layers of osi model and types of IP versions and different classes

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.