osi layer by cisco

©2000, Cisco Systems, Inc. www.cisco.com

OSIReference Model

Presented by Muktianto


OSI Layer Overview

1-3Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com

Why a Layered Network Model?

• Reduces complexity

• Standardizes interfaces

• Facilitates modular engineering

• Ensures interoperable technology

• Accelerates evolution

• Simplifies teaching and learning

Application

Presentation

Session

Transport

Network

Data Link

Physical1

2

3

4

5

6

7


Layer Functions

Application

Presentation

Session

Transport

Network

Data Link

Physical1

2

3

4

5

6

7 Network processes to applications

Data representation

Inter host communication

End-to-end connections

Addresses and best path

Access to media

Binary transmission


Peer-to-Peer Communication

Physical

Data Link

Network

Transport

Session

Presentation

Application

Physical

Data Link

Network

Transport

Session

Presentation

Application

segment

packet

frame

bit


Data Encapsulation

Application

Presentation

Session

Transport

Network

Data Link

Physical

Host A

Application

Presentation

Session

Transport

Network

Data Link

Physical

Host B

Data

Network

HeaderData

Frame Frame

Header Trailer

Network

HeaderData

010010011010101


Upper Layer Overview


Application Layer

Word ProcessingSpreadsheetDatabaseDesign/ManufacturingProject PlanningOthers Browser FilezilaMs. Outlook

Electronic MailFile TransferRemote AccessClient/Server ProcessNetwork ManagementOthers

Electronic Data InterchangeWorld Wide WebE-Mail GatewaysSpecial-Interest Bulletin BoardsFinancial Transaction ServicesInternet Navigation UtilitiesConferencing (Video, Voice, Data)Others

Internetwork application can extend beyond the enterprise


Presentation Layer

• Text• Data

ASCIIEBCDICEncrypted

• Graphics• Visual Images

PICTTIFFJPEGGIF• Sound

• VideoMIDIMPEGQuick Time

Provides code formatting and conversion for applications


Session Layer

Network File System (NFS)Structured Query Language (SQL)Remote-Procedure Call (RPC)X Window SystemAppleTalk Session Protocol (ASP)DNA Session Control Protocol (SCP)

Service Request

Service Reply

Coordinates applications as they interact on different hosts


Transport Layer Overview


Transport Layer

• Segments upper-layer applications

• Establishes an end-to-end connection

• Sends segments from one end host to another

• Optionally, ensures data reliability


Segment Upper-Layer Applications

Application

Presentation

Session

Transport segments share traffic stream

Transport Application port

DataApplication

portData

Application port

Data

Electronic Mail

File Transfer

Terminal Session


Establishes Connection

SENDER RECEIVER

Synchronize

Negotiate Connection

Synchronize

Acknowledge

Connection EstablishedNegotiate Connection

(Send Segments)


Sends Segments with Flow Control

Buffer Full

ProcessSegments

Buffer OK

Stop

SENDER RECEIVER

Transmit

Not Ready

Ready

Resume TransmissionGo


Reliability with Windowing

Send 1 Window size = 1

SENDER RECEIVERSend 2

Send 3

Recv 1 Ack 2Recv 2 Ack 3

Send 1 Window size = 3

SENDER RECEIVER

Send 2Send 3

Recv 1Recv 2Recv 3Ack 4Send 4


Network Layer Overview


Network Layer: Path Determination

Layer 3 functions to find the best path through the internetwork

Which Path?


Network Layer: Communicate Path

Addresses represent the path of media connections

1

2

3

4

5

6

7

8

9

1011


Addressing: Network and Host

• Network address - Path part used by the router• Host address - Specific port or device on the network

1.1

2.1

3.1

1.2

1.3

Network Host

1 123

2 1

3 1


Routing Uses Network Addresses

• Network portion of address used to make path selections• Node portion of address refers to router port to the path

Destination Network

Direction and Router Port

1.0

2.0

3.0

1.1

2.1

3.1

1.0

3.13.0

2.1

2.0

1.1


Network-Layer Protocol Operations

X Y

A

B

C

Application

Presentation

Session

Transport

Network

Data Link

Physical

X

Network

Data Link

Physical

Network

Data Link

Physical

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

Y

A B C

Each router provides its services to support upper-layer functions


Physicaland

Data LinkOverview


Physical and Data-Link Types

Data Link(frames)

Physical(bits,

signals,clocking)

Ethernet

802.2 LLC

802.3

802.5

FDDI

Dial on

DemandSDLC HDLC

X.25

Frame Relay

ISDN

PPP

V.24EIA/TIA-232 G.703

V.35EIA/TIA-449 EIA-530

HSSI

LAN WAN

Separate physical and data link layers for LAN and WAN


LAN Data Link Sublayers

Network

Data Link

Physical

LLC

MAC

Logical Link Control

Media Access Control

MAC Frame 802.2 LLC Packet or Datagram

• LLC refers upward to higher-layer software functions• MAC refers downward to lower-layer hardware functions


Physical and Logical Addressing

0000.0c12.3456


MAC Address

Vendor Code Serial Number

0000.0c12.3456

ROM

RAM

MAC address is burned into ROM on a network interface card

24 bits 24 bits


Finding the MAC Address

Broadcast Host Z MAC ? Host Z

ARP RequestHost Y Host Z

Host Y MAC

Host Z MAC

ARP ReplyExample 1 : TCP/IP destination local

Broadcast Host Z MAC ? Host Z

ARP Request

Host YHost Z

Host Y MAC

Router MAC

ARP ReplyExample 2 : TCP/IP destination not local

Router A

RoutingTable:Net forHost Z

• An example: TCP/IP Address Resolution Protocol (ARP)• ARP finds the MAC address for a data-link connection


WAN Technology Overview

SDLC

HDLCLAPBPPP

X.25Frame RelayISDN


Physical Layer: WAN

DSU/CSU

EIA/TIA-232V.35X.21HSSIothers

(Modem)

DTEData Terminal Equipment

End of the user’s device on the WAN link

DCEData Circuit-Terminating

EquipmentEnd of the WAN provider’s

side of the communication facility


Data Link Layer: WAN Protocols

DSU/CSU

(Modem)

DSU/CSU

(Modem)

• SDLC - Synchronous Data Link Control

• HDLC - High-Level Data Link Control• LAPB - Link Access Procedure Balanced• Frame Relay - Simplified version of HDLC framing

• PPP - Point-to-point Protocol

• X.25 - Packet level protocol (PLP)• ISDN - Integrated Services Digital Network (data-link signaling)


End Of Session

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