Kapitel 1 - Introduktion Välkommen till kurserna Multimedie- och kommunikationssystem, 6 hp för civilingenjör data och elektro Industriell datakommiunikation, 7,5 hp för automationsingenjörer Kapitel 1 - Introduktion Föreläsningsmaterialet är författat av Magnus Eriksson. Material är även hämtat från Iskra Popova samt Behrouz Fourozan.

Introduction to Information Technologies Fall 2004 Chapter 1 Introduction Computer Networks A History of Internet Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Tänk på ett tal mellan 0 och 31

Amount of information Think about a number between 0 and 15. I am now going to guess it using as few yes and no questions as possible. I start by asking: Is the number larger than or equal to 8? Yes Is it larger than or equal to 12? (The interval is successively divided by 2.) No. Is the number larger than or equal to 10? Is the number larger than or equal to 9? Yes. The amount of information you give me when you tell me that the number is 9 is 4 bits, because the amount of information in bits is the minimum number of yes and no questions that are required. We had 16 options, which is = 24 = 2·2·2·2, corresponding to 4 bits. If the number of options was 32 = 25 , it would require 5 bits. If yes is represented by the binary digit ”1”, and no by ”0”, the value in the above example can be represented by 1 0 1 1.

Bits and Bytes N bit can represent M=2N different values. M values can be represented by N = 2log M =log M / log 2 values Example: The N=7 bit ASCII character code consists of M=128 codes. 8 bits = 1 byte (a unit for measuring amount of data) 1 kbit = 1000 bit (previously 1024 bit). 1 Mbit = 1000 kbit (previously 1024 kbit). 1 Gbit = 1000 Mbit. 1 Tbit = 1000 Gbit.

Introduction to Information Technologies Fall 2004 Data Representation Text – using different codes Each character is represented by certain number of bits The number of bits in the code determins the number of different characters ASCII (7 bits), Extended ASCII (8 bits), Unicode (16 bits), ISO (32 bits) Numbers – Binary number system Images – A matrix of pixels represented by bit patterns Video – A combination of images Audio – Digitized voice and music Computer Networks A History of Internet

Bandbredd kan betyda många saker Analog bandbredd i Hertz. Övre gränsfrekvens minus undre gränsfrekvens. Net bit rate = Digital bandbreddskapacitet i Bit/s. = Datatakt exklusive felupptäckande koder. Net bit rate ≤ Gross bit rate Maximal genomströmninshastighet = Maximal throughput Genomströmningshastighet = Throughput = Digital bandbreddskonsumtion Goodput = Filöverföringshastighet

Introduction to Information Technologies Fall 2004 Figure 1.1 Five components of data communication Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. Computer Networks A History of Internet

Introduction to Information Technologies Fall 2004 Figure 1.2 Simplex communication Example: Video monitor. TV and radio broadcasting. Computer Networks A History of Internet

Introduction to Information Technologies Fall 2004 Figure 1.3 Half-duplex communication One at a time. Example: Communication radio. 2-wire Ethernet. Computer Networks A History of Internet

Introduction to Information Technologies Fall 2004 Figure 1.4 Full-duplex communication Example: Telephony. 4-wire Ethernet. Computer Networks A History of Internet

Introduction to Information Technologies Fall 2004 1-2 NETWORKS A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, hub, switch, router, modem, or any other device capable of sending and/or receiving data generated by other nodes on the network. Computer Networks A History of Internet

Different Line Configurations Introduction to Information Technologies Fall 2004 Different Line Configurations Point-to-point Two devices on a single channel (dedicated channel) Multipoint Many devices on a single channel (shared channel) Example: Bus Networks. Ring networks. Wireless Networks Computer Networks A History of Internet

Introduction to Information Technologies Fall 2004 Topology of Networks Topology defines the arrangement of links in a network Topology Ring Partial Mesh Full Mesh Bus Star Computer Networks A History of Internet

Introduction to Information Technologies Fall 2004 Figure 1.5 Full mesh topology (Maskformigt nätverk) How many links with N nodes? Computer Networks A History of Internet

Introduction to Information Technologies Fall 2004 Figure 1.5 Mesh topology (Maskformigt nätverk) Example: 5 stations. 4 ports per station. 4+3+2+1=10 links. Computer Networks A History of Internet

Introduction to Information Technologies Fall 2004 Figure 1.7 Bus topology (Bussnätverk) Examples: ”Old” ethernet with coaxial cable Cable TV networks with cable modems Computer Networks A History of Internet

Introduction to Information Technologies Fall 2004 Figure 1.6 Star topology (Stjärnnätverk) Hub (Nätnav) or switch (växel) Examples: Ethernet with twisted pair cable Telephone networks Computer Networks A History of Internet

Introduction to Information Technologies Fall 2004 Figure 1.8 Ring topology (Ringnätverk) Example: Token ring and FDDI networks Computer Networks A History of Internet

Introduction to Information Technologies Fall 2004 Figure 1.9 A hybrid topology: a star backbone with three bus networks Hub (Nätnav) or switch (växel) Computer Networks A History of Internet

LAN – Local Area Network (Lokalt nätverk) Introduction to Information Technologies Fall 2004 LAN – Local Area Network (Lokalt nätverk) Single building LAN Backbone (ryggradsdatanät) Multiple building LAN Computer Networks A History of Internet

MAN - Metropolitan Area Network (Stadsnät) Introduction to Information Technologies Fall 2004 MAN - Metropolitan Area Network (Stadsnät) Public city network Computer Networks A History of Internet

WAN – Wide Area Network (nationellt eller globalt nätverk) Introduction to Information Technologies Fall 2004 WAN – Wide Area Network (nationellt eller globalt nätverk) Computer Networks A History of Internet

Introduction to Information Technologies Fall 2004 The Internet Internet routers are network nodes that interconnect different networks. Network Access Points (NAP) are routers that interconnect national ISP:s. ISP = Internet Service Provider (internetleverantör) Computer Networks A History of Internet

The internet versus the Internet Introduction to Information Technologies Fall 2004 The internet versus the Internet Internetwork or internet (small ”i”) – generic term to mean an interconnection of networks Internet (Uppercase I) – the specific worldwide network that uses the IP protocol (Internet protocol) Computer Networks A History of Internet

Introduction to Information Technologies Fall 2004 Computer Networks A History of Internet