP addresses. In our next module, we're going to talk about IP and MAC addresses, what they are. We've already talked about how they're used with routers and switches, but we're going to talk more about what they do, the functions of them, and how they work on our networks.
