Open System Interconnection .ppt (Size: 1.27 MB / Downloads: 143)
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