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8/14/2019 OSI Model (Cybentizen.tk)
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LectureRoadmap
Need of a Layered Architecture OSI Model
7 Layers of OSI Model Functional Details of OSI Layers
Physical Layer Data Link Layer Network Layer Transport Layer Session Layer
Presentation Layer Application Layer
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Layered Architecture
Design Philosophy of Layered Architecture The complex task of communication is broken into
simpler sub-tasks or modules Each layer performs a subset of the required
communication functions Each layer relies on the next lower layer to perform
more primitive functions Each layer provides services to the next higher layer Changes in one layer should not require changes in
other layers Helps in troubleshooting and identifying the problem
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An example Sending a letter
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OSI Model
To standardize the design of communicationsystem, the ISO created the OSI model.
Open Systems Interconnection Developed by the International Organization
for Standardization (ISO) Contains Seven layers It describes the functions to be performed at
each layer
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OSI Model
ISO Established in 1947ISO Established in 1947 ISO standard that covers all aspects of networkISO standard that covers all aspects of network
communications is the Open Systems Interconnectioncommunications is the Open Systems Interconnection((OSIOSI ) model.) model.
First introduced in the late 1970s.First introduced in the late 1970s. A layer model Each layer performs a subset of the required
communication functions Each layer relies on the next lower layer to
perform more primitive functions Each layer provides services to the next
higher layer Changes in one layer should not require
changes in other layers
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ISO is the organization.OSI is the model.
Note
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OSI Model
ApplicationPresentation
Session Transport
NetworkData Link
Physical
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Peer-to-Peer Process
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An exchange using the OSI model
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OSI Model Physical Layer
Physical Physical interface between devices handles the transmission of bits over a
communications channel Choice of Wired / wireless medium Data is converted into signals Includes voltage levels, connectors, media
choice modulation techniques EIA/TIA-232, RJ45, NRZ.
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The physical layer is responsible for movements of individual bits from one hop (node) to the next.
Note
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OSI Model Data Link Layer
Data Link Transforms data into a frame Means of activating, maintaining and
deactivating a reliable link Error detection and control Flow Control Higher layers may assume error free
transmission Examples :- Ethernet, Frame Relay, FDDI.
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Data Link Layer
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The data link layer is responsible for movingframes from one hop (node) to the next.
Note
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OSI Model Network Layer
Network Transport of information Higher layers do not need to knowabout underlying technology
Responsible for creating, maintainingand ending network connections
Transfers a data packet from node tonode within the network .
Routing Not needed on direct links Examples :- IP, IPX, AppleTalk.
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Network Layer
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The network layer is responsible for the delivery of individual packets from the source host to thedestination host.
Note
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Transport Layer
Transport Exchange of data between end
systems (end to end flow control)
Error free In sequence
Quality of service Layer 4 protocols include TCP (Transmission
Control Protocol) and UDP (User DatagramProtocol).
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Transport Layer
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The transport layer is responsible for the deliveryof a message from one process to another.
Note
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OSI Model Session Layer
Session Control of dialogues between
applications Half Duplex Full Duplex
Synchronization Points (backup points)
Examples :- SQL, ASP(AppleTalk SessionProtocol), NETBIOS, RPC, PAP.
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The session layer is responsible for dialog control andsynchronization.
Note
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OSI Model PresentationLayer
Presentation Data formats and coding
Data compression Encryption Examples :- JPEG, MPEG, ASCII,
EBCDIC, HTML.
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The presentation layer is responsible for translation,compression, and encryption.
Note
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OSI Model ApplicationLayer
Application Layer where the application using thenetwork resides.
Common network applications include remote login file transfer e-mail
web page browsing etc. Means for applications to access OSIenvironment
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The application layer is responsible for providingservices to the user.
Note
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Summary of layers
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OSI Layers
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The OSI Environment
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The OSI Environment
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TCP/IP Protocol Suit
TCP/IP suite is the set of protocols thatimplement the protocol stack on whichthe Internet runs. It is sometimes calledthe Internet Model.
This model consists of five orderedlayers
In a protocol stack, each layer solves aset of problems involving thetransmission of data, and provides awell-defined service to the higher layers
Developed by research foundation byUS department of defense
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Internet layers
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TCP/IP Protocol ArchitectureModel
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Some Protocols in TCP/IP Suite