A User -Perceived Availability Evaluation of a Web-based Travel - - PowerPoint PPT Presentation

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A User -Perceived Availability Evaluation of a Web-based Travel - - PowerPoint PPT Presentation

Jul 27, 2023 306 likes •484 views

A User -Perceived Availability Evaluation of a Web-based Travel Agency Mohamed Kaniche, Karama Kanoun, Magnos Martinello Partially supported by the European Community, DSoS - Project IST-1999-11585 DSN-2003, IPDS, 22-25 June 2003, San

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A User -Perceived Availability Evaluation of a Web-based Travel Agency

Mohamed Kaâniche, Karama Kanoun, Magnos Martinello

DSN-2003, IPDS, 22-25 June 2003, San Francisco, CA, USA Partially supported by the European Community, DSoS - Project IST-1999-11585

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Hierarchical modeling framework Assess the impact of failures on the quality of service provided to the users Support e-business system designers in making objective architectural decisions

e-Business key players User 1 User 2 External Suppliers e-Business service provider Supplier 1 Supplier 2 Supplier n Internet

Context and motivations

Case study: Travel agency

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Context and motivations

Case study: Travel agency

Flight reservation system Flight reservation system User 1 User 2

Web-based Travel Agency

Flight reservation system

Internet

Hotel reservation system Hotel reservation system Hotel reservation system Hotel reservation system Hotel reservation system Car reservation system

AF, KLM, BA, … Sheraton, Sofitel … Hertz, Visa …

External Suppliers

Hierarchical modeling framework Assess the impact of failures on the quality of service provided to the users Support e-business system designers in making objective architectural decisions

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A(user1) A(userN)

Availability modeling at the user level …

A(Fn ) A(Sep) A(F1 )

…

A(Se1)…

Availability modeling at the function level

A(Si1) A(Sik )

… Availability modeling at the service level

A(Rep) A(Re1) …

User level

User 1 User k

…

User 2

User operational profile

Function level Service level Resource level

F1

… functions invoked by the users

F2 Fn Si1 e-business provider External suppliers

…

Internal & external services implementing functions and their interactions

Si2 Sim

…

Se2 Sep Se1

Architecture on which the services are implemented

e-business provider External suppliers Ri1

…

Ri2 Rik

…

Re2 Rep Re1

Hierarchical modeling framework

E-business system description E-business availability modeling

A(Ri1) A(Rim )

… Availability modeling at the resource level

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Function and User levels

pij Probability of invoking Fj after Fi p12 Search Browse Start Book Exit Pay p13 p23 p32 Home p44 p33 p24 p34 p45 p56 p57 p47 p27 p37 p67 p54 Functions invoked from “Start” to “Exit” ⇔ User scenario

User level User 1 User k … User 2 Function level F1 … F2 Fn Service level Si1 internal external … Si2 Sim … Se2 Sep Se1 Resource level internal external Ri1 … Ri2 Rik … Re2 Rep Re1

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User execution scenarios

4.5 9.4 6.4 3.3 6.9 4.7 9.7 20.4 13.9 4.2 6.6 10.0 Class B (%) 1.5 12: Start-{Home - Browse}*- {Search-Book}*- Pay-Exit 2.4 11: Start-Browse- {Search-Book}*- Pay-Exit 3.6 10: Start-Home- {Search-Book}*-Pay-Exit 1.3 9: Start-{Home; Browse}*- {Search-Book}*-Exit 2.0 8: Start-Browse- {Search-Book}*-Exit 3.0 7: Start-Home- {Search-Book}*-Exit 7.6 6: Start-{Home; Browse}*-Search-Exit 12.2 5: Start-Browse-Search-Exit 18.4 4: Start-Home-Search-Exit 11.3 3: Start-{Home; Browse}*-Exit 26.7 2: Start-Browse-Exit 10.0 1: Start-Home-Exit Class A (%) User scenario

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User execution scenarios

4.5 9.4 6.4 3.3 6.9 4.7 9.7 20.4 13.9 4.2 6.6 10.0 Class B (%) 1.5 12: Start-{Home - Browse}*- {Search-Book}*- Pay-Exit 2.4 11: Start-Browse- {Search-Book}*- Pay-Exit 3.6 10: Start-Home- {Search-Book}*-Pay-Exit 1.3 9: Start-{Home; Browse}*- {Search-Book}*-Exit 2.0 8: Start-Browse- {Search-Book}*-Exit 3.0 7: Start-Home- {Search-Book}*-Exit 7.6 6: Start-{Home; Browse}*-Search-Exit 12.2 5: Start-Browse-Search-Exit 18.4 4: Start-Home-Search-Exit 11.3 3: Start-{Home; Browse}*-Exit 26.7 2: Start-Browse-Exit 10.0 1: Start-Home-Exit Class A (%) User scenario

} } } }

SC1 SC2 SC3 SC4

7.5% 20.3%

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Service and function levels

  Flight External services   Hotel   Car     Pay    Book    Search    Browse   Home Payment Database Application Web Internal services

Browse

Begin AS DS AS 1 2 4 7 WS WS End End 3 5 WS End 6 q1,2 q7,8 q8,9 q9,10 8 9 10 q4,7 q2,4 q2,3 q4,5 q5,6

User level User 1 User k … User 2 Function level F1 … F2 Fn Service level Si1 internal external … Si2 Sim … Se2 Sep Se1 Resource level internal external Ri1 … Ri2 Rik … Re2 Rep Re1

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Service and Resource levels

 External service: modeled as a black box  Internal services: detailed analysis of e-business provider architecture solutions

  • Organization of services on the hardware support
  • Dedicated hosts for each server ↔ Multiple servers on the same host
  • Fault tolerance strategies
  • Non-redundant servers ↔ Replicated servers
  • Maintenance policies
  • Dedicated ↔ Shared repair resources
  • Immediate↔ Delayed maintenance
  • Fault assumptions
  • permanent, transient

User level User 1 User k … User 2 Function level F1 … F2 Fn Service level Si1 … Si2 Sim … Se2 Sep Se1 Resource level Ri1 … Ri2 Rik … Re2 Rep Re1 internes externes internes externes

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Resource level: TA example

E-business Provider site Database server Web server Application server Disk Web server 1 Database server 1 Web server 2 Web server NW Application server 2 D1 Application server 1 Database server 2 D2 Flight reservation component system #NC Internet Payment server Car reservation component system #1 #NH Hotel reservation component system #1 Flight reservation component system #NF Flight reservation component system #1

Basic architecture Redundant architecture

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TA availability modeling

Function level Service level Resource level User level

Two operational profiles: A, B Home, Browse, Search, Book, Pay WS, AS, DS

Internal External

Flight, Hotel, Car, Pay

Basic architecture Redundant architecture Perfect coverage Imperfect coverage Internal External Flight res. system: AFi i = 1.. NF Hotel res. system: AHi i = 1.. NH Car res. system: ACi i = 1.. NC Payment: APS, Network: Anet

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Web service: Modeling approach

Composite Availability-Performance model

System behaviour resulting from request arrival/service processes conditioned on system states System states resulting from hardware and software failures and recoveries

A(Web service) = 1 - Prob. {WS in a down state or overloaded}

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Web service: Modeling example

 Redundant architecture: imperfect coverage

  • Availability model
  • Performance model: M/M/i/K
  • pK(i): probability a request rejected in state i due to WS buffer full

Nwcλ µ (Nw-2) cλ µ µ ……. µ λ Nw Nw-1 Nw-2 2cλ µ 1 yNw-1 yNw-2 y2 Nw(1-c)λ β β β 2 (1-c)λ

A(Web service) = 1

i

i=1 Nw

  • pK(i) +

i

y i=1 Nw2

  • +
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Evaluation results: example

Redundant architecture: imperfect coverage

1 2 3 4 5 6 7 8 9 10

α = 50/sec α = 100/sec 10-1

Number of web servers (Nw) 1- A(WS)

1 10-2 10-3 10-4 10-5 10-6 10-7 λ = 10-4/h λ = 10-3/h λ = 10-2/h

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User level availability

 Composition

  • Service and Function level availabilities
  • Operational profile

0.978251879 0.978228688 0.978019988 0.975935054 0.955291581 0.768755879

A A (B users)

0.980197168 10 0.980181909 5 0.980044591 4 0.97867277 3 0.965090024 2 0.842355482 1

A A (A users)

NF = NH = NC

173 hours/year 190 hours/year User perceived unavailability ☞

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User level availability

SC4: Scenarios that end up with a payment

43 hours downtime per year 16 hours downtime per year

570 Million€

Loss of revenue

Transaction rate: 100per sec Revenue per transaction: 100€ 1.55 Billion€ 1 2 3 4 5 6 7 8 9 10 NF=NH=NC UA(SC2) UA(SC4) UA(SC1) UA(B users) UA(SC3) 10-1 1 10-2 10-3 User perceived Unavailability 1 2 3 4 5 6 7 8 9 10 NF=NH=NC 10-1 1 10-2 10-3 UA(SC3) UA(A users) UA(SC4) UA(SC2) UA(SC1)

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 Contribution

  • Hierarchical modeling framework ↔ user perceived availability
  • Example: travel agency
  • Illustration of the main concepts of the proposed framework
  • Examples of dependability analysis results to support design solutions

 State of the art

  • Measurement-based evaluation
  • Modelling:performance oriented

 Extensions to handle more complex assumptions

Conclusion