Data Communication and Internet Technology
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noitcudortnI :1 retpahC noitcudortnI :1 retpahC Dr. rer. nat. Dirk Thißen Lehrstuhl für Informatik IV, RWTH Aachen Ahornstraße 55, 52074 Aachen Room 4226 Phone: 0241 / 80 - 21450 eMail: [email protected] Contact Information for questions regarding lecture/exercises At the end of winter term Written Exam 3 egaP http://www-i4.informatik.rwth-aachen.de/content/teaching/lectures/sub/datkom/WS04-05-bonn/index.html • Copies to the lecture slides as well as exercise sheets are placed on the web page to the lecture: Slide Copies Organization emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL Dr. rer. nat. Dirk Thißen In principle, every 14 days Exercise is given on Tuesday Frontal exercise Exact dates depend upon the lecture dates November 04th 2004 November 25th 2003 November 18th 2003 4. Application Protocols in the Internet • Higher protocols (FTP, HTTP, E-Mail, ...) 3. Internet Protocols • Internet/Intranet: the TCP/IP Reference Model • Network protocols (the Internet Protocol IP) • Transport protocols (TCP and UDP) 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) • Wireless Networks (WLAN) • Networks and Network Topologies • Communication Protocols 1. Introduction Content noitcudortnI :1 retpahC Prof. Dr. Otto Spaniol • • • • Exercises No lecture: November 23rd 2004 November 16th 2004 November 9th 2004 November 2nd 2004 October 26th 2004 October 19th 2004 4 egaP 1 egaP Lehrstuhl für Informatik IV RWTH Aachen • Lecture takes place on Thursday, 10:00 – 11:30 and 13:45 - 15:15 • The lecture is planned with 3 hours / week • Not each date is needed, some are skipped • First lecture dates are planned, the further dates are announced in time emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL Data Communication and Internet Technology Lecture Organization 2 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL 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,-. noitcudortnI :1 retpahC • • • • Example for comparison: • Continuously decreasing costs for hardware... • ... while computing power is increasing. Computing power is very cheap The „driving power“ for the enormous growing importance of data communications: Evolution of Data Communication 7 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC • J. Schiller: Mobile Communications. 2nd Edition, Addison Wesley, 2003. → How to achieve a reliable and efficient transfer? → Design of uniform data units for transfer Communication Protocols (Internet Technology) → How to coordinate the access of several computers to the medium? → How to represent digital data on the medium? → Which media can be used for data transport? → How to connect several computers? Wide range of usage: offices, factories, at home, … Increasing number of applications and users Increasing system diversity Increasing computing power leads to new possibilities in data processing: • Speech processing • Image processing • Multimedia authoring • Video conferencing • ...... Applications noitcudortnI :1 retpahC 5 egaP • Cisco Systems: Internetworking Technologies Handbook. 3rd Edition, Cisco Press, 2001. Computer Networks Data communication comprises two topical areas: 8 egaP • J.F. Kurose, K.W. Ross: Computer Networking: A Top-Down Approach Featuring the Internet. Addison-Wesley, 2002. emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC • A.S. Tanenbaum: Computer Networks. 4th Edition, Prentice Hall, 2002. Data communication is the processing and the transport of digital data over connections between computers and/or other devices (generally over large distances) Data Communication 6 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL Literature emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC Server WWW Server Domain Name System (DNS) FTP Server Client WWW Browser eMail Program FTP Client Examples for Client/Server systems Client Program (process) which uses a service offered by a server. 11 egaP 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/Server Systems emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC Example for interworking of two parties: Client/Server principle 9 egaP • 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 • Procedures for efficient interworking (CSCW = Computer Supported Cooperative Work) Efficient methods to share data between the components of a distributed system • Essential: • Access to foreign resources by communication networks to achieve reasonable usage Network Client Process Client Reply Advantages Request → Cost reduction → Better usage of resources → Modular extensions → Reliability by redundancy Network Server Process Server • Best example: File Sharing, e.g. Napster, Gnutella • Establishment of a whole network of connections • Connections between any pair of computers • Equal partners, no fixed client and server roles Another principle: Peer-to-Peer noitcudortnI :1 retpahC Sharing resources lowers costs The Client/Server Principle emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL Reducing Costs 21 egaP 01 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC Terminals Operator Mainframe Peripherals Demultiplexer Computing Center First Generation Computer Networks emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC • ...... Rest of the world Multiplexer Terminals Telephone lines • Annoyance through anonymous or unwanted messages (SPAM) of the whereabouts of people • Control over the productivity of employees, • Potential censorship? • Juridical aspects (legislation) • Responsibility 51 egaP • Eventually dubious or forbidden contents Building C Building B Building A Terminals Operator Mainframe Rest of the world Peripherals Router Computing Center Introduction of Local Area Networks Fixed lines Computer Networks noitcudortnI :1 retpahC 31 egaP Communication networks enable a faster and cheaper exchange/distribution of information. There is however a large number of social, ethnical, cultural, juridical, ... side effects. 61 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL Non-technical aspects 41 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL Switch Clients Backbone Classification by Distance Classification of Networks Country Planet 10000 km Town 10 km Continent Campus 1 km 1000 km Building 100 m noitcudortnI :1 retpahC 100 km Room 10 m 1m Router Switch Server Peripherals Router Mainframe Network and system administrator Computing Center Internet Wide Area Network (WAN) Metropolitan Area Network (MAN) Local Area Network (LAN) Personal Area Network (PAN) emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC Router Local Server Building B Router Switch Fixed lines, ISDN, Provider ... Rest of the world (Internet) 91 egaP Clients 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 Point-to-Point Network • A pair of computers is directly connected by one cable • Meshed network • Tree • Ring • Star • Bus Topologies • Simple connection structures (“Simple is beautiful”) LAN • Transmission delay of a message in the range of milliseconds (~10 ms) • Transmission capacity up to 1,000 Mbit/s • Linked are PCs/Workstations/...., for exchanging information and sharing peripherals and resources • Usually maintained by one local organization • Communication infrastructure for a restricted geographical area (10 m up to some km) Local Area Networks noitcudortnI :1 retpahC 71 egaP Local Server emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC Building A Classification of Networks 02 egaP 81 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL Global Networking emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL A Ω Example: Ethernet B Router Backbone Repeater D Branch 2 C noitcudortnI :1 retpahC + Minimization of the cable length necessary + Adaptation to given geographical structure + Bridging of large distances • Branching elements can be active (Router) or passive (Repeater) • Topology: Connection of several busses or stars Tree A Branch 1 LANs: Tree emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC + The breakdown of a station does not influence the rest of the network + No choose of path to target (= routing) necessary + Simple, cheap, easy to connect new stations - Restriction of the extension and number of stations to connected - (+) Passive coupling of stations 32 egaP 12 egaP • 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. Bus Ω B Example: Fast Ethernet A B B A Example: Token Ring, FDDI LANs: Ring noitcudortnI :1 retpahC Terminating resistor stations are connected by two opposed rings • Variant: bidirectional ring + Only N connections for N stations + Easy connection of new stations + Large extent possible – Breakdown of the whole network in case of failure of one single station or connection • Active stations: messages are regenerated by the stations (Repeater) • Chain of point-to-point connections • Broadcast Network Ring + Easy connection of new stations + N connections for N stations + Definite path, no routing – Vulnerability through central station (Redundancy possible) – Expensive central station • Broadcast network (Hub) or point-topoint connections (Switch) • Designated computer as central station: a message of station A is forwarded to station B via the central station Star 42 egaP LANs: Star emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL LANs: Bus 22 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL N ( N − 1) 2 connections are noitcudortnI :1 retpahC Example: Distributed Queue Dual Bus (DQDB, IEEE 802.6) • 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 • Difference to LANs: Time slots Metropolitan Area Network (MAN) emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC and congestion control become necessary (Wide Area Networks) Partly meshed network: cheaper, but routing, flow control MAN 72 egaP 52 egaP + Maximal connection availability through routing integration + Redundant paths + No routing – Connecting a new station is a costly process – For N stations, needed 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 Fast Ethernet (IEEE 802.3u, 100 MBit/s) - at the moment the most widely spread network - extension of Ethernet for small distances Token Ring (IEEE 802.5, 4/16/100 MBit/s) - for a long time the Ethernet competitor - extended to FDDI (Fiber Distributed Data Interface) Ethernet (IEEE 802.3, 10 MBit/s) - originally the standard network - available in an „immense number“ of variants LAN WAN Host Router Bridging of any distance Connects LANs and MANs over large distances Irregular topology, based on current needs Consists out of stations which are connected through point-to-point with each other • Mostly quite complex interconnection of subnetworks which are owned by independent organizations • • • • Wide Area Network (WAN) noitcudortnI :1 retpahC • Point-to-Point connections between all stations 82 egaP Fully Meshed Network LANs: Examples emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL LANs: Meshed Networks 62 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC Communication Protocols 13 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC • Wireless MANs/WANs • E.g. common telecommunication networks like GSM. • Range of several kilometers („worldwide") • Transmission capacity below 1 MBit/s • IEEE WirelessMAN (IEEE 802.16) as MAN for data transmission • 802.8 Fiber Optic Technical Advisory Group (FOTAG) • 802.7 Broadband Technical Advisory Group (BBTAG) • 802.6 DQDB (Distributed Queue Dual Bus) • 802.5 Token Ring • 802.4 Token Bus • 802.3 CSMA/CD („Ethernet“) • 802.2 Logical Link Control (LLC) • 802.1 Overview and Architecture of LANs • 802.16 WirelessMAN • 802.15 Personal Area Networks (Bluetooth) • 802.14 Cable modems • 802.12 Demand Priority (HP’s AnyLAN) • 802.11 Wireless LAN (WLAN) • 802.10 Standard for Interoperable LAN Security (SILS) • 802.9 Integrated Services LAN (ISLAN) Interface www.ieee.org application processes with the purpose of a common communication A protocol is defined as the whole set of agreements between 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 → → → → → → → To enable understanding in communication, all communication partners have to speak the same „language“. Why Protocols? noitcudortnI :1 retpahC • 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 • Standardization e.g. of the IEEE 802.XStandards for Local Area Networks Institute of Electrical and Electronic Engineers - IEEE 23 egaP 92 egaP • System Interconnections (PANs) • direct connection between the components of a computer (Example: Bluetooth) Standards Organizations - IEEE emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL Wireless Networks 03 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC • Consequence: Standardization processes are very slow (due to many, often non-technical reasons). Confidentially restrictions hinder the information flow 53 egaP • 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 Standardization Indispensable for the area-wide practical use of communication systems: Standardization emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC The implementation takes place in layer models. Accepted today: solution 2. and overhead. 33 egaP • Disadvantage: Fixed structures of program interworking; adds more complexity • Advantage: Very flexible, since single components can be exchanged. process. For each application, the needed programs can be combined. Solution 2: Write a set of small programs specialized to special tasks of the communication • Disadvantage: No flexibility! Adoptions require large efforts. Interpreter A Network Electrical signals in correct order Uninterpreted characters www.iso.ch (OSI: Open Systems Interconnection) • 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! • Interworking with ITU-T regarding telecommunication standards, (ISO is a member of ITU-T). • 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 • Organisation, which is working on a volunteer basis (since 1946). • Members: standards organizations in approx. 90 countries International Standards Organization - ISO Standards Organizations - ISO Recognizes single characters and sends them in Morse Technical Expert B Recognizes single characters and sends them in Morse Technical Expert A Language: Spanish Interpreter B additionally: English i.e. no knowledge about politics Uninterpreted sentences, Language: Spanish Philosopher B additionally: English Language: Chinese noitcudortnI :1 retpahC • Advantage: efficient data exchange for a given application. Language: Chinese Thoughts about world politics 63 egaP to establish a communication process. Philosopher A emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC Solution 1: Write one large „Communication Program“ which fulfills all requirements needed Example: Exchange of ideas between philosophers 43 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL Implementation of Protocols emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL Application Presentation Session Transport Network Data Link Physical 6 5 4 3 2 1 Layer 5 and 6 are rarely being implemented Generally to much overhead – some details are unnecessary, some are overloaded Network-independent end-to-end data transfer Addressing and routing of “packets” 93 egaP noitcudortnI :1 retpahC 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. 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. Layer Tasks Transmission medium („Layer 0”) Securing of “frames”; Flow Control Signal representation, character transmission Criticism of the model: Common services for the end user 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. 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. Layer Tasks noitcudortnI :1 retpahC emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC 7 04 egaP 73 egaP 7 layers: 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), … emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC Reduce the complexity of a communication process (all details to be considered) through layers. Layer Tasks 83 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL The ISO/OSI reference model emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer Application process H H H H A-PDU Data T-PDU S-PDU P-PDU Bit stream N-PDU H H Data T Transmission medium Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer Application process 34 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC The whole Communication Process 14 egaP 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. Layer (n-1) Data (n-1)-PDU H n-PDU H: Header, e.g. control information of the layer Layer (n-1) Layer n • 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: The Communication Process noitcudortnI :1 retpahC 7. Application Layer (ISO/OSI) Layer n • For layer (n-1), these PDUs are the data to be transmitted. • Two communication partners on layer n exchange PDUs by using the communication service of the nearest lower lying layer (n-1). • 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). 44 egaP 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-1) offers its functionality to the above lying layer n as a communication service. emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC 6. Presentation Layer Interplay between the Layers 24 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL Layer Tasks emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL Router B Router A Internal Protocols Network Layer Data Link Layer Physical Layer Network Layer Data Link Layer Physical Layer Transport Protocol Session Protocol Presentation Protocol Don´t exist Presentation Layer noitcudortnI :1 retpahC ISO/OSI Physical Layer TCP/IP Host-to-Network Layer Internet Layer Network Layer Data Link Layer Transport Layer Transport Layer Session Layer Application Layer Host B Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer The TCP/IP Reference Model emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC Host A Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer 74 egaP Application Protocol www.ietf.org • 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 • Works on evolution of the Internet architecture and the smooth operation of the Internet. • Several working groups on Internet protocols, applications, routing, security, … • 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. 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). 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. The Tasks of the TCP/IP Layers noitcudortnI :1 retpahC 54 egaP Application Layer Internet Engineering Task Force - IETF 84 egaP Application process emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC Application process Standards Organizations - IETF 64 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL The OSI Reference Model in the Network emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL noitcudortnI :1 retpahC noitcudortnI :1 retpahC 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. 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. 5. Hurriedly product implementation 15 egaP 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. 4. Political reasons OSI vs. TCP/IP 94 egaP 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. 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”! Very high and partly unneeded expense in the OSI specification (thousands of pages of specification descriptions). 3. Complicatedness 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. 2. Freedom from obligation The TCP/IP protocols were already widely used before OSI had finished the standardization activities. 1. Time noitcudortnI :1 retpahC 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). OSI vs. TCP/IP 05 egaP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL The Layers of TCP/IP emetsyS etlietrev dnu noitakinummoK 4 kitamrofnI rüf lhutsrheL