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Introduction

Socket programming forms the foundation of network communication. Understanding how to work with TCP and UDP sockets is essential for building networked applications from scratch.
This is part of Week 1 – Networking from Scratch in the “From CPU to the Browser” course.

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Socket types

1

TCP sockets

Transmission Control Protocol (TCP) provides reliable, ordered, and error-checked delivery of data between applications. TCP sockets establish a connection before data transfer and maintain that connection throughout the communication.Key characteristics:
  • Connection-oriented protocol
  • Guaranteed delivery and ordering
  • Flow control and congestion control
  • Higher overhead than UDP
2

UDP sockets

User Datagram Protocol (UDP) is a connectionless protocol that sends messages (datagrams) without establishing a connection. It’s faster but doesn’t guarantee delivery or ordering.Key characteristics:
  • Connectionless protocol
  • No delivery guarantees
  • Lower latency and overhead
  • Suitable for real-time applications

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TCP socket workflow

1

Create socket

Initialize a socket using the appropriate system call. The socket acts as an endpoint for network communication.
2

Bind to address

Associate the socket with a specific IP address and port number. This step is typically done on the server side.
3

Listen for connections

For TCP servers, put the socket in listening mode to accept incoming connection requests.
4

Accept connections

Accept incoming client connections, creating a new socket for each connection.
5

Send and receive data

Exchange data between client and server using send/receive operations.
6

Close connection

Properly close the socket when communication is complete.

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UDP socket workflow

1

Create socket

Initialize a UDP socket for datagram communication.
2

Bind to address

Bind the socket to an address and port (server side).
3

Send and receive datagrams

Use sendto() and recvfrom() to exchange messages without establishing a connection.
4

Close socket

Close the socket when done.

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Use cases

TCP use cases

  • Web servers (HTTP/HTTPS)
  • Email protocols (SMTP, IMAP)
  • File transfer (FTP)
  • Any application requiring reliable delivery

UDP use cases

  • Video streaming
  • Online gaming
  • DNS queries
  • VoIP applications
Always handle socket errors properly and implement timeouts to prevent indefinite blocking in production applications.

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Network debugging tools

When working with sockets, these tools are essential for debugging:
  • tcpdump: Command-line packet analyzer for capturing network traffic
  • Wireshark: GUI-based network protocol analyzer with powerful filtering capabilities
  • Network simulation: Tools to simulate latency and packet loss for testing

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Next steps

TCP basics

Learn about the three-way handshake, flow control, and HTTP parsing