Skip to main content

Network Protocols

  • IP packets, TCP headers, HTTP requests
  • these low-level networking concepts are essential to understanding how machines in a system communicate with one another
  • it will consists of messages that are gonna be sent and received by machines, clients, and servers over the network
    • it contains
      • the type of messages
      • the format of the messages
      • how they are structured
      • the order of those messages if they have an order
      • whether or not they should be some sort of response to a message if there should be
      • what that response should look like
      • whether or not there should be rules around when messages can be sent to one another

Protocol​

  • it is an agreed upon set of rules for an interaction between 2 parties
  • analogy example
    • when 2 people who vaguely know each other cross each other while walking down a hallway
      • typically, they will have some kind of exchange
        • chat with one another with small talk then say bye

Key Terms​

IP​

  • stands for Internet Protocol
  • the modern internet effectively runs on IP
    • meaning that when a machine or a client tries to interact with another machine or a server and it sends data to that other machine
      • that data is going to be sent in the form of IP Packet
  • this network protocol outlines how almost all machine-to-machine communications should happen in the world
  • other protocols like TCP, UDP and HTTP are built on top of IP
  • IP has 2 versions
    • IPv4: most of the modern day internet uses
    • IPv6: now being used more and more

TCP​

  • stands for Transimission Control Protocol
  • built on top of the Internet Protocol (IP)
  • allows for ordered, reliable data delivery between machines over the public internet by creating a connection
  • TCP is usually implemented in the kernel, which exposes sockets to applications that they can use to stream data through an open connection
  • it is meant to send IP Packets in an ordered way, and in a reliable way guaranteeing that the IP Packets sent will be received by the destination
    • you will know if some packets keep failing from getting received and in the error free way
      • this means that if the data sent was corrupted, you will know and will be able to resend those packets
  • TCP is used in virtually all web applications and allows you to send arbitrarily long pieces of data to other machines
  • TCP example
    • when a machine wants to communicate with another machine over TCP
      • when your browser wants to communicate with a website's servers
        • 1st it will create a TCP connection with the destination computer / server through a handshake
          • handshake:
            • is a special TCP interaction where 1 computer contacts the other by sending a packet or a few packets stating that it wants to connect with the other computer, the other computer will response and say ok
            • the client that was trying to establish the connection will reresponds again and say that the the 2 computers are connected and there is an open connection
        • once the connection is established, both machines can freely send data to one another
          • however, if one of the 2 machines doesn't send data in a given amount of period, the connection can be timed out
          • if one of the machines wants to end the connection, it can do so be sending a special message to the other machine know about the ending of the connection
  • summary: it is a more powerful and more functional wrapper around IP, but still lacks a robust framework that developers can use to ready define meaningful and easy to use communication channels for clients and servers in the system
    • HTTP solves this issue

HTTP​

  • the HyperText Transfer Protocol is a very common network protocol implemented on top of TCP
  • follows the request response paradigm
  • clients make HTTP requests, and servers respond with a response
  • requests typically have the following schema
    host: string (example: algoexpert.io)
    port: integer (example: 80 or 443)
    method: string (example: GET, PUT, POST, DELETE, OPTIONS or PATCH)
    path: string (example: /payments)
    headers: pair list (example: "Content-Type" => "application/json")
    body: opaque sequence of bytes
    • path: servers might have multiple paths for different services
      • clients will issue requests to these various paths
        • depending on the path, different business logic will occur
    • headers: contain important meta-data about the request
  • responses typically have the following schema
    status code: integer (example: 200, 401)
    headers: pair list (example: "Content-Length" => 1238)
    body: opaque sequence of bytes

IP Packet​

  • it is made up (stored in) of bytes
  • sometimes more broadly referred to as just a (network) packet
  • an IP Packet is effectively the smallest unit used to describe data being sent over IP from 1 machine to another
  • asides from bytes, an IP Packet consists of 2 main sections:
    • an IP header:
      • contains the source and destination IP addresses as well as other information related to the network
      • the total size of the packet
      • the version of the IP packet is operating by
      • header size is between 20 to 60 bytes
    • a payload: is just the data being sent over the network
      • contains a TCP header
        • contains the information about the ordering of packets
      • the rest will be the actual data portion
  • IP Packet are limited in size
    • are only 2^16 bytes (65,536 bytes)
    • only way to send more data is to use multiple IP Packets
      • if multiple IP Packets are being sent from one machine to another and is only using IP
        • there is no way of guaranteeing that these packets are gonna be received
          • some of the packets might get lost over the network
        • there is no guarantee in the order in which those packets will be read or interpreted
      • TCP is required to solve this issue