Introduction to OSI Layer

8/13/2019 Introduction to OSI Layer

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1

Objectives

On completion of this chapter , you will beable to perform the following tasks:

Describe how data traffic is exchanged

between source and destination devicesIdentify the roles and functions of a hub,

switch, and router, and where they best fit

in the network

Select the appropriate Cisco equipment

for a given set of network requirements


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2

Network Structured Defined By

Hierarchy

Core Layer

DistributionLayer

AccessLayer


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3

Access Layer Characteristics

Access Layer

End station entry pint to the network


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4

Access Layer

Aggregation Point

Router traffic Broadcast / Multicast

Domains

Media Transiation

Security

Possible point for remote access

Distribution Layer

Characteristics


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Core Layer Characteristics

Core Layer

Fast transport to enterprise services

No packet manipulation


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6

OSI Model Overview

Application

(upper)

Layers

Reduces complexity

Standardizes interfaces

Facilitates modular

engineering

Ensures interoperabletechnology

Accelerates evolution

Simplifies teaching andlearning

Application

Presentation

Session

Transport

Network

Data Link

Physical

7

6

5

4

3

2

1

Data FlowLayers


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Application

Presentation

Session

Transport

Data Link

Network

Physical

EXAMPLES

Telnet

HTTP

ASCII, EBCDIC

JPEG

Operating System /Application AccessScheduling

Role of Application Layers


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Application

Presentation

Session

Transport

Network

Data Link

Physical

7

6

5

4

3

2

1

Reliable Or Unreliable delivery

Error correction before retransmit

Provide logical addressing which routers use for path

determination

Combine bits into bytes and bytes into frames

Access to media using MAC addressError detection not correction

Move bits between devices

Specifies voltage , wire speed and pin-out cables

Role of Data Flow Layers

EXAMPLES

TCP

UDP

SPX

IP

IPX

802.3/802.2

HDLC

WIA/TIA-232

V.35


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Application

Presentation

Session

Transport

Network

Data Link

Physical

Data

Data

Upper layer data

Upper layer dataTCP Header

DataIP Header

LLC Header

MAC Header

0101110101001000010

Encapsulation Data

PDU

Bits

Frame

Packet

Segment


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Application

Session

Presentation

Transport

Data Link

Network

Physical

Upper Layer Data

Upper Layer Data

TCP+Upper Layer Data

IP+TCP+Upper Layer Data

MAC Header

TCP Header

LLC Hdr+IP+TCP+Upper Layer Data

LLC Header

IP Header

0101110101001000010

De-Encapsulation Data


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Physical Layer Functions

Signaling Type

Connector

Media Type

Defines

Physical Ethernet 802.3 V.35EIA/TIA-232


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Host

10 Base 2__ Thick Ehernet

10 Base 2__ Thick Ehernet

Hub

Hosts

10 Base T _ Twisted Pair

Physical Layer :Ethernet/802.3


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Physical

All devices in the same collisions domain

All devices in the same broadcast domain

Devices share the same bandwidth

Hubs operate at Physical Layer

AB C D


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Data Link Layer Functions

802.2

HDLC

Data

Link

Physical Ethernet 802.3EIA/TIA_232

V.35

Frame

Relay

Defines

Physical source and destination

address

Higher layer protocol

(Service Access Point)

associated with frame

Network topology

Frame sequencing

Flow control

Connection-oriented orconnectionless


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Data Link Layer Functions

0000.0c xx.xxxx

8

Preamble Dest Add Source Add Length Data FCS

6 6 2

Variable

4

Ethernet II uses Type here and does not use

802.2

IEEE

assigned

Vender

assigned

MAC Layer -802.3

# Bytes


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OR

Data Link

Switches and Bridges Operate

at Data Link Layer

Each segment has its own collision domain

All segments are in the same broadcast domain


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Physical

Ethernet 802.3EIA/TIA_232

V.35

Frame

Relay

Network

Data Link

IP, IPX

802.2 HD

L

C

Network Layer Functions

Interconnects multiple data

links

Defines paths through

network

Defines logical source

and destination addresses

associated with a specific

protocol


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Network Layer Functions

Network Layer End Station Packet

Source

addressIP Header

Destination

address Data

172.15.1.1

Logical

Address

Network Node


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172.16.122.204 255.255.0.0

10101100 00010000 01111010 11001100

11111111 11111111 00000000 00000000

172 16 122204

255 255 0 0

Host

Network Layer Functions(cont.)

Network

Address Mask

Binary

Address

Binary

Mask


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Routing Table

NET INT Metric

Routing Table

INTNET Metric

1

2

4

E0

S0

S0

0

0

1

12

4

S0S0

E0

1

0

0

1.1

1.2

1.0

E 0 S 0

1.32.1

2.2

4.3

S 0 E 0

4.0 4.1

4.2

Network Layer Function (cont.)

Logical addressing allows for hierarchical network

Configuration required

Uses configured information to identify paths to networks


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Routers: Operate at the

Network Layer

Broadcast control

Connects to WAN

services

Traffic management

Multicast control

Multicast Path

determination

U i R P id


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Telecommuter

Mobile User

Branch Office

Main Office

Internet

Using Routers to Provide

Remote Access

Modem or ISDN TA


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Connection-Oriented Sessions

Synchronize

Synchronize

Acknowledge

Negotiate Connection

Data Transfer

(Send Segments)

Sender Receiver

Connection EstablishedConnection EstablishedConnection Established


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Introduction to OSI Layer

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