Data and Computer Communications - cpe.ku.ac.th

1 data and Computer Communications1/18 Applied Network Research GroupDepartment of Computer Engineering, Kasetsart University1/18 data and ComputerCommunicationsSurasak updated: 11 July 2000 data and Computer Communications2/18 Applied Network Research GroupDepartment of Computer Engineering, Kasetsart University2/18A Communications ModeloutputinformationSourcedeviceSource deviceTransmitterTransmitterTransmission mediumTransmissionmediumReceiverReceiver DestinationdeviceDestinationdeviceinputi nformationinput datatransmitted signalreceived signaloutput datadata :A represent of facts ,concepts in a formalizedmanner suitable forcommunicationsinformation :The meaningthat is currently assigned todata by means of theconventions applied to thosedataThe fundamental purpose of data Communications is to exchange informationbetween two parties.

2 The source device generate the data to be transmitter transform and encodes the input data into the appropriateform of signals that can be transmitted across the transmission medium. Thereceiver accepts the signal and converts it into a from that can be handled bythe destination and Computer Communications3/18 Applied Network Research GroupDepartment of Computer Engineering, Kasetsart University3/18 communication TaskszError detectionzError correctionzRecoveryzProtectionzInterfaci ngzSignal generationzMessage formattingzTransmission systemutilizationzExchange managementzSystem managementzAddressingzFlow controlzRoutingAbove lists are keys task that must be performed in a data and Computer Communications4/18 Applied Network Research GroupDepartment of Computer Engineering.

3 Kasetsart University4/18 data communication SchematicCommunicationNetworkCommunicati onNetwork NodeNetwork StationData communication takes place between two devices that are connected. It isimpractical for any two devices to be directly, point-to-point connectedbecause of :- The devices are very far Some device may require a link to many of the solution is to attach each device to a network. The devices are known asstations or network stations may be Computer or othercommunicating devices. Each station attaches to anetwork node,whichperforms communication and Computer Communications5/18 Applied Network Research GroupDepartment of Computer Engineering, Kasetsart University5/18 data communication NetworkszPublic Switched Telephone Network (PSTN)zLocal Area Network (LAN)zLeased lineszPublic Switched data Network (PSDN)zIntegrated Services Digital Network (ISDN)

4 The type of data communication facility used is a function of the nature of theapplication, the number of computers involved, and their physical and Computer Communications6/18 Applied Network Research GroupDepartment of Computer Engineering, Kasetsart University6/18 PSTN modemmodemPSTNzDistanced stations are connected via public carrier,normally telephone is required to convert digital data to analog beforetransmitting to to telephone destination modem converts analog signal back todigital carrier orPublic Switch Telephone Network(PSTN)is normally usedto connected distanced stations. This requires a device known as amodem(Modulator-Demodulator) to convert digital data to analog before transmittingto to telephone line.

5 The destination modem converts analog signal back todigital and Computer Communications7/18 Applied Network Research GroupDepartment of Computer Engineering, Kasetsart University7/18 LANhubhubhubhubrouterGeneral Characteristics :zConfined geographical areazUnder single managementzHighdatarateserverstationstat ionstationCommunications network that serves users within a confined area is known asaLocal Area Network(LAN). Computers (server and workstations) arenormally distributed around a single office or building, including networkdevice like hub, bridge or and Computer Communications8/18 Applied Network Research GroupDepartment of Computer Engineering, Kasetsart University8/18 Leased Lines Lease public circuits to connect different sites communication channel is privateLANV oiceLANV oiceLANV oiceleased circuitPublic carrier circuit have been normally used for connected computers indifferent sites.

6 The resulting network is known as aWide Area Network(WAN). One approach is to lease transmission lines from the public carriersand install a private switching system at each site to create anEnterpriseWide Private Network. Such networks normally incorporate both voice anddata benefits are such as communication channel is private and online,several data transmission rate is provided from low speed to high and Computer Communications9/18 Applied Network Research GroupDepartment of Computer Engineering, Kasetsart University9/18 PSDNLANLANLANPSDN PSDN is designed specifically for the transmission ofdata rather than voice communication is shared Example : and Frame Relay, ATMT elephone companies normally provide a public data service.

7 Such networksis known asPublic Switch data Network(PSDN), like the PSTN, are nowinterconnected internationally and have been designed specifically for thetransmission of data rather than voice. A network is public in the sense thatmany company share a switching network. A cost of this service is normallylower than a leased and Computer Communications10/18 Applied Network Research GroupDepartment of Computer Engineering, Kasetsart University10/18 ISDNISDNNTENTENTENTENTE=Networkterminati on equipmentISDN= Integrated servicesdigital networkUsing ISDN to carry both voice and dataIntegrated Serviced Digital Networks(ISDN) is designed for transmittingvoice, video and data over a digital line.

8 ISDN services come in two forms :(1) BRI (Basic rate Interface) provides two 64 Kbps channel plus a 16 Kbpscontrol channel (144 Kbps).(2) PRI (Primary rate Interface) provides twenty three (in North America) 64 Kbps channel and one 64 Kbps control channel ( Mbps) data and Computer Communications11/18 Applied Network Research GroupDepartment of Computer Engineering, Kasetsart University11/18 Computer communication ArchitecturesCommunication-related messagesNetworkinterfaceFile and file transfer commandCommunicationnetworkFile transferapplicationCommunicationsservice moduleNetwork accessmoduleComputer AComputer BFile transferapplicationCommunicationsservice moduleNetwork accessmoduleInstead of a single module for performing Communications , there is astructured set of modules that implements the communication function.

9 Thatstructure is referred to as a Communications and Computer Communications12/18 Applied Network Research GroupDepartment of Computer Engineering, Kasetsart University12/18 Three-layers ModelApplicationsTransportNetwork accesszThree-layers model involves three agents:applications, computers, and task can be organized into threerelatively independent layerssupport user applicationsreliability in of dataCommunications can be said to involved three agents: applications,computers, and networks. communication task can be organized into threerelatively independent layers :Network access: concern with the exchange of data between a Computer andthe attached : assured that the data arrive at the destination applications and inthe same order.

10 Also take care of reliability in : support user and Computer Communications13/18 Applied Network Research GroupDepartment of Computer Engineering, Kasetsart University13/18 ApplicationsTransportNetwork accessApplicationsTransportNetwork accessProtocol Architectures and NetworksApplicationsTransportNetwork access12 34() () () ()123() () ()12() ()CommunicationnetworkService Access PointNetwork AddressEach Computer on the network must have uniquenetwork addressin order todeliver data to the proper destination. Each application must also have ansoftware address that is unique within that Computer to allow the transportlayer to deliver data to the proper application.