02 OSI Reference

8/10/2019 02 OSI Reference

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1999, Cisco Systems, Inc.www.cisco.com

OSI Reference Model


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CSE: Networking FundamentalsOSI Model 1999, Cisco Systems, Inc. www.cisco.com

Agenda

The Layered Model

Layers 1 & 2: Physical &Data Link Layers

Layer 3: Network Layer

Layers 47: Transport,Session, Presentation,

and Application Layers


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The Layered Model

1999, Cisco Systems, Inc. www.cisco.com


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Layered Communication

Source: Tanenbaum, 199

I like

rabbits

L: Dutch

Ik hou

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Message

Information

for theRemote

Translator

Information

for theRemote

Secretary

Location A


5/58CSE: Networking FundamentalsOSI Model 1999, Cisco Systems, Inc. www.cisco.com


I like

rabbits

L: Dutch

Ik hou

van

konijnen

L: Dutch

Ik hou

van

konijnen

Fax #:---

L: Dutch

Ik hou

van

konijnen

Fax #:---

L: Dutch

Ik houvan

konijnen

Jaime

les lapins

Information

for theRemote

Translator

Information

for theRemote

Secretary

Location A Location B

Message




I like

rabbits

L: Dutch

Ik hou

van

konijnen

L: Dutch

Ik houvan

konijnen

Fax #:---

L: Dutch

Ik hou

van

konijnen

Fax #:---

L: Dutch

Ik houvan

konijnen

Jaime

les lapins

Information

for theremote

translator

Information

for theremote

secretary

Location A Location B

1

2

3

Layers

Message



Why a Layered Network Model?

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

Reduces complexity (one bigproblem to seven smallerones)

Standardizes interfaces

Facilitates modularengineering

Assures interoperabletechnology

Accelerates evolution Simplifies teaching and

learning



Devices Function at Layers

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

NIC Card

Hub



Host Layers

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

Host layers: Provideaccurate data delivery betwee

computers}


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Media Layers

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

Host layers:Provideaccurate data delivery betwee

computers

Media layers:Controlphysical delivery of messages

over the network}}


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Layer Functions

Provides network services to applicati

processes (such as electronic mail, file

transfer, and terminal emulation)

7 Application


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Layer Functions

Network services to applications

Ensures data is readable by

receiving system

Format of data

Data structures

Negotiates data transfer

syntax for application layer

7 Application

6 Presentation Data representation


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Layer Functions

Inter-host communication

Establishes, manages, andterminates sessions between

applications

7 Application

6 Presentation

5 Session


Data representation


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Layer Functions

7 Application

6 Presentation

5 Session

Transport4



Data representation

End-to-end connection reliability Concerned with data transport

issues between hosts

Data transport reliability

Establishes, maintains, and

terminates virtual circuits Fault detection and recovery

Information flow control


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Layer Functions

7 Application

6 Presentation

5 Session

Transport4

Network3



Data representation

End-to-end connection reliability

Addresses and best path Provides connectivity and path

selection between two end

systems Domain of routing


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Layer Functions

7 Application

6 Presentation

5 Session

Transport4

Network3

Data Link2



Data representation


Addresses and best path

Access to media Provides reliable transfer of data

across media Physical addressing, network

topology, error notification, flow

control


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Layer Functions

7 Application

6 Presentation

5 Session

Transport4

Network3

Data Link2

Physical1



Data representation


Addresses and best path

Access to media

Binary transmission Wires, connectors, voltages,

data rates


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7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

Host A

Peer-to-Peer Communications

Application

Presentation

Session

Transport

Network

Data Link

PhysicalBits

Frames

Packets

Segments

Host B


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Data Encapsulation

Application

Presentation

Session

Transport

Network

Physical

Data Link

Application

Presentation

Session

Transport

Network

Physical

Data Link

Host A Host B

Data} {


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Data Encapsulation

Application

Presentation

Session

Transport

Network

Physical

Data Link

Application

Presentation

Session

Transport

Network

Physical

Data Link

Data} {DataNetwork

Header

Host A Host B


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Data Encapsulation

Application

Presentation

Session

Transport

Network

Physical

Data Link

Application

Presentation

Session

Transport

Network

Physical

Data Link

Data} {DataNetwork

Header

FrameHeader

Frame

TrailerDataNetworkHeader

Host A Host B


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Data Encapsulation

Application

Presentation

Session

Transport

Network

Physical

Data Link

Application

Presentation

Session

Transport

Network

Physical

Data Link

Data} {DataNetwork

Header

FrameHeader

Frame

TrailerDataNetworkHeader

0101101010110001

Host A Host B


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Layers 1 & 2:Physical & Data Link

Layers



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Physical and Logical Addressing

0000.0c12.3456


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MAC Address

24 bits

ROM

RAM

24 bits

0000.0c12. 3456

Serial NumberVendor Code

MAC address is burned into ROM on a

network interface card


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Layer 3:

Network Layer


N k P h D i i


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Network Layer: Path Determination

Which Path?Which Path?

Layer 3 functions to find the best

path through the internetwork

N t k L C i t P th


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Network Layer: Communicate Path

1

2

3

4

5

6

7

8

9

1011

Addresses represent the path of media

connections

Routing helps contain broadcasts

Add i N t k d N d


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AddressingNetwork and Node

Network Node

1

2

123

1

3 1

1.1

2.1

3.1

1.2

1.3

Network addressPath part used by the router Node addressSpecific port or device on the network

P t l Add i V i ti


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Protocol Addressing Variations

Network Node

1 1

GeneralExample

Network Host

10. 8.2.48

TCP/IPExample (Mask 255.0.0.0)

Network Node

1aceb0b. 0000.0c00.6e25

Novell IPXExample

Network Layer


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Network LayerProtocol Operations

Each router provides its services tosupport upper layer functions

X Y

AA

CC

Network Layer


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Network LayerProtocol Operations

Each router provides its services tosupport upper layer functions

BB

X Y

AA

CC

Presentation

Data Link

Physical

Data Link

Physical

Router A Router B Router C

Data Link

Physical

Data LinkNetworkTransportSessionPresentationApplication

Physical

Host X Host Y

Data LinkNetworkTransportSession

Application

Physical

Network Network Network

M ltiprotocol Ro ting


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Multiprotocol Routing

IP 15.17.132.6

IP 15.16.42.8

IP 15.16.50.3

Routing Tables

IP

TokenRing

TokenRing

AppleTalk 200.167

AppleTalk 100.110

Apple

IPX 4b.0800.0121.ab13

IPX 3a.0800.5678.12abNovell

DECnet 5.8

DECnet 10.1

DEC

VAX

VAX

Routers pass traffic from all routed protocols over the internetwork

Routed Versus Routing Protocol


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Routed protocolused between

routers to direct

user traffic

1.02.03.0

1.12.13.1

DestinationNetwork

NetworkProtocol

Protocol Name

Examples: IP, IPX,

AppleTalk, DECnet Exit Portto Use



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Routed protocolused betweenrouters to directuser traffic

Examples: IP, IPX,

AppleTalk, DECnet

Routing protocolused only betweenrouters to maintain

routing tablesExamples: RIP, IGRP, OSPF

Static Versus Dynamic Routes


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Static Versus Dynamic Routes

Uses a protocol route that a networkadministrator enters into the router

Static Route

Uses a route that a network protocoladjusts automatically for topology ortraffic changes

Dynamic Route

Static Route Example


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Static Route Example

Point-to-point orcircuit-switched

connection

Stub network

Only a single networkconnection with no need

for routing updates

AA

BB

Fixed route to address reflectsadministrators knowledge

Adapting to Topology Change


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AA BB

CCDD

Can an alternate route substitutefor a failed route?



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AA BB

CCDDXX



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AA BB

CCDDXX

Can an alternate route substitutefor a failed route?

YesWith dynamic routing enabled

LAN-to-LAN Routing Example


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LAN-to-LAN Routing Example

Network 1

Network 3

E0E1 To0

Host 5Host 4

Network 2

TokenRing

802.3 Net 2, Host 5

Routing Table

DestinationNetwork

OutgoingInterface

123

E0To0E1

LAN-to-LAN Routing


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LAN-to-LAN Routing

Network 1

Network 3

E0E1 To0

Host 5Host 4

Network 2

TokenRing

802.3 Net 2, Host 5

Routing Table

Net 2, Host 5802.5

From LAN to LAN

DestinationNetwork

OutgoingInterface

123

E0To0E1

LAN-to-WAN Routing


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LAN-to-WAN Routing

Data

1.3 2.4 Data

AA

TokenRing

2.4

Token Ring 1.3 2.4 Data

BB

1.3FromLAN

FrameRelay

ToWAN

ToLAN

LAN-to-WAN Routing


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LAN-to-WAN Routing

Data

1.3 2.4 Data

AA

TokenRing

2.4


BB

1.3FromLAN

Frame Relay 1.3 2.4 DataFrameRelay

1.3 2.4 Data

ToWAN

ToLAN

LAN-to-WAN Routing


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LAN to WAN Routing

Data

1.3 2.4 Data

AA

TokenRing

2.4


BB

1.3FromLAN

Frame Relay 1.3 2.4 DataFrameRelay

1.3 2.4 Data

ToWAN

Ethernet

Data

1.3 2.4 Data

1.3 2.4 Data

ToLAN

1.3 2.4 Data


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Layers 47:Transport, Session,

Presentation, andApplication Layers


Transport Layer


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Transport Layer

Segments upper-layer applications Establishes an end-to-end connection

Sends segments from one end host to another

Optionally, ensures data reliability

Transport LayerS t U L A li ti


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Segments Upper-Layer Applications

Electronic

Mail

File

Transfer

Application

Presentation

Session

Segments

DataApplication

PortTransport Data

Application

Port

Terminal

Session

Transport LayerE t bli h C ti


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Establishes Connection

Synchronize

Synchronize

Acknowledge

Negotiate Connection

Receiver

Data Transfer

Connection Established

(Send Segments)

Sender

Transport LayerS d S t ith Fl C t l


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Sends Segments with Flow Control

Transmit

Buffer FullNot Ready

StopProcessSegments

Buffer OKReadyGo

Resume Transmission

ReceiverSender

Transport LayerR li bilit ith Wi d i


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Reliability with Windowing

Window Size = 1

Sender

Send 1 Receive 1

Receiver

Ack 2

Send 2 Receive 2Ack 3

Sender

Send 1

Send 2Receive 1Receive 2

Receiver

Window Size = 3

Send 3 Receive 3Ack 4

Send 4

Transport LayerAn Acknowledgement Technique


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An Acknowledgement Technique

Sender Receiver

Send 2Send 1

Send 3

Ack 4

Send 5Send 4

Send 6

Ack 5Send 5

Ack 7

1 2 3 4 5 6 7 1 2 3 4 5 6 7

Transport to Network Layer


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p y

End-to-End Segments

Routed Packets


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Presentation Layer


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y

ASCIIEBCDICEncrypted

Text Data

login:

PICTTIFFJPEGGIF

Graphics Visual images

Sound

VideoMPEGQuickTime

MIDI

Provides code formatting andconversion for applications

Application Layer


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pp y

Word Processor

Presentation Graphics

Spreadsheet

Database

Design/ManufacturingProject Planning

Others

COMPUTERAPPLICATIONS

Electronic Mail

File Transfer

Remote Access

Client-Server ProcessInformation Location

Network Management

Others

NETWORKAPPLICATIONS INTERNETWORKAPPLICATIONS

Electronic Data Interchange

World Wide Web

E-Mail Gateways

Special-Interest Bulletin Boards

Financial Transaction Services

Internet Navigation Utilities

Conferencing (Voice, Video, Data)

Others

Internetwork applicationscan extend beyond theenterprise (i.e., to suppliers, etc.)

Summary


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y

OSI reference model describes buildingblocks of functions for program-to-program communications between

similar or dissimilar hosts Layers 47 (host layers) provide accurate

data delivery between computers

Layers 13 (media layers) control

physical delivery of data over the network


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Presentation_ID 1999, Cisco Systems, Inc. www.cisco.com

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