2. 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.

3. Introduction to Information Technologies
Fall 2004
Chapter 1
Introduction
Computer Networks A
History of Internet
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4. Tänk på ett tal mellan 0 och 31

5. 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

6. 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.

7. 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
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8. 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

9. 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

10. Introduction to Information Technologies
Fall 2004
Figure Simplex communication
Example: Video monitor.
TV and radio broadcasting.
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11. Introduction to Information Technologies
Fall 2004
Figure Half-duplex communication
One at a time.
Example: Communication radio. 2-wire Ethernet.
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12. Introduction to Information Technologies
Fall 2004
Figure Full-duplex communication
Example: Telephony. 4-wire Ethernet.
Computer Networks A
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13. 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
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14. 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
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15. 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
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16. Introduction to Information Technologies
Fall 2004
Figure 1.5 Full mesh topology (Maskformigt nätverk)
How many links with N nodes?
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17. Introduction to Information Technologies
Fall 2004
Figure 1.5 Mesh topology (Maskformigt nätverk)
Example: 5 stations. 4 ports per station =10 links.
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18. Introduction to Information Technologies
Fall 2004
Figure 1.7 Bus topology (Bussnätverk)
Examples:
”Old” ethernet with coaxial cable
Cable TV networks with cable modems
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19. 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
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20. Introduction to Information Technologies
Fall 2004
Figure 1.8 Ring topology (Ringnätverk)
Example: Token ring and FDDI networks
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21. Introduction to Information Technologies
Fall 2004
Figure 1.9 A hybrid topology: a star backbone with three bus networks
Hub (Nätnav) or switch (växel)
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22. 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
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23. MAN - Metropolitan Area Network (Stadsnät)
Introduction to Information Technologies
Fall 2004
MAN - Metropolitan Area Network (Stadsnät)
Public city network
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24. WAN – Wide Area Network (nationellt eller globalt nätverk)
Introduction to Information Technologies
Fall 2004
WAN – Wide Area Network (nationellt eller globalt nätverk)
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25. 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)
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26. 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)
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27. Introduction to Information Technologies
Fall 2004
Computer Networks A
History of Internet