Unit 2: The Internet

  • ARPANET - Advanced Research Projects Agency Network
  • Types of Networks
    • Centralized
    • Distributed - a distributed packet-switched network
  • The internet is made up of an incredibly large number of independently operating networks
    • Completely independent, no central control on how packets are routed
  • Computing Device - a machine that can run a program, including computers, tablets, servers, routers, and smart sensors
  • Computing System - a group of computing devices and programs working together for a common purpose
  • Computer Network - a group of interconnected computing devices capable of sending or receiving data
  • Path - the series of connections between computing devices on a network starting with a sender and ending with a receiver
  • Bandwith - the maximum amount of data that can be sent in a fixed amount of time, usually measured in bits per second
  • In the 1970s, there was no standard method for networks to communicate
  • Vint Cert and Bob Kahn invented the Internetworking Protocol (the internet)
  • Internet Service Provider - ISP
  • The internet is really a design philosophy expressed in a set of protocols
    • Design philosophy is being used to adapt and absorb new communication technologies
  • Protocol - a well-known set of rules and standards used to communicate between machines (and specify the behavior of some systems)
  • All the different devices on the internet have unique addresses
    • An address on the internet is just a number that’s unique to each device on the network
  • Internet Protocol - IP
    • The computer’s address is called the IP address (the protocol for sending data across the Internet that assigns unique numbers to each connected device
  • Traditional IP addresses are 32 bits long, with 8 bits for each part of the address
    • The first part of the address identifies the country/network, then the region/network, then the subnetworks, and then the device address
    • It is the unique number assigned to each device
    • It is no longer countries and regions, it’s now networks and sub-networks
    • IPv4 - provides more than 4 billion unique addresses
  • IPv6 - 128 bits per address and 340 undecillion unique addresses
  • Domain Name System (DNS) - corresponds to the website domain with the IP address
    • DNS Servers are connected in a distributed hierarchy
    • DNS was created to be an open public communication protocol for government and educational institutions
    • the system responsible for translating domain names like example.com into IP addresses
  • DNA Spoofing - sending people to an imposter website
  • DNS and IP are designed to scale no matter how much the internet grows
  • Router - a type of computer that forwards data across a network
  • Redundancy - the inclusion of extra components so that a system can continue to work even if individual components fail, for example by having more than 1 path between any 2 connected devices in a network
  • Fault Tolerant - can continue to function even in the event of individual component failures. This is important because elements of complex systems like a computer network fail at unexpected times, often in groups
  • User Datagram Protocol (UDP)
    • Main Idea: Like Protocol 1 or clearing out the library as fast as you can, the goal is to send information quickly without worrying about accuracy.
    • Basics of how it works: Send all the packets but don’t check if they get through or arrive in the right order.
    • Use in real life: Useful when split seconds matter more than correcting errors, like video conferencing, live streaming, and online gaming.
    • Summary: a protocol for sending packets quickly with minimal error-checking and no resending of dropped packets
  • Transmission Control Protocol (TCP)
    • Main Idea: Like Protocol 2 or numbering every book in the library. It’s slower but more accurate.
    • Basics of how it works: Number packets so they can be re-ordered, confirm all were received, and resend any missing packets. Multiple back-and-forth confirmations between sender and receiver.
    • Use in real life: Useful when accuracy matters more than saving a split second, like sending emails, photos, or just browsing websites.
    • TCP - manages the sending and receiving of all your data as packets
  • Direct dedicated connections - impossible to keep things working
  • Data travels on the internet in a much less direct fashion
    • The information does not need to follow a fixed path
    • They send in packets of information
  • Many kinds of digital information can be sent with IP packets
    • Packets have the address of where they came from and where it is going
  • Routers (or computing devices) act like traffic managers to keep packets moving smoothly and packets are reassembled in order
    • However, packets may arrive at different times or orders
    • Routers choose the cheapest available path for each piece of data
    • “Cheapest” - time, politics, relationships
    • Often the best route for data to travel isn’t the most direct
  • TCP + Router systems - scalable
    • Grow and scale the internet without interrupting service
  • Principles of fault tolerance and redundancy, more routers = more reliable
  • Different systems that make up the internet connect, communicate with each other, and collaborate because of agreed-upon standards for how data is sent around the internet
  • Datastream - information passed through the internet in packets
  • Packet Metadata - data added to packets to help route them through the network and reassemble the original message
  • Packet - a chunk of data sent over a network. Larger messages are divided into packets that may arrive at the destination in order, out-of-order, or not at all
  • URL - Uniform Resource Locator
  • HTTP - HyperText Transfer Protocol
    • the language used to communicate between web browsers and servers
    • “Get” requests
    • Send information (in a form or search query)
    • a protocol for computers to request and share the pages that make up the world wide web on the Internet
  • HTML - HyperText Markup Language
  • Cookies - what websites use to remember who you are (an ID number that remembers you)
  • The internet…
    • is completely open
    • the connections are shared
    • and information is sent in plain text
  • Safe websites prevent snooping & tampering by communicating on a secure channel
    • Secure Sockets Layer (SSL) & its successor, Transport Layer Security (TLS) are a layer of security wrapper around your communications
    • They are active when there is a lock in the address bar, next to the HTTPS
    • The HTTPS protocols make sure the HTTP requests are secured and protected
  • Digital certificate - ID card proving that it is the website that it claims to be, which is published by
    • Certificate authorities - trusted entities that verify the identities of websites and issue certificates for them
    • Browser will warn you if there is not a proper certificate
  • HTTP & DNS manage the sending & receiving of web files
    • TCP/IP & Routing that break down and transport packets
    • Wires, cables & WiFi are made using binary sequences of 1’s and 0’s that are sent physically
  • Scalability - the capacity for the system to change in size and scale to meet new demands
  • World Wide Web - a system of linked pages, programs, and files
  • The World Wide Web is different from the Internet. The World Wide Web are files, web pages, and media. The Internet is the network we use to access those files.
  • The DNS is an important system in helping the Internet scale.
  • Digital Divide - differing access to computing devices and the Internet, based on socioeconomic, geographic, or demographic characteristics
    • Can affect both individuals and groups
    • Raises ethical concerns of equity, access, and influence globally and locally
    • Affected by the actions of individuals, organizations, and governments