Computer Networks Performance Metrics Computer Networks Term A15.
Operating Systems and Computer Networks L8 …...Operating Systems and Computer Networks L8...
Transcript of Operating Systems and Computer Networks L8 …...Operating Systems and Computer Networks L8...
Operating Systems and Computer Networks
L8 – Introduction to computer networks
Prof. Dr.-Ing. Axel HungerAlexander Maxeiner, M.Sc.
Institute of Computer EngineeringFaculty of Engineering
University Duisburg-Essen
Dr.-Ing. Pascal A. Klein & Alexander Maxeiner M.Sc.
Alexander Maxeiner, M.Sc.University Duisburg-Essen
2Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
ISO/OSI Model
Data Transmission
Network Transmission
Code efficiency
Transmission protocols
TCP/IP
Network topologies
Routing protocols
Routing algorithms
Overview of content
Alexander Maxeiner, M.Sc.University Duisburg-Essen
3Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Computer networks consist of several autonomous devices interconnected through a series of wires, routing systems and/or wireless transmitters/receivers.
The origin of computer networks begin in the 1950’s. The American defense agency wanted a network capable of enduring a nuclear war.
Telephone services back then were organized like interconnected star networks.
Paul Baran of the RAND Corporation presented a mesh network as a solution to the problem.
AT&T was ordered to realize the network. But the didn’t want to.
History of networks I
Alexander Maxeiner, M.Sc.University Duisburg-Essen
4Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
In 1967 a network implemented at the National Physical Laboratory in GB presented a working design of connecting several computer systems at the campus.
The groundwork of this network then resulted in the ARPANET.
This network used IMP’s (Interface Message Processors) that stored the received data, divided them into packages and transmitted the data with 56 kbit/s.
The network was then realized and tested at several universities within the USA.
The experiment showed that ARPANET protocols were insufficient to connect multiple networks. TCP/IP was invented.
History of networks II
Alexander Maxeiner, M.Sc.University Duisburg-Essen
5Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
During the 80’s and 90’s several regional networks were connected to each others with the TCP/IP stack protokolls.
A computer that has an IP address and can send TCP/IP packages (and is physically connected to the network) is part of the internet.
At first this network was mainly for research, companies and governments.
CERN Physicist Tim Berners-Lee invented the WWW-application, that streamlined the transmission of data and in combination with the Mosaic-Viewer a GUI for websites were invented.
www.spacejam.com
History of networks III
Alexander Maxeiner, M.Sc.University Duisburg-Essen
6Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Networks today:
LAN
Bluetooth
Modem
Network providers
Mobile Internet
WAN
Internet
Networks
Alexander Maxeiner, M.Sc.University Duisburg-Essen
7Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Application on top level of computer starts a data request (browser)
Task is translated to lower level.
Data transmission protocols are activated, physical connection established, packages send/received.
Data received is processed, functions depending on data executed.
Tasks result in change of GUI -> Display is refreshed.
Connection closed.
Architecture
Alexander Maxeiner, M.Sc.University Duisburg-Essen
8Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Example for the functions of networking
Visual example
Manager X wants to communicate with Manager Y
Secretary knows Address and
Department
English is taken as a common
understood language
Official
signature is
added
International Post-ZIP-Code added
Alexander Maxeiner, M.Sc.University Duisburg-Essen
9Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Each layer does not know (need to know) how each other layer works.
Privacy between each layer. Work on a strict need-to-know basis.
Each layer can be changed due to technical inventions.
As long as there is an interface between each layer, they can be viewed as individual modules.
Necessary that each interface has established standards to re-translate the original data correct.
Analogy
Alexander Maxeiner, M.Sc.University Duisburg-Essen
10Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Model -> Realisation
Department / Room = Port-Number
Page-Number = Sequence Number
House Number & Post-ZIP-Code
= IP-Address
ISO/OSI
ModelExample Protocols DoD Model
Alexander Maxeiner, M.Sc.University Duisburg-Essen
11Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
OSI Model = Open System Integration model.
Published 1984, first step to standardize several communication protocols.
Protocols are rarely used, was cast aside in favor of the TCP/IP routing protocols.
The model is still valid and based on:
– Knowledge of technology
– Human communication
– Link different systems in a transparent way
– Cover all fields from application to technical data
OSI Model
Alexander Maxeiner, M.Sc.University Duisburg-Essen
12Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
OSI layer model
data linkdata link
networknetwork
transporttransport
sessionsession
presenta-tion
presenta-tion
AppApp
physicalphysical
application protoccol
presentation protoccol
session protoccol
transport protoccol
network network
data link data link
1
3
2
4
5
6
7
bit
packet
frame
message
message
message
message
network (routing) protocol
Communication subnetA B
Unit
Data link protocol
physical physical
Alexander Maxeiner, M.Sc.University Duisburg-Essen
13Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Layers & Interfaces
Layer 1Layer 1
Layer 2Layer 2
Layer 3Layer 3
Layer 4Layer 4
Layer 5Layer 5
physicalphysical
Layer 1 - protocol
Layer 5 - protocol
Layer 4 - protocol
Layer 3 - protocol
Layer 2/3-Interface
Layer 1/2-Interface
Layer 3/4-Interface
Layer 4/5-Interface
Layer 2 - protocol
Host 1 Host 2
Alexander Maxeiner, M.Sc.University Duisburg-Essen
14Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Flow of information
M
MediaMedia
destinationSource
Layer 5 - protocol
Layer 4 - protocol
Layer 3 - protocol
L5
Layer 2 - protocol
Host 1 Host 2
Header 4
M1H4H3 M1H4H3
M1H4H3H2 T2
M1H4H3 M1H4H3
MHeader 4
M1H4H3H2 T2
L4
L3
L2
Alexander Maxeiner, M.Sc.University Duisburg-Essen
15Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
ARPANET connections between universities over telephone cables usually without problems, but satellite and wireless networks caused complications.
New reference was necessary to connect/disconnect devices more easy.
The new internet layer works on a package based network, where a constant connection is not necessary.
Data packages can be send to it’s destination without regards of correct order. The IP protocol is tasked with correct transmission.
The TCP (Transmission Control Protocol) disassembles the incoming bytes and relays them to the internet layer.
TCP/IP Model
Alexander Maxeiner, M.Sc.University Duisburg-Essen
16Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Comparison OSI – TCP/IP
Comparision OSI/TCP
Routing
Transport
Session
Visualisation
L7 Application
Security
OSI
Bit-transmission
L6
L5
L4
L3
L2
L1
Internet
Transport
Not part of model
Not part of model
L7 Application
Host-to-network
TCP/IP
L6
L5
L4
L3
L2
L1
Alexander Maxeiner, M.Sc.University Duisburg-Essen
17Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
TCP/IP has no visualization- and session layers. Most applications do not need them.
Earlier inventions of the application layer consists of TELNET, FTP, SMTP.
Later inventions include DNS and HTTP.
Below the internet layer the information are rare.
The TCP/IP reference model only states a protocol must maintain a connection to the network.
With network access IP packages can be transmitted to its destination.
Those protocols are undefined in the reference model and depend on the network.
TCP Layers
Alexander Maxeiner, M.Sc.University Duisburg-Essen
18Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
OSI and TCP/IP reference models have several similarities. Both act on a stack of independent protocols.
Layers up to the transport layers serve the availability for a network independent end-to-end transport service.
The OSI model was designed before the protocols were designed. Inventions for broad networks stood in contrast to the model, therefore the model needed to be changed.
The TCP/IP model was designed after the protocols were established. It was therefore more adapt to its structure but cannot be used to describe non-TCP/IP networks.
OSI- & TCP/IP-Reference
Alexander Maxeiner, M.Sc.University Duisburg-Essen
19Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
The lowest level of the OSI-reference model consists of the bit-layer.
This layer handles the physical transmission of signals from one source to one destination.
At the next physical destination, the transmitted bits are re-translated into data for further processing.
A transmission from one computer to another through a network will be translated into bits, send, received by a routing device, retranslated into bytes and its information content used for further transmission until the final destination.
This delay during the transmission is known as the network latency.
Bit layer
Alexander Maxeiner, M.Sc.University Duisburg-Essen
20Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
During the 19th century a French mathematician named Jean-Baptiste Fourier proved that a periodically function within reasonable parameters and period T can be portrayed as a (maybe indefinitely) function of sine and cosine functions.
This discovery allows for data transmission the conversion of discrete into continuous signals and also with the knowledge of the harmonics of the signal the correct interpretation of a continuous signal for its discrete values.
The frequency range of the transmission channel defines its bandwidth.
The bandwidth of the channel defines the highest possible harmonic that can be transmitted,
Fourier
Alexander Maxeiner, M.Sc.University Duisburg-Essen
21Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
H. Nyquist discovered that even perfect channels can only transmit a certain number of bits.
Any signal wandering through a LPF of bandwidth H can only have 2H exact sampling values.
With V discrete values in each signal the Nyquist theorem results in:
𝑀𝑎𝑥, . 𝐷𝑎𝑡𝑎𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑠𝑠𝑖𝑜𝑛 = 2𝐻 log2 𝑉 𝐵𝑖𝑡𝑠
Meaning a 2kHz Signal can only transmit binary signals with 4000 Bits/sec.
This works only for noise free channels, as soon as there is noise interfering with the transmission medium the maximum transmission rate of all channels is limited by the SNR.
Transmission rate
Alexander Maxeiner, M.Sc.University Duisburg-Essen
22Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Damping and propagation speed are dependent on frequencies therefor a signal should not include too many frequencies
Rectangular signals have a broad frequency spectrum and are therefor only suitable for short distances and low transmission rates.
For long range transmission AC-signals are used, that can be modulated by:
– Frequency
– Amplitude
– Phase modulation
Transmission methods
Alexander Maxeiner, M.Sc.University Duisburg-Essen
23Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Frequency modulation
Frequency modulation – Source: Wikipedia
Still used in radio transmission
Alexander Maxeiner, M.Sc.University Duisburg-Essen
24Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Amplitude mod
Amplitude modulation – Source: Wikipedia
Still used in radio transmission
Alexander Maxeiner, M.Sc.University Duisburg-Essen
25Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Phasenmodulation – Source: Elektronik-compendium.de
Alexander Maxeiner, M.Sc.University Duisburg-Essen
26Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Phase modulation allows the coding of carrier wavesto specific binary values.
Every phase shift of X-degrees from its original phase depicts another binary value.
Every transmission interval the frequency shift is calculated and the original binary value decoded.
In modern transmission devices a combination of several modulation methods are used.
QAM-16 for example uses 4 phase shifts and 4 amplitude shifts. This means in every period a 4 Bit symbol can be transmitted.
This allows for the transmission of 9.600 Bits on a 2.400 Baud cable. (Baud = Symbols per second)
Phase modulation
Alexander Maxeiner, M.Sc.University Duisburg-Essen
27Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
As soon as there is a connection available on the physical level and all transmission parameters are set, the connected devices need to talk to each others.
Usually one device sends on one channel and the other responds to the received data.
The response of the receiver consists usually of a data package containing a NAK (not Acknowledged) or an ACK (Acknowledged)
Three basic transmission methods are introduced here:
– Stop-and-wait
– Go-back-n
– Selective repeat
Handshakes
Alexander Maxeiner, M.Sc.University Duisburg-Essen
28Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Stop-and-wait
:Host A :Host B
Alexander Maxeiner, M.Sc.University Duisburg-Essen
29Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Go-back-n
:Host AData A
Data B
Data C
:Host B
Alexander Maxeiner, M.Sc.University Duisburg-Essen
30Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Go-back-n 𝒕𝒐𝒖𝒕 error
:Host A :Host B
Data B
Data A
Data B
Data C
Data D
Alexander Maxeiner, M.Sc.University Duisburg-Essen
31Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Selective repeat
:Host AData A
Data B
Data C
:Host B
Alexander Maxeiner, M.Sc.University Duisburg-Essen
32Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Selective repeat 𝒕𝒐𝒖𝒕 error
:Host A :Host B
Data B
Data A
Data B
Data C
Data D
Alexander Maxeiner, M.Sc.University Duisburg-Essen
33Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
The Go-back-n and Selective repeat protocols are also so called ‘sliding window’ protocols. The data is stored in a buffer of the size n (window).
When a data set from the window is acknowledged it gets marked ‘ACK’. Then if the first Data set within the buffer is marked ACK the window slides further, deleting the data and adding the next package from the pipeline.
In go-back-n only the first package within the window can be marked ACK.
In selective repeat the window slides through all ACK frames until it reaches an unacknowledged.
More @ the exercises.
Sliding window
Alexander Maxeiner, M.Sc.University Duisburg-Essen
34Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Questions?
Alexander Maxeiner, M.Sc.University Duisburg-Essen
35Prof. Dr.-Ing. Axel HungerInstitute of Computer Engineering OSCN – Process Scheduling
Tanenbaum, Andrew S., “Computer Networks”, 4th edition, Pearson Education Inc, Amsterdam, Netherlands, 2003.
Tanenbaum, Andrew S., “Computernetzwerke”, 4th edition, Pearson Education Inc, Amsterdam, Netherlands, 2003.
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