The Internet

Networks, IP, TCP

Local Area Network (LAN)

Connect a small group of devices

A modem connected to a router showing wifi communication to a laptop

Internet Service Provider (ISP)

Connect customers to The Internet

Diagram showing an ISP connecting 5 different customers to the Internet. The customers are government, home, large corporation, small business, and an educational institution

Image of utility poles in a suburban neighborhood

Tier 1 Networks

Tier 1 networks form the backbone of the Internet

Map of the CenturyLink tier 1 network covering the United States

Map of the Level 3 tier 1 network covering the United States

Map of the AT&T tier 1 network covering the United States

Data Centers Power Apps

Ariel image of the Lockport data center

Inside of a data center showing dozens of racks of servers

It's all Cables!

A technician working in a room with 100's of ethernet cables

Map of the earth showing cables the cross the oceans and connect continents

How do we use these cables?..

Internet Protocol

Internet Protocol (IP) Address

  • Every device has an IP Address
    • Use this address to send messages to that device
    • Ex: 172.217.12.211
  • Use DNS (Domain Name Server) to lookup IP address by domain name
Diagram showing a computer sending a request to a server for the IP address of CSE312.com. The server replies with 159.89.179.140

Data is sent over the Internet in packets/datagrams

  • Each packet contains headers containing information about the packet

  • Large messages are sent in multiple packets

IPv4 header diagram

Routing Packets

  • To route a packet through the Internet, a router will
    1. Check the destination IP address of the packet
    2. Send the packet to the next router on its path
    3. Fuhgettaboutit
Routers sending a packet through the Internet between 2 devices. There are 2 different paths and only 1 was used

The Internet is Unreliable

Many factors cause packets to be dropped

Same diagram as the previous slide, but with a storm severing one of the connections that was used. This packet will be lost

Transmission Control Protocol

Transmission Control Protocol (TCP)

  • Makes the Internet reliable
  • Detect and resend dropped packets
  • Adds port numbers to identify specific programs
  • Connect to a port number/IP address combination (TCP/IP)
    • 127.0.0.1:8080
TCP 3-way handshake

TCP/IP in CSE312

  • Use libraries to do all this for us
  • Assume TCP/IP works and that we have reliable communication over the Internet
  • Freely send and receive messages (As bytes)
  • Your code (HW) will start with HTTP
  • Much deeper TCP/IP coverage, and more, in CSE489: Modern Networking Concepts

Further Reading