The TCP/IP five layer model

1. Physical Layer: Represents the physical devices that interconnect computers. Includes specifications for cables, connectors, and even how signals are sent over these connections.
2. Data Link Layer (Network interface or network access layer): Responsible for defining a common way of interpreting these signals (sent on the physical layer), so network devices can communicate. The most common protocol on this layer is Ethernet, although wireless technologies are becoming more and more popular. Beyond specifying physical layer attributes, the Ethernet standards also define a protocol responsible for getting data to nodes on the same network or link.
3. Network Layer (or Internet Layer): It's this layer that allows different networks to communicate with each other through devices known as routers. Internetwork - A collection of networks connected together through routers is an internetwork, the most famous of these being the Internet. The most common protocol available at this layer is IP. It is the heart of the Internet and most small networks around the world.
4. Transport Layer: While the network layer delivers data between two individual nodes, the transport layer sorts out which client and server programs are supposed to get that data. Protocols - TCP (Transmission Control Protocol) & UDP (User Datagram Protocol). The big difference between the two is that TCP provides mechanisms to ensure that data is reliably delivered while UDP does not.
5. Application Layer: There are lots of different protocols at this layer, and as you might have guessed from the name, they are application-specific. Protocols used to allow you to browse the web or send receive email are some common ones. Ex - HTTP, SMTP, etc.

You can think of layers like different aspects of a package being delivered. The physical layer is the delivery truck and the roads. The data link layer is how the delivery trucks get from one intersection to the next over and over. The network layer identifies which roads need to be taken to get from address A to address B. The transport layer ensures that the delivery driver knows how to knock on your door to tell you your package has arrived. And the application layer is the contents of the package itself.

In addition to the five-layer model we are working with, it’s important to note that other models exist. The traditional TCP/IP Model only has four layers, as it doesn’t differentiate between the physical layer and the data link layer, but is otherwise very similar to the one we’ll be working with. The most well-known other model is the OSI model. The primary difference between our five-layer model and the seven-layer OSI model is that the OSI model abstracts the application layer into three layers total.

The basics of Networking Devices

Cables

Cables are what connect different devices to each other, allowing data to be transmitted over them. They can be split into 2 major categories - Copper and Fiber.

Copper Cables

Copper cables are the most common form of networking cable. They're made up of multiple pairs of copper wires inside a plastic insulator. The sending device communicates binary data across these copper wires by changing the voltage between two ranges. The system at the receiving end is able to interpret these voltage changes as binary ones and zeros, which can then be translated into different forms of data. The most common forms of copper twisted-pair cables used in networking, are Cat 5, Cat 5e, and Cat 6 cables. These are all shorthand ways of saying category 5 or category 6 cables. These categories have different physical characteristics, like the number of twists in the pair of copper wires that results in different usable lengths and transfer rates. The important thing to know is that differences in how the twisted pairs are arranged inside these cables can drastically alter how quickly data can be sent across them and how resistant these signals are to outside interference. Cat 5e cables have mostly replaced those older Cat 5 cables because their internals reduce crosstalk. Crosstalk - Crosstalk is when an electrical pulse on one wire is accidentally detected on another wire. Cat 6 cables can transfer data faster and more reliably than Cat 5e cables can, but because of their internal arrangement, they have a shorter maximum distance when used at higher speeds.

Fiber cables

Fiber cables contain individual optical fibers, which are tiny tubes made out of glass about the width of a human hair. Unlike copper, which uses electrical voltages, fiber cables use pulses of light to represent the ones and zeros of the underlying data. Fiber can also transport data over much longer distances than copper can without suffering potential data loss.