The OSI Reference Model - PowerPoint Presentation

Slide1

The OSI Reference Model

Open Systems Interconnection Reference ModelSlide2

Agenda

Define OSI Model

Explain why it is importantReview each of 7 levels

DefinitionExamples

OSI PackagingReviewSlide3

The OSI Model Definition

Internationally recognized: Established by the International Organization of Standardization

Non-proprietary: Public domain. Can be freely used by any vendor.

The OSI model is a layered model that describes how information moves from an application program running on one networked computer to an application program running on another networked computer.

Open Systems Interconnection (OSI) Reference Model is a set of internationally recognized non-proprietary standards for networking and for operating systems involved in networking functions. Slide4

OSI Model Definition – 7 Layers

Layer 1 – Physical

Layer 2 – Data LinkLayer 3 – NetworkLayer 4 – Transport

Layer 5 – SessionLayer 6 – Presentation

Layer 7 - Application

PleaseDo

Not

Throw

Sausage

Pizza

AwaySlide5

Why is the OSI model important?

To the computer industry:Change

DesignTroubleshooting

Training and education

Interoperability between vendors

To you:

Help with troubleshooting network problems

Will be on certification exams

MCP

CCNA

Will be asked in an interviewSlide6

An Analogy

Application

Presentation

Session

Transport

Network

Data Link

PhysicalSlide7

The 7 Layers of the OSI Model Slide8

Layer 7 - Application

Examples:

Internet Explorer, Safari, and other browsers

FTPMail

Many applications that run on your computer are NOT part of the Application layer. This means that the following are not part of layer 7 because they do not request network services:

Microsoft Word or ExcelAdobe Photoshop

The Application layer provides services to the software through which the user requests network services.

Physical – Data Link – Network – Transport – Session – Presentation - ApplicationSlide9

Layer 6 - Presentation

For outgoing messages, it converts data into a generic format for network transmission; for incoming messages, it converts data from the generic network format to a format that the receiving application can

understand

This layer is also responsible for certain protocol conversions, data encryption/decryption, or data compression/decompression

Examples:MIDI

JPG, GIF, TIF

MPEG

Manages data-format information for networked communications (the network’s translator)

Physical – Data Link – Network – Transport – Session – Presentation - ApplicationSlide10

Layer 5 - Session

Responsible for initiating, maintaining and terminating sessions

Responsible for security and access control to session information (via session participant identification

)Responsible for synchronization services, and for checkpoint services

Examples:

NFS

SQL

RPC

The Session layer establishes, maintains, and manages the communication session between computers.

Physical – Data Link – Network – Transport – Session – Presentation - ApplicationSlide11

Layer 4 - Transport

Manages the transmission of data across a network

Manages the

flow (flow control) of data between parties by segmenting long data streams into smaller data chunks (based on allowed “packet” size for a given transmission medium

) (packet sequencing)Provides acknowledgements of successful transmissions and requests

retransmission for packets which arrive with

errors (error detection and recovery)

Examples:

TCP

UDP

The functions defined in this layer provide for the reliable transmission of data segments, as well as the disassembly and assembly of the data before and after transmission.

Physical – Data Link – Network – Transport – Session – Presentation - ApplicationSlide12

Layer 3 - Network

Handles addressing messages for delivery, as well as translating logical network addresses and names into their physical

counterparts (Logical Addresses are managed by local network

admins.)Responsible for deciding how to route transmissions between

computersThis layer also handles the decisions needed to get data from one point to the next point along a network

path

This layer also handles packet switching and network congestion control

Example:

IP

Network routers

The Network layer defines the processes used to route data across the network and the structure and use of logical addressing.

Physical – Data Link – Network – Transport – Session – Presentation - ApplicationSlide13

Layer 2 – Data Link

Handles special data frames (packets) between the Network layer and the Physical

layer

At the sending end this layer handles conversion of data into raw formats that can be handled by the Physical Layer. At

the receiving end, this layer packages raw data from the physical layer into data frames for delivery to the Network layer

The

data link layer is often conceptually divided into two

sub-layers

:

logical link control (LLC)

and

media access control (MAC)

.

Examples:

Network bridges

Ethernet

Wi-Fi

Concerned

with the linkages and mechanisms used to move data about the

network and

deals with the ways in which data is reliably transmitted

.

Physical – Data Link – Network – Transport – Session – Presentation - ApplicationSlide14

Layer 1 - Physical

Converts bits into electronic signals for outgoing

messages. Converts electronic signals into bits for incoming

messages. (Performs bit synchronization.) This layer manages the interface between

the computer and the network medium (coax, twisted pair, etc

.)This layer tells the driver software for the MAU (media attachment

unit

)

(

eg

.

network interface cards (

NICs), modems)

what needs to be sent across the medium

Examples:

Network hubs and repeaters LAN and WAN topology

This layer defines the electrical and physical specifications for the networking media that carry the data bits across a network.

Physical – Data Link – Network – Transport – Session – Presentation - ApplicationSlide15

The 7 Layers of the OSI Model Slide16

Summing up

What is the ISO Model?

Why is it important?What are the 7 layers?

Homework

Review the definitions and examples of each layerTake the test

Repeat as necessary

Questions?Slide17

Additional Resources

http://georgech.com/osi-model/

Presentation and class notesHomework

Links for additional information and referenceGlossary of terms

Class forumGeorge Chmielecki

george.chmielecki@verizon.netSlide18

Class dismissed!