Communications Technology: Network Protocols

This section explores fundamental network protocols essential for understanding how data is transmitted across networks. We will delve into TCP/IP, HTTP, and FTP, examining their roles, functionalities, and how they contribute to network communication.

TCP/IP (Transmission Control Protocol/Internet Protocol)

Overview

TCP/IP is not a single protocol but a suite of protocols that govern communication on the internet and most modern networks. It's the foundational protocol stack used for reliable data transmission.

Layers of the TCP/IP Model

The TCP/IP model is typically depicted as having four layers:

• Application Layer: Provides network services to applications (e.g., HTTP, SMTP, FTP).
• Transport Layer: Handles reliable data delivery between applications (e.g., TCP, UDP).
• Internet Layer: Responsible for logical addressing and routing of packets (e.g., IP).
• Network Access Layer: Handles physical transmission of data over the network medium (e.g., Ethernet, Wi-Fi).

TCP (Transmission Control Protocol)

TCP is a connection-oriented protocol, meaning it establishes a connection before data transfer and ensures reliable delivery. Key features include:

• Reliable Data Transfer: Guarantees that data arrives in the correct order and without errors through mechanisms like acknowledgements and retransmissions.
• Connection-Oriented: Uses a three-way handshake to establish a connection and a four-way handshake to terminate it.
• Flow Control: Prevents a fast sender from overwhelming a slow receiver.
• Congestion Control: Adapts the transmission rate to avoid network congestion.

IP (Internet Protocol)

IP is responsible for addressing and routing packets across networks. It uses logical addresses (IP addresses) to identify devices. Key aspects include:

• Addressing: Assigns unique IP addresses to devices on the network.
• Routing: Determines the best path for packets to travel from source to destination.
• Packetization: Divides data into packets for transmission.
• Unreliable Delivery: Does not guarantee delivery of packets; relies on TCP for reliable data transfer.

Table: TCP/IP Layer Functions

Layer	Protocol	Function
Application	HTTP, SMTP, FTP	Provides network services to applications.
Transport	TCP, UDP	Handles reliable or unreliable data delivery.
Internet	IP, ICMP	Handles addressing and routing of packets.
Network Access	Ethernet, Wi-Fi	Handles physical transmission of data.

HTTP (Hypertext Transfer Protocol)

Overview

HTTP is the foundation of data communication on the World Wide Web. It's used to transfer hypertext (HTML), images, and other resources between web servers and web browsers.

Request-Response Model

HTTP operates on a request-response model:

1. Client (e.g., web browser) sends a request to a server.
2. Server processes the request and sends back a response.
3. Response contains the requested data (e.g., HTML code).

HTTP Methods

HTTP defines various methods to indicate the desired action:

• GET: Retrieves data from the server.
• POST: Sends data to the server to create or update a resource.
• PUT: Replaces an existing resource with new data.
• DELETE: Deletes a specified resource.
• PATCH: Applies partial modifications to a resource.

Status Codes

Servers respond with status codes indicating the outcome of the request (e.g., 200 OK, 404 Not Found, 500 Internal Server Error).

FTP (File Transfer Protocol)

Overview

FTP is a standard network protocol used for transferring files between a client and a server over a TCP/IP network.

Client-Server Architecture

FTP utilizes a client-server architecture:

• FTP Client: The software on the user's machine that initiates the file transfer.
• FTP Server: The software on the remote machine that stores and manages files.

Control and Data Connections

FTP uses two separate connections:

• Control Connection: Used for sending commands and receiving responses (e.g., login, file listing).
• Data Connection: Used for actual file data transfer. This can be a control connection or a separate dedicated connection.

Modes of Operation

FTP operates in two modes:

• Active Mode: The client initiates a connection to the server for data transfer.
• Passive Mode: The server initiates a connection to the client for data transfer. This is commonly used to overcome firewall issues.

Table: Protocol Comparison

Protocol	Primary Use	Connection Type	Reliability
TCP/IP	Foundation of internet communication	Connection-oriented	Reliable
HTTP	Web data transfer	Connection-oriented	Reliable (using TCP)
FTP	File transfer	Uses control and data connections	Reliable (using TCP)