Internet basic


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This tutorial, produced in the framework of DC-NET project, gives basic information on Internet: How does it run? Which are the differences between Internet and the Web? What is an IP address? What is a router?

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Internet basic

  1. 1. basicsGabriella Paolini (GARR) 27/05/11 - ICCU Roma1How INTERNET works !
  2. 2. Internet …2It’s a collection of networks interconnected with each otherall over the planetIt has specific and shared rules of operation, followed by allthe networks in order to make the system work properlyIt is governed neither by a group nor by an institution or acompanyIt is not centrally managed as all the single networks whichforms INTERNET have an autonomous managementsystemIt is not a synonymous of World Wide Web27/05/11 - ICCU RomaGabriella Paolini (GARR)
  3. 3. Communication Data Protocol27/05/11 - ICCU RomaGabriella Paolini (GARR)3A communication data protocol is a formaldescription of digital message formats and rulesfor exchanging digital data throughout a networkmade of computing systemsCommunications among computing systems need astandard and shared mechanism for message formatand exchange mechanismProtocols define the shared rules to handshakemessages (the same as human dialogue)
  4. 4. Internet works thanks to TCP/IP27/05/11 - ICCU RomaGabriella Paolini (GARR)4The task of TCP protocol consists in splitting «files»into many little packets, appending new field:destination address and a progressive number. Whenthe packet arrives this protocol have to reassemblecorrectly the file starting from all the partsIP protocol forwards packets through the networkchoosing the best route, if necessary it might split thepackets into little frames while it is working onriassembling it, in order to give it back to TCP layer
  5. 5. TCP/IP in a more comprehensive contest27/05/11 - ICCU RomaGabriella Paolini (GARR)5Standardization process has achieved a solutionnamed protocol stacksThere is no one protocol that manages all the phases of acommunication, but a series of changeover, each of whichdeals with a different and well-defined taskThe approach is more easyIt is possible to choose different protocols belonging to thesame layer according to the service you want to call
  6. 6. Protocols stack27/05/11 - ICCU RomaGabriella Paolini (GARR)6Each layer “talks” to a layer just underneath, it should notcare about layers that are located even more at the bottomof the stack (layer abstraction concept)To send an e-mail you don’t need to know if you will use awireless or a fiber link, but you need to know if yourmessagge has been correctly delivered to the destinationThe same when you send out a letter, the user requires aservice but he does not know how the letter will betrasported and which streets or cities it will get across
  7. 7. ISO/OSI stack (Open System Interconnection)27/05/11 - ICCU RomaGabriella Paolini (GARR)7
  8. 8. Internet stack27/05/11 - ICCU RomaGabriella Paolini (GARR)8Similar to ISO/OSI stackIt has less layers - only 5 in the protocol stackLayers sometimes include funcionalities belonging tomore than one ISO/OSI level, sometimes includeonly part of a particular funcionality
  9. 9. ISO/OSI vs. Internet27/05/11 - ICCU RomaGabriella Paolini (GARR)9
  10. 10. Physical and Data link27/05/11 - ICCU RomaGabriella Paolini (GARR)10Tha same as in ISO/OSI stackPhysical layerIt deals with the definition of:Bit-level electrical/light communication across the channelVoltage/current levels, signal strenght, connector an mediaSignals modulation typeData link layerIt deals with flow regulation, error detection and control, lossof frames. These functions are applied to a single linkIt could claim for a re-transmission of frames that have notbeen correctly deliveredSome examples: ethernet, wlan, token ring, PPP
  11. 11. Network layer27/05/11 - ICCU RomaGabriella Paolini (GARR)11It deals with a correct forwarding of packets comingfrom a source up to the destinationRelating to this layer it exists only one protocol. Thisis the main difference between the other layer in theInternet stackIt does not provide flow control and sequence packetcheckThis level make the network transparent to theapplications
  12. 12. IP protocol27/05/11 - ICCU RomaGabriella Paolini (GARR)12This protocol defines how to deliver packets from asender host to a recipient hostMain features:Connection less: each packet is handled indipendently onefrom each other;Un-reliable: there is not any mechanism that can guaranteespacket delivery (packets could be lost, duplicated, delayed ordelivered out-of-order)
  13. 13. IP Protocol27/05/11 - ICCU RomaGabriella Paolini (GARR)13The network is a set of nodes, named “Router” … thatis forwardersEach router receives a packet and transmits it usingwhat it thinks is the best exitThere are a large set of mechanism to forwardpackets
  14. 14. Transport Layer27/05/11 - ICCU RomaGabriella Paolini (GARR)14It deals with defining the type of service that isrequired by applicationsErrors checkflow and congestions control (if required)out-of-order packet check (if required)Tha main protocols areTCPUDP
  15. 15. TCP27/05/11 - ICCU RomaGabriella Paolini (GARR)15Transmission control protocolIt guaranties a reliable service over an un-reliablenetwork (such as IP network)Connection oriented:Two hosts exchange “port numbers” informationEach packet received is notified to the source with an ACKmessagge (acknowledgement)The connection is closed when the trasmission finishTCP is used when the transmission has not a strict delayrequirement but it requires high reliability
  16. 16. UDP protocol27/05/11 - ICCU RomaGabriella Paolini (GARR)16It is used when you need totransfer packets as fast aspossible and you can toleratesome levels of lost packetsPackets might be lost andnever reach the destinationhostthe source cannot be informedThere is no flow andcongestion controlExamples: multimediastreaming
  17. 17. Data Flow27/05/11 - ICCU RomaGabriella Paolini (GARR)17
  18. 18. Application Layer27/05/11 - ICCU RomaGabriella Paolini (GARR)18It is the highest layer in the Internet stackIt deals with data processing made by the source andthe destination hostsIt knows only transport layer . It don’t know hownetwork is built.Example :Email (SMTP,POP,IMAP)Web browsing (HTTP)File transfer (FTP)streaming server/client
  19. 19. What happens to data ?27/05/11 - ICCU RomaGabriella Paolini (GARR)19DataApplicationLayerTransportLayerNetwork LayerDatalink LayerPhysical Layer
  20. 20. Packet switching27/05/11 - ICCU RomaGabriella Paolini (GARR)20Mechanism used for sending data with InternetEach message is divided in many numbered packetsPackets have a fixed lengthEach packet contains destination host computeraddress and source host computer addressEach packet is sent separately and it can beforwarded following a completely different path onefrom the other
  21. 21. Packet switching27/05/11 - ICCU RomaGabriella Paolini (GARR)21
  22. 22. Packet switching27/05/11 - ICCU RomaGabriella Paolini (GARR)221 221DataPacketSourceDestinationHeader Data
  23. 23. Packet switching27/05/11 - ICCU RomaGabriella Paolini (GARR)231Source Destination1
  24. 24. Packet switching27/05/11 - ICCU RomaGabriella Paolini (GARR)241Source Destination1 2 2
  25. 25. Internet: a complex packet network27/05/11 - ICCU RomaGabriella Paolini (GARR)25