14.1 - Protocols

• Set of rules or standards that define how data is transmitted and received between computers in a network.
• Ensures consistent communication, error handling, flow control, security, and structured data exchange between devices.
• Viewed as a stack, with each layer handling a specific function like transmission, routing, or formatting, ensuring organized and efficient communication.

TCP/IP Protocol

• Consists of four layers: Application, Transport, Internet, and Link (Data Link).

• Each layer communicates only with its adjacent layers (the layer directly above or below it).

• Each layer uses specific protocols to perform its functions (e.g., TCP and IP).

• The user interacts with the Application layer to send or receive data.

• When sending, data travels from the Application layer down to the Link layer, with each layer adding its own header

• When receiving, data travels from the Link layer up to the Application layer, with each layer removing its own header

• The Link layer communicates directly with the network to transmit and receive data.

• TCP (Transmission Control Protocol)

  • Manages the connection between two devices and ensures reliable data delivery
  • Used in the transport layer
  • Responsibilities: Host to host communication, Retransmitting missing packets, Reassembling packets in correct order

• IP (Internet Protocol)

  • Sets the rules for packet exchange and determines the routing path for those packets
  • Used in Internet Layer
  • Responsibilities: Correct routing, communication between networks, handles addressing, adds IP header

• Application Layer

  • Provides services for user applications like web browsing, email, or file transfer.
  • Provides the user interface
  • Prepares data for transmission by formatting it and applying application-specific protocols (e.g., HTTP, FTP, SMTP).
  • Sending a message: The user’s message is created here and passed to the Transport Layer
  • Receiving a message: Performs the action requested by the user

• Transport Layer

  • Ensures reliable or efficient delivery of data between two devices
  • Sending a message: Splits data from the application layer into individual packets, adds headers, and sends them to the internet layer. It manages packet flow, detects loss or corruption, and ensures reliable delivery
  • Receiving a message: It reads packet headers to identify the correct application layer, removes the headers, and forwards the data

• Internet Layer

  • The internet layer manages data transmission using IP addresses
  • It identifies the target network and host, then sends packets via the data link layer, routing each packet along the best available path
  • Defines the addressing method e.g. subnetting
  • Sending a message: Adds sender and receiver IP addresses and an error checking method.
  • Receiving a message: Reassembles packet fragments, removes the IP header, and passes the data to the transport layer.

• Data Link Layer/Network Interface Layer

  • Converts electrical data into signals for transmission, giving upper layers access to the physical network
  • Formats data into frames, links IP addresses to MAC addresses, and ensures proper network protocols are used.
  • Sending a message: Sends data over the physical medium (e.g., Ethernet cable or Wi-Fi) to the next device.
  • Receiving a message: Checks the checksum for errors, then forwards the data to the internet layer.

Protocols Examples

• HTTP/S (HyperText Transfer Protocol/Secured)
  • Used for accessing and transferring web pages and other content from a web server to a web browser (client).
• FTP (File Transfer Protocol)
  • Used for transferring files between computers on a network. Supports uploading and downloading files to and from servers.
• POP3 (Post Office Protocol version 3)
  • Retrieves emails from a server, downloading them to the user’s device and usually deleting them from the server afterward.
• IMAP (Internet Message Access Protocol)
  • Allows users to view and manage emails directly on the mail server without downloading them, supporting access from multiple devices.
• SMTP (Simple Mail Transfer Protocol)
  • Used for sending and forwarding emails from a client to a server or between email servers.
• BitTorrent Protocol
  • Provides peer-to-peer (P2P) file sharing network model
  • Allows users to download and upload pieces of a file from multiple users at once instead of relying on a single server
  • Better speed and efficiency
  • Swarms: All peer computers connected, each holding all or part of the file being shared.
  • Tracker: Central server that keeps track of which peers have which file parts and shares their IP addresses so they can connect with one another.
  • Seed: Peer that has the complete file and uploads it to others.
  • Process:
    • A client software is available to download by the user
    • The user opens a torrent descriptor file using a BitTorrent client
    • The file is divided into many small pieces.
    • The client downloads pieces from multiple peers and uploads pieces to others at the same time.
    • As soon as the user has at least one piece, they start sharing it with the swarm.
    • For downloading to work, at least one peer in the swarm must have the complete file.