Tài liệu Chapter 5: LAN ARCHITECTURE ATHENA . pdf

ATHENA Chapter 5: LAN ARCHITECTURE ATHENA Objectives ~ Identify the seven protocol layers of the Open System Interconnection (OSI) Reference Model ~ Discuss the functional attributes of each layer of the Open Systems Interconnection Reference Model ~ Understanding Putting Data on the Cable and Access Methods ATHENA Content ~ Introduction ~ Open Systems Interconnection (OSI) Reference Model ~ How network sends data ~ Access Method ~ Summary ATHENA Introduction ~ Sending Data • Recognize data • Divide data into manageable chunks • Add information to each chunk – Location of data – Identify receiver • Add timing and error checking • Put data on the network and send it ~ Protocols: procedures to send data ATHENA 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 1984 ~ First standard to describe architecture for dissimilar devices to communicate ~ Best known and widely used ATHENA Open Systems Interconnection ~ The OSI model organizes communication protocols into seven levels: • The Physical Layer • The Data Link Layer • The Network Layer • The Transport Layer • The Session Layer • The Presentation Layer • The Application Layer ATHENA Open Systems Interconnection (2) ATHENA Packet Assembly & Disassembly Process ATHENA Layer 7: The Application Layer ~ Topmost layer ~ Window 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 ATHENA Layer 6: The Presentation Layer ~ Determines format to be used to exchange data ~ Called the network translator ~ Responsible for protocol conversion, translating data, encrypting data ~ Manages data compression ~ Redirector utility operates at this layer [...] .. . Physical Layer (2) ATHENA How Networks Send Data Two reasons why large chunks of data tie up network • Large chunk of data generate a problem traffic during transmission • Timely interaction and communication impossible ATHENA How Networks Send Data (2) Large Streams of Data ATHENA How Networks Send Data (3) Why network divided data to packets? • Packets : small chunks/frames of data ATHENA How Networks .. . that tell network how to pass data • Info for receiving computer on how to reassemble packets • Error checking info ATHENA How Networks Send Data (7) Components have three sections: • Header • Data • Trailer ATHENA How Networks Send Data (8) ATHENA How Networks Send Data (9) Header • • • • ATHENA Alert signal indicating packet is being sent Source address Destination address Clock info to synchronize .. . done on data ATHENA How Networks Send Data (11) Packet Creation • Begins at Application layer • As data descends through each layer, more info is added at each layer ATHENA How Networks Send Data (12) Presentation Presentation Session Transport Network Data Link Physical ATHENA De-Encapsulate Application Encapsulate Application Session Transport Network Data Link Physical Access Methods ATHENA Access .. . device looking for a clear channel before sending a message IEEE 80 2.3 ATHENA CSMA/CD (2) Checks the cable for network traffic • Computer listens to the network • If the network is not busy, that computer can send data • If the network is busy, the computer refrains from transmitting until the network quiets down ATHENA CSMA/CD (3) ATHENA .. . simultaneous access to the cable ATHENA Contention Contention 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 occurs Contention-based access methods include: • CSMA/CD ATHENA Contention (2) Collision occur ATHENA CSMA/CD CSMA/CD is .. . layer ATHENA Layer 2: The Data Link Layer (2) ATHENA Layer 1: Physical Layer Responsible 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 computers Defines how the cable is attached to the NIC Transmit bit (0,1) from one computer to another ATHENA. .. handling, solves transmission problems ATHENA Layer 3: The Network Layer Addresses messages, translates logical addresses/names into physical addresses Organizes data into packets then forwards them to their destination Determines the best route on the network based on network conditions, priority of service Manages traffic problems and controls congestion of data ATHENA Layer 2: The Data Link Layer Sends .. . disassembled data in small chunks • Reassemble the data in the proper order at destination • Check data for errors ATHENA 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) ATHENA How Networks Send Data (6) Packet components: • • • • Source address Data intended for transmission .. . Layer 5: The Session Layer Performs 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 ATHENA Layer 4: The Transport Layer Ensures packets are . ATHENA Chapter 5: LAN ARCHITECTURE ATHENA Objectives ~ Identify the seven protocol layers of. Presentation Layer • The Application Layer ATHENA Open Systems Interconnection (2) ATHENA Packet Assembly & Disassembly Process ATHENA Layer 7: The Application