Data Communication and Internet Technology

Lehrstuhl für Informatik 4

Kommunikation und verteilte Systeme

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Chapter 1: Introduction

Data Communication

and Internet Technology

Lehrstuhl für Informatik 4

RWTH Aachen

Dr. rer. nat. Dirk Thißen

Prof. Dr. Otto Spaniol

Lehrstuhl für Informatik 4

Kommunikation und verteilte Systeme

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Chapter 1: Introduction

Organization

• More or less fortnightly • Thursday 15:30 – 17:00 h • Lecture hall AH 5

• Presence exercise

Exercises to the lecture

Dirk Thißen

Lehrstuhl für Informatik 4, Room 4226 (Building part E1) Phone: 0241 / 80 - 21450

E-Mail: [email protected]

Contact information

http://www-i4.informatik.rwth-aachen.de/content/teaching/lectures/sub/datkom/WS05-06/index.html

Material (Slide copies, exercise sheets, video recordings)

At the end of winter term, February 24th

Written exam

Note: exercise dates are oriented at lecture content! No fixed dates, only

announcements in the lecture.

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Chapter 1: Introduction

1. Introduction

• Networks and Network Topologies • Communication Protocols

2. Computer Networks

• Network principles

• Network Components (Cables, Repeaters, Hubs, Bridges, Switches, Routers) • Local Area Networks (Ethernet, Token Ring, FDDI, DQDB)

• Wide Area Networks (Frame Relay, ATM, SDH)

3. Internet Protocols

• Internet/Intranet: the TCP/IP Reference Model • Network protocols (the Internet Protocol IP) • Next Generation Internet

• Transport protocols (TCP and UDP)

4. Application Protocols in the Internet

• Higher protocols (FTP, HTTP, E-Mail, ...)

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Chapter 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. Addison-Wesley, 2002.

• Cisco Systems: Internetworking Technologies Handbook. 3rd _{Edition, Cisco}

Press, 2001.

Related courses:

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Chapter 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 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:

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Chapter 1: Introduction

The „driving power“ for the enormous growing importance of data communications:

• Continuously decreasing costs for hardware... • ... while computing power is increasing.

Example for comparison:

• A PC today costs less than €

1.000,-• It has more computing power than a 10 years old mainframe • It contains more than 100 Million transistors

• A comparable number of other components would be prohibitively expensive – e.g. 100 Million sheets of paper would cost more than € 50,000,-.

Computing power is nearly

for free

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Chapter 1: Introduction

Increasing computing power leads to new possibilities in data processing: • Speech processing

• Image processing • Multimedia authoring • Video conferencing • ...

Increasing system diversity

Increasing number of applications and users

Wide range of usage: offices, factories, at home, …

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Chapter 1: Introduction

Sharing resources lowers costs

• Access to foreign resources by communication networks to achieve reasonable usage

• Essential:

Efficient methods to share data between the components of a distributed system

• Procedures for efficient interworking

(CSCW = Computer Supported Cooperative Work)

• 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

Example for interworking of two parties: Client/Server principle

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Chapter 1: Introduction

→ Better usage of resources

→ Modular extensions

→ Reliability by redundancy

Advantages

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Chapter 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 Server

Program (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).

Client

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Chapter 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. Napster, Gnutella

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Chapter 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, ethnical, cultural, juridical, ... side effects.

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Chapter 1: Introduction

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Chapter 1: Introduction

First Generation Computer Networks

Mainframe Operator Peripherals Terminals Rest of the world

Computing Center

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Chapter 1: Introduction

Introduction of Local Area Networks

Mainframe Operator Peripherals Terminals

Computing Center

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Chapter 1: Introduction

Global Networking

Computing Center

Router Server Network and system administrator Backbone Rest of the world (Internet) ISDN, Provider ...

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Chapter 1: Introduction

Classification of Networks

Point-to-Point Network

• A pair of computers is directly connected by one cable

Broadcast Network

• One-to-all (e.g.: radio, television)

• All connected stations are sharing 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

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Chapter 1: Introduction

Classification of Networks

Local Area Network (LAN)

Metropolitan Area Network (MAN) Wide Area Network (WAN)

Personal Area Network (PAN)

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Chapter 1: Introduction

• Communication infrastructure for a restricted geographical area (10 m up to some km)

• Usually maintained by one local organization

• Linked are PCs/Workstations/...., for exchanging information and sharing peripherals and resources

• Transmission capacity up to 1,000 Mbit/s

• Transmission delay of a message in the range of milliseconds (~10 ms) • Simple connection structures (“Simple is beautiful”)

LAN Topologies • Bus • Star • Ring • Tree • Meshed network

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Bus

• Broadcast Network: if station A intends to send data to station B, the message reaches all connected stations. Only station B processes the data, all other stations are ignoring it.

- (+) Passive coupling of stations

- Restriction of the extension and number of stations to connected + Simple, cheap, easy to connect new stations

+ No choose of path to target (= routing) necessary

+ The breakdown of a station does not influence the rest of the network Example: Ethernet

LANs: Bus

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Star

• Designated computer as central station: a message of station A is forwarded to station B via the central station

• Broadcast network (Hub) or point-to-point connections (Switch)

– Expensive central station

– Vulnerability through central station (Redundancy possible)

+ Definite path, no routing

+ N connections for N stations + Easy connection of new stations Example: Fast Ethernet

LANs: Star

B

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Chapter 1: Introduction

Tree

• Topology: Connection of several busses or stars

• Branching elements can be active (Router) or passive (Repeater) + Bridging of large distances

+ Adaptation to given geographical structure + Minimization of the cable length necessary

Backbone Branch 1 Branch 2 Repeater Router A B D C

LANs: Tree

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Chapter 1: Introduction

Ring

• Broadcast Network

• Chain of point-to-point connections

• Active stations: messages are regenerated by the stations (Repeater)

– Breakdown of the whole network in case of failure of one single station or connection + Large extent possible

+ Easy connection of new stations + Only N connections for N stations • Variant: bidirectional ring

stations are connected by two opposed rings

LANs: Ring

Example: Token Ring, FDDI

B

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Chapter 1: Introduction

Fully Meshed Network

• Point-to-Point connections between all stations

– For N stations, connections are needed

– Connecting a new station is a costly process

+ No routing

+ Redundant paths

+ Maximal connection availability through routing integration

Partly meshed network: cheaper, but routing, flow control

and congestion control become necessary (Wide Area Networks)

2 ) 1 (N− N

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Chapter 1: Introduction

Ethernet (IEEE 802.3, 10 MBit/s)

- originally the standard network

- available in an „immense number“ of variants

Token Ring (IEEE 802.5, 4/16/100 MBit/s)

- for a long time the Ethernet competitor

- extended to FDDI (Fiber Distributed Data Interface)

Fast Ethernet (IEEE 802.3u, 100 MBit/s)

- at the moment the most widely spread network - extension of Ethernet for small distances

Gigabit Ethernet (IEEE 802.3z, 1,000 MBit/s)

- very popular at the moment; 10 GBit/s are already in the planning phase at the moment

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Chapter 1: Introduction

• Designed for larger distances than a LAN, usage e.g. in a whole town

• Similar technologies as in a LAN

• In general, only 1 or 2 cables without additional components

• Main difference to LANs: Time slots

MAN

Metropolitan Area Network (MAN)

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Chapter 1: Introduction

• Bridging of any distance

• Connects LANs and MANs over large distances • Irregular topology, based on current needs

• Consists out of stations (routers) which are connected through point-to-point with each other

• Mostly quite complex interconnection of subnetworks which are owned by independent organizations

WAN

Router Host

LAN

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Chapter 1: Introduction

Wireless Networks

• System Interconnections (PANs)

• direct connection between the components of a computer (Example: Bluetooth)

• Wireless LANs

• Communication of computers connected by a base station (Access Point) in a local area, or direct

connection between computers

(Example: IEEE 802.11 Wireless LAN, WLAN) • Range of 10 – 100 meters

• Transmission capacity of up to 100 MBit/s

• Wireless MANs/WANs

• E.g. common telecommunication networks like GSM • Range of several kilometers (“worldwide”)

• Transmission capacity below 1 MBit/s

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Chapter 1: Introduction

Institute of Electrical and Electronic Engineers - IEEE

• Standardization e.g. of the IEEE

802.X-Standards for Local Area Networks www.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)

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Chapter 1: Introduction

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Chapter 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

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Chapter 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.

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Chapter 1: Introduction

Example: Exchange of Ideas between

Philosophers

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

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Chapter 1: Introduction

Standardization

Indispensable for the area-wide practical use of communication systems:

• Consequence:

Standardization processes are very slow (due to many, often non-technical reasons).

• On the national as well as the international level!

Complex technical problems have to be solved

The involved parties, e.g. companies are often working against each other

Confidentially restrictions hinder the information flow • Successful standardization is quite difficult due to:

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Chapter 1: Introduction

International Standards Organization - ISO

• Organisation, which is working on a volunteer basis (since 1946). • Members: standards organizations in approx. 90 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 ITU-T regarding telecommunication standards, (ISO is a member of ITU-T).

• Pioneering work of ISO regarding data communication: the

ISO/OSI reference model

• Notice: only the concept is pioneering – not the products developed from those concepts!

www.iso.ch

Standards Organizations - ISO

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Chapter 1: Introduction

Layer 5 and 6 are rarely being implemented Application 7 Presentation 6 Session 5 Transport 4 Network 3 Data Link 2 1

Common services for the end user

Network-independent end-to-end data transfer

Addressing and routing of “packets” Securing of “frames”; Flow Control

Physical _{Signal representation,}

character transmission

Criticism of the model: 7 layers:

Transmission medium („Layer 0”)

Generally to much

overhead – some details are unnecessary, some are overloaded

Reduce the complexity of a communication process (all details to be considered) through layers.

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Chapter 1: Introduction

Layer Tasks

1. Physical layer

This 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), …

2. Data Link Layer

Ensures 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.

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Chapter 1: Introduction

Layer Tasks

3. Network Layer

This 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 (the routers) manage tables with routing information and use the uniform addresses to make a decision about the best path to the receiver.

4. Transport Layer (ISO/OSI)

Layer 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 (sequence numbers, acknowledgements) to detect missing or wrong ordered data units. Beneath this, the current network state is considered to not only adapt to the receiver, but to the network capacities as well. Addressing is a topic here as well. On the transport layer, a single communication process on receiver side is addressed.

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Chapter 1: Introduction

Layer Tasks

5. Session Layer

This layer (like the transport layer) manages reliable data transport between the computers. However also additional services are being offered, like e.g. the

possibility for dialogue control. I.e. it can be defined in which direction the transmission can take place.

Closely related with this topic is the token management which also belongs to level 5. During the transmission so called tokens can be exchanged. With certain

operations only the communication partner which owns the token is allowed to conduct the operation.

Token management is also used here for other purposes, i.e. a set of tokens exist 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.

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Layer Tasks

6. Presentation Layer

The task of this layer is to display the data to transmitted that 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 an abstract (and commonly recognized) data format before the

transmission and are being translated back by the receiver into its own personal data format.

7. Application Layer (ISO/OSI)

In this layer (standard-) protocols are being provided which can be used from a whole set of applications/systems. One example is file transfer. On the application layer a universally valid protocol including an interface of 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 file transfer, e-mail, remote operations etc.

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Chapter 1: Introduction

Interplay between the Layers

Layer (n-1) Layer (n-1)

Layer n n-PDU Layer n

Data H

(n-1)-PDU H: 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).

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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 Data H A-PDU H P-PDU H S-PDU H T-PDU H N-PDU H Transmission medium Bit stream T Application process Application Layer

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Chapter 1: Introduction

The Communication Process

• Not necessarily a one-to-one mapping between layers

• Depending on the protocol, n-PDUs can be segmented into several (n-1)-PDUs before transmission:

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Chapter 1: Introduction

Host A Router A Router B Host 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

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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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Chapter 1: Introduction

The TCP/IP Reference Model

Don´t exist

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

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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 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 over 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).

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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).

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 what is to be done, but not how to do it. Result: incompatibility of products.

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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.

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Chapter 1: Introduction

1. Introduction

• Networks and Network Topologies • Communication Protocols

2. Computer Networks

• Network principles

• Network Components (Cables, Repeaters, Hubs, Bridges, Switches, Routers) • Local Area Networks (Ethernet, Token Ring, FDDI, DQDB)

• Wide Area Networks (Frame Relay, ATM, SDH)

3. Internet Protocols

• Internet/Intranet: the TCP/IP Reference Model • Network protocols (the Internet Protocol IP) • Next Generation Internet

• Transport protocols (TCP and UDP)

4. Application Protocols in the Internet

• Higher protocols (FTP, HTTP, E-Mail, ...)