This document provides an overview of the OSI model and IP addressing. It describes the seven layers of the OSI model from physical to application layer and their key functions. It then explains IP addressing structure including classes A through E, reserved addresses, subnetting, and the transition from IPv4 to IPv6. The OSI model is a conceptual framework for understanding network communication architecture, while IP addresses provide unique identification of devices on the internet.

1. Outline
 Introduction of OSI model
 Layers of OSI model
 Addressing Schemes in OSI model
 Internet Protocol

2. What is OSI?
 Developed by the International Standard
Organization (ISO) in 1977.
 The primary architectural model for inter computer
communications.
 A conceptual model composed of seven layers, each
specifying particular network functions.
 Describes how information from a software
application in one computer moves through a network
medium to a software application in another
computer.

3. Why Study OSI?
 Still an excellent model for
conceptualizing and understanding
protocol architectures
 Key points:
 Modular
 Hierarchical

5. OSI Lower Layers
 Physical – Layer 1
 Data Link – Layer 2
 Network – Layer 3

6. OSI Physical Layer
 Responsible for transmission of bits
 Responsible for the actual physical
connection between the devices.
 Always implemented through hardware
 Encompasses mechanical, electrical,
and functional interfaces
 e.g. RS-232

7. Physical layer

8. OSI Data Link Layer
 Responsible for error-free, reliable
transmission of data
 Flow control, error correction
 e.g. HDLC

9. OSI Data Link Layer
IEEE has subdivided data link layer into two sub-layers.

10. OSI Network Layer
 Responsible for routing of messages
through network
 Concerned with type of switching used
 Handles routing between networks, as well
as through packet-switching networks
 Concerned with exchange of data between
computer and network
 Includes addressing, routing, prioritizing,
etc

11. OSI Upper Layers
 Transport
 Session
 Presentation
 Application

12. OSI Transport Layer
 Isolates messages from lower and
upper layers
 Monitors quality of communications
channel
 It is responsible for source process to
destination process delivery of entire
message.
 Concerned with reliable transfer of
information between applications

13. Transport Layer
 Breaks down message size
 Make sure that the message is delivered
to the correct process on destination
machine.
 Includes aspects like flow control and
error checking

14. OSI Session Layer
 Establishes logical connections
between systems.
 Manages log-ons, password exchange,
log-offs.
 Terminates connection at end of
session.

15. OSI Presentation Layer
 Provides format and code conversion
services.
 Examples
 File conversion from EBCDIC to ASCII-
coded files.
 Invoking character sequences to generate
bold, italics, etc on a printer.

16. OSI Application Layer
 Provides access to network for end-
user
 User’s capabilities are determined by
what items are available on this layer
 Logic needed to support various
applications
 Each type of application (file transfer,
remote access) requires different
software on this layer

17. THE INTERNET PROTOCOL

18. What is an IP address?
 It is a logical address.
 It specifies the location of a client on the
internet.
 It is a unique identifier.

19. IP Usage
 It is helpful in connecting one device to another.
 It helps in the sharing of files on the network.

20. IP Structure
 IP address consists of four sections.
 Each section is 8 bit long.
 Each section ranges from 0 to 255.
 A dotted decimal number system is used for
representation.
 These four sections comprise of 2 parts: network
ID and host ID.

21. IP Structure
 The network portion is assigned.
 The host portion is determined by the network
administrator.
 IP addresses are classified in 2 parts: classful
and classless.
 Classful portion is again classified in 5 classes.

22. Class A IP Address
 It consist of 8 bits of network ID and 24 bits of
host ID.
 It’s minimum limit is 0.
 It’s maximum limit is 127.

23. Class B IP Address
 It consist of 16 bits of network ID and 16 bits of
host ID.
 It’s minimum limit is 128.
 It’s maximum limit is 191.

24. Class C IP Address
 It consists of 24 bits of network ID and 8 bits of
host ID.
 It’s minimum limit is 192.
 It’s maximum limit is 223.

25. Class D and Class E
Class D
 Class D is reserved for multi-casting.
 It is assigned to a group of networks and not just
a unique address.
Class E
 Class E is reserved for future use.

26. Reserved Addresses
 Any IP starting with 0 cannot be allotted to any
machine.
 Any IP starting with 127 indicates that the
machine is subjected to loop back or internal
testing.
 Any IP having all host ID as 0 cannot be
assigned to any machine.
 All host bits as 1 cannot be used.

27. Subnetting
 Subnet Mask: This is the mask which helps in
determining the number of bits for network. In
other words, it helps in determining network ID
of an address.
 Chopping up of a network into a number of
smaller networks is called subnetting.

28. Subnetting- Why?
 Division of networks.
 Greater number of networks.
 Simplified addressing.

29. The Upgradation
 The version 4 is running out.
 It is being upgraded to IPv6.
 IPv6 is represented in hexadecimal form.
 IPv4 has only 32 bits whereas IPv6 has 128 bits.
 IPv6 has security features also.

30. OSI Application Layer
 Provides access to network for end-
user.
 User’s capabilities are determined by
what items are available on this layer.
 Peforms functions like synchronizing
communication.