1. Communication: Before sending the information every device translates it into binary code, which is a value that is either 0 or 1
1.1. There are three types of physical medium
1.1.1. Electricity
1.1.1.1. If there's a signal the bit is 1, otherwise it's 0 so the information can being sent by turning on and off electricity
1.1.1.2. It's a cheap way of sending pieces of information
1.1.1.3. Signals travel through copper cables RJ45 but they can't go farther than 100 meters because the cable suffers from signal loss
1.1.2. Light
1.1.2.1. Bits can be sent as light beams using a fiber optic cable which is a thread of glass engineered to reflect light
1.1.2.2. These signals don't degrade over long distances
1.1.2.3. It's really expensive and hard to work with
1.1.3. Radio waves
1.1.3.1. Wireless devices use radio signal to send bits
1.1.3.2. Wireless has made out internet mobile
1.1.3.3. It has a short range
2. The internet is an architecture expressed in a set of protocols
2.1. It supports lots of different services, one of which is World Wide Web
2.1.1. The protocol used to send and receive webpages is http
2.1.1.1. This protocol uses a get request [GET "name of the page"] to get the webpage from the server
2.1.1.2. Everything that isn't text is not included in the webpage and needs to be requested with another http request, that's why the page loads slower
2.1.1.3. When the server send the web page back it also send a cookie to identify the user, so the next time he wants to visit the web site the browser send the cookie back to the server
2.1.2. HTML is a markup language, used to tell a web browser how to make a page look
2.1.2.1. The language uses different tags like <html> <body> <img> to identify the thing you want to make
2.1.3. The problem is:
2.1.3.1. The internet is completely open
2.1.3.2. The connections are shared
2.1.3.3. Information is sent in plain text
2.1.4. So a hacker can intercept and see your private pieces of information
2.1.4.1. Web servers prevent this by communicating on a secure channel with SSL and TLS
2.1.4.2. SSL and TLS are active when the browser shows a lock next to the url
2.1.4.3. A server identifies itself with a digital certificate. If the certificate is not valid the browser will warn you
2.2. A Protocol is a well known set of rules and standards that allow communication between two hosts which use the same protocol
2.2.1. All devices on the internet have unique addresses and this address is a part of the Internet protocol, that's why it is called IPv4 address
2.2.1.1. Since IP addresses are running out pretty quickly, it's born the new standard IPv6 which provides over 340 undecillion unique addresses
2.2.2. DNS, or domain name system, associates a domain name (like www.polterino.ga ) with the corresponding ip address
2.2.2.1. There are multiple dns server connected in a distribuited hierarchy
2.2.2.2. The problem is that dns is vulnerable. A hacker can do a dns spoof and change the original ip of a server in order to redirect the user to a malicious site
3. It is made up of a very large number of independently operated networks that are fully distributed, so there is no central control
3.1. The internet is not made of direct dedicated connetions
3.2. Every information doesn't follow a fixed path and is sent as a packet of information
3.2.1. Every packet as a maximum size so if the information is too big it gets broken into smaller IP packets and reassembled when it gets to the destination
3.2.2. Each packet has the IP address of where it came from and where it's going. Routers keep the packets moving through the networks smoothly
3.2.2.1. Everytime a router needs to send information it chooses the cheapest path available based on destination IP address of the packet
3.2.3. TCP is the protocol that manages the sending and receiving of all your data as packets
3.2.3.1. When packets arrive tcp checks if the information is complete. If so the connection is closed. Otherwise tcp will asks for the remaining packets and it will reassemble them