Question

Suppose that a Web server runs in Host C on port 80. Suppose this Web server uses persistent connections, and is currently receiving requests from two different Hosts, \(\mathrm{A}\) and \(\mathrm{B}\). Are all of the requests being sent through the same socket at Host C? If they are being passed through different sockets, do both of the sockets have port 80 ? Discuss and explain.

Short answer

Each host's requests use different sockets with the server, but all sockets have port 80 on the server side.

Step-by-step solution

Understanding Sockets

A socket is a communication endpoint that consists of an IP address and a port number. It is used for sending and receiving data between hosts in a network.

Persistent Connections Overview

Persistent connections allow multiple requests and responses to be sent over a single connection without closing it after each exchange. This is often used to enhance performance by reducing the need to establish a new connection for each request.

Analyzing Socket Use for Different Hosts

Each client (Host A and Host B) will maintain its own separate TCP connection to the server (Host C). Therefore, each connection will have a unique socket characterized by the client's IP address and a unique ephemeral port number, even though the server listens on the same port 80.

Understanding Server Sockets

On Host C, the TCP protocol ensures that separate sockets are used for each client connection. While the server is listening on port 80, each established connection has a different socket defined by a combination of the server's IP and the client's IP and port.

Conclusion on Socket Ports

Both Host A and B are connected to Host C on port 80, which is the server-side listening port. However, each connection is handled via separate sockets due to the unique combination of client IPs and ports, but all server-side sockets will have port 80.

Key concepts

Web Server

A web server is a specialized computer program that provides content to satisfy web page requests from clients. Whenever a user navigates the web, they are usually interacting with a browser-based client that communicates with web servers to access information like websites, graphics, and other web content.
Web servers play a crucial role in the functioning of the Internet by managing data delivery between users and the server. The server listens for incoming requests on a specified port (commonly 80 for HTTP traffic), processes these requests, and sends back the appropriate content.
In this exercise, the server is configured to handle persistent connections, ensuring efficient data transfers by using fewer resources and providing a quicker response to repeated requests from the same client.

Persistent Connections

Persistent connections are a significant functionality of web servers, particularly relevant to the HTTP protocol. They allow clients and servers to maintain an open connection channel, allowing multiple data exchanges over the same connection without closing it after each transaction.
This approach drastically enhances web performance because:

• It reduces the time delay caused by the repetitive opening and closing of connections.
• It decreases network congestion and server workload.

Persistent connections are often described as keep-alive connections, meaning that they stay open and ready for further request-response communication until it is completed or is not necessary anymore.

Sockets

Sockets are core communication tools in networking, acting as an interface that facilitates sending and receiving data between devices over a network. They can be thought of as an endpoint consisting of a unique IP address and a port number, where digital conversations can occur seamlessly.
Sockets provide full-duplex communication channels and are integral to both client and server architecture.
In this context:

• Each client (like Host A or B) connects to the server through a socket.
• The server can serve multiple clients simultaneously by creating separate socket instances, each identified by a distinct combination of client IP and port numbers, while the server's port remains constant, such as port 80.

Sockets ensure that dedicated channels are used for efficiently managing data exchanges between different hosts.

TCP Protocol

The TCP (Transmission Control Protocol) is an essential networking protocol that ensures reliable data transfer across networks. It is one of the foundational protocols of the Internet's communication suite and works hand-in-hand with the Internet Protocol (IP).
TCP ensures:

• Reliable delivery through data packet sequencing.
• Error-checking which guarantees the integrity of data transferred.
• Flow control to prevent overwhelming a network with too much data at once.

In the scenario presented in this exercise, TCP ensures that multiple clients can connect to a server concurrently without data losses, maintaining orderly communication via a series of unique sockets. Although the server listens constantly on port 80, TCP manages distinct connections using different client-side ports, ensuring data is correctly routed and distinguished among various originating hosts.