Data Communication and Internet Technology - Informatik 4

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Organization Exercises to the lecture • • • •

Data Communication and Internet Technology

More or less fortnightly Thursday 16:30 – 18:00 h Lecture hall AH 5 Presence exercise

Note: exercise dates are oriented at lecture content! No fixed dates, only announcements in the lecture. First exercise date: November, 2nd, 6th, or 9th – to be announced. ☺

Material (Slide copies, exercise sheets, video recordings)

Lehrstuhl für Informatik 4 RWTH Aachen

http://www-i4.informatik.rwth-aachen.de/content/teaching/lectures/sub/datkom/WS06-07/index.html

Written exam At the end of winter term

Dr. rer. nat. Dirk Thißen

Contact information Dirk Thißen Lehrstuhl für Informatik 4, Room 4226 (Building part E1) Phone: 0241 / 80 - 21450 E-Mail: [email protected]

Prof. Dr. Otto Spaniol Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Content

Literature and Related Courses

1. Introduction • A.S. Tanenbaum: Computer Networks. 4th Edition, Prentice Hall, 2002.

• 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, Token Bus, FDDI, DQDB) • Wide Area Networks (Frame Relay, ATM, SDH, Resilient Packet Ring) 3. Internet Protocols • Internet/Intranet: the TCP/IP Reference Model • Network protocols (the Internet Protocol IP, Routing protocols) • Next Generation Internet • Transport protocols (TCP and UDP)

• 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: • Mobile Communications (starting Wednesday, 25th)

4. Application Protocols in the Internet • Higher protocols (FTP, HTTP, E-Mail, ...)

Chapter 1: Introduction

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Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Data Communication

Evolution of Data Communication

Data communication is the processing and the transport of digital data over connections between computers and/or other devices (generally over large distances)

Sharing resources saves costs: • By communication, one can access resources of other parties – this reduces the costs (compared to buying own resources) • Several institutions can share expensive resources which cannot by completely utilized by a single institution

Data communication comprises two topical areas: Computer Networks

• Needed:
Efficient mechanisms for data exchange between components of a distributed systems

→ How to connect several computers? → Which media can be used for data transport?


Mechanisms for efficient interaction

→ How to represent digital data on the medium?

The “driving power” for the enormous increasing significance of data communication:

→ How to coordinate the access of several computers to the medium? Communication Protocols (Internet Technology)

• Decreasing costs for hardware... • … while the computing power increases.

→ Design of uniform data units for transfer → How to achieve a reliable and efficient transfer?

Interaction of several communication partners: usually Client/Server principle

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Chapter 1: Introduction

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

The Client/Server Principle

Client/Server Systems

Client

Server

Client Process

Server Process

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 Program (process) which uses a service offered by a server. Examples for Client/Server systems

Request Network

Network

Reply

Advantages

Chapter 1: Introduction

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Chapter 1: Introduction

→ Cost reduction → Better usage of resources → Modular extensions → Reliability by redundancy

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Chapter 1: Introduction

Client

Server

WWW Browser

WWW Server

eMail Program

Domain Name System (DNS)

FTP Client

FTP Server

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Another principle: Peer-to-Peer

Non-technical Aspects Communication networks enable a faster and cheaper exchange/distribution of information. There is however a large number of social, ethnical, cultural, juridical, ... side effects.

• Eventually dubious or forbidden contents • Responsibility • Juridical aspects (legislation) • Potential censorship? • Control over the productivity of employees,

• Equal partners, no fixed client and server roles

of the whereabouts of people

• Connections between any pair of computers

• Annoyance through anonymous or unwanted messages (SPAM)

• Establishment of a whole network of connections

• ......

• Best example: File Sharing, e.g. Napster, Gnutella

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Chapter 1: Introduction

Chapter 1: Introduction

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Why Protocols? 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

Data Communication = Protocols

A protocol is defined as the whole set of agreements between application processes with the purpose of a common communication

Chapter 1: Introduction

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Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Example: Exchange of Ideas between Philosophers

Implementation of Protocols Solution 1: Write one large „Communication Program“ which fulfills all requirements needed

Philosopher A

Philosopher B

Thoughts about world politics

Language: Chinese

Language: Spanish

to establish a communication process. • Advantage: efficient data exchange for a given application. • Disadvantage: No flexibility! Adoptions require large efforts.

Interpreter B

Interpreter A

Solution 2: Write a set of small programs specialized to special tasks of the communication

Language: Chinese

Uninterpreted sentences,

Language: Spanish

i.e. no knowledge about politics additionally: English

additionally: English

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

Recognizes single characters and sends them in Morse

and overhead.

Uninterpreted characters in correct order Electrical signals

Accepted today: solution 2.

Recognizes single characters and sends them in Morse

Network

The implementation takes place in layer models.

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Chapter 1: Introduction

Technical Expert B

Technical Expert A

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

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Chapter 1: Introduction

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Standardization

Standards Organizations - ISO International Standards Organization - ISO

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

• Organisation, which is working on a volunteer basis (since 1946). • Members: standards organizations in approx. 90 countries

Standardization

www.iso.ch

• On the national as well as the international level! • Successful standardization is quite difficult due to:
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

• 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!

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

Chapter 1: Introduction

• 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

(OSI: Open Systems Interconnection)

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Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

The ISO/OSI Reference Model

Layer Tasks

Reduce the complexity of a communication process (all details to be considered) through layers. 7 layers: 7

Application

6

Presentation

5

Session

4

Transport

3

Network

2

Data Link

1

Physical

Common services for the end user

Criticism of the model:

Network-independent end-to-end data transfer

Layer 5 and 6 are rarely being implemented

Addressing and routing of “packets”

Generally to much overhead – some details are unnecessary, some are overloaded

Securing of “frames”; Flow Control Signal representation, character transmission

Transmission medium („Layer 0”)

Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

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.

Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Layer Tasks

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 prerequisite 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.

Chapter 1: Introduction

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), …

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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.

Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Layer Tasks

Interplay between the Layers • Layer (n-1) offers its functionality to the above lying layer n as a communication service.

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.

• 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. Layer n

n-PDU

Layer n

Data

Layer (n-1)

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

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Application process H

Presentation Layer

H

Session Layer

H

Transport Layer

H

Network Layer Data Link Layer

H H

(n-1)-PDU

Chapter 1: Introduction

H: Header, e.g. control information of the layer

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The Communication Process Data

Application process

Data

Application Layer

Session Layer

P-PDU

Transport Layer

S-PDU

Network Layer

T-PDU N-PDU

• 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:

Presentation Layer

A-PDU

Physical Layer

T

Data Link Layer Physical Layer

Bit stream

Chapter 1: Introduction

H

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

The whole Communication Process

Application Layer

Layer (n-1)

Transmission medium

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Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

The OSI Reference Model in the Network Application process

Application process Application Protocol

Application Layer

Application Layer Presentation Protocol

Presentation Layer

Presentation Layer

Session Protocol

Session Layer

Transport Protocol

Transport Layer Network Layer Data Link Layer Physical Layer Host A

Transport Layer

Network Layer Data Link Layer Physical Layer

Network Layer Data Link Layer Physical Layer

Data Link Layer

Router A

Router B

Host B

Network Layer

Physical Layer

Internal Protocols

Chapter 1: Introduction

Computer Networks

Session Layer

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

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Chapter 1: Introduction

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

First Generation Computer Networks

Introduction of Local Area Networks Building A

Computing Center Operator

Rest of the world

Rest of the world

Fixed lines

Mainframe Building B

Telephone lines

Computing Center Operator

Demultiplexer

Mainframe

Multiplexer Router Building C Terminals

Terminals

Chapter 1: Introduction

Peripherals

Terminals

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Chapter 1: Introduction

Peripherals

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Global Networking

Important Terms

Building A

Rest of the world (Internet)

Clients Local Server

Fixed lines, ISDN, Provider ...

Switch

Computing Center

Router Router

Server

Network and system administrator

Router

Backbone Building B Clients Local Server

Switch Peripherals Switch

Mainframe

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 other computers or switches. Routers are used to manage global address information 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.

Router

Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Classification of Networks

Classification of Networks

Point-to-Point Network • A pair of computers is directly connected by one cable

Classification by Distance 1m

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 Addresses are used

Chapter 1: Introduction

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Chapter 1: Introduction

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Personal Area Network (PAN)

10 m

Room

100 m

Building

1 km

Campus

10 km

Town

100 km

Country

1000 km

Continent

10000 km

Planet

Chapter 1: Introduction

Local Area Network (LAN)

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

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Networks

Networks Connection to a WAN

Switch

Router

Local Networks (LAN)

Metropolitan Network (MAN), Backbone for a town or a region

Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

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Chapter 1: Introduction

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Networks

Networks Router 10 GBit/s 2,4 GBit/s 2,4 GBit/s 622 MBit/s

Backbone in Germany Rostock Kiel Hamburg

Global Upstream

Oldenburg

Braunschweig

Hannover Berlin

Magdeburg Bielefeld Essen

Göttingen

Leipzig

St. Augustin

Dresden

Marburg Aachen

Ilmenau Würzburg

Frankfurt

Erlangen

Central entry router of RWTH.

GEANT

Heidelberg Karlsruhe

Regensburg

Kaiserslautern Stuttgart

Augsburg

Garching

Point-to-Point connections

Chapter 1: Introduction

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Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Networks

Standards Organizations - IEEE Institute of Electrical and Electronic Engineers - IEEE • Standardization e.g. of the IEEE 802.XStandards for Local Area Networks

Central node Frankfurt – connection to the European research network Géant.

• • • • • • •

Also in Frankfurt and Hamburg: intercontinental connections.

Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

802.1 802.2 802.3 802.4 802.5 802.6 802.7

Overview and Architecture of LANs Logical Link Control (LLC) CSMA/CD („Ethernet“) Token Bus Token Ring DQDB (Distributed Queue Dual Bus) 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)

Chapter 1: Introduction

www.ieee.org • 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 • 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) Page 38 • 802.21 Media Independent Handover

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Standards Organizations - IETF Internet Engineering Task Force - IETF

www.ietf.org

Communication Protocols

• 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

Chapter 1: Introduction

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Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

The TCP/IP Reference Model

The Tasks of the TCP/IP Layers

Application Layer

Application Layer

Presentation Layer

Don´t exist

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.

Session Layer Transport Layer

Transport Layer

Network Layer

Internet Layer

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).

Data Link Layer Host-to-Network Layer Physical Layer

ISO/OSI Chapter 1: Introduction

TCP/IP Page 41

Chapter 1: Introduction

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

The Layers of TCP/IP

OSI vs. 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 reassembled 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.

Chapter 1: Introduction

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1. Time The TCP/IP protocols were already widely used before OSI had finished the standardization activities.

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.

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”!

Chapter 1: Introduction

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Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme

OSI vs. TCP/IP

And now… 1. Introduction

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.

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.

2. Computer Networks • Network principles • Network Components (Cables, Repeaters, Hubs, Bridges, Switches, Routers) • Local Area Networks (Ethernet, Token Ring, Token Bus, FDDI, DQDB) • Wide Area Networks (Frame Relay, ATM, SDH, Resilient Packet Ring) 3. Internet Protocols • Internet/Intranet: the TCP/IP Reference Model • Network protocols (the Internet Protocol IP, Routing protocols) • Next Generation Internet • Transport protocols (TCP and UDP)

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.

Chapter 1: Introduction

• Networks and Network Topologies • Communication Protocols

4. Application Protocols in the Internet • Higher protocols (FTP, HTTP, E-Mail, ...)

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Chapter 1: Introduction

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