Question

What is a socket? Which socket is used for Client and Server in TCP?

Short answer

A socket is an endpoint for network communication. In TCP, the client uses an active socket, and the server uses a passive socket.

Step-by-step solution

Understanding Sockets

A socket is an endpoint for sending or receiving data across a computer network. It is a software entity that allows network communication between two machines. Sockets use protocols like TCP (Transmission Control Protocol) or UDP (User Datagram Protocol) to facilitate this communication.

Identifying Client and Server Sockets

In TCP, communication is established using a socket pair: one for the client and one for the server. The client socket actively requests a connection from the server, while the server socket waits for incoming connection requests from clients.

Socket Types in TCP

TCP uses two types of sockets: the socket on the client side is known as an "active socket" because it initiates the connection, and on the server side, it is known as a "passive socket" because it waits for the incoming connections.

Clarification on Usage in TCP

In practical terms, a server uses a 'listening socket' to listen for requests and then a new socket is created for each established connection with a client. The client uses an 'active socket' to initiate a connection to a server's listening socket.

Key concepts

TCP Protocol

The Transmission Control Protocol (TCP) is a fundamental protocol in network communication, ensuring reliable data transfer between devices. It is part of the Internet Protocol Suite, commonly referred to as TCP/IP, and plays a critical role in how computers communicate over the internet. TCP establishes a connection between devices, maintaining the order and guaranteeing the integrity of data packets. This reliable communication is achieved through acknowledgment mechanisms, retransmissions, and error-checking procedures. The use of TCP means data is sent in sequences where each packet is acknowledged upon receipt.

Because of these features, TCP is preferred for applications where accuracy is critical, such as web browsing and email. TCP ensures that all pieces of data reach the final destination correctly and in the right order.

Client-Server Communication

Client-server communication is a foundational model for creating networked applications. In this architecture, the server provides resources or services, while the client requests and uses them. This interaction is typically managed via network sockets in conjunction with a protocol like TCP.

In a TCP-based client-server communication, the process begins when the client creates a socket and initiates a connection to the server's socket. The server, which is passively waiting ("listening"), accepts the connection request from the client's active socket. Once connected, both parties can exchange data bi-directionally as needed.

• Client sends a request
• Server processes the request
• Server sends a response

Client-server communication allows applications to scale efficiently, leveraging the server's capacity to handle multiple clients at once.

Active and Passive Sockets

When working with TCP, understanding active and passive sockets is essential for establishing successful connections. An active socket is used by the client to initiate communication. It actively reaches out to servers, requesting a connection.

Conversely, a passive socket belongs to the server. The server "listens" on a designated port, waiting for connection requests. This passive nature is what allows the server to manage multiple client connections effectively. After the initial handshake using the listening socket, the server creates a new socket for each client to maintain individualized connections.

• Active socket: Initiates connections (client-side)
• Passive socket: Waits for connections (server-side)

This differentiation ensures structured communication and resource allocation on the network.

Network Programming

Network programming involves writing software that enables computers to communicate over a computer network. It is a crucial component in the development of applications like web browsers, email clients, and server software.

At the core of network programming is the ability to use sockets effectively, particularly with TCP. This involves understanding how data is formatted, transmitted, and received, as well as managing connection states.
With knowledge in network programming, developers can create applications that require real-time communication, allow multiple clients to interact with a single server, and ensure secure and efficient data exchange.

Network programming with TCP sockets allows developers to:

• Establish reliable, ordered, and error-checked connections
• Handle multiple simultaneous connections
• Implement protocols for complex interactions

Mastery in this area equips developers to build robust networked applications efficiently.