Open System Interconnection (OSI) ppt.
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12-01-2011, 12:07 PM
Open System Interconnection .ppt (Size: 1.27 MB / Downloads: 133)
Project Guided By : Bhavna madam
OSI REFERENCE MODEL
1. Physical Layer
a) Convert the logical 1’s and 0’s coming from layer 2 into electrical signals.
b) Transmission of the electrical signals over a communication channel.
RS232 and RS422 standards
Hubs (multi-port repeater)
2. Data Link Layer
a) Error control to compensate for the imperfections of the physical layer.
b) Flow control to keep a fast sender from swamping a slow receiver.
Error detection and correction methods
IEEE LAN standards
Switches (multi-port bridges)
3. Network Layer
a) Controls the operation of the subnet.
b) Routing packets from source to destination.
c) Logical addressing.
Internet Protocol (IP) addressing
4. Transport Layer
a) Provides additional Quality of Service.
b) Heart of the OSI model.
Connection-oriented and connectionless services
Transmission Control Protocol (TCP)
User Datagram Protocol (UDP)
5. Session Layer
a) Allows users on different machines to establish sessions between them.
b) One of the services is managing dialogue control.
c) Token management.
6. Presentation Layer
a) Concerned with the syntax and semantics of the information.
b) Preserves the meaning of the information.
c) Data compression.
d) Data encryption.
7. Application Layer
a) Provides protocols that are commonly needed.
File Transfer Protocol (FTP)
HyperText Transfer Protocol (HTTP)
Simple Mail Transfer Protocol (SMTP)
Simple Network Management Protocol (SNMP)
Network File System (NFS)
Each layer provides services to the layer above it.
Entities – active elements in each layer (e.g. process, intelligent I/O chip).
Peer Entities – entities in the same layer on different machines.
Service Provider – Layer N.
Service User – Layer N + 1.
Service Access Points – places where layer N + 1 can access services offered by layer N.
2. Connection-Oriented and Connectionless
Connection-Oriented – before data is sent, the service from the sending computer must establish a connection with the receiving computer.
Connectionless – data can be sent at any time by the service from the sending computer.
3. Service Primitives
Request – entity wants the service to do some work
Indicate – entity is to be informed about an event
Response – entity responds to an event
Confirm – entity is to be informed about its request
Sending Computer Receiving Computer
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28-04-2011, 12:44 PM
osi.ppt (Size: 1.43 MB / Downloads: 60)
• An ISO standard covering all aspects of network communications
• Allows different systems to communicate regardless of their underlying architecture or supplier
• Ensures complete transparency between otherwise incompatible systems
• Consists of seven different layers each defining a segment of the process of moving info. across a network
HEADERS & TRAILERS
• Each layer adds its own information to the message it receives from the layer just above it
• On the receive side, layers strip information added on peer layer of transmit side before passing the message to next higher layer
• Added “control data” is placed to the beginning (header) or/and end of a data packet (trailer)
• The whole package is passed to the layer just below it
• Headers are added to the message at layers 6, 5, 4, 3, and 2. A trailer is added only at layer 2
• Examples of header info: checksum, sender/receiver address, service type
• Purpose: Coordinates the functions required to transmit and receive streams of bits, over physical communication medium
• what type of signals & how are bits represented by signals?
• what physical medium & interface to use?
• How bits are synchronized in Tx and Rx?
DATA LINK LAYER
• Purpose: error-free delivery of frames between two systems on the same network (Node-to-Node)
• what information goes into header/trailer & how are stations addressed?
• how are transmission errors detected and corrected?
• how is transmission flow between stations regulated?
• how is access to “shared transmission channel” regulated?
• Purpose: source to destination delivery of packet , possibly across multiple networks
• what info goes into header?
how is packet routed from source to destination
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