Course 34310 Introduction to Communication Technology Course 34311 Introduction to Networks for Telecommunication and Data Communication Communication Networks, Protocols, LANs and the Internet August 29, 2010 Lars Staalhagen ([email protected]) Contents 1 Introduction 3 1.1 Notationused.................................... 4 2 Communication networks and transfer methods 5 2.1 What is a communication network? . ...... 5 2.2 Networktopologies ............................... .... 7 2.3 AccessandCorepartofanetwork . ..... 7 2.4 Networktransfermodes . .. .. .. .. .. .. .. .. .... 8 2.4.1 Circuitswitchedtransfermode . ..... 9 2.4.2 Packetswitchedtransfermode . 11 2.4.3 Comparisonoftransfermodes. 16 3 Introduction to Communication Protocols 17 3.1 Fundamentalsofprotocols . ...... 17 3.1.1 Whatisaprotocol? .............................. 17 3.1.2 Scopeofprotocols .............................. 18 3.1.3 Connectionless or Connection–oriented Protocols . ............ 18 3.2 Protocolprocedures .............................. 20 3.2.1 Generalscenario ............................... 20 3.2.2 Encapsulation................................. 20 3.2.3 Segmentation and Reassembly . 21 3.2.4 Addressing ................................... 22 3.2.5 Multiplexing .................................. 22 3.2.6 FlowControl .................................. 23 3.2.7 Error–detecting and error–correcting codes . .......... 27 3.2.8 Error–control ................................. 30 3.3 GenericDataLinkProtocol . ..... 33 3.4 Protocolreferencemodels . ...... 36 3.4.1 Generic layering concepts in the OSI reference model . ........... 37 3.4.2 LayersintheOSIreferencemodel . 37 3.4.3 Information exchange in the OSI reference model . ......... 39 4 Local Area Networks 41 4.1 Introduction.................................... 41 4.2 Classification of Computer Networks . ........ 41 4.3 MediumAccessControl ............................. 42 4.3.1 MACframes .................................. 44 4.4 EthernetLANs .................................... 45 4.4.1 Background................................... 45 1 4.4.2 Bus–topology .................................. 45 4.4.3 Star–topology................................. 48 4.5 TokenRingLANs ................................... 51 4.6 WirelessLANs .................................... 55 4.6.1 Network structure and bit rates . ..... 56 4.6.2 Medium Access Control for Wireless LANs . ..... 57 4.7 InterconnectionofLANs. ..... 61 5 The Internet 64 5.1 Background...................................... 64 5.2 InternetProtocol(IP) . .. .. .. .. .. .. .. ..... 65 5.2.1 Packetformat.................................. 65 5.2.2 IPAddresses .................................. 66 5.2.3 RoutinginIPnetworks . .. .. .. .. .. .. .. .. 69 5.2.4 Fragmentation ................................. 73 5.2.5 AddressResolutionProtocol . 76 5.2.6 ICMP ...................................... 78 5.2.7 NATandNAPT ................................ 78 5.2.8 DHCP...................................... 80 5.2.9 DNS....................................... 82 5.2.10 IPversion6................................... 88 5.3 UserDatagramProtocol . 89 5.4 TransmissionControlProtocol . ....... 90 5.4.1 Connection establishment and termination . ......... 91 5.4.2 FlowControlinTCP ............................. 92 5.4.3 OtherfeaturesofTCP. .. .. .. .. .. .. .. .. 93 5.5 Applicationlayer ................................ 95 5.5.1 Webbrowsing.................................. 95 5.5.2 Sendingandreceivingemails . 96 5.5.3 Filetransfers ................................. 102 5.6 ResidentalInternetaccess . ....... 103 5.6.1 Dial-upaccess................................. 103 5.6.2 xDSL ...................................... 107 Bibliography 110 A Amplitude Modulation 112 B Number systems 114 2 Chapter 1 Introduction The ability to communicate electronically with other people regardless of their locations has become an important part of the modern society, but this communication is only possible with the help of various communication networks that are used to transfer the information between people. Contemporary examples of these communication networks include: • The traditional telephone network, where every subscriber has a telephone connected to a plug in the wall. • Mobile communication networks that allow people to use mobile telephones to talk and/or exchange data, while walking, driving, and so on. • Local area networks (LANs) that are used to interconnect computers, printers, etc., in a limited geographical area. • The Internet that covers the entire Earth, which was originally used for data communica- tion, such as web surfing, file transfers, emails, etc., but is now increasingly used for newer services, e.g., Internet-telephony, Video-streaming, etc. The purpose of this lecture note is to introduce the reader to the area of data communication networks; both general concepts and specifically LANs and the Internet. The lecture note is intended for use in courses 34310 Introduction to Communication Technology and 34311 Introduction to Networks for Telecommunication and Data Communication. It is structured as follows. Chapter 2 introduces the general concept of communication networks consisting of network nodes and communication links, including a discussion of the various transfer methods that can be used in these networks. Chapter 3 describes the concept of communication protocols, including common protocol mechanisms, and also the concept of protocol reference models with emphasis on the OSI reference model. Chapter 4 presents a specific type of communication networks known as local area networks (LANs), both in general, but also includes a description of most common examples today: Ethernet and wireless LANs. The ubiquitous Internet is the topic for chapter 5, which describes aspects of the fundamental IP protocol, the UDP and TCP transport protocols and some common application protocols for web browsing, emails and file transfers. At the end of the lecture note are two appendices on Amplitude Modulation and Number Systems, respectively. The lecture note will focus on the general aspects of these topics to permit the reader to gain a basic understanding of the topics. Readers with an interest in the more advanced and detailed aspects of the topics are referred to advanced courses, e.g., course 34341 Advanced Data Communication or other courses. 3 Although this lecture note has been proofread many times, it is bound to contain numer- ous errors, so please inform the author (email: [email protected]) if you find any. Any comments or suggestions that might improve the lecture note are also appreciated. 1.1 Notation used In the following chapters in this lecture note, it is often relevant to describe how information, e.g., in form of messages are exchanged between different users, network equipment, and so on. A number of different ways that is used to illustrate these information exchanges is shown in figure 1.1. (a) (b) (c) Figure 1.1: Types of figures used to illustrate exchanges of information. The vertical lines in figure 1.1 represent the different users, network equipment, etc., that gen- erate and/or receive information, while the arrows represent the actual messages. The timing of messages uses the fact that time progresses downward, i.e., if message B is transmitted after message A, then the arrow representing message B is drawn below the arrow that represents message A. Figure 1.1a) is the simplest message exchange, where only the order of messages is relevant. However, as it takes some time for a message to travel from one device in the network to another, the message will arrive at the destination device some amount of time after it was transmitted by the source device. This fact is illustrated in figure 1.1b) by slanted arrows. Also indicated in this figure is the propagation delay, i.e., the delay from a message was transmitted until it was received. Finally, it may also be relevant to describe that the transmission of a message also take some time, i.e., that there is a transmission delay involved. This is illustrated in figure 1.1c). 4 Chapter 2 Communication networks and transfer methods 2.1 What is a communication network? The purpose of any communication network is to permit users (in a very general sense) in different locations to exchange information. A well-known example is the traditional telephone network (also called the Public Switched Telephone Network (PSTN)) where two people can talk with each other, even though they could be located in different continents. In general, a generic communication network consists of a number of terminals and network nodes that are interconnected by communication links in some structure. The structure of a communication network (i.e., how the network nodes are interconnected by the communication links) is also referred to as the network’s topology, or sometimes the network architecture. A generic terminal is a device that is the originator and/or destination of some information, which is often operated by a human user. Examples of terminals from existing communication networks are telephones (both traditional fixed and mobile) and personal computers. A device such as a webserver, which is not operated directly by a human user, is also a terminal by this definition. The purpose of a generic network node is to be able to receive information from a terminal or other network node, analyze and possibly process this information and ultimately forward the information towards the destination. The network nodes in real communication networks