Download Topology of Networks

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Kapitel 1 - Introduktion
Föreläsningsmaterialet är författat av Magnus Eriksson. Material är även hämtat från
Iskra Popova samt läroboksförfattaren Behrouz Fourozan.
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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.
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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.
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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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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
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Chapter 1
Introduction
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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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.
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Figure 1.2
Simplex communication
Example: Video monitor.
TV and radio broadcasting.
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Figure 1.3
Half-duplex communication
One at a time.
Example: Communication radio. 2-wire Ethernet.
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Figure 1.4
Full-duplex communication
Example: Telephony. 4-wire Ethernet.
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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.
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Different Line Configurations
 Point-to-point
 Two devices on a
single channel
(dedicated channel)
 Multipoint
 Many devices on a single
channel (shared channel)
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Example:
Bus Networks.
Ring networks.
Wireless Networks
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Topology of Networks
 Topology defines the arrangement of links in a
network
Topology
Partial Mesh
Full Mesh
Star
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Bus
Ring
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Figure 1.5 Mesh topology (Maskformigt nätverk)
Example: 5 stations. 4 ports per station. 4+3+2+1=10 links.
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Figure 1.7 Bus topology (Bussnätverk)
Examples:
-”Old” ethernet with coaxial cable
- Cable TV networks with cable modems
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Figure 1.6 Star topology (Stjärnnätverk)
Hub (Nätnav) or switch (växel)
Examples:
-Ethernet with twisted pair cable
-Telephone networks
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Figure 1.8 Ring topology (Ringnätverk)
Example: Token ring and FDDI networks
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Figure 1.9 A hybrid topology: a star backbone with three bus networks
Hub (Nätnav) or
switch (växel)
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LAN – Local Area Network (Lokalt nätverk)
Single building LAN
Backbone
(ryggradsdatanät)
Multiple building LAN
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MAN - Metropolitan Area Network (Stadsnät)
Public city network
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WAN – Wide Area Network (nationellt eller
globalt nätverk)
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Figure 1.12 A heterogeneous network made of four WANs and two LANs
LAN = Local Area Network
WAN = Wide Area Network
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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.
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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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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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