OSI Model, Encapsulation & Modulation, PDF

OSI Model, Encapsulation & modulation, Chapter 2 OSI Model brief description. Application > Provides an user interface, file, print, message, database/application services. Presentation > Presents data, handles processing encryption, data encryption, compression/ translation services. Session > Ke...

OSI Model, Encapsulation & modulation, Chapter 2 OSI Model brief description. Application > Provides an user interface, file, print, message, database/application services. Presentation > Presents data, handles processing encryption, data encryption, compression/ translation services. Session > Keep different application data seperate dialog control. Transport > Provides reliable/un realiable delivery, performs error correction before retransmitting end - end connection. Network > Provides logical addressesing, which router uses for path determination routing. Data link > Combines packets into byte & bytes into frames, provide access to media using MAC, performs error detection not correction. Physical > Move bits between devices, physical topology specifies voltage, wire speed and pinout of cable. OSI divided into two groups (upper & lower) Top layers Application, presentation & session Rules for how applications work within host machine. Bottom layers Transport, Network, Data link & Physical Defines how data is transmitted from end to end. OSI Model Layers detailed notes Applications > Choose/determines availability of communications partners along with resources to make connection. Application layer is interface between apps, web browser aren't in application layer, HTPP is protocol which enable communication. Presentation layer > Presents data to application layer, translate data, cod formatting. Adapt data into standard format before transmission. Compression/decompression Encryption/decryption Session layer > Sets up, manage, stop session between presentation layer, provides dialogue control between devices/nodes. Co-ordinates communication between systems & organise them by using; Simplex > one direction Half duplex > only one direction at a time Full duplex > Bi directional Transport layer > Segments & reassembles data into data stream, handles data from upper layers apps and units into same data stream. End to end transport services Create virtual connections, tears down virtual circuits, connectionless or connection orientated. Flow control > Ensure data integrity, uses can request replicate data transport, govern amount of data sent by senders. Buffering > Transport layer can send not ready/stop to sender of source. Windows > Control the amount of outstanding unacknowledge data segments. Acknowledgements > Receiving host fails to receive all segments that it should acknowledge, host can improve communication session by decreasing the window size. Postitive acknowledgement with retransmission > Receiving machine communicates with transmission so by sendinf acknowledgement. Network layer > Manages logical device addressing, determines best routes. X2 types of packets used, route & update. Update > updates router about connected network to all routers within internetwork. Route > routing protocols, RIP,RIPV2, OSPF and enhanced interior gateway routing protocol "EIGRP". These protocols maintain routing table on each router, routers maintains routing table for all routing protocols. Interface > Exit interface packet takes when destined for a specific network. Metric > "distance to the remote network" routers break up broadcast domains, reduce network traffic. Switches break up collision domains Routers use logical addresses to determine next hops Routers can provide layer 2 bridging function and simulataneously route through same interface. Data Link Layer > Transmission of data handles error notification network topology / flow control. Uses MAC to ensures messages are delivered on LAN and translate messages from network layer into bits for physical layer to transmit. Messages are data frame, header is added contains destination source hardware addresses. Responsible for unique identification of devices on local network. LLC > "Logical link control" IEEE 802.2. Identifies network layer protocols and encapsulate them, LLC header tells data link layer what to do with a packet once a frame is received. Physical layer> Send/recieve bits, specifies electrical/mechanical, procedural, functionality requirements for activating, maintaining/deactivating physical links between end systems. Identifies interface between DTE & DTC. DTE > "Data terminal equipment" attached to device. DCE > "data communication equipment" Encapsulation> Transmitted data is wrapped with protocols information at each layer on OSI. Each layer uses protocol data unit "PDU", PDU hold control info attached to data at each layer of OSI, attached to data at each layer of OSI, attached to header in front of data field, also can be in trailer. Steps of encapsulation 1 > User info converted to data transmitted on network. 2 > Data converted to segments, reliable connection is setup between transmitting/receiving hosts. 3 > Segemtns converted to packets/datagrams, logical address placed in header, enable each packet to be routed. 4 >Packets/datagrams converted to frames from transmission. Ethernet addresses used to identify host on local network segment, frame carry packets. 5 > Frames converted to bits, digital encoding/clockinh scheme is used. Modulation techniques Modulation process, varying one/more wave form properties called carrier signal, contains info to be transmitted. Modulation of waveform transforms baseband message signal into Passband Passband > Range of frequencies/wavelength that can pass through a filter without attenuation. Modulator > Digital modulation transfer digital bit stream over analog bandpass channel. Analog/digital modulation uses FDM"Frequency-division multiplexing" several low pass info signals are transferred simultaneously over shared physical network. Digital Baseband Modulation > Line coding, transfer digital bit stream over baseband channel, baseband signal being modulated uses all available bandwidth. TDM > "Time division multiplexing" transmit.receives many independent signal over common signal path, uses sync network devices at each end of transmission line, each signal appears on line only at alternating pattern in fraction of time delay.