Local Networks and the Internet

From Protocols to Interconnection

Laurent Toutain, Ana Minaburo

• Verlag: Wiley-ISTE
• Jahr: 2013
• ISBN:
  9781118599891
• Auflage: 1
• Thema: Technology & Engineering
• Thema: Electrical Engineering & Telecommunications

This title covers the most commonly used elements of Internet and Intranet technology and their development. It details the latest developments in research and covers new themes such as IP6, MPLS, and IS-IS routing, as well as explaining the function of standardization committees such as IETF, IEEE, and UIT. The book is illustrated with numerous examples and applications which will help the reader to place protocols in their proper context.

Chapter 1

Introduction

1.1. Why a network?

A network transmits information from point-to-point from an office, company, school, aircraft carrier or, more generally, from anywhere on the planet. Very often associated with the Internet, it has completely transformed the design of traditional computer systems. To remember this, one need only read the short story by sciencefiction writer Isaac Asimov who in the 1970s offered his vision of the computer industry evolution in the short story All the Troubles of the World¹. For the 2000s, he forecast a gigantic computer called “the multivac”, which would control the entire planet. He went as far as predicting the election of the world president by this computer. Asimov writes that it encompassed Washington D.C. and its suburbs and that an army of civil servants was needed to run it.

To foresee the computer of the future, Asimov simply described the situation of the centralized computer systems of the 1970s and increased everything: the size of central units and the number of people needed to make them run. The footprint, the design and maintenance cost mean that this type of equipment is limited and reserved for important research and general interest tasks. Information is necessarily centralized in these points and resorting to a network is pointless.

What we can observe, in the 21st century, is radically opposed to Asimov’s vision. The systems are decreasing in size, increasingly powerful, numerous and specialized and their maintenance is simpler and increasingly limited. This dispersion of computing power and information is not due to the reduction of computer power. Networks are not solely responsible for this spectacular change in the design of computer systems, but they allow the interconnection of all these different “small” systems to make them cooperate and exchange information. These systems, more flexible and, in the end, more powerful and able to evolve, have gained acceptance.

Networks existed at the time Asimov wrote his book, but they were used to connect terminals to the central computer. In the current networks, information processing is most often done locally, i.e. on the computer sitting on the user’s desk or in the company, whereas information originates at the other end of the campus or planet. The information transported by these networks is not directly usable by a human being, but is meant for programs that must process it before a human being can access it. With the increase in available network rates, we are witnessing the increasing integration of new data types (for computer scientists), such as voice or animated pictures.

This vision of large and expensive centralized computing still has some consequences nowadays, which can be found in particular in the architecture of the Internet. Thus, the Internet Protocol (IP) that is used to transport data from one network point to another was conceived around this time. It was never planned that it would become the quasi-universal protocol that we know today. The addresses used be dimensioned to support slightly more than four billion pieces of equipment — a number that seemed unrealistic in the 1970s, but that causes enormous problems nowadays, since we are approaching saturation of the addressing space. Studies are underway to replace the current protocol (IPv4) with a version allowing quasi-unlimited equipment addresses (IPv6). In light of the scope of this task, this will take several years.

Mobility was also an element not taken into account at the start. In the 1970s, with computers weighing several tons and limited to air-conditioned rooms, it was unrealistic to move them from network to network. With the advent of wireless technologies and the miniaturization of equipment, these constraints have been lifted, but addressing in Internet does not take this into account. This has led to the need for a complete overhaul of the architecture of the Internet. Studies are underway in the normalization instances.

This book, through a vision organized around the Internet, will describe the main protocols, such as local Ethernet or wireless networks, and architectures such as ADSL. The organizations which participate in this standardization effort or help run the network will also be described.

1.2. Network classification

The Internet is often called a network of networks because it offers a common exchange format allowing switching from one network technology to another. These networks, for which the Internet is the link, are very diverse, but several criteria facilitate their classification.

1.2.1. Function of distance

This first criterion can be the area covered. Technologies can be divided into several categories, of which the frontiers are relatively blurred and can evolve in time with technological advances.

They are designated by WAN (Wide Area Network), MAN (Metropolitan Area Network) and LAN (Local Area Network). Table 1.1 indicates the characteristics of these different types of networks. In more recent classifications, metropolitan networks can be considered as access networks.

Table 1.1. Different types of networks

1.2.1.1. Local networks

A LAN is mainly characterized by its reduced performance: its relatively short distance and resistance to scalability (i.e. performance drops as the number of pieces of equipment connected increase) is much smaller.

A local network thus generally serves a company office, floor or building. The network and machines’ administration is usually done by the same service. The cost using a local network is mainly that of computers and cables.

Ethernet and Wi-Fi networks are the most common local network technologies. Historically the range of an Ethernet network was theorically 2.5 km, but with the progress made in electronics and in particular the decreased cost and increased reliability of interconnection equipment, the size of networks has greatly shrunk. Current cabling rules state that a wired network should not span beyond a few hundred meters. For wireless networks, coverage is around 10 meters.

Parallel to the decrease in network size, the number of users directly connected has also fallen. Historically, a network could connect at least two pieces of equipment to a few hundred users. Currently, 50 users is an acceptable number. On wired networks (such as the Ethernet) with commutation techniques preventing sharing the medium between pieces of equipment we are going back to point-to-point communications between two pieces of equipment on the network: the station and the switch; see Chapter 3.

The data rate is usually 100 Mbit/s for wired networks and varies between a few tens and 100 Kbit/s for wireless networks. Except under special circumstances, increasing the data rate for these types of networks is no longer necessary since a rate of 100 Mbit/s, in the case of wired networks, is decreasingly shared between users and is dedicated to each piece of equipment. Nevertheless gigabit technologies are spreading rapidly.

On the other hand, some networks are not increasing their speed but prefer to limit energy consumption. This is the case for Wireless Sensor Networks (WSN), which may interconnect equipment at 250 kbit/s.

1.2.1.2. Metropolitan network or access network

The separation between a local network and a metropolitan network can be very blurred. The functioning principles are sometimes quite similar. Metropolitan networks or MANs allow us to connect a certain number of sites together or to attach them to a public network. They are often referred to as a backbone.

Access networks, such as ADSL (asymmetric digital subscriber lines) or WiMAX, can be included in this category because they interconnect local networks to public networks.

If local networks need to be interconnected, the administration of a metropolitan network can be given to a common structure that groups all users or even the company itself if it is the only user of the network. Billing is flat and not based on the number of bytes transmitted. It covers the network use, maintenance and administration costs. If it consists of connecting to public networks, the cost can be based on the connection data rate.

For access networks, data rates are usually lower than for local and public networks. They generally constitute a bottleneck (sometimes deliberate when billing is based on data rate or technology).

Since it is a network most often implemented with fiber optics, and built in a protected site, the error rate is relatively low, transmission delays are reduced and routing is quite simple. The old FDDI (fiber data distributed interface) technology, covering a distance of 200 km and offering a data rate of 100 Mbit/s, is a metropolitan network.

Wired access networks, such as ADSL, are built around a point-to-point topology, but, for example, fiber optic access networks could use a shared access mode. For broadcast networks, the question is irrelevant given the nature of the medium.

1.2.1.3. Public networks

These networks (WANs) are usually meshed networks made of high data rate point-to-point links between interconnection nodes.

Historically, the data rate was relatively low; it could go as low as 50 bit/s for the Telex network and reach up to 2 Mbit/s for the users. One of the most important revolutions in the networks has been the large rise of the data rate for this type of network. For years it has represented a bottleneck for communications. Nowadays, with the progress of transmission technologies, data rates can reach several Gigabit/s or even a few Terabit/s.

Even if in most cases these networks no longer constitute a bottleneck in the transmission part, it is still difficult to switch, i.e. the data routing process in the network to one link or another. The nature and length of these lines make the error rate relatively high. Error corrector or detector codes must be used that further reduce the data rate. Errors caused by noise on the transmission line are becoming rare and are most often due to saturation of the intermediate equipment, which loses information.

Transmission delay is quite large. In addition to the propagation delay (for example due to the use of a satellite in some networks), the message is copied from node-to-node until reaching its destination.

Lastly, routing, i.e. the path the information must follow to reach its destination, may be very complex. It consists of finding the best path that, from the user’s point of view, maximizes the data rate and minimizes the transmission delay and, from the operator’s point of view, maximizes the load on all the network links. In doing so, at each moment each node would have a complete vision of the network. This would lead to a paradoxical situation where all the network capacity would be used to transmit the state of the network to the different nodes, without leaving any room for the useful traffic. A relatively complicated algorithm must be used to try to reach the optimal routing.

1.2.2. Function of the topology

Different topologies, i.e. network shapes, can be used to classify the types of network. Each topology has its strengths and weaknesses. Each topology has different corresponding access methods with their own physical medium. Figure 1.1 tries to exhaustively represent the different topologies that can be found. Only a small number of these possibilities will really be employed in network architectures:

— point-to-point links are the easiest links to operate since they do not require addressing to identify the transmitter (the message always comes from the other end) or the receiver (it propagates to the other end). In general, these links are bi-directional and do not require access management mechanisms. As soon as a piece of equipment wants to transmit a message, it can transmit it on the dedicated medium. Unfortunately, a point-to-point link only reaches one piece of equipment. To allow us to build a network, several architectures are built around point-to-point links:

Figure 1.1. Different topologies

– complete mesh: this consists of putting point-to-point links in place between all the pieces of equipment that ...

Inhaltsverzeichnis

• Cover
• Title Page
• Copyright
• Chapter 1: Introduction
• Chapter 2: Standardization and Wiring
• Chapter 3: Ethernet and IEEE 802.3 Protocols
• Chapter 4: The LLC and SNAP Sublayers
• Chapter 5: Interconnection by Bridges: The Spanning Tree Algorithm
• Chapter 6: Internet
• Chapter 7: IP Protocols
• Chapter 8: Level 4 Protocols: TCP, UDP and SCTP
• Chapter 9: Address Resolution and Automatic Configuration Protocols
• Chapter 10: Routing Protocols
• Chapter 11: Internal Routing Protocols
• Chapter 12: External Routing Protocols
• Chapter 13: Virtual Local Networks
• Chapter 14: MPLS (Multi Protocol Label Switching)
• Chapter 15: IP on Point-to-Point Links: PPP
• Chapter 16: Network Administration
• Chapter 17: Security
• Chapter 18: Flow Management
• Bibliography
• Index