2. Objectives
● To get an overview of the OSI 7 layer model
● To get a general understanding of each level of the model
● To understand why the model exists
● To understand the background of the OSI model
3. Layer 7: Application
● This is the interface between the applications we use and the
underlying layers. Not to be confused with the actual applications
this is the protocols used by the application to communicate to the
lower layers.
● Examples would be FTP, HTTP, SMTP, TELNET and many more
● This level communicates with the presentation layer below
4. Layer 6: Presentation
● This layer is responsible for compression, encryption and
formatting of the data to be sent
● Depending on the data to be sent the presentation layer will convert
the information to the appropriate form
● Encryption (if required) is handled at this layer
5. Layer 5: Session
● This layer has responsibility for establishing connections
● It also maintains open connections
● Finally, when the connection is no longer needed it will close the
connection
6. Layer 4: Transport
● At the source side this layer accepts data from the session layer and
breaks it into manageable chunks called packets
● These packets are then sent to the network layer
● At the destination this layer accepts data from the network layer
● Then it reassembles the packets back to the original data
● The data is then passed up to the session layer
● Using TCP / UDP this layer is responsible for flow control and
error checking
7. Layer 3: Network
● The network layer handles all the addressing issues
● It handles routeing of packets
● There are 3 types of routing: static route, static line and dynamic
changing paths
● A static route through a network never changes
● A static line is similar but only remains for the duration of a session
● A dynamic changing path changes on the fly depending on network
status between nodes
● Routers and IP addresses are part of this level
8. Layer 2: Data link
● The data link layer deals in frames
● Frames are formed at the source side
● Addressing information and CRC error checking is managed at this
level
● At the destination side, if the CRC error checking fails a request is
sent back to the sender to retransmit the frame
9. Layer 1: Physical
● This is the layer that point to point communication is dealt with
● This layer handles the conversion of data into electronic signal
which can be transmitted across the communication medium
● This layer deals in voltage levels, data rates and bandwidths
● Cables, optical fibres and network cards all belong to this level
