Post on 16-Dec-2014
description
THE OSI MODEL
(Open Systems Interconnection)
GORVAM SADDAR
The Open Systems Interconnection The Open Systems Interconnection ((OSIOSI)) is the layered model for the network is the layered model for the network system, Designed by system, Designed by ISOISO ( ( International International Organization StandardizationOrganization Standardization ). OSI ). OSI enables devices in the network to enables devices in the network to communicate with each other.communicate with each other.
The OSI 7-layer Model
All
People
Seem
To
Need
Data
Processing
Away
Pizza
Sausage
Throw
Not
Do
Please
• Defined in 1984 and become an international standard
Relationship of OSI layers
PhysicalCommunication
1. Physical Layer
• Responsible for transmitting bits from one computer to another
Example protocols: Ethernet, Token Ring (Physical part)
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
Converts bits into electronic signals for outgoing messages.
Defines the way in which two or more devices can be connected physically.
2. Data Link Layer
• Provides for flow of data over a single link from one device to another.
• Packets placed into frames at this layer
• Provide error-free frame transfer by acknowledgment and retransmission
Example protocols: Ethernet, Token Ring
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
3. Network Layer
• Logical address to physical address translation
For TCP/IP running on Ethernet
Logical address: IP address
158.132.148.99
Physical address: Ethernet address
00 00 E2 15 1A CA
• Determine the route from source to destination computer
Example protocols: IP, IPX
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
4. Transport Layer
• Ensure packets are delivered error free, in sequence
• Translate between packets and message
• Control flow of data and acknowledges successful receipt of data.
1 2 3
Sending
Example protocols: TCP, SPX, NWLink
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
5. Session Layer Example application program: Winsock, UNIX Socket
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
• Establishment, maintaining and release of session
• Provide dialog management
• Regulate which side transmit, when, for how long (Sync.)
• Provide synchronization between user tasks
6. Presentation Layer Example application program: redirector (NT), SSL
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
• Translate data from Application Layer to the format suitable for session layer (the network)
• Provide data encryption, compression
• Changing or converting character set, graphic, and file format
7. Application Layer Example protocols: FTP, Telnet, HTTP
• Entry point for application to access network
• Directly support user applications
• E.g. File transfer, email
• General capabilities:
Network access, flow control, Error recovery
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
Example: File Transfer
PictureTelPictureTel
PictureTel
FTP ServerFTP Client
Network
• The most traditional network task
• Implemented by a simple Application Layer protocol called FTP