Computer Networks A1

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.

3 Tänk på ett tal mellan 0 och 31

4 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 = 2 4 = 2·2·2·2, corresponding to 4 bits. If the number of options was 32 = 2 5, 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

5 Bits and Bytes  N bit can represent M=2 N different values.  M values can be represented by N = 2 log 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.

Computer Networks A6 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

7 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

Computer Networks A8 Chapter 1 Introduction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Computer Networks A9 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 A10 Figure 1.2 Simplex communication Example: Video monitor. TV and radio broadcasting.

Computer Networks A11 Figure 1.3 Half-duplex communication One at a time. Example: Communication radio. 2-wire Ethernet.

Computer Networks A12 Figure 1.4 Full-duplex communication Example: Telephony. 4-wire Ethernet.

Computer Networks A 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 A14 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 A15 Topology of Networks Topology Bus Star Full Mesh Ring Partial Mesh  Topology defines the arrangement of links in a network

Computer Networks A16 Figure 1.5 Mesh topology (Maskformigt nätverk) Example: 5 stations. 4 ports per station =10 links.

Computer Networks A17 Figure 1.7 Bus topology (Bussnätverk) Examples: -”Old” ethernet with coaxial cable - Cable TV networks with cable modems

Computer Networks A18 Figure 1.6 Star topology (Stjärnnätverk) Hub (Nätnav) or switch (växel) Examples: -Ethernet with twisted pair cable -Telephone networks

Computer Networks A19 Figure 1.8 Ring topology (Ringnätverk) Example: Token ring and FDDI networks

Computer Networks A20 Figure 1.9 A hybrid topology: a star backbone with three bus networks Hub (Nätnav) or switch (växel)

Computer Networks A21 LAN – Local Area Network (Lokalt nätverk) Single building LAN Backbone (ryggradsdatanät) Multiple building LAN

Computer Networks A22 MAN - Metropolitan Area Network (Stadsnät) Public city network

Computer Networks A23 WAN – Wide Area Network (nationellt eller globalt nätverk)

Computer Networks A24 Figure 1.12 A heterogeneous network made of four WANs and two LANs LAN = Local Area Network WAN = Wide Area Network

Computer Networks A25 Nättopologier för WAN Hopkopplade LAN och WAN = internetwork T.ex. Internet. Växlat WAN (stjärnnät) T.ex. X.25 eller ATM Växel. Kopplar ihop punkt-till-punkt-länkar. Datorer, terminaler, skrivare, etc. Router=vägväljare, kopplar ihop nätverk med olika teknologier. Nätnoder:

Computer Networks A26 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 A27 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 A28