Network Protocols §

A protocol is an agreed-upon set of rules for communication. Clients and servers communicate via various existing protocols.

IP (Internet Protocol) §

• Yes, this is what the IP in IP Address stands for
• Data sent from one machine to another is sent via IP packets at it’s most basic level
• These packets contain a header & data:

Header	Payload
Source IP destination IP size of packet IP version - IPv4 or IPv6	Arbitrary data

(Ignore the scaling of the diagram - in reality, the payload is much larger)

• These packets are $2^{16}$ bytes maximum - this isn’t a lot of data! Therefore a great many packets have to be sent across the wire
• IP does not guarantee ordering
• IP has no way of confirming that the recipient received anything
• No error correction

TCP (Transmission Control Protocol) §

• To address the shortcomings of IP, TCP was created
• This has a way to see if data was received and guarantees the correct ordering
• Allows you to send arbitrarily long pieces of data

Header	TCP Header	Payload
Source IP destination IP size of packet IP version - IPv4 or IPv6	Info about payload Ordering data	Arbitrary data

• For a client and a server to communicate, a TCP connection is made and this connection is held open until a timeout or the client or server requests to end the connection
• This connection is opened via a handshake

HTTP (HyperText Transfer Protocol) §

• A higher level abstraction designed for developers which builds ontop of TCP Transmission Control Protocol
• Uses a request <-> response paradigm

Requests §

• host -> adambennett.dev
• port -> typically 80 or 443
• path -> /posts
• method -> GET, POST, PUT, DELETE
• headers -> content-type: application/json, content-length: 51
• body -> arbitray data, typically JSON

Responses §

• status code -> 200, 404, 500 etc
• headers -> content-type: application/json, access-control-allow-origin: 'https://adambennett.dev'
• body -> arbitray data, typically JSON

For more, see REST API Design.

Summary §

graph LR
	IP --> TCP
	TCP --> HTTP