1. Kashif Latif

2. OSI - THE MODEL
 A layer model (Open Systems Interconnection)
 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

3. LAYERS- MODEL

4. WHY LAYERS…?
 A layered architecture allows us to discuss a well-
defined ,specific part of a large and complex system.
 Breaks down the complex operation of networking
into simple elements.
 Helps developers in developing software.
 It is also much easier to change the implementation
of the service provided by the layer.
 Helps in troubleshooting and identifying the
problem.
 It provides a way to understand how an internet
work operates.
 Task broken into subtasks

5. REAL TIME EXAMPLE

6. PHYSICAL LAYER
 The physical layer is responsible for transmitting
individual bits from one node to the next.
 The physical layer defines Media type ,Connector type
and Signaling type .
 Physical layer defines the following characteristics of
interface between data transmission device (e.g.
computer) and transmission medium or network.
 Mechanical
 Electrical
 Functional
 Procedural
 Representation of bits
 Data rates

7. PHYSICAL LAYER

8. DATA LINK LAYER
 Data link layer is responsible for activating,
maintaining and deactivating a reliable link
between two nodes.
 The data link layer is responsible for transmitting
frames from one node to another.
1. Framing
2. Physical Addressing
3. Flow control
4. Error control
5. Access control

9. DATA LINK LAYER

10. NETWORK LAYER
The network layer is responsible for the
delivery of packets from the original source to
the
final destination.
1. Data is in the form of Packets
2. Logical (IP) Addressing
3. Routing
4. Main protocols at this layer are IP ,ICMP ,ARP

11. NOTE
 The network layer is responsible for the source
to destination delivery of a packet possibly
across multiple networks.
 Where as the data link layer oversees the
delivery of the packet between two systems on
the same network.

12. NETWORK LAYER

13. TRANSPORT LAYER
The transport layer is responsible for delivery
of a message from one process to another.
It defines:
1. Reliable delivery of data
2. Ordering of delivery
3. Port addressing
4. Segmentation and reassembly
5. Connection control
6. Flow control and Error control
7. Main protocols are TCP and UDP

14. TRANSPORT LAYER

15. TRANSPORT LAYER

16. SESSION LAYER
 This OSI layer, as the name implies:
1. Establishes
2. Maintains
3. Ends sessions between nodes
4. Manage transmit data
 Dialog controller i.e. whether connection is
half duplex or full duplex.

17. PRESENTATION LAYER
 Defines the format of data being sent
 The presentation layer is designed to handle the syntax
and semantics of the information exchanged between
two systems
 Main functions of this layer are
1. Compression
2. Encryption and Decryption
 Some Examples of services used are listed below:
1. HTML (Hyper Text Markup Language)
2. GIF (Graphics Interchange Format )
3. JPEG (Joint Photographic Experts Group)
4. ASCII (American Standard Code for Information
Interchange)

18. APPLICATION LAYER
 The application layer is responsible for
providing services to the user.
 The application layer enables the user to access
the network.
1. Mail services
2. File transfer and access
3. Remote log-in
4. Accessing the world wide web
5. Main protocols at this layer are
HTTP, SMTP, SNMP, FTP, TELNET

19. APPLICATION LAYER

20. Kashif Latif