TCP/IP Fundamentals

This document provides a comprehensive overview of the Transmission Control Protocol/Internet Protocol (TCP/IP) suite, the foundational communication protocols used for the internet and most private networks.

The TCP/IP Model

The TCP/IP model is a conceptual framework that divides network communication into four layers:

1. Application Layer: Where network applications operate (e.g., HTTP, FTP, SMTP).
2. Transport Layer: Manages end-to-end communication, providing services like reliability and flow control. Key protocols here are TCP and UDP.
3. Internet Layer (Network Layer): Handles addressing and routing of packets across different networks. The primary protocol is IP.
4. Network Access Layer (Link Layer): Deals with the physical transmission of data over the network medium (e.g., Ethernet, Wi-Fi).

Key Protocols

Internet Protocol (IP)

IP is responsible for addressing and routing packets of data so they can travel across networks and reach the correct destination. It is a connectionless, best-effort delivery protocol, meaning it doesn't guarantee delivery or order of packets.

• IPv4: The current dominant version, using 32-bit addresses (e.g., 192.168.1.1).
• IPv6: The next generation, using 128-bit addresses to accommodate the vast number of internet-connected devices.

Transmission Control Protocol (TCP)

TCP is a connection-oriented protocol that provides reliable, ordered, and error-checked delivery of a stream of bytes between applications running on hosts communicating over an IP network.

• Connection Establishment: Uses a three-way handshake (SYN, SYN-ACK, ACK) to establish a connection before data transfer.
• Reliability: Achieved through sequence numbers, acknowledgments (ACKs), and retransmissions of lost packets.
• Flow Control: Prevents a fast sender from overwhelming a slow receiver.
• Congestion Control: Manages network traffic to avoid overloading the network.

User Datagram Protocol (UDP)

UDP is a simpler, connectionless transport layer protocol. It offers a faster, but less reliable, way to send data compared to TCP. It is often used for applications where speed is more critical than guaranteed delivery, such as streaming media or online gaming.

How TCP/IP Works Together

When an application sends data:

1. The Application Layer creates the data.
2. The Transport Layer (e.g., TCP) adds a header containing port numbers and control information.
3. The Internet Layer (IP) adds an IP header with source and destination IP addresses.
4. The Network Access Layer encapsulates the IP packet into a frame suitable for the physical network medium.

This process is reversed at the receiving end.

Common TCP/IP Ports

TCP and UDP use port numbers to distinguish between different applications and services running on a host. Some common ports include:

• 80: HTTP (Web browsing)
• 443: HTTPS (Secure web browsing)
• 21: FTP (File Transfer Protocol)
• 22: SSH (Secure Shell)
• 25: SMTP (Email sending)
• 53: DNS (Domain Name System)

Further Reading

• Sockets Programming Guide
• UDP Protocol Details
• Windows Sockets API (Winsock)