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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 1Chapter 1: Introduction
Data Communication and Internet Technology
Lehrstuhl für Informatik 4RWTH Aachen
Prof. Dr. Otto Spaniol
Dr. Dirk Thißen
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 2Chapter 1: Introduction
Organization
• Fortnightly• Thursday 15:45 – 17:15 h
• Lecture hall AH 5• Presence exercise
Exercises to the lecture
Otto Spaniol / Dirk ThißenLehrstuhl für Informatik 4Phone: 0241 – 8021400 / 8021450
E-Mail: {spaniol, thissen}@informatik.rwth-aachen.de
Contact information
http://www-i4.informatik.rwth-aachen.de/content/teaching/lectures/sub/datkom/WS07-08/index.html
Material (Slide copies, exercise sheets)
At the end of winter termWritten exam
Note: first exercise date: November, 8th
The dates for the following exercise hoursare announced in the first exercise hourresp. on the lecture‘s web page
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 3Chapter 1: Introduction
1. Introduction
• Communication Protocols• Computer Networks
2. Computer Networks
• Network principles
• Network topologies and components• Local Area Networks (Ethernet, Token Ring, Token Bus, FDDI, DQDB)
• Wide Area Networks (Frame Relay, ATM, SDH, ISDN/DSL)
3. Internet Protocols
• Internet/Intranet: the TCP/IP Reference Model• Network protocols (the Internet Protocol IP, Routing protocols)
• Quality of Service in the Internet• Transport protocols (TCP and UDP)
4. Application Protocols in the Internet
• Higher protocols (FTP, HTTP, E-Mail, ...)
Content
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 4Chapter 1: Introduction
Literature and Related Courses
• A.S. Tanenbaum: Computer Networks. 4th Edition, Prentice Hall, 2002.
• J.F. Kurose, K.W. Ross: Computer Networking: A Top-Down Approach Featuring the Internet. 3rd Edition, Addison-Wesley, 2005.
• Cisco Systems: Internetworking Technologies Handbook. 3rd Edition, Cisco Press, 2001.
Related courses:
• Mobile Communications (starting Monday, 22th, 16:30 in AH 5)
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 5Chapter 1: Introduction
Data communication is the processing and the transport of digital data over connections between computers and/or other devices
(generally over large distances)
Computer Networks
→ How to connect several computers?
→ Which media can be used for data transport?
→ How to represent digital data on the communication medium?
→ How to coordinate the access of several computers to the medium?
Communication Protocols (Internet Technology)
→ Design of uniform data units for transfer
→ How to achieve a reliable and efficient transfer?
Data communication comprises two topical areas:
Data Communication
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 6Chapter 1: Introduction
Computing Power is cheap...
• Today, “everybody” has a computer (at work as well as privately)
• Possible applications: file sharing, efficient interworking(CSCW = Computer Supported Cooperative Work)
• And: Sharing resources lowers costs
� Access to foreign resources by communication networks to achievereasonable usage
� Agreements for shared usage of devices which are too expensive to buy for one single organization and/or have no use for the total capacity
• Essential: Efficient methods to share/transfer data between the components of a system of interconnected devices
Example for interworking of two parties: Client/Server principle
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 7Chapter 1: Introduction
Client Server
ClientProcess
ServerProcess
Request
Reply NetworkNetwork
→ Cost reduction→ Better usage of resources
→ Modular extensions→ Reliability by redundancy
Advantages
The Client/Server Principle
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 8Chapter 1: Introduction
Client/Server Systems
Client Server
WWW Browser WWW Server
eMail Program Domain Name System(DNS)
FTP Client FTP Server
Examples for Client/Server systems
ServerProgram (process) which offers a service over a network. Servers receive requests and return a result to the inquiring party. The services offered include simple operations (e.g. name server) or a complex set of operations (e.g. web server).
ClientProgram (process) which uses a service offered by a server.
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 9Chapter 1: Introduction
Another principle: Peer-to-Peer
• Equal partners, no fixed client and server roles
• Connections between any pair of computers
• Establishment of a whole network of connections
• Best example: File Sharing, e.g. Gnutella, BitTorrent
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 10Chapter 1: Introduction
• Eventually dubious or forbidden contents
• Responsibility• Juridical aspects (legislation)
• Potential censorship?• Control over the productivity of employees,
of the whereabouts of people
• Annoyance through anonymous or unwanted messages (SPAM)• ......
Communication networks enable a faster and cheaper exchange/distribution of information. There is however a large number of social, ethical, cultural, juridical, ... side effects.
Non-technical Aspects
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 11Chapter 1: Introduction
Data Communication
=
Protocols
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 12Chapter 1: Introduction
To enable understanding in communication, all communication partners have to speak the same „language“.
→ Data formats and their semantics
→ Control over media access→ Priorities→ Handling of transmission errors
→ Sequence control→ Flow control mechanisms
→ Segmentation and composition of long messages
→ Multiplexing→ Routing
A protocol is defined as the whole set of agreements between
application processes with the purpose of a common communication
Why Protocols?
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 13Chapter 1: Introduction
Implementation of Protocols
Solution 1:Write one large „Communication Program“ which fulfills all requirements needed
to establish a communication process• Advantage: efficient data exchange for a given application
• Disadvantage: No flexibility! Adoptions require large efforts
Solution 2:Write a set of small programs specialized to special tasks of the communication
process. For each application, the needed programs can be combined.• Advantage: Very flexible, since single components can be exchanged• Disadvantage: Fixed structures of program interworking; adds more complexity
and overhead
Accepted today: solution 2.
The implementation takes place in layer models
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 14Chapter 1: Introduction
Example: Exchange of Ideas between Philosophers
Philosopher A
Language: Chinese
Interpreter A
additionally: English
Recognizes single characters and sends
them in Morse
Network
Thoughts about world politics
Uninterpreted sentences,
i.e. no knowledge about politics
Uninterpreted characters
in correct order
Electrical signals
Technical Expert A
Language: Chinese
Philosopher B
Language: Spanish
Interpreter B
additionally: English
Recognizes single characters and sends
them in Morse
Technical Expert B
Language: Spanish
protocolsservice
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 15Chapter 1: Introduction
International Standards Organization - ISO
• Organisation, which is working on a volunteer basis (since 1946)
• Members: standards organizations in more than 150 countries• Deals with a very broad range of standards• 200 Technical Committees (TC) for specific tasks
(e.g. TC97 for computer and information processing)• TCs consist of subcommittees comprising in turn several working
groups• Interworking with International Telecommunication Union (ITU-T)
regarding telecommunication standards
• Pioneering work of ISO regarding data communication: the ISO/OSI reference model (OSI: Open Systems Interconnection)
• Notice: only the concept is pioneering – not the products developed from those concepts!
www.iso.ch
Standards Organizations - ISO
Necessary for world-wide usage of common protocols: standardization
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Layer 5 and 6 are rarely being implemented
Application7
Presentation6
Session5
Transport4
Network3
Data Link2
1
Standard interfaces forcommonly usedcommunication services
Network-independentend-to-end data transfer
Addressing androuting of “packets”
Protection of “frames”;Flow Control
Physical Signal representation, character transmission
Criticism of the model:
7 layers:
Transmission medium (“Layer 0”)
Generally too much overhead – some details are unnecessary, some are overloaded
Reduce the complexity of a communication process (all details to be considered) through layers.
The ISO/OSI Reference Model
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Kommunikation und verteilte Systeme
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Layer Tasks
1. Physical layerThis layer is responsible for transmitting single bits over the medium. Signal representation is defined here to ensure that a sent „1“ is understood by the receiver as „1“. For this, e.g. on a copper cable it is defined, which voltage is used to represent a „1“ resp. a „0“ and how long this voltage has to be for one bit.Moreover details are being defined like the type of cables, meaning of pins of network connectors, transmission direction on the cable (uni-/bidirectional), data rate, …
2. Data Link LayerEnsures an error-free data transmission between two neighbored hosts (e.g. in a sub-network). Therefore the incoming data are segmented into so-called frames which are being transmitted separately. The receiver, which identifies the start and the end of a frame e.g. with a bit pattern, checks if the transmission has been correct (e.g. with the help of a checksum). Additionally, flow control is used to control the re-transmission of corrupt frames and protect the receiver from overload.An additional task in broadcast networks is the control of medium access, i.e. the stations are coordinated in some way to prevent from access conflicts.
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 18Chapter 1: Introduction
Layer Tasks
3. Network LayerThis layer is responsible for the data transmission over larger distances and between heterogeneous sub-networks. The main task is (worldwide) uniform addressing of hosts and choosing a path through the whole network (routing). A necessary pre-requisite for doing so is among other things a common address range and an agreement about a maximum size of the transferred data units. Intermediate stations (so-called routers) manage tables with path information and use the uniform addresses to make a decision about the best path to the receiver.
4. Transport LayerLayer 4 manages end-to-end communication between two processes. It is responsible for ensuring that the received data are complete and in correct order. For this, again flow control is used to detect missing or wrong ordered data units. In this flow control, the current network state is considered to not only adapt to the receiver, but to the network capacities as well.
Again, addressing is a topic here as well. While on layer 3 the receiving host isaddressed, here a single communication process on this host is addressed.
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Layer Tasks
5. Session LayerThis layer offers the possibility for dialogue control, i.e. it can be defined which data streams on layer 4 together are forming a dialogue, in which pattern communication partners are allowed to send data, and (in case of a half-duplex communication medium) at which time data can be transferred in which direction.
Part of this is the so-called token management. During the transmission tokens can be exchanged. With certain operations only the communication partner which owns the token is allowed to conduct the operation. That means, a set of tokens exists to coordinate several operations. One important operation is to set synchronization points in the communication process, to restart the transmission at the point it has ended in case of a connection loss.
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 20Chapter 1: Introduction
Layer Tasks
6. Presentation Layer
The task of this layer is to display the data to be transmitted in a way that they can be handled from a lot of different systems. So computers code a string with ASCII characters, others use Unicode, some for integers the 1-, other the 2-complement. Instead of defining a new transmission syntax and semantics for every application, it is tried to provide a universally valid solution. Specific data are encoded in a specific abstract data format before the transmission and are being translated back by the receiver into its own personal data format.
7. Application Layer
In this layer standardized interfaces are being provided for commonly used application services. One example is file transfer. On the application layer a universally valid protocol including an interface for file transfer is being provided. For systems from different manufacturers only the link-up into the local file system has to be realized. Other examples are e-mail, remote operations etc.
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Kommunikation und verteilte Systeme
Page 21Chapter 1: Introduction
Interplay of the Layers
Layer (n-1) Layer (n-1)
Layer n Layer nn-PDU
DataH
(n-1)-PDUH: Header, e.g. control information of the layer
• Layer (n-1) offers its functionality to the above lying layer n as a communication service.
• Layer n enhances the data to be sent with control information (Header) and sends the data together with the header as Protocol Data Units (PDU).
• Two communication partners on layer n exchange PDUs by using the communication service of the nearest lower lying layer (n-1).
• For layer (n-1), these PDUs are the data to be transmitted.
servicerequest
servicereceived from
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 22Chapter 1: Introduction
The whole Communication Process
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application process
Data
DataH
A-PDUH
P-PDUH
S-PDUH
T-PDUH
N-PDUH
Transmission mediumBit stream
T
Application process
Application Layer
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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The Communication Process
• Not necessarily a one-to-one mapping between layers
• Depending on the protocol, a n-PDU can be segmented into several (n-1)-PDUs before transmission (or vice versa):
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 24Chapter 1: Introduction
Physical Layer
Data Link Layer
Network Layer
Physical Layer
Data Link Layer
Network Layer
Host A Host BRouter A Router B
Transport Protocol
Session Protocol
Presentation Protocol
Application Protocol
The OSI Reference Model in the Network
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application process
Application Layer
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application process
Application Layer
Internal Protocols
Net
wo
rk/t
ran
s-m
issi
on
-ori
ente
dA
pp
licat
ion
-ori
ente
d
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 25Chapter 1: Introduction
Computer Networks(= Layer 1&2, also partly layer 3)
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 26Chapter 1: Introduction
First Generation Computer Networks
MainframeOperator
PeripheralsTerminals
Rest of the world
Computing Center
Terminals
MultiplexerDemultiplexer
Telephone lines
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 27Chapter 1: Introduction
Introduction of Local Area Networks
MainframeOperator
PeripheralsTerminals
Computing Center
Fixed lines
Router
Building C
Building B
Building A
Rest of the world
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Page 28Chapter 1: Introduction
Global Networking
Mainframe
Peripherals
Computing Center
Router
Building A
Router
Switch
ClientsLocal
Server
Building B
Router
Switch
ClientsLocal
Server Switch
Router Server Network and system administrator
Backbone
Rest of the world
(Internet)Fixed lines, ISDN, Provider ...
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Important Terms
Switch A switch has several connectors, from each connector a cable can be drawn to a computer. These computers then are linked to a small network. The switch knows which computer is plugged in at which connector (address of the network interface card) and forwards data to a destination computer.
Router A switch only knows which computers are connected to it directly; if someone wants to send data to a computer far away, some instance is needed which knows the way to the destination over several othercomputers or switches. Routers are used to manage global addressinformation and forward data through complex networks.
Backbone A backbone is a set of computers (usually routers) which are connected by point-to-point links over large distances. A backbone serves for covering a large region with a communication network which can interconnect small, local networks of single institutions.
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Classification of Networks
Point-to-Point Network• A pair of computers is directly connected by one cable
Broadcast Network• One-to-all: when one station sends, all others receive• All connected stations are sharing only one transmission channel• For ensuring that the data are sent the correct receiver, they have to
marked with the destination address of the receiving computer• Data are being packed into packets with the Unicast Address of the
receiver
• Every computer connected controls each received packet for its destination address. Only the addressed computer processes the data, all others are simply deleting them.
• To address all connected stations at once, so-called Broadcast Addresses are used
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Classification of Networks
Classification by Distance
1 m
10 m Room
100 m Building
1 km Campus
10 km Town
100 km Country
1000 km Continent
10000 km Planet
Local Area Network (LAN)
Metropolitan Area Network (MAN)
Wide Area Network (WAN)
Personal Area Network (PAN)
Internet
Better classification scheme:
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Kommunikation und verteilte Systeme
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Networks
Switch
Local Networks (LANs)
MetropolitanNetwork (MAN),
backbone for a town or a region
Router
Connectionto a WAN
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Networks
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Networks
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Networks
FFO
KIE
HUB
ADH
EWE
GIE
GAR
ERL
BAY
MUE
FZJ
AAC BIR
HAM
DES
POTTUB
FZK
GSI
DUI
BRE
HAN
BRA MAGBIE
FRA
HEI
STU
REG
DRE
CHE
ZIB
ILM
ROS
LEI
JEN
ESF
AWI
GOEKAS
MAR
GRE
WUE
AUG
SAA
KEH
Surfnet
Switch/GARR
Renater
Geant2
“Dark Fiber”rented wavelength
• German research network X-WIN –backbone based on optical fiber, for universities and research institutes with a data rate of 10 GBit/s
• Additionally: DWDM (Dense Wavelength Division Multiplexing): up to 160 simultaneous transmissions on different wavelengths:1.6 TBit/s capacity!
• Connection to other backbone networks (international as well as to other German backbone networks)
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Networks
Central node Frankfurt – connection to the European research network Géant.
Also in Frankfurt and Hamburg: intercontinental connections.
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Institute of Electrical and Electronic Engineers - IEEE• Standardization e.g. of the IEEE 802.X-
Standards for Local Area Networkswww.ieee.org
Standards Organizations - IEEE
• 802.1 Overview and Architecture of LANs• 802.2 Logical Link Control (LLC)• 802.3 CSMA/CD („Ethernet“)• 802.4 Token Bus • 802.5 Token Ring • 802.6 DQDB (Distributed Queue Dual Bus)• 802.7 Broadband Technical Advisory
Group (BBTAG)• 802.8 Fiber Optic Technical Advisory
Group (FOTAG)• 802.9 Integrated Services LAN
(ISLAN) Interface• 802.10 Standard for Interoperable
LAN Security (SILS)• 802.11 Wireless LAN (WLAN)
• 802.12 Demand Priority (HP’s AnyLAN)
• 802.14 Cable modems• 802.15 Personal Area Networks
(Bluetooth)• 802.16 WirelessMAN (WiMAX)• 802.17 Resilient Packet Ring• 802.18 Radio Regulatory Technical
Advisory Group (RRTAG)• 802.19 Coexistence Technical
Advisory Group• 802.20 Mobile Broadband Wireless
Access (MBWA)• 802.21 Media Independent Handover• 802.22 Wireless Regional Area
Networks (WRAN)
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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IEEE 802.11 Variants
Improved measurement/evaluation/management of radio parameters (e.g. signal strength), e.g. for enabling location based services
802.11k
Japanese variant of 802.11a for the frequency range of 4,9 GHz - 5 GHz802.11j
Authentication/encryption for 802.11a/b/g/h802.11i
54 MBit/s WLAN in the 5 GHz band with dynamic adaptation of channel and frequency choice as well as automatic adaptation of transmission power (enhancement of IEEE 802.11a for Europe)
802.11h
54 MBit/s WLAN in the 2,4 GHz band 802.11g
Roaming for 802.11a/g/h (Inter Access Point Protocol IAPP) between Access Points of different vendors
802.11f
QoS und streaming enhancement for 802.11a/g/h 802.11e
"World Mode", Adaptation to regional regulations (e.g. used frequency ranges)802.11d
Wireless Bridging between Access Points802.11c
11 MBit/s WLAN in the 2,4 GHz band 802.11b
54 MBit/s WLAN in the 5 GHz band 802.11a
Each IEEE standard has lots of variants – e.g. here for Wireless LAN:
Lehrstuhl für Informatik 4
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IEEE 802.11 Variants
3650-3700 Operation in the U.S. 802.11y
Protected Management Frames 802.11w
Wireless network management802.11v
Interworking with non-802 networks (for example, cellular) 802.11u
Wireless Performance Prediction (WPP) - test methods and metrics Recommendation
802.11t
ESS Mesh Networking 802.11s
Fast roaming802.11r
WAVE - Wireless Access for the Vehicular Environment (such as ambulances and passenger cars)
802.11p
Enhancement for a future, faster WLAN with data rate of 108 – 320 MBit/s802.11n
Summary of earlier enhancements, correction of errors in former specifications (maintenance)
802.11m
Only few standards (the grey shaded) are “standalone” standards defining data exchange – the others are supplements for network variants, or enhancements like security, QoS, etc.
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Kommunikation und verteilte Systeme
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Internet Protocols(= Layer 3 – 7)
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Standards Organizations - IETF
Internet Engineering Task Force - IETF
• Forum for the technical coordination of the work regarding Arpanet, the precursor of the Internet (since 1986)
• Evolution to a large, open, and international community of administrators, vendors and researchers
• Works on evolution of the Internet architecture and the smooth operation of the Internet.
• Several working groups on Internet protocols, applications, routing, security, …
• Standard draft proposals can become a full standard only if an implementation of the proposal is successfully tested at two independent locations for at least four month
• Result of such a standardization process: the resounding success of the Internet protocols TCP/IP
www.ietf.org
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The TCP/IP Reference Model
Don´t exist,integrated into layer 7, if needed
Host-to-Network Layer
Application Layer Application Layer
Presentation Layer
Session Layer
Transport Layer Transport Layer
Network Layer Internet Layer
Data Link Layer
Physical Layer
ISO/OSI TCP/IP
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The Tasks of the TCP/IP Layers
Host-to-Network Layer (corresponds to ISO/OSI 1-2)Not defined exactly. The design does not matter, it is only defined that a host must be connected to the network via a protocol in a way that it is able to send and receive IP datagrams. The protocol design is left over to other standards organizations to cover heterogeneous networks of all kinds.
Internet Layer (corresponds to ISO/OSI 3)The term Internet refers here to the interworking of different networks, therefore not on “the Internet” itself. The protocol enables communication between hosts beyond the own network borders. In the Internet, the transmission is connectionless, meaning that the data are segmented into packets which are addressed and sent independently into the network. On each network border, a router takes over the forwarding of the packets. The choice of path can be dynamic, depending on the current network load. As a result, single packets can get lost by overload situations or received in wrong order. Such faults are not handled (this task is left over to the transport layer).In contrast to ISO, only one packet format is defined, together with a connectionless protocol, the Internet Protocol (IP). But, several enhancements are done in the meantime, e.g. MPLS for a connection-oriented transfer of data (see QoS chapter).
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The Layers of TCP/IP
Transport Layer (corresponds to ISO/OSI 4)This layer covers the communication between the end systems. To adapt to different applications, two protocols are defined.TCP (Transmission Control Protocol) is a reliable, connection-oriented protocol to protect the transmission of a byte stream between two hosts. The byte stream is segmented to fit into IP packets. On the receiving side the packets are re-assembled in the original order with the purpose of restoring the original data stream. It also includes flow control to adapt to the receiver‘s capabilities and to overcome the faults caused by the connectionless IP. UDP (User Datagram Protocol) is an unreliable and connectionless protocol („best effort“). No error correction is integrated, thus the transmission is used when the speed of the data transmission is more important than the reliability (speech, video), or when only very small messages have to be sent.
Application Layer (corresponds to ISO/OSI 7)This layer defines common communication services. This comprises TELNET (remote work on another computer), FTP (file transfer), SMTP (electronic mail), DNS („phonebook“ for the Internet), HTTP (used for World Wide Web), etc.
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1. Time
The TCP/IP protocols were already widely used before OSI had finished the standardization activities.
3. Complicatedness
Very high and partly unneeded expense in the OSI specification (thousands of pages of specification descriptions).
By the wish to consider all special cases, lots of options were included, making the products lavish, unhandy, and for too expensive - “The option is the enemy of the standard”!
2. Freedom from obligation
A „reference model“ like OSI is free from obligation. It only defines whatis to be done, but not how to do it. Result: incompatibility of products.
OSI vs. TCP/IP
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5. Hurriedly product implementation
The first OSI products were implemented too fast (driven by the success of TCP/IP protocols), were covered with faults, and had an overall low performance.
In contrast, the “theoretically far more unmodern“ TCP/IP protocols were continuously modified and improved. They were of a high quality level and successfully tested before deployment and cheap to buy due to high production numbers.
4. Political reasons
OSI was dominated too much by Europe – especially from the national telecommunication companies which had lucrative monopolies. The real market power was in the USA – nobody was interested in OSI over there.
OSI vs. TCP/IP
The TCP/IP protocols are used, from ISO/OSI only the terminology remained
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Cross-Layer Protocol Design
ISO/OSI clearly defines independent layers, in the Internet protocols the layers theoretically are also independent (in reality, there are some mix-ups between TCP and IP)
But sometimes it makes sense to violate the layer concept and to allow inter-layer exchange of information or even interaction:
Avoid overhead of layer concept:• Minimize energy consumption for small devices with low capabilities• Consider characteristics of communication medium at time of protocol design
• Performance increase
Goal: lightweight (i.e. simplified) protocols, specially tailored to a certain application
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Cross-Layer Protocol Design
Examples for cross-layer interaction:• In wireless transmission, common control of data rate (layer 2) and sending
power (layer 1) is useful
• Routing protocols (layer 3) in wireless mesh networks can use information about signal-to-noise ratio and interference (layer 1) in path decisions
Disadvantages:• Flexibility is lost – exchange of single protocols is not longer possible
• Solutions are tailored to certain application scenarios, usage is restricted
Concept for low-capability devices / wireless communication
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And now…
1. Introduction
• Communication Protocols• Computer Networks
2. Computer Networks
• Network principles
• Network topologies and components• Local Area Networks (Ethernet, Token Ring, Token Bus, FDDI, DQDB)
• Wide Area Networks (Frame Relay, ATM, SDH, ISDN/DSL)
3. Internet Protocols
• Internet/Intranet: the TCP/IP Reference Model• Network protocols (the Internet Protocol IP, Routing protocols)
• Quality of Service in the Internet• Transport protocols (TCP and UDP)
4. Application Protocols in the Internet
• Higher protocols (FTP, HTTP, E-Mail, ...)