rtft15 unit 6

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UNIT 6Practical Systems for FaultTolerance:

Application:

Ad-hoc wireless network - Application:

NASA Remote Exploration &

Experimentation

Sstem Architect!re: "a!lt tolerant

comp!ters

#eneral p!rpose commercial sstems-

"a!lt tolerant m!ltiprocessor and $%SI

ased comm!nication architect!re'

"a!lt tolerant so(tware:)esi*n-N-+ersion Roll No: ,

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Ad hoc Wireless Networks

Ad-hoc network.

a %AN or other small network/ with wireless

connections

de+ices are part o( the network onl (or the

d!ration o( a comm!nications session

0r while in close proximit to the network

)ecentrali1ed

E'*': 2l!etooth

Real Time and "a!lt Tolerance

)e3nition

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Ad hoc Wireless Networks

The principle ehind ad hoc networkin* is m!lti-hop

relain* in which messa*es are sent (rom the

so!rce to the destination relain* thro!*h the

intermediate hops 4nodes5'

In m!lti-hop wireless networks/ comm!nication

etween two end nodes is carried o!t thro!*h a

n!mer o( intermediate nodes whose (!nction is to

rela in(ormation (rom one point to another'Real Time and "a!lt Tolerance

)e3nition

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A static strin* topolo* is an example o( s!chnetwork:

In the last (ew ears/ eorts ha+e een (oc!sed onm!lti-hop 7ad hoc7 networks/ in which relain* nodesare in *eneral moile/ and comm!nication needs areprimaril etween nodes within the same network'


8 , 9 ; 6

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=ilitar applications

Ad hoc wireless networks is !se(!l in estalishin*

comm!nication in a attle 3eld'

>ollaorati+e and )istri!ted >omp!tin*

A *ro!p o( people in a con(erence can share data in ad hoc

networks'

Streamin* o( m!ltimedia o?ects amon* the participatin*

nodes'

Emer*enc 0perations

Ad hoc wireless networks are !se(!l in emer*enc

operations s!ch as search and resc!e/ and crowd control'

Applications o( Ad hoc @ireless

Networks


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=!st r!n in distri!ted en+ironment

m!st pro+ide loop-(ree ro!tes

m!st e ale to 3nd m!ltiple ro!tes

m!st estalish ro!tes !ickl m!st minimi1e o+erhead in its comm!nication B

reaction to topolo* chan*e

Iss!es in Crotocol )esi*n


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Remote Exploration Experimentation

The *oal o( the Remote Exploration

&Experimentation 4REE5 is

to mo+e s!percomp!tin* into space in a costeecti+e manner

to allow the !se o( inexpensi+e/ state o( the art/

commercial-o-the-shel( 4>0TS5 components and

s!sstems in these space-ased

s!percomp!ters'

Introd!ction

somodD*mail'com

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Some of the responsi!ilities of the REE system softwareinclude:,' =ana*in* sstem reso!rces 4maintainin* state

in(ormation ao!t each node and ao!t the *loal

sstem/ per(ormin* sstem reso!rce dia*nostics/etc'5'

9' o sched!lin* 4*loall sched!lin* ?os across the

sstem/ local ?o sched!lin* within the node/

allocation o( reso!rces to ?os/ etc'5'

' =ana*in* the scienti3c applications 4la!nchin* the

applications/ monitorin* the applications (or (ail!re/

initiatin* reco+er (or applications/ etc'5Real Time and "a!lt Tolerance

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The immediate concern o( the Applications =ana*er is to

o+ersee the exec!tion o( the scienti3c applications'

As the applications represent the !ltimate Fc!stomerG o( the

REE en+ironment/ eHcientl s!pportin* their re!ired

dependailit le+el is paramo!nt'

The Applications =ana*er monitors the science application

(or externall +isile si*ns o( (a!lt eha+ior as well as (ormessa*es *enerated internall the applications

re!estin* (a!lt tolerance ser+ices

somodD*mail'com

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Fault tolerant computers

"a!lt-tolerant comp!tin* is the art and science o(

!ildin* comp!tin* sstems that contin!e to

operate satis(actoril in the presence o( (a!lts'

A (a!lt-tolerant sstem ma e ale to tolerate

one or more (a!lt-tpes incl!din*

i5 transient/ intermittent or permanent hardware

(a!lts/

ii5 so(tware and hardware desi*n errors/

iii5 operator errors/

i+5externall ind!ced !psets or phsical dama*e'Real Time and "a!lt Tolerance

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Fault"tolerant computer systemsare sstems

desi*ned aro!nd the concepts o( (a!lt tolerance'

In essence/ the m!st e ale to contin!e workin*

to a le+el o( satis(action in the presence o( (a!lts'

Fault"tolerant computer systems


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concept!al desi*n o( a se*re*ated-component

(a!lt-tolerant comp!ter desi*n

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Fault Tolerant #ultiprocessor

"a!lt tolerance is o(ten considered as a *ood additional

(eat!re (or m!ltiprocessor sstems !t nowadas it is

ecomin* an essential attri!te'

"a!lt tolerance can e achie+ed the !se o( dedicated

c!stomi1ed hardware that ma ha+e the disad+anta*e o(

lar*e cost'

Another approach to (a!lt tolerance is to exploit existin*

red!ndanc in m!ltiprocessor sstems +ia a task sched!lin*

so(tware strate* ased on time red!ndanc'

Introd!ction


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N-$ersion Cro*rammin*

Reco+er 2lock Approach


"a!lt tolerant so(tware

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The N-+ersion so(tware concept attempts to parallel the

traditional hardware (a!lt tolerance concept o( N-wared!ndant hardware'

In an N-+ersion so(tware sstem/ each mod!le is madewith !p to N dierent implementations' Each +ariant

accomplishes the same task/ !t hope(!ll in a dierent

wa'

Each +ersion then s!mits its answer to +oter or

decider which determines the correct answer/ andReal Time and "a!lt Tolerance

N-$ersion Cro*rammin*

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This sstem can hope(!ll o+ercome the desi*n (a!ltspresent in most so(tware relin* !pon the desi*ndi+ersit concept'

An important distinction in N-+ersion so(tware is the(act that the sstem co!ld incl!de m!ltiple tpes o(hardware !sin* m!ltiple +ersions o( so(tware'

The *oal is to increase the di+ersit in order to a+oidcommon mode (ail!res'

Usin* N-+ersion so(tware/ it is enco!ra*ed that eachdierent +ersion e implemented in as di+erse amanner as possile/ incl!din* dierent tool sets/dierent pro*rammin* lan*!a*es/ and possildierent en+ironments


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The reco+er lock operates with an ad?!dicator which

con3rms the res!lts o( +ario!s implementations o( thesame al*orithm'

In a sstem with reco+er locks/ the sstem +iew isroken down into (a!lt reco+erale locks'

The entire sstem is constr!cted o( these (a!lt tolerant

locks' Each lock contains at least a primar/

secondar/ and exceptional case code alon* with an

ad?!dicator Real Time and "a!lt Tolerance

Reco+er 2lock Approach

" lt t di

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Alternati+el/ i( oth inp!t e+ents m!st occ!r inorder (or the o!tp!t e+ent to occ!r/ then the are

connected an AN) *ate'

"i*!re , shows a simple (a!lt tree dia*ram inwhich either A or 2 m!st occ!r in order (or the

o!tp!t e+ent to occ!r' In this dia*ram/ the twoe+ents are connected to an 0R *ate

"a!lt tree dia*rams


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T$AN% &'(

rtft15 unit 6

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