Basic Network Management - Chapter 5: LAN Architecture

Chapter 5: LAN ARCHITECTUREObjectivesIdentify the seven protocol layers of the Open System Interconnection (OSI) Reference ModelDiscuss the functional attributes of each layer of the Open Systems Interconnection Reference Model Understanding Putting Data on the Cable and Access MethodsContentIntroductionOpen Systems Interconnection (OSI) Reference ModelHow network sends dataAccess MethodSummaryIntroduction Sending DataRecognize dataDivide data into manageable chunks Add information to each chunk Location of dataIdentify receiverAdd timing and error checking Put data on the network and send itProtocols: procedures to send data Introduction (2)To solve the problem of networks being incompatible and unable to communicate with each other, the International Organization for Standardization (ISO) released the Open Systems Interconnection (OSI) reference model in 1984First standard to describe architecture for dissimilar devices to communicateBest known and widely used Open Systems Interconnection The OSI model organizes communication protocols into seven levels: The Physical LayerThe Data Link LayerThe Network LayerThe Transport LayerThe Session LayerThe Presentation LayerThe Application LayerOpen Systems Interconnection (2)Packet Assembly & Disassembly ProcessLayer 7: The Application LayerTopmost layerWindow for application processes to access network services User-end interface that support transfer files, access database, e-mail Handles general network access, flow control, error recovery Layer 6: The Presentation LayerDetermines format to be used to exchange dataCalled the network translator Responsible for protocol conversion, translating data, encrypting data Manages data compressionRedirector utility operates at this layer Layer 5: The Session LayerPerforms name recognition and allows two applications on different computers establish, manage and end a connection (session)Provides synchronization between user tasks by placing checkpoints in the data stream Implements dialog control between communicating processes Layer 4: The Transport LayerEnsures packets are delivered error free, in sequence, no losses or duplicationRepackages messages, breaking up into smaller packets Unpacks message at receiving end and sends acknowledgement Provides flow control, error handling, solves transmission problems Layer 3: The Network LayerAddresses messages, translates logical addresses/names into physical addressesOrganizes data into packets then forwards them to their destination Determines the best route on the network based on network conditions, priority of serviceManages traffic problems and controls congestion of data Layer 2: The Data Link LayerSends data frames from network layer to physical layerData frame: organized logical structure in which data can be placedSimple data frame: Destination ID, Sender ID, Control, Data, CRC (cyclical redundancy check) Provides error free transfer of frames from one computer to another through the physical layer Layer 2: The Data Link Layer (2)Layer 1: Physical LayerResponsible for the mechanical, electrical and procedural characteristics of the transmission (transmit the unstructured raw bit stream over a physical link)Establishes and maintains physical link between communication computersDefines how the cable is attached to the NICTransmit bit (0,1) from one computer to anotherLayer 1: Physical Layer (2)How Networks Send DataTwo reasons why large chunks of data tie up network Large chunk of data generate a problem traffic during transmissionTimely interaction and communication impossibleHow Networks Send Data (2)Large Streams of DataHow Networks Send Data (3)Why network divided data to packets? Packets : small chunks/frames of data How Networks Send Data (4)Special control info sent with each packet Send the original, disassembled data in small chunks Reassemble the data in the proper order at destination Check data for errors How Networks Send Data (5)Packets may contain: Information such as messages Types of computer control data, commands, service requests Session control codes (error correction)How Networks Send Data (6)Packet components: Source address Data intended for transmission Destination address Instructions that tell network how to pass dataInfo for receiving computer on how to reassemble packets Error checking info How Networks Send Data (7)Components have three sections: Header Data Trailer How Networks Send Data (8)How Networks Send Data (9)Header Alert signal indicating packet is being sent Source addressDestination address Clock info to synchronize transmissionHow Networks Send Data (10)DataActual data being sent Size 512 byte to 4K Trailer Contains error checking component (CRC) CRC is a mathematical calculation done on data How Networks Send Data (11)Packet Creation Begins at Application layer As data descends through each layer, more info is added at each layer How Networks Send Data (12)ApplicationPresentationSessionTransportNetworkData LinkPhysicalApplicationPresentationSessionTransportNetworkData LinkPhysicalEncapsulateDe-EncapsulateAccess MethodsAccess Methods (2)An access method is a set of rules defining how a computer puts data on and takes off a network cablePrevent simultaneous access to the cableContentionContention means that the computer are contending for use of the transmission medium (first come, first served)Specifications for contention-based access methods include procedure for how to avoid collisions and what to do if collision occursContention-based access methods include:CSMA/CDContention (2)Collision occurCSMA/CD CSMA/CD is stand for Carrier-Sense Multiple Access/Collision DetectionMultiple access is when two devices begin to talk at the same timeCarrier sensing refers to the process of a device looking for a clear channel before sending a messageIEEE 802.3CSMA/CD (2)Checks the cable for network trafficComputer listens to the networkIf the network is not busy, that computer can send data If the network is busy, the computer refrains from transmitting until the network quiets downCSMA/CD (3)CSMA/CD (4)Carrier detection mechanism:Computers continue to listen to the network as they transmitIf a computer detects another signal that interferes with the signal it is sending, it stops transmittingBoth computers then wait a random amount of time and attempt to retransmitSummaryThis topic examined:OSI and seven layersHow network sends dataAccess Methods