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Computer Networks A 1 DT024G, Datornätverk A, 7,5 hp DT075G, Multimedie- och kommunikationssystem, 6 hp Kapitel 1 - Introduktion Föreläsningsmaterialet är författat av Magnus Eriksson. Material är även hämtat från Iskra Popova samt läroboksförfattaren Behrouz Fourozan. Tänk på ett tal mellan 0 och 31 3 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? Yes 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. 4 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. 5 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 6 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 7 Chapter 1 Introduction Computer Networks A Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8 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 9 Figure 1.2 Simplex communication Example: Video monitor. TV and radio broadcasting. Computer Networks A 10 Figure 1.3 Half-duplex communication One at a time. Example: Communication radio. 2-wire Ethernet. Computer Networks A 11 Figure 1.4 Full-duplex communication Example: Telephony. 4-wire Ethernet. Computer Networks A 12 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 13 Different Line Configurations Point-to-point Two devices on a single channel (dedicated channel) Multipoint Many devices on a single channel (shared channel) Computer Networks A Example: Bus Networks. Ring networks. Wireless Networks 14 Topology of Networks Topology defines the arrangement of links in a network Topology Partial Mesh Full Mesh Star Computer Networks A Bus Ring 15 Figure 1.5 Mesh topology (Maskformigt nätverk) Example: 5 stations. 4 ports per station. 4+3+2+1=10 links. Computer Networks A 16 Figure 1.7 Bus topology (Bussnätverk) Examples: -”Old” ethernet with coaxial cable - Cable TV networks with cable modems Computer Networks A 17 Figure 1.6 Star topology (Stjärnnätverk) Hub (Nätnav) or switch (växel) Examples: -Ethernet with twisted pair cable -Telephone networks Computer Networks A 18 Figure 1.8 Ring topology (Ringnätverk) Example: Token ring and FDDI networks Computer Networks A 19 Figure 1.9 A hybrid topology: a star backbone with three bus networks Hub (Nätnav) or switch (växel) Computer Networks A 20 LAN – Local Area Network (Lokalt nätverk) Single building LAN Backbone (ryggradsdatanät) Multiple building LAN Computer Networks A 21 MAN - Metropolitan Area Network (Stadsnät) Public city network Computer Networks A 22 WAN – Wide Area Network (nationellt eller globalt nätverk) Computer Networks A 23 Figure 1.12 A heterogeneous network made of four WANs and two LANs LAN = Local Area Network WAN = Wide Area Network Computer Networks A 24 Nättopologier för WAN Växlat WAN (stjärnnät) Hopkopplade LAN och WAN = internetwork T.ex. X.25 eller ATM T.ex. Internet. Nätnoder: Växel. Kopplar ihop punkt-till-punkt-länkar. Datorer, terminaler, skrivare, etc. Router=vägväljare, kopplar ihop nätverk med olika teknologier. Computer Networks A 25 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 26 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 27 Computer Networks A 28