Send bits through electricity, light or radio.

Bit transfer

  • 1 bit is a boolean
  • 1 byte = 8 bits
  • 8 million bits = 1 MB

  • To transfer 1 you send one electric pulse.

  • To transfer 0 you omit the electric pulse and this has to be in a time frame. eg. bit per second


Transmission capacity, measured by bitrate

  • Bitrate: the number of bits per second a system can transmit
  • Latency: time it takes for a bit to travel from sender to receiver

Transfer medium

  • Electricity through copper wires eg. Ethernet, is cheap but has a lot of signal loss.
  • Light is faster, minimal signal loss, can be transferred by fiber-optic cable.
  • Radio waves are used for wireless transmission

DNS (Domain Name System)

Domain name mapping

Connected through a domain name hierarchy

  • A record maps a domain name directly to an IP address (preferred)
  • CNAME record maps one domain name to another and are less flexible.

  • domain mapping is usually aggressively cached (can take up to 48 hours to update)

  • if you want to show the change immediately, redirect the current server to the Coming soon while you wait for the DNS to update the cache.

DNS Spoofing

  • When a hacker breaks into a DNS Server and changes a domain name cache to point to a different IP address.

Packets and routers

  • Data is chunked into packets and each of these travel in different routes from sender to receiver.
  • The packets my arrive to the receiver at different times but the receiver will wait untill all is ready to assemble.
  • each packet contains it's IP address of where it came from and where it's going
  • if one of the network routes is congested, the router might send the packets in different routes and in different order
  • Routers are computers dedicated to forward packets to their destination and balance the network traffic
  • The diversification of routes makes the internet reliable and difficult to take down

TCP (Transmission Control Protocol)

Manages all your sending and receiving your data as packets

  • TCP makes sure all packets arrived and send a confirmation status to the sender.
  • If there are any packets missing, TCP will request the sender to re-send those packets.


  • the internet is open
  • all connections are shared
  • information is sent in plain text

URL (Uniform Resource Locator)

HTTP (HyperText Transfer Protocol)

Language used to communicate between browsers and servers

HTML (HyperText Markup Language)

SSL (Secure Sockets Layer)

TLS (Transport Layer Security)

SSL's successor

  • adds a layer of protection to the HTTP connection to prevent sniffing and tampering

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