161: MAC: Media Access Control Address.

A MAC address is a physical address unique to your computer. Think of it like this: you want to send a letter to your friend so you put your friend’s mailing address on the envelope. This is good enough at first. But right before the post office puts your letter in your friend’s mailbox, the address gets changed to you friend’s fingerprint instead. This is because computers don’t have a simple mailbox where letters and other messages can be delivered until somebody goes to check the mail. But why switch from an address to a fingerprint in the first place? The reason is because there are different layers to the communication. I won’t go into all the details, but in 1984 there was a standard document that was published called the Open Systems Interconnection Reference Model, or just the OSI model for short. This document describes a design that consists of seven layers. Each layer is responsible for specific functionality. And in order to get something running such as browsing the internet, you need pieces from each of these seven layers. I’ve already described IP which exists in layer 3 of this document and both TCP and UDP which can both be found in layer 4. I didn’t want to go right into this document because it would seem too much like a bunch of theory. But now that you understand a few distributed computing concepts, it’s time to describe where everything fits in the OSI model. Listen to the full episode for a description of the first four layers as well as why MAC addresses are needed and how they fit into the OSI model. Or you can also read the full transcript below. Transcript I explained IP addresses in episode 158. You should also listen to episodes 159 and 160 before this episode. An IP address is a virtual address because it can change. When communicating with other computers, we need something that won’t change. Something that’s unique. Think of it like this: you want to send a letter to your friend so you put your friend’s mailing address on the envelope. This is good enough at first. But right before the post office puts your letter in your friend’s mailbox, the address gets changed to you friend’s fingerprint instead. This is because computers don’t have a simple mailbox where letters and other messages can be delivered until somebody goes to check the mail. But why switch from an address to a fingerprint in the first place? The reason is because there are different layers to the communication. I won’t go into all the details, but in 1984 there was a standard document that was published called the Open Systems Interconnection Reference Model, or just the OSI model for short. This document describes a design that consists of seven layers. Each layer is responsible for specific functionality. And in order to get something running such as browsing the internet, you need pieces from each of these seven layers. I’ve already described IP which exists in layer 3 of this document and both TCP and UDP which can both be found in layer 4. I didn’t want to go right into this document because it would seem too much like a bunch of theory. But now that you understand a few distributed computing concepts, it’s time to describe where everything fits in the OSI model. Let’s start with layer one. This is the physical layer. Now I know. I started out this episode saying that a MAC address is a physical address. That’s a different kind of physical. Layer one is concerned about really physical things such as the wires connecting your computer to the internet. Or if you connect wirelessly, then the first layer is concerned with things such as the frequency of the radio waves and how they’re formed. With wires, this layer is concerned about voltages and currents. We live in a noisy world. And I’m not talking about all the extra noise I hear these days in New York from car horns and police sirens. I’