What The F*ck Is The Internet?Vol 1: Bits, Encoding, Packets, and Protocols

Alex C. Viana (@AlexVianaPro)

Motivation: To Understand* How Networks WorkPhysics background → understand* how electronics work

Dev experience → understand* how software works

… everything in the middle is kinda ¯\_(ツ)_/¯

So this is me trying to fill in the gaps.

Everything I Previously Knew About NetworksData is digital (0’s and 1’s)

IP addresses are a thing

The internet exists

Sometimes computers are called “nodes”, this is usually about where I get lost

Sometimes people say the word “sockets” when explaining things to me

The PlanThere’s a lot of hand waving here, but I suspect this is the case for a lot of people.

So, with apologies to the devops who live and breath this stuff…

Let’s just start from the bottom and work our way up!

Bits, Bytes, and EncodingStarting from the bottom

Binary: 0’s and 1’sThe atomic unit of digital data is a “bit” which can either a 0 or a 1.

Everything digital, from Snapchat, to webpages, to Matchlight, is composed of bits.

The only reason bits can convey any information is because we have conventions

about what sequences of bits mean.

Binary: Numbers Other Than 0 or 1All integers can be represented in binary as some combination of the powers of 2:

1, 2, 4, 8, 16, ...

For example, here are all the numbers you can make with 2 bits:

00 (binary)= ((2 x 0) + (1 x 0)) = 0 + 0 = 0 (decimal)01 (binary)= ((2 x 0) + (1 x 1)) = 0 + 1 = 1 (decimal)10 (binary)= ((2 x 1) + (1 x 0)) = 2 + 0 = 2 (decimal)11 (binary)= ((2 x 1) + (1 x 1)) = 2 + 1 = 3 (decimal)

This is just a convention, there is no magic here.

Binary: Bits into Bytes8 bits together are called a byte:

10000001 (binary) = 129 (decimal)

This is where we get the terms we use for the size of data:

Kilobytes = 1,000 bytesMegabytes = 1,000,000 bytesGigabytes = 1,000,000,000 bytes

Ok so we can make numbers, but what else?

Binary: From Numbers to LettersSimilarly, by convention, numbers (in binary), can be mapped to letters, according to a

convention, called an encoding:

Binary Code | ASCII Code | Letter 01000001 | 065 | A 01000010 | 066 | B 01000011 | 067 | C

The convention above is called ASCII but there are others, such as UTF-8.

Computers have to agree/understand (in binary) what encoding is being used.

Binary: What’s Next? So you’re a computer. You’re sitting on a network. You get sent this:

11100011 10101101 01001110 00110100 00010000 01001011 01000000 01010001 10111001 00100100 01001101 10100101 11100010 10001011 01011101 00011111 00100000 01001100 11101111 11000011 11010000 01110100 10111001 00101100

Is this a series of letters? Is this a huge number? Something else? What now?

Protocols and PacketsMaking sense of bytes

Protocols: How Computers CommunicateIn the same way encodings allows us to turn bits into letters, another type of

convention, a protocol, allows us to make sense of the bits over a network.

There are lots of protocols, you can even write your own.

Packets: The Atomic Unit of a NetworkData is sent over a network in sequences of bits called packets

Packets typically have a header, which is metadata, and a payload, which contains the

data.

Let’s look at a header from a common type of protocol called IP (Internet Protocol)

Packets: Internet Protocol Header

IP Headers: VersionThe 1st 4 bits of an IP packet header are used to identify the IP protocol version.

This can be either IPv4 or IPv6, encoded by convention as a 4 or 6 in binary.

IPv4 : 0100 : 0 + 4 + 0 + 0 = 4IPv6 : 0110 : 0 + 4 + 2 + 0 = 6

Note that there is “room” in a 4-bit sequence for numbers up to 15.

The next header field implicitly begins at the 5th bit. There is no comma or period or

space.

IP Headers: AddressesThe source and destination address are 32-bit words that encode the IP address of the

sender and the receiver.

01001010011111010010101101100011 = 1249717091

While the above is technically correct, a 32-bit IP address is understood be composed

of 4 bytes (8-bit words). Adding dots for clarity:

01001010.01111101.00101011.01100011 = 74.125.43.99

This is just to emphasize that it’s the context of the protocol that gives the bits their

meaning.

IP Headers: IP AddressesAn IP address uniquely identifies a machine on a network.

In an IP header the Source and Destination Address fields tell every computer that

interacts with a packet where it is coming from and where it is going.

What happens next depends on the role of the machine in the network. This could be

as easy a printing from the printer right next to you or as complex as fetching a

webpage from Australia.

IP Headers: ProtocolThe protocol header is an 8-bit word that specifies the protocol used in the data

portion of the packet.

Using the same pattern as with letters, binary values map to decimal values which map

to a table of values, this time a table of possible protocols.

But isn’t the protocol already the IP protocol?

The Internet Protocol SuiteIt’s turtles all the way down!

The IP Suite: LayersThere are lots of protocols!

Protocols that serve roughly the same

purpose in a network are organized

into layers.

Layers work together to relay

information across a network.

This is also called the OSI model

The IP Suite: EncapsulationProtocols work together by completely

encapsulating packets as they move

between layers.

A packet (header + data) will be

encapsulated as a data in a new packet

with a new header appropriate for that

layer.

So an IP header, the protocol field

encodes the type of packet

encapsulated in the IP data.

SummaryAll digital data is just 0’s and 1’s

Conventions allow us to encode more complicated information as bits

Packets are digital data sent over the network

The contents of the bits in a packet are governed by protocols

Packet headers tell computers what the packets contain and what to do with them

This is the foundation of network communication

Future WorkI’m probably going to make more networking presentations as a way to teach myself.

Right now I’m really interested in what I see as the next step in this process: routing

and sockets.

That is what machines do with IP packets and how.

Also, interested how IP layers interact.

Thanks!