WHITE PAPER

IP-based Networks:
Basics

TABLE OF CONTENTS

1. Introduction.. 3

2. Basics in network communication.. 3

3. Transmission Fundamentals.. 5

4. The Local Area Network Infrastructure.. 6

5. Interconnecting LANs in an IP-based Architecture.. 10

6. Benefit from the IP-based Architecture.. 11

7. Convergence.. 12

8. Conclusion.. 12

1. Introduction

Modern digital technology allows different sectors, e.g. telecom, data, radio and television, to be merged together. This occurrence, commonly known as convergence, is happening on a global scale and is drastically changing the way in which both people and devices communicate. At the center of this process, forming the backbone and making convergence possible, are IP-based networks.

Services and integrated consumer devices for purposes such as telephony, entertainment, security or personal computing are constantly being developed, designed and converged towards a communication standard that is independent from the underlying physical connection. The cable network, for instance, first designed for transmitting television to the consumer, can now also be utilized for sending e-mail, surfing the Web or even monitoring a network camera sending live pictures from another continent. Furthermore, these features are also available over other physical networks, e.g. telephone, mobile phone, satellite and computer networks.

This white paper introduces the central components of IP-based network technology, and in doing so it will demonstrate the tremendous benefits this new technology has to offer.

2. Basics in network communication

The Internet has become the most powerful factor guiding the ongoing convergence process. This is mainly due to the fact that the Internet protocol suite has become a shared standard used with almost any service. The Internet protocol suite consists primarily of the Internet Protocol (IP) and the Transport Control Protocol (TCP); consequently, the term TCP/IP commonly refers to the whole protocol family.

IP-based networks are of great importance in today’s information society. At first glance, this technology might appear a bit confusing and overwhelming. Therefore, we’ll start by presenting the underlying network components upon which this technology is built.

A network is comprised of two fundamental parts, the nodes and the links. A node is some type of network device, such as a computer. Nodes are able to communicate with other nodes through links, like cables. There are basically two different network techniques for establishing communication between nodes on a network: the circuit-switched network and the packet-switched network techniques. The former is used in a traditional telephone system, while the latter is used in IP-based networks.

A circuit-switched network creates a closed circuit between two nodes in the network to establish a connection. The established connection is thus dedicated to the communication between the two nodes. One of the immediate problems with dedicated circuits is wasted capacity, since almost no transmission uses the circuit 100 percent of the time. Also, if a circuit fails in the middle of a transmission, the entire connection must be dropped and a new one established. For illustration purposes, take a look at a telephone connection over a circuit-switched network (Figure 1).

Figure 1: A circuit-switched network utilizes a dedicated closed circuit

IP-based networks on the other hand utilize a packet-switched network technology, which uses available capacity much more efficiently and minimizes the risk of possible problems, such as a disconnection. Messages sent over a packet-switched network are first divided into packets containing the destination address. Then, each packet is sent over the network with every intermediate node and router in the network determining where the packet goes next. A packet does not need to be routed over the same links as previous related packets. Thus, packets sent between two network devices can be transmitted over different routes in the event of a link breakdown or node malfunction (Figure 2).

Figure 2: A packet-switched network routes each packet independently

3. Transmission Fundamentals

IP-based network solutions are both flexible and economical substitutes for solutions that utilize old network technologies. The diverse properties between these technologies result from how information is represented, transmitted and managed. Information is simply structured collections of data, and thus takes its meaning from the interpretation we give it. There are two fundamental types of data, analog and digital, and both possess different behaviors and characteristics.

Analog data is expressed as continuously variable waves and thus takes on continuous values. Examples include voice and video.

Digital data on the other hand is represented as a sequence of bits, or ones and zeros. This digitization allows any kind of information to be measured and represented as digital data. So, text, sound and pictures can be represented as a sequence of bits. Digital data can also be compressed to allow higher transmission rates and it can be encrypted for secure transmissions. In addition, a digital signal is exact and any related noise can easily be filtered out. Digital data can be transmitted through three general types of media—metal such as copper; optical fiber or radio waves.

The techniques represented below offer the first building block for digital communications, the cable and antenna layer (Figure 3). This layer allows us to send and receive digital data over a wide variety of media. However, more building blocks are required for successful digital communication.

Figure 3: Cable and antenna layer - the first building block

4. The Local Area Network Infrastructure

This section will go one step further by discussing digital communication. You might ask, “What is the difference between transmission and communication?” Consider an analogy from human speech. Think about the acoustic waves in the air generated by speaking. These waves are transmitted, but they are a long way from communicating. The words that come out must be organized to make any sense. If they come out to quickly or too slowly, the speaker will not be understood. If many people speak simultaneously no one is understood. If someone speaks a language you don’t understand, information is lost. Speaking generates information, but it is not necessarily communicated, or understood.

Digital communication has similar problems that need to be overcome. The receiver must know how message bits are organized to understand the message. The receiver must know the rate at which the bits are arriving to interpret the message. Additionally, some rules must specify what will happen if many network devices try to use a shared media simultaneously. The best way to ensure that network devices send and receive in compatible ways is to adhere to standardized protocols that define the rules and the manner in which the devices initiate and carry on communication.

We have until now focused on communication between two network devices. However, several different connection strategies and protocols exist that can be used to maintain communication among many network devices.

Local Area Networks (LANs) are used for connecting network devices over a relatively short distance. Typically, a LAN operates in a limited space, such as an office building, a school or a home. LANs are usually owned and managed by a single person or organization. They also use certain specific connectivity technologies, often some type of shared media.

An important feature of a LAN is its topology, where the term topology refers to the layout of connected network devices on a network. We can think of topology as a network's shape. Network topologies can be categorized into the following basic types:

· The bus topology uses a shared communication medium, often referred to as a common bus, to connect all network devices (Figure 4). A device that wants to communicate with another device on the network sends the packet onto the bus. All devices that are connected to the bus will receive the sent packet but the intended recipient is the only device that actually accepts and processes the packets.

Figure 4: Bus topology uses a common bus to connect network devices

· The ring topology is structured in such a way that every network device on the network has exactly two neighbors for their communication purposes. All packets travel along a ring in the same direction (Figure 5).

Figure 5: Ring topology uses a ring structure to connect network devices

· The star topology features a logical communication center to which all network devices are directly connected. Each device requires a separate cable to the central point and consequently all packets will travel through the communication center (Figure 6).

Figure 6: Star topology uses a star-shaped network to connect network devices

There are several different protocols that can be utilized together with each network topology. Aside from identifying the standards of communications between the network devices, a protocol sets the technical specifications needed to transmit data within a network. To transmit a message to another device in a network, the message is split into data packets. These data packets are then transmitted via the communication media and are reassembled again at the receiving end.

The standardized protocols utilize different network topologies together with the cable and antenna layer to build different LAN architectures that are either wired or wireless. These protocols offer the second building block for successful digital communications, the transmission layer (Figure 7).

Figure 7: Transmission layer - the second building block

5. Interconnecting LANs in an IP-based Architecture

So far, we have described how network devices can communicate over different types of LANs. However, different LANs are designed for different goals and needs. Hence, every so often it is necessary to interconnect several LANs to allow communication over the network boundaries. Such a geographically scattered, interconnected collection of LANs is commonly referred to as a Wide Area Network (WAN). Probably the most familiar WAN is the Internet, which spans most of the globe.

Shared communication architecture is required for all users, such as private persons, enterprises, public administration offices and other organizations, to be able to exchange digital information with one another over a WAN. This architecture should be an open standard and support different transmission layer protocols, particularly those that can be used over a variety of transmission media. Fortunately, the Internet protocol suite provides a well-designed solution that fits these requirements.

5.1 The Internet protocol suite

The Internet protocol suite is a layered protocol family where each layer builds upon the layer below it, adding new functionality. The lowest layer is concerned purely with sending and receiving data utilizing the transmission layer. At the top are protocols designed for specific tasks, such as sending and receiving motion pictures, sound and control information. The protocols in between handle things such as dividing the message data into packets and forwarding them reliably between network devices.

5.2 Internet Protocol

The Internet Protocol (IP) is the basis of the Internet protocol suite and is the single most popular network protocol in the world. IP enables data to be transmitted across and between local area networks, hence the name: Inter-net Protocol. Data travels over an IP-based network in the form of IP packets (data units). Each IP packet includes both a header and the message data itself, where the header specifies the source, the destination, and other information about the data.

IP is a connectionless protocol where each packet is treated as a separate entity, like a postal service. Any mechanisms for ensuring that sent data arrives in a correct and intact manner are provided by higher-layer protocols in the suite.

Each network device has at least one IP address that uniquely identifies it from all other devices on the network. In this manner, intermediate nodes can correctly guide a sent packet from the source to the destination.

5.3 Transport Protocol

The Transport Control Protocol (TCP) is the most common protocol for assuring that an IP packet arrives in a correct and intact manner. TCP provides reliable transmission of data for upper layer applications and services in an IP environment. TCP offers reliability in the form of a connection-oriented, end-to-end packet delivery through an interconnected network.

5.4 An Internet Protocol suite summary