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Computer Science · Networks

How the Internet Works

Break a message into packets, follow them across a 3D globe of undersea cables, cut a cable and watch the traffic reroute, then see what really happens when you type a URL.

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The course

7 worlds · 30 lessons

World 1 · Packets: Breaking a Message Apart

FREEWhy every photo, song and message travels in small numbered pieces
  1. 01What is the Internet?A network of networks · 11 min
  2. 02Why packets?Sending a message in pieces · 12 min
  3. 03Headers and payloadAn address on every piece · 13 min
  4. 04Putting it back togetherReassembly and checks · 12 min

World 2 · Routers and the Path

PRONobody plans the whole route, and yet the packet gets there
  1. 01HopsPassing the parcel · 12 minPRO
  2. 02TTL and tracerouteMapping the path · 13 minPRO
  3. 03When a link failsRerouting · 12 minPRO
  4. 04The network of networksISPs, peering and BGP · 13 minPRO

World 3 · Undersea Cables Around the World

PROThe Internet crosses the oceans on glass threads
  1. 01The ocean floor is the Internet's backboneWhy "the cloud" lies under the sea · 11 minPRO
  2. 02Light in glassHow data crosses an ocean · 13 minPRO
  3. 03Cut!Anchors, earthquakes and repair ships · 12 minPRO
  4. 04Great circles and cablesWhy cables take the routes they do · 12 minPRO

World 4 · What Happens When You Type a URL

PROFrom a typed name to a page on the screen, one step at a time
  1. 01Names instead of numbersThe DNS idea · 11 minPRO
  2. 02A lookup, step by stepThe resolver chain and the cache · 13 minPRO
  3. 03DNS recordsA, AAAA, CNAME, MX and friends · 12 minPRO
  4. 04Connecting, encrypting, askingTCP, TLS and HTTP · 14 minPRO
  5. 05Why is it slow?Reading the waterfall · 13 minPRO

World 5 · TCP: Did You Get That?

PROHow an unreliable network delivers a perfect file
  1. 01Reliable delivery on an unreliable networkWhat TCP is for · 12 minPRO
  2. 02The three-way handshakeSYN, SYN-ACK, ACK · 12 minPRO
  3. 03Lost packetsTimeouts and retransmission · 12 minPRO
  4. 04Slow start and fairnessNot breaking the network · 14 minPRO

World 6 · Wireless: Wi-Fi and Satellites

PROThe last few metres and the very long jumps
  1. 01Radio waves in your roomFrequency and wavelength · 12 minPRO
  2. 02Signal lossDistance and walls · 13 minPRO
  3. 03Channels, interference and sharing the airOne room, many networks · 13 minPRO
  4. 04Satellites vs fibreWho wins on delay? · 14 minPRO
  5. 05The last mileCable, fibre and 5G · 12 minPRO

World 7 · Staying Safe Online

PROSpot the bait, protect your accounts and know who to ask
  1. 01Phishing basicsSpotting the bait · 12 minPRO
  2. 02Passwords and two-step sign-inProtecting your accounts · 13 minPRO
  3. 03The padlock and public Wi-FiWhat HTTPS guarantees and what it does not · 12 minPRO
  4. 04Kind and careful onlinePrivacy and trusted adults · 12 minPRO
How the Internet Works — interactive 3D lab · Novareka