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CALCE Electronic Products and Systems Center University of Maryland
Computer Network Refresh Planning Example
(Preliminary Results)
Peter SandbornUniversity of Maryland
(301) [email protected]
CALCE Electronic Products and Systems Center University of Maryland
Application of Bayesian Networks to a Technology Obsolescence System Planning
Problem
Quality Group (15)
Maintenance Group (10)
Design Group (25)
Common Printer
Quality Group (15)
Maintenance Group (10)
Design Group (25)
Common Printer Consider a computer
network that services 3 groups. The network consists of hardware and software, and must be sustained for 20 years.
CALCE Electronic Products and Systems Center University of Maryland
The network has been simplified to have the following components:
Computer Network Example
Software Components • Operating System (OS)• Application 1• Application 2• Application 3
Hardware Components • Processor• RAM• Bus• Mass Memory• Removable Memory
Characterized by:• Reliability• Actual obsolescence forecast• Procurement price
Characterized by:• Functional obsolescence forecast
(associated with hardware changes)• Actual obsolescence forecast• Procurement price
CALCE Electronic Products and Systems Center University of Maryland
Single-Component Upgrade Decision Network
Part upgrade is prudent
Current refresh date
Next refresh date
Quantity in the system
Forecasted obsolescence date
Availability of newer parts
Cost of mitigation if not upgraded now
HW cost of replacement now
SW cost of replacement now
Cost of upgrading now
Value of upgrading now
Performance value
Reliability value
HW re -qualification?
Mitigation approach
Short Term Mitigation Approach
SW re-qualification?
CALCE Electronic Products and Systems Center University of Maryland
Bayesian Network Nodes• Component-Specific Nodes
– Probability of obsolescence at the current refresh– Probability of obsolescence at the next refresh– Probability of availability of component at the current refresh– Probability of availability of component at the next refresh– Probability of component in-stock at the current date– Component obsolescence mitigation strategy decision– Component obsolescence mitigation strategy cost– Aggregate component obsolescence
• General Nodes– Quantity of component– Coupled nodes:
• Current design refresh date• Next design refresh date• Reliability• Performance• Re-qualification
Decision Node
Chance Node
Utility Node
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Bayesian Network Construction
Extending the single component standard architecture for multiple part BN construction
Component-specific nodes that are repeated to construct coupled multiple component networks
CALCE Electronic Products and Systems Center University of Maryland
Complete Bayesian Network (BN) for the Example Case
Bus
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CALCE Electronic Products and Systems Center University of Maryland
• The general example system suffers from actualobsolescence (unavailability and discontinuance) and functional obsolescence.
• Functional Obsolescence: A part or system is considered functionally obsolete when it is no longer satisfactory for use, i.e., it may be available for procurement but it no longer satisfies the system requirements.e.g., the original processor may be available but is not of any use since it is not compatible with the upgraded version of the operating system.
• Functional obsolescence is modeled similar to reliability:– Components wear out with respect to their application (i.e., changing another
component makes them unusable or the world makes them unusable) – Upgrading functionally obsolete components is analogous to spare
replenishment
Obsolescence
CALCE Electronic Products and Systems Center University of Maryland
Modeling Technology Lifetimes
Component
OS
Processor
RAM
Time Period, Value
2000 2002 20062004 2008 2010 2012
• Time Period – lifetime of the component– Hardware (obtained from technology roadmapping and obsolescence
forecasting)– Software (tied to hardware changes in the system and world changes)
• Value – value of an upgrade to the system (performance, reliability, recurring cost), application specific – generally dependent on previous values
Current Generation 0
Generation 1Generation 2
CALCE Electronic Products and Systems Center University of Maryland
Computer Network Example Characteristics
• Initial system deployment, and system expansion schedule
– 2000, 2003, 2006, 2009, 2012, 2015• Operating System, Processor, RAM, Mass
Memory (Quantity = 50)• Bus, Data Acquisition, Software
Application 1, Software Application 2, Software Application 3 (Quantity = 25)
• Spare replenishment schedule– Processor
• 2006, 2009, 2012, 2015, 2018• Quantity = 25
– RAM• 2007, 2010, 2013, 2016, 2019• Quantity = 25
– Operating System• 2008, 2011, 2014, 2017• Quantity = 25
• Operation and support until – 2020
Part Name Cost Obs Date
Processor 800 2005
RAM 200 2006
Bus 100 2005
Data Acquisition 250 2004.5
Power Supply 150 2007
Operating System 1000 2005
Software Application 1 2000 2004.5
Software Application 2 1600 2007
Software Application 3 5000 2004
Actual Obsolescence
Date
Mass Memory
Removable Memory
CALCE Electronic Products and Systems Center University of Maryland
Application-Specific Inputs
(BOM)
Decision Network Construction
(component-to-component coupling and refresh-to-
refresh coupling)
Generation of Design Refresh Plan Candidates
Bayesian Decision Network Analysis• Obsolescence status• Value (performance, reliability)• Cost
Cost Analysis
Network Analysis
Part upgrade is prudent
Current refresh date
Next refresh date
Quantity in the system
Forecasted obsolescence date
Availability of newer parts
Cost of mitigation if not upgraded now
HW cost of replacement now
SW cost of replacement now
Cost of upgrading now
Value of upgrading now
Performance value
Reliability value
HW re-qualification?
Mitigation approach
Short Term Mitigation Approach
SW re-qualification?
Dates
Component Management
Decisions
Rank Refresh Plans
How each component in the system should be handled at each design refresh event.• Upgrade• Do not upgrade• Obsolescence mitigation approach
MOCA
Hugin
CALCE Electronic Products and Systems Center University of Maryland
Computer Network Example Results(One design refresh allowed in lifetime)
Replace what’s obsolete: Best solution –refresh in year 2005
With BN: Best solution – refresh in year 2015
Difference of $672,000
CALCE Electronic Products and Systems Center University of Maryland
(Without BN) Analysis rules: Replace all obsolete parts at a design refresh within the look-ahead time (1 year)
• OS (obsolete), Processor (obsolete), Application 1 (obsolete), Application 3 (obsolete), Mass Memory (obsolete), Bus (obsolete)
• Design refresh in the year 2005
(With BN) Analysis rules: Replace parts as decided by BN at a design refresh
• OS (obsolete), Processor (obsolete), Application 1 (obsolete), Application 3 (obsolete), RAM (obsolete), Application 2 (obsolete)
• Design refresh in the year 2015
What’s Different?
The Mass Memory and Bus components are obsolete before the year 2005 but they are re-acquired rarely after this year as there are fewer system expansion events or spares needed after 2005 for these components.
CALCE Electronic Products and Systems Center University of Maryland
Computer Network Example Results(Multiple design refreshes allowed in lifetime)
Difference of $1,571,000
With BN: Best solution – refreshes in years 2005, 2015
Replace what’s obsolete: Best solution –refreshes in years 2005, 2015
CALCE Electronic Products and Systems Center University of Maryland
(With BN) Analysis rules: Replace parts as decided by BN at a design refresh• Redesign 1 = OS (obsolete), Processor (not-obsolete), Application 1 (obsolete),
Application 3 (obsolete), RAM (not-obsolete)• Redesign 2 = OS (obsolete), Processor (obsolete), Application 1 (obsolete),
Application 3 (obsolete), RAM (obsolete), Application 2 (obsolete)
(Without BN) Analysis rules: Replace all obsolete parts at a design refresh within the look-ahead time
• Redesign 1 = OS (obsolete), Processor (obsolete), Mass Memory (obsolete),Application 1 (obsolete), Bus (obsolete), Application 3 (obsolete)
• Redesign 2 = OS (obsolete), Processor (obsolete), RAM (obsolete), Mass Memory (obsolete), Application 2 (obsolete), Application 1 (obsolete), Bus (obsolete), Removable Memory (obsolete), Application 3 (obsolete)
What’s Different?Without BN analysis, some of the obsolete parts replaced at the first and second design refresh are counterproductive as they are rarely reordered during the lifetime of the system, e.g., Mass Memory, Removable Memory, and Bus. BN analysis chooses to replace RAM without it being obsolete because it becomes obsolete and is used later during sparing.