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Network+ Guide to Networks

6th Edition

Chapter 2 Networking Standards and the OSIModel



Objectives

• Identify organizations that set standards for networking

• Describe the purpose of the OSI model and each of its

layers

•

Explain specific functions belonging to each OSI modellayer

• nderstand how two network nodes communicate

through the OSI model

•

Discuss the structure and purpose of data packets andframes

• Describe the two types of addressing covered by the OSI

model

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"etworking Standards Organizations

• Standard

– Documented agreement

– 'echnical specifications(precise criteria

–

Stipulates design or performance of particular productor service

• Standards important in the networking world

– )ide variety of hardware and software

– Ensure network design compatibility• Standards define minimum acceptable performance

– "ot ideal performance

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"etworking Standards Organizations

+cont,d-.

• /any different organizations oversee computer

industry standards

• Example0 1"SI and IEEE set wireless standards

–

1"SI standards apply to type of "I2 – IEEE standards involve communication protocols

• "etwork professional,s responsibility

– 3e familiar with groups setting networking standards

– nderstand critical aspects of standards re4uired byown networks

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1"SI

• 1"SI +1merican "ational Standards Institute.

– 6777# representatives from industry and government

– Determines standards for electronics industry and

other fields• 8e4uests voluntarily compliance with standards

• Obtaining 1"SI approval re4uires rigorous testing

• 1"SI standards documents available online




EI1 and 'I1

• EI1 +Electronic Industries 1lliance.

– 'rade organization

• 8epresentatives from nited States electronics

manufacturing firms

– Sets standards for its members

– :elps write 1"SI standards

– ;obbies for favorable computer and electronics

industries legislation

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EI1 and 'I1 +cont,d-.

• 'I1 +'elecommunications Industry 1ssociation.

– EI1 subgroup merged with former nited States

'elecommunications Suppliers 1ssociation +S'S1.

•

<ocus of 'I1 – Standards for information technology% wireless%

satellite% fiber optics% and telephone e4uipment

• 'I1(EI1 9&=>3 Series

–$uidelines for installing network cable in commercialbuildings

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IEEE

• IEEE +Institute of Electrical and Electronics

Engineers.

– International engineering professionals society

•

$oal of IEEE – @romote development and education in electrical

engineering and computer science fields

• :osts symposia% conferences% and chapter meetings

• /aintains a standards board• IEEE technical papers and standards

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ISO

• ISO +International Organization for Standardization.

– :ead4uartered in $eneva% Switzerland

– 2ollection of standards organizations

•

8epresents 6&! countries• $oal of ISO

– Establish international technological standards to

facilitate global information exchange and barrier free

trade• )idespread authority

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I'

• I' +International 'elecommunication nion.

– Specialized nited "ations agency

– 8egulates international telecommunications

–

@rovides developing countries with technical expertiseand e4uipment

– <ounded in 6=&9B joined nited "ations in 6A5?

– /embers from 6A* countries

•<ocus of I' – $lobal telecommunications issues

– )orldwide Internet services implementation

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ISO2

• ISO2 +Internet Society.

– <ounded in 6AA!

– @rofessional membership society

–

Establishes technical Internet standards• 2urrent ISO2 concerns

– 8apid Internet growth

– Ceeping Internet accessible

– Information security – Stable Internet addressing services

– Open standards

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I1"1 and I21""

• I@ +Internet @rotocol. address

– 1ddress identifying computers in '2@(I@ based

+Internet. networks

–

8eliance on centralized management authorities• I@ address management history

– Initially0 I1"1 +Internet 1ssigned "umbers 1uthority.

– 6AA?0 'hree 8I8s +8egional Internet 8egistries.

• 18I" +1merican 8egistry for Internet "umbers.

• 1@"I2 +1sia @acific "etwork Information 2entre.

• 8I@E +8seaux I@ Europens.

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'he OSI /odel

• /odel for understanding and developing network

computer>to>computer communications

• Developed by ISO in the 6A=7s

•

Divides network communications into seven layers – @hysical% Data ;ink% "etwork% 'ransport% Session%

@resentation% 1pplication

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'he OSI /odel +cont,d-.

• @rotocol interaction

– ;ayer directly above and below

• 1pplication layer protocols

–

Interact with software• @hysical layer protocols

– 1ct on cables and connectors


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'he OSI /odel +cont,d-.

• 'heoretical representation describing network

communication between two nodes

• :ardware and software independent

•

Every network communication process represented• @Ds +protocol data units.

– Discrete amount of data

– 1pplication layer function

– <low through layers &% 9% 5% *% !% and 6

• $eneralized model and sometimes imperfect


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6&

<igure !>6 <low of data through the OSI model


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Courtesy Course Technology/Cengage Learning



1pplying the OSI /odel

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'able !>6 <unctions of the OSI layers




1pplication ;ayer

• 'op +seventh. OSI model layer

• Does not include software applications

• @rotocol functions

–<acilitates communication between softwareapplications and lower>layer network services

– "etwork interprets application re4uest

– 1pplication interprets data sent from network

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1pplication ;ayer +cont,d-.

• Software applications negotiate with application

layer protocols

– <ormatting% procedural% security% synchronization% and

other re4uirements

• Example of 1pplication layer protocol0 :''@

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!7

<igure !>! 1pplication layer functions while retrieving a )eb page


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@resentation ;ayer


– 1ccept 1pplication layer data

– <ormat data

•

nderstandable to different applications and hosts• Examples of file types translated at the presentation

layer

– $I<% @$% 'I<<% /@E$% Fuick'ime

• @resentation layer services manage data encryptionand decryption

– Example protocol0 Secure Sockets ;ayer +SS;.

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!!

<igure !>* @resentation layer services while retrieving a secure )eb page


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Session ;ayer


– 2oordinate and maintain communications between

two network nodes

•

Session – 2onnection for ongoing data exchange between two

parties

• 2onnection between remote client and access server

•

2onnection between )eb browser client and )ebserver

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Session ;ayer +cont,d-.

• <unctions

– Establishing and keeping alive communications link

• <or session duration

–

Ceeping communications secure – Synchronizing dialogue between two nodes

– Determining if communications ended

• Determining where to restart transmission

–

'erminating communications – Set terms of communication

– Identify session participants

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!9

<igure !>5 Session layer protocols managing voice communications


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'ransport ;ayer

• @rotocol functions – 1ccept data from Session layer

– /anage end>to>end data delivery

– :andle flow control

• 2onnection>oriented protocols – Establish connection before transmitting data

– Example0 '2@ three>way handshake• SG" +synchronization. packet• SG">12C +synchronization>acknowledgment.• 12C

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'ransport ;ayer +cont,d-.

• 2hecksum

– ni4ue character string

– 1llows receiving node to determine if arriving data

matches sent data• 2onnectionless protocols

– Do not establish connection with another node before

transmitting data

–

Do not check for data integrity – <aster than connection>oriented protocols


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• Segmentation

– 3reaking large data units received from Session layer

into multiple smaller units called segments

–

Increases data transmission efficiency on certainnetwork types

• /' +maximum transmission unit.

– ;argest data unit network will carry

–

Ethernet default0 6977 bytes – Discovery routine used to determine /'


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• 8eassembly

– 8ecombining the segmented data units

• Se4uencing

–

Identifying segments belonging to the same group ofsubdivided data

– Specifies order of data issue

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*7

<igure !>9 Segmentation and reassembly


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"etwork ;ayer


– 'ranslate network addresses into physical

counterparts

– Decide how to route data from sender to receiver

• 1ddressing

– System for assigning uni4ue identification numbers to

network devices

•

'ypes of addresses – "etwork addresses +logical or virtual addresses.

– @hysical addresses


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"etwork ;ayer +cont,d-.

• "etwork address example0 67-*5-AA-6!

• @hysical address example0 77&7A?*EA?<*

• <actors used to determine path routing

–

Delivery priority – "etwork congestion

– Fuality of service

– 2ost of alternative routes

• 8outers belong in the network layer


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"etwork ;ayer +cont,d-.

• 2ommon "etwork layer protocol

– I@ +Internet @rotocol.

• <ragmentation

–

Subdividing 'ransport layer segments – @erformed at the "etwork layer

• Segmentation preferred over fragmentation for

greater network efficiency

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Data ;ink ;ayer

• <unction of protocols

– Divide data received into distinct frames for

transmission in @hysical layer

•

<rame – Structured package for moving data

– Includes raw data +payload.% sender,s and receiver,s

network addresses% error checking and control

information

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Data ;ink ;ayer +cont,d-.

• 'wo Data ;ink layer sublayers

– ;;2 +;ogical ;ink 2ontrol. sublayer

– /12 +/edia 1ccess 2ontrol. sublayer

•

/12 sublayer – /anages access to the physical medium

– 1ppends physical address of destination computer

onto data frame

•@hysical +/12. address – <ixed number associated with each device,s network

interface

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*&

<igure !>= 'he Data ;ink layer and its sublayers


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@hysical ;ayer

• <unctions of protocols

– 1ccept frames from Data ;ink layer

– $enerate signals as changes in voltage at the "I2

•

2opper transmission medium – Signals issued as voltage

• <iber>optic cable transmission medium

– Signals issued as light pulses

• )ireless transmission medium – Signals issued as electromagnetic waves

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@hysical ;ayer +cont,d-.

• @hysical layer protocols, responsibilities whenreceiving data – Detect and accept signals

– @ass on to Data ;ink layer

– Set data transmission rate

– /onitor data error rates

– "o error checking

• Devices operating at @hysical layer – :ubs and repeaters

• "I2s operate at both @hysical layer and Data ;inklayers

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1pplying the OSI /odel

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'able !>6 <unctions of the OSI layers




2ommunication 3etween 'wo Systems

• Data transformation

– Original software application data differs from

application layer "I2 data

• Information added at each layer

• @Ds +@rotocol Data nit.

– $enerated in 1pplication layer

• Segments

–

$enerated in 'ransport layer – nit of data resulting from subdividing larger @D

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+cont,d-.

• @ackets

– $enerated in "etwork layer

– Data with logical addressing information added to

segments

• <rames

– $enerated in Data ;ink layer

– 2omposed of several smaller components or fields

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+cont,d-.

• Encapsulation

– Occurs in Data ;ink layer

– @rocess of wrapping one layer,s @D with protocol

information

• 1llows interpretation by lower layer

• @hysical layer transmits frame over the network

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5*

<igure !>66 Data transformation through the OSI model

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<rame Specifications

• <rames

– 2omposed of several smaller components or fields

• <rame characteristic dependencies

–

"etwork type where frames run – Standards frames must follow

• Ethernet

– Developed by Herox

– <our different types of Ethernet frames – /ost popular0 IEEE =7!-* standard




<rame Specifications +cont,d-.

• 'oken ring

– Developed by I3/

– 8elies upon direct links between nodes and ring

topology

– "early obsolete

– Defined by IEEE =7!-9 standard

• Ethernet frames and token ring frames differ

–

)ill not interact with each other – Devices cannot support more than one frame type per

physical interface or "I2




IEEE "etworking Specifications

• IEEE,s @roject =7! – Effort to standardize physical and logical network

elements• <rame types and addressing

• 2onnectivity• "etworking media• Error>checking algorithms• Encryption

•

Emerging technologies• =7!-*0 Ethernet

• =7!-660 )ireless

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5?

'able !>! IEEE =7! standards

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Summary

• Standards help ensure interoperability between

software and hardware from different manufacturers

• ISO,s OSI +Open Systems Interconnection. model

–

8epresents communication between two networkedcomputers

– Includes seven layers

• IEEE,s @roject =7! aims to standardize networking

elements• Significant IEEE =7! standards include =7!-*

+Ethernet.% =7!-66 +wireless.% and =7!-6& +/1"s.

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Documents

Dc 6th Ppt Foundation (2)