Experiential Learning Of Networking Technologies: Evolution Of Socket Programming – Part I

Abstract

In the 21st century, the internet has become essential part of everyday tasks including banking, interacting with government services, education, entertainment, text/voice/video communication, etc. Individuals access the internet using client-side applications such as a browser or an app on their mobile phone or laptop/desktop. This client-side application communicates with a server-side application, typically running on a web server, which in turn may interact with other business applications. The underlying protocol is typically HTTP [1] running on top of the TCP/IP protocol [2][3]. A typical web server supports a large number (hundreds or thousands) of concurrent TCP connections. The most commonly deployed web servers in use today are Apache server [4], Nginx [5], or Microsoft Internet Information Server (IIS)[6]. Nginx is mostly used on Linux and IIS runs only on Windows OS. In contrast, Apache web server (which is almost as old as the web itself) is supported on all platforms (Linux, Windows, MacOS, etc.). In its initial release in 1995 (version 1.3), Apache server could serve only a few concurrent clients, but its current release (2.4.41) can support a huge number of concurrent clients. In this article (as well as Part II that will follow), we will present a simplified view of this evolution that nevertheless explains how current web manage such high levels of concurrency. To do so, we will delve into socket programming, which is at the heart of managing TCP connections, and we will examine the key role that it plays in delivering high performance. We have studied both transport layers protocol i.e., TCP [2] and UDP [7], in detail in the last few articles, and we have developed a basic understanding of the working of the transport layer. This is a communication-enabling layer used by applications to exchange application-level data. Simple working of applications using TCP (providing reliable delivery) and UDP (providing best effort delivery) socket programming are provided in [8]. In this article, however, we will discuss increasingly complex levels of socket programming, from simple socket connections to complex connection management that are necessary to attain high TCP performance. We will focus on TCP Socket programming only. UDP socket programming is simply a best effort delivery and socket implementation support does not impact the application communication performance.