Outline Introduction of OSI model Layers of OSI modelAddressing Schemes in OSI model Internet Protocol

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.

Why Study OSI?Still an excellent model for

conceptualizing and understanding protocol architectures

Key points: Modular Hierarchical

OSI Lower LayersPhysical – Layer 1Data Link – Layer 2Network – Layer 3

OSI Physical LayerResponsible for transmission of bitsResponsible for the actual physical

connection between the devices.Always implemented through

hardwareEncompasses mechanical, electrical,

and functional interfacese.g. RS-232

Physical layer

OSI Data Link LayerResponsible for error-free, reliable

transmission of data Flow control, error correctione.g. HDLC

OSI Data Link LayerIEEE has subdivided data link layer into two sub-layers.

OSI Network LayerResponsible for routing of messages

through networkConcerned with type of switching usedHandles routing between networks, as

well as through packet-switching networks

Concerned with exchange of data between computer and network

Includes addressing, routing, prioritizing, etc

OSI Upper LayersTransportSessionPresentationApplication

OSI Transport Layer Isolates messages from lower and

upper layersMonitors 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

Transport LayerBreaks 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

OSI Session LayerEstablishes logical connections

between systems.Manages log-ons, password

exchange, log-offs.Terminates connection at end of

session.

OSI Presentation LayerProvides 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.

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

THE INTERNET PROTOCOL

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.

IP Usage

It is helpful in connecting one device to another.

It helps in the sharing of files on the network.

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.

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.

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.

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.

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.

Class D and Class EClass 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.

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.

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.

Subnetting- Why?

Division of networks. Greater number of networks. Simplified addressing.

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.

OSI Application LayerProvides access to network for

end-user.User’s capabilities are determined

by what items are available on this layer.

Peforms functions like synchronizing communication.