Introduction

Currently, networking technology is experiencing its third major wave of revolution. The first was the move from circuit-switched mode to packet-switched mode, the second from hardwired to wireless mode, and finally the third revolution, which we will examine in this book, is the move from hardware to software mode. Let us briefly examine these three revolutions, before focusing more particularly on the third, which will be studied in detail in this book.

I.1. The first two revolutions

A circuit is a collection of hardware and software elements, allocated to two users - one at each end of the circuit. The resources of that circuit belong exclusively to those two users; nobody else can use them. In particular, this mode has been used in the context of the public switched telephone network (PSTN). Indeed, telephone voice communication is a continuous application for which circuits are very appropriate.

A major change in traffic patterns brought about the first great revolution in the world of networks, pertaining to asynchronous and non-uniform applications. The data transported for these applications make only very incomplete use of circuits, but are appropriate for packet-switched mode. When a message needs to be sent from a transmitter to a receiver, the data for transmission are grouped together in one or more packets, depending on the total size of the message. For a short message, a single packet may be sufficient; however, for a long message, several packets are needed. The packets then pass through intermediate transfer nodes between the transmitter and the receiver, and ultimately make their way to the endpoint. The resources needed to handle the packets include memories, links between the nodes and sender/receiver. These resources are shared between all users. Packet-switched mode requires a physical architecture and protocols - i.e. rules - to achieve end-to-end communication. Many different architectural arrangements have been proposed, using protocol layers and associated algorithms. In the early days, each hardware manufacturer had their own architecture (e.g. SNA, DNA, DecNet, etc.). Then, the OSI (Open System Interconnection) model was introduced in an attempt to make all these different architectures mutually compatible. The failure of compatibility between hardware manufacturers, even with a common model, led to the re-adoption of one of the very first architectures introduced for packet-switched mode: TCP/IP (Transport Control Protocol/Internet Protocol).

The second revolution was the switch from hardwired mode to wireless mode. Figure I.1 shows that, by 2020, terminal connection should be essentially wireless, established using Wi-Fi technology, including 3G/4G/5G technology. In fact, increasingly, the two techniques are used together, as they are becoming mutually complimentary rather than representing competition for one another. In addition, when we look at the curve shown in Figure I.2, plotting worldwide user demand against the growth of what 3G/4G/5G technology is capable of delivering, we see that the gap is so significant that only Wi-Fi technology is capable of handling the demand very strongly until 2020, and then less and less due to the massive opening of new frequencies, especially those higher than 20 GHz. We will come back to wireless architectures, because the third revolution also has a significant impact on this transition towards radio-based technologies, especially 5G technology.

Figure I.1. Terminal connection by 2020

Figure I.2. The gap between technological progress and user demand. For a color version of the figure, see www.iste.co.uk/pujolle/software2.zip

I.2. The third revolution

The third revolution, which is our focus in this book, pertains to the move from hardware-based mode to software-based mode. This transition is taking place because of virtualization, whereby physical networking equipment is replaced by software fulfilling the same function.

Let us take a look at the various elements which are creating a new generation of networks. To begin with, we can cite the Cloud. The Cloud is a set of resources which, instead of being held at the premises of a particular company or individual, are hosted on the Internet. The resources are de-localized and brought together in resource centers, known as datacenters.

The reasons for the Cloud's creation stem from the low degree of use of server resources worldwide: only 10-20% of servers' capacities are actually being used. This low value derived from the fact that servers are hardly used at all at night-time, and see relatively little use outside of peak hours, which represent no more than 4-5 hours each day. In addition, the relatively low cost of hardware meant that, generally, servers were greatly oversized. Another factor that needs to be taken into account is the rising cost of personnel to manage and control the resources. In order to optimize the cost of both resources and engineers, those resources need to be shared. The purpose of Clouds is to facilitate such sharing in an efficient manner.

Figure I.3 shows the growth of the public Cloud services market. Certainly, that growth is impressive, but in the final analysis, it is relatively low in comparison to what it could have been if there were no problems of security. Indeed, as the security of the data uploaded to such systems is rather lax, there has been a massive increase in private Clouds, taking the place of public Cloud services. In Chapter 11, we will examine the advances made in terms of security, with the advent of secure Clouds.

Figure I.3. Public Cloud services market and their annual growth rate

Virtualization is also a key factor, as indicated at the start of this chapter. The increase in the number of virtual machines is undeniable, and in 2019, three quarters of the servers available throughout the world are virtual machines. Physical machines are able to host increasing numbers of virtual machines. This trend is shown in Figure I.4. In 2019, each physical server hosts approximately 10 virtual machines.

The use of Cloud services has meant a significant increase in the data rates being sent over the networks. Indeed, processing is now done in datacenters, and both the data and the signaling must be sent to these datacenters and then returned to the user after processing. We can see this increase in data rate requirement by examining the market of Ethernet ports for datacenters. Figure I.5 plots shipments of 1 Gbps Ethernet ports against those of 10, 40 and 100 Gbps ports. As we can see, 1 Gbps ports, which are already fairly fast, are being replaced by ports that are ever more powerful.

Figure I.4. Number of virtual machines per physical server

Figure I.5. Ethernet port shipment

The world of the Cloud is, in fact, rather diverse, if we look at the number of functions which it can fulfill. There are numerous types of Clouds available, but three categories, which are indicated in Figure I.6, are sufficient to clearly differentiate them. The category that offers the greatest potential is the SaaS (Software as a Service) cloud. SaaS makes all services available to the user - processing, storage and networking. With this solution, a company asks its Cloud provider to supply all necessary applications. Indeed, the company subcontracts its IT system to the Cloud provider. With the second solution - PaaS (Platform as a Service) - the company remains responsible for the applications. The Cloud provider offers a complete platform, leaving only the management of the applications to the company. Finally, the third solution - IaaS (Infrastructure as a Service) - leaves a great deal more initiative in the hands of the client company. The provider still offers the processing, storage and networking, but the client is still responsible for the applications and the environments necessary for those applications, such as the operating systems and databases.

Figure I.6. The three main types of Cloud

More specifically, we can define the three Cloud architectures as follows:

• - IaaS (Infrastructure as a Service): this is the very first approach, with a portion of the virtualization being handled by the Cloud, such as the network servers, the storage servers and the network itself. The Internet network is used to host PABX-type machines, firewalls or storage servers, and more generally, the servers connected to the network infrastructure.
• - PaaS (Platform as a Service): this is the second Cloud model whereby, in addition to the infrastructure, there is an intermediary software program corresponding to the Internet platform. The client company's own servers only handle the applications.
• - SaaS (Software as a Service): with SaaS, in addition to the infrastructure and the platform, the Cloud provider actually provides the applications themselves. Ultimately, nothing is left to the company, apart from the Internet ports. This solution, which is also called Cloud computing, outsources almost all of the company's IT and networks.

Figure I.7 shows the functions of the different types of Cloud in comparison with the classical model in operation...