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Cisco Networking Academy Program Semester 1

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The OSI Model

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The OSI layer was introduced by the InternationalOrganization for Standardization (ISO) in 1984 in orderto provide a reference model to make sure products ofdifferent vendors would interoperate in networks.

OSI is short for Open Systems Interconnection.

The OSI layer shows WHAT needs to be done tosend data from an application on one computer, trougha network, to an application on another computer, not

HOW it should be done. A layer in the OSI model communicates with threeother layers: the layer above it, the layer below it, andthe same layer at its communication partner.

The OSI Reference Model

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Data transmitted between software programspasses all 7 OSI layers.

The Application, Presentation and Session layersare also known as the Upper Layers.

The Data Link and Physical layers are oftenimplemented together to define LAN and WAN

specifications.

The OSI Reference Model

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What is a Protocol?A Protocol is a set of rules that makecommunication on a network more efficient.

E.G. - When answering the telephone,

someone says, "Hello," then the person callingsays, "Hello. This is.... "; and so it goes backand forth

One technical definition of a data

communications protocol is: a set of rules, oran agreement, that determines the format andtransmission of data. Layer n on one computercommunicates with Layer n on another

computer.

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What are the 7 layers of the OSI Model?

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Why use a Layered Model?

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Remembering the OSI Model

All 7 - Application

People 6 - Presentation

Seem 5 - Session

To 4 - Transport

Need 3 - Network

Dominos 2 - Data LinkPizza 1 - Physical

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Remembering the OSI Model

Away 7 - Application

Pizza 6 - Presentation Sausage 5 - Session

Throw 4 - Transport

Not 3 - Network

Do 2 - Data Link

Please 1 - Physical

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The physical layer defines the electrical, mechanical,procedural, and functional specifications for activating,maintaining, and deactivating the physical link betweencommunicating network systems.

Physical layer specifications define characteristics such

as:

voltage levels

timing of voltage changes

physical data rates

maximum transmission distances

physical connectors

Physical layer implementations can be categorized aseither LAN or WAN specifications.

more on next slide

Layer 1 Physical Layer

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Examples of LAN specifications are:

Ethernet

FastEthernet

Token Ring

FDDI

Examples of WAN specifications are:

HSSI

V.24

V.35

BRI

RS-232

Transmits bits. (bitstream)

Repeaters operate at this layer.

Layer 1 Physical Layer

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10 Base 2 Co Ax

Fibre Optic Connectors

10 Base 5 Thicknet

Some Layer 1 Examples

UTP

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Defines physical addressing, network topology, and is also

concerned with error notification, sequencing of frames and flowcontrol.

Examples of network topologies are:

Star

Bus

Ring

Physical addresses are also known as hardwareand BIA's (BurnedIn Addressess) but most commonly as MAC addresses.

Examples of Data Link LAN specifications are:

Ethernet

FastEthernet

Token Ring

FDDI

Layer 2 Data Link Layer

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Examples of Data Link WAN specifications are:

Frame Relay (operates also on the Physical layer)

PPP (operates also on the Physical layer)

X.25 (operates also on the Physical and Network layer)

Transmits Frames.

Bridges and Switches operate at this layer.

The Data Link layer consists of two sublayers:

LCC (Logical Link Control) sublayer

Manages communication between devices over a single link

of a network.

Enables multiple higher-layer protocols to share a singlephysical data link.

MAC sublayer

Manages protocol access to the physical network medium.

Determines hardware addresses.

Layer 2 Data Link LayerContinued

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Network InterfaceCard (NIC)

Workgroup Switch

Some Layer 2 Examples

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Defines logical addressing for nodes andnetworks/segments.

Enables internetworking, passing data from one network toanother.

Defines the logical network layout so routers can determine

how to forward packets trough an internetwork.

Routing occurs at this layer, hence Routed and Routingprotocols reside on this layer.

Routed protocols are used to encapsulate data into packets.

The header added by the Network layer contains a networkaddress so it can be routed trough an internetwork.

Examples of Network layer Routed protocols are:

IP, IPX, AppleTalk

Layer 3 Network Layer

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Routing protocols are used to createrouting tables; routing tables are used todetermine the best path / route. Routingprotocols provide periodic communication

between routers in an internetwork tomaintain information on network links in arouting table.

Transmits Packets. Routers operate at this layer.

Layer 3 Network Layer

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The main purpose of this layers is making surethat the data is delivered error-free and in thecorrect sequence.

Establishes, maintains and terminates virtual

circuits. Provides error detection and recovery.

Is concerned with reliable and unreliable transport.When using a connection-oriented, reliable

transport protocol, such as TCP, acknowledgmentsare send back to the sender to confirm that the datahas been received.

Provides Flow Control and Windowing.

Layer 4 Transport Layer

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Provides multiplexing; the support of different flowsof data to different applications on the same host.

Examples of Transport layer protocols are:

TCP (connection-oriented, reliable, provides

guaranteed delivery.)

UDP (connectionless, unreliable, lessoverhead, reliability can be provided by theApplication layer)

SPX

Transmits Segments.

Layer 4 Transport Layer

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The session layer establishes, manages,maintains and terminates communicationchannels between software programs onnetwork nodes.

Provides error reporting for theApplication and Presentation layer.

Examples of Session layer protocols are:

NFS SQL

RPC

Transmits Data.

Layer 5 Session Layer

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Defines coding and conversion functions.

Ensures that information sent from theapplication layer of one system is readable bythe application layer of another system.

Includes common data representationformats, conversion of character representationformats, common data compression schemes,and common data encryption schemes,common examples of these formats and

schemes are: MPEG, QuickTime

ASCII, EBCDIC

GIF, TIFF, JPEG

Transmits Data.

Layer 6 Presentation Layer

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Provides network services directly to

applications. Software programs itself are not partof the OSI model.

Determines the identity and availability ofcommunication partners, and determines if

sufficient resources are available to startprogram-to-program communication.

This layer is closest to the user.

Examples of Application layer protocols are:

Telnet SMTP

FTP

SNMP

Transmits Data.

Layer 7 Application Layer

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Data Encapsulation is the process of adding a header to

wrap the data that flows down the OSI model.

Each OSI layer may add it's own header to the datareceived from above. (from the layer above or from thesoftware program 'above' the Application layer.)

The 5 Steps of Data Encapsulation are:1. The Application, Presentation and Session layers createDATA from users input.

2. The Transport layer converts the DATA to SEGMENTS

3. The Network layer converts the SEGMENTS to PACKETS(or datagrams)

4. The Data Link layer converts the PACKETS to FRAMES

5. The Physical layer converts the FRAMES to BITS.

Data Encapsulation

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Data Encapsulation Diagram

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Each layer contains a Protocol Data Unit (PDU). PDUs areused for peer-to-peer conversations.

What are PDUs?

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The TCP/IP Model was develop by theDepartment of Defense in the late 60s to

ensure data communications would not beinterrupted even under the worse

circumstances.

Since then, TCP/IP has become the de factomethod we use for data communications onthe Internet.

The TCP/IP Model

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Application

Transport

Internet

Network Access

Includes all thefunctions of the OSIs

Application,Presentation, & Session

layers including:

Data representation

Data encryption and

Dialog control

Exploring the 4 Layers of the TCP/IP Model

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Application

Transport

Internet

Network Access

FTP-File TransferProtocol

HTTP-Hypertext

Transfer Protocol SMTP-Simple MailTransfer Protocol

DNS-Domain NameService

TFTP-Trivial FileTransfer Protocol

Application Layer Protocols

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Application

Transport

Internet

Network Access

Uses the TCP protocoland is responsible forquality of service issuesincluding:

Reliability

Flow Control and

Error Correction

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Application

Transport

Internet

Network Access

TCP-Transmission

Control Protocol UDP-UserDatagram Protocol

Transport Layer Protocols

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Application

Transport

Internet

Network Access

Uses the IP protocoland is responsible for:

Path determinationand

Packet switching.


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Application

Transport

Internet

Network Access

IP Internet Protocol

Internet Layer Protocols

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Application

Transport

Internet

Network Access

Includes all thefunctions of the OSIs

Data Link & Physicallayers including:

Processes required byIP to ensure a packetreaches its destination.

All the various LAN &

WAN Technologies suchas 100BaseTX & FrameRelay.

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Application

Transport

Internet

Network Access

LAN and WANTechnologies

Network Access Layer Protocols

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Application

Transport

Internet

Application

Presentation

Session

Transport

Network

Data Link

PhysicalNetwork Access

TCP/IP OSI

Comparing the 2 Models

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TCP/IP is the most popular protocolspecific model used on the Internet.

However, TCP/IP does not cover all the

protocols and standards we will beexploring.

The OSI Model is protocolindependent. Therefore, all topics

covered in the curriculum can fit into itsframework.

Why are there 2 models?

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What should I know for the test?

The OSI Models layers & their keycharacteristics and functions.

The process of data encapsulation and

the various PDUs.

The TCP/IP layers and itscorresponding protocols.

Comparison of the two models layers.

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In the TCP/IP model which layer would deal withreliability, flow control, and error correction?

A Transport LayerB Internet Layer

C Network Layer

D Application Layer

Sample CCNA Question #1

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Sample CCNA Answer #1

In the TCP/IP model which layer would deal withreliability, flow control, and error correction?

A Transport LayerB Internet Layer

C Network Layer

D Application Layer

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Sample CCNA Question #2

What is the control information called that is placed beforedata when encapsulating that data for networktransmission?

A Frame

B Header

C Capsule

D Routing Information

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Sample CCNA Answer #2

What is the control information called that is placed beforedata when encapsulating that data for networktransmission?

A Frame

B Header

C Capsule

D Routing Information

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THANK YOU VERY

MUCH

OSI Model2[1]

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