CALCE Electronic Products and Systems Center University of Maryland

Computer Network Refresh Planning Example

(Preliminary Results)

Peter SandbornUniversity of Maryland

(301) 405-3167Sandborn@eng.umd.edu

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

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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

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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

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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.