Systems Engineering for the Internet and the Web

1
Systems Engineering for the Internet and the Web

• Rob Oshana
• oshana_at_airmail.net
• 214-415-9690

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My Background

• Defense business experience
• Internet/web experience
• Commercial shrink wrap experience
• SMU adjunct (CSE, EETS)
• Consulting with telecom
• E-Commerce certificate

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So Why am I Talking About This ?

• I learned a lot about system engineering in DoD
  environment
• I saw a need for sound system engineering
  principles in the internet space (currently
  chaotic)
• I believe there is an opportunity in the
  educational space

4
Introduction

• The Internet has increased the scope and
  complexity of information technology systems,
  placing even greater importance on system
  planning and design
• System engineering for rapid, iterative
  methodologies of the Internet world

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System

• A system can be defined as
• an integrated composite of people, products, and
  processes that provide a capability to satisfy a
  need or objective MIL-STD-499B
• a collection of components organized to
  accomplish a specific function or set of
  functions
• an interacting combination of elements, viewed in
  relation to function INCOSE 95

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System

• A system may be a product that is hardware only,
  hardware/software, software only, or a service
• the sum of the products being delivered to the
  customer(s) or user(s) of the products
• achieve the overall cost, schedule, and
  performance objectives of the business entity
  developing the product

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Systems engineering process

• Systems engineering process is a comprehensive
  problem-solving process used to
• transform customer needs and requirements into a
  life-cycle balanced solution set of system
  product and process designs
• generate information for decision makers
• provide information for the next product
  development or acquisition phase

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SE-CMM Process Areas
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Applicable Process Areas

• Analyze Candidate Solutions
• Derive and Allocate Requirements
• Evolve System Architecture
• Integrate Disciplines
• Integrate System
• Understand customer needs
• Coordinate with suppliers, etc

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Analyze Candidate Solutions

• Identifies the characteristics of a process for
  choosing a solution from several alternatives
• design decision
• production decisions
• life-cycle cost decisions
• human factors decisions
• risk reduction decisions

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Derive and Allocate Requirements

• Typical Work Products
• operational concept
• user interaction sequences
• maintenance operational sequences
• timelines
• simulations
• usability analysis

12
Understand Customer Needs and Expectations

• Interface control working groups
• Questionnaires, interviews, operational scenarios
  obtained from users
• Prototypes and models
• Brainstorming
• Market surveys
• Observation of existing systems, environments,
  and workflow patterns

13
Coordinate with Suppliers

• Typical Work Products
• make-vs.-buy trade study
• list of system components
• sub set of system components for outside
  organizations to address
• list of potential suppliers
• beginnings of criteria for completion of needed
  work

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System Engineering Applied to Internet
Infrastructure
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Example - Campus Network
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/ 01ccie.htm35145
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Determining Requirements

• Understand requirements
• Selecting capability and reliability options that
  meet these requirements
• Solution must reflect the goals, characteristics,
  and policies of the organizations in which they
  operate

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Determining Requirements

• Two primary goals drive design and implementation
• Application availability
• Cost of ownership
• IS budgets today often run in the millions of
  dollars as large organizations increasingly rely
  on electronic data for managing business
  activities
• A well-designed solution can help to balance
  these objectives!!

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The Design Problem Optimizing Availability and
Cost

• Design problem consists of the following general
  elements
• Environmental givens
• location of hosts, servers, terminals, and other
  end nodes
• the projected traffic for the environment
• projected costs for delivering different service
  levels

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Optimizing Availability and Cost

• Performance constraints
• network reliability
• traffic throughput
• host/client computer speeds (for example, network
  interface cards and hard drive access speeds).
• Internetworking variables
• network topology
• line capacities
• packet flow assignments

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Optimizing Availability and Cost

• Goal is to minimize cost based on these elements
  while delivering service that does not compromise
  established availability requirements
• Primary concerns are availability and cost
• essentially at odds
• increase in availability must generally be
  reflected as an increase in cost

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General Network Design Process
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Assessing User Requirements

• Users primarily want application availability in
  their networks
• response time
• interactive online services, such as automated
  tellers and point-of-sale machines
• throughput
• file- transfer activities (low response-time
  requirements)
• always a tradeoff think Size/Weight/Power!

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Assessing User Requirements

• reliability
• Financial services, securities exchanges, and
  emergency/police/military operations
• high level of hardware and topological redundancy
• Determining cost of any downtime is essential in
  determining the relative importance of reliability

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Assessing User Requirements

• User community profiles
• Interviews, focus groups, and surveys
• Interviews with key user groups
• Focus groups
• Formal surveys can be used to get a statistically
  valid reading of user sentiment
• Human factors tests

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Assessing Proprietary and Nonproprietary Solutions

• Compatibility, conformance, and interoperability
  are related to the problem of balancing
  proprietary functionality and open
  internetworking flexibility
• Multivendor environment or specific, proprietary
  capability
• Open routing protocol can potentially result in
  greater multiple-vendor configuration complexity

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Assessing Proprietary and Nonproprietary Solutions

• Gaining a measure of interoperability versus
  losing functionality
• Previous internetworking (and networking)
  investments and expectations for future
  requirements have considerable influence over
  choice of implementations

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Assessing Proprietary and Nonproprietary Solutions

• Must consider
• installed internetworking and networking
  equipment
• applications running (or to be run) on the
  network
• traffic patterns
• physical location of sites, hosts, and users
• rate of growth of the user community
• physical and logical network layout

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Assessing Costs

• Internetwork is a strategic element in customers
  overall information system design
• cost of internetwork is much more than the sum of
  your equipment purchase orders.
• Must be viewed as a total cost-of-ownership issue
• Must consider the entire life cycle of your
  internetworking environment

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Costs to Consider

• Equipment hardware and software costs
• initial purchase and installation, maintenance,
  and projected upgrade costs
• Performance tradeoff costs
• cost of going from a five-second response time to
  a half-second response time

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Costs to Consider

• Installation costs
• Installing a site's physical cable plant can be
  the most expensive element of a large network
• installation labor
• site modification
• fees associated with local code conformance
• costs incurred to ensure compliance with
  environmental restrictions (such as asbestos
  removal)

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Costs to Consider

• Expansion costs
• cost of ripping out all thick Ethernet, adding
  additional functionality, or moving to a new
  location
• Projecting future requirements and accounting for
  future needs saves time and money

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Costs to Consider

• Support costs
• Complicated internetworks cost more to monitor,
  configure, and maintain
• training
• direct labor (network managers and
  administrators)
• sparing
• replacement costs
• Also out-of-band management, SNMP management
  stations, and power

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Costs to Consider

• Cost of downtime
• Evaluate the cost for every minute that a user is
  unable to access a file server or a centralized
  database
• If the cost is high enough, fully redundant
  internetworks might be best option

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Costs to Consider

• Opportunity costs
• Every choice made has an opposing alternative
  option
• specific hardware platform
• topology solution
• level of redundancy
• system integration alternative

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Costs to Consider

• Opportunity Costs
• opportunity costs of not switching to newer
  technologies and topologies might be lost
  competitive advantage, lower productivity, and
  slower overall performance
• Any effort to integrate opportunity costs into
  your analysis can help to make accurate
  comparisons at the beginning of the project

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Costs to Consider

• Sunken costs
• Investment in existing cable plant, routers,
  concentrators, switches, hosts, and other
  equipment and software are sunken costs
• If the sunken cost is high, might need to modify
  networks so that existing internetwork can
  continue to be utilized

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Estimating Traffic Work Load Modeling

• Empirical work-load modeling
• instrumenting a working internetwork
• monitoring traffic for a given number of users,
  applications, and network topology
• Characterize activity throughout a normal work
  day
• type of traffic passed
• level of traffic
• response time of hosts
• time to execute file transfers

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Work Load Modeling

• Extrapolating to the new internetwork's number of
  users, applications, and topology
• Tools
• Passive monitoring of an existing network
• Measure activity and traffic generated by a known
  number of users

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Work Load Modeling

• Problem with modeling workloads on networks is
  that it is difficult to accurately pinpoint
  traffic load and network device performance as
  functions of the number of users, type of
  application, and geographical location

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Work Load Modeling

• Factors that influence the dynamics of the
  network
• The time-dependent nature of network access
• Differences associated with type of traffic
• Routed and bridged traffic place different
  demands
• The random (nondeterministic) nature of network
  traffic

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Sensitivity Testing

• Sensitivity testing involves breaking stable
  links and observing what happens
• how traffic is rerouted
• speed of convergence
• whether any connectivity is lost
• and whether problems arise in handling specific
  types of traffic

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Sensitivity Testing

• This empirical testing is a type of regression
  testing
• A series of specific modifications (tests) are
  repeated on different versions of network
  configurations
• By monitoring the effects on the design
  variations, you can characterize the relative
  resilience of the design

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System Engineering Techniques Applied to the Web
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Quantitative Analysis
Business model measurable goals
E-Business site architecture
1
2
Predict E-Business Site performance
Measure E-Business Site
8
3
Forecast Workload Evolution
Characterize Customer Behavior
7
4
Obtain Performance Parameters
Characterize Site Workload
6
5
Develop Performance Models
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Customer, Workload, and Resource Models
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What is a performance model?

• A model of a system helps one understand some
  fundamental characteristics of the system
• All models are wrong, but some are useful!

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Zipfs Law

• If one ranks the popularity of words in a given
  text (p) by their frequency (f) then f 1/p
• A few elements score very high and a very large
  number of elements score very low
• Many phenomena on the web can be modeled by Zipfs
  law

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Zipfs Law

• P k/r where P is the number of references to a
  document, r is the rank, k is a positive constant
• Some documents are very popular while most
  documents receive just a few references
• Can use Zipfs law to understand some asymptotic
  properties of web caching performance

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Zipfs Law

• Results obtained from Zipfs model are useful
• to characterize WWW workloads
• analyze document dissemination and replication
  strategies
• model the behavior of caching and mirroring
  systems

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Other Types of Models

• CBMG
• CSID
• Resource model represents the structure and the
  various components of an e-business site
• Performance model represents the way systems
  resources are used by the workload and capture
  the main factors determining system performance

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Other Types of Models

• Analytic models specify the interaction between
  the various components of a system via formulas
• Example minimum possible HTTP transaction time
• Rtmin RTT requestmin SiteProcessingTime
  replymin
• RTTround trip delay in network comm, requestmin
  RequestSize/Bandwidth min time needed to send
  the request to the site

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Other Types of Models

• Simulation models mimic the behavior of the
  actual system by running a simulation program
• Mimics the transitions among the system states
  according to the occurrence of events in the
  simulated system
• Measure performance by counting events
• Expensive to develop and run
• How long to you run it ?

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Why do we need models?

• Help us understand the quantitative behavior of
  complex systems
• Commerce is a transaction based system
• Useful for analyzing document replacement
  policies in caching proxies
• Useful for analyzing bandwidth capacity of
  certain network links
• Good essential tool for studying resource
  allocation problems in the context of e-commerce

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A Modeling Paradigm

• View from different perspectives
• Modeling/prediction paradigm
• Modeling the system
• Analytic models
• Validating the model
• Obtain necessary input parameters
• Make proper assumptions
• Using the model to predict future system
  performance
• Analytic or simulation techniques

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Modeling/Prediction Paradigm
Analyzing
Modeling
Predicting
Build a model
Performance Of projected system
Actual system
Obtain Parameters
Collect data
Solve the model
Solve the model
Change Validated model
Performance measurement
Validate The model
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A Modeling Paradigm

• Accuracy of results
• Response time of e-commerce transaction computed
  by model should be compared against actual data
• Rules of thumb
• Resource utilization 10
• System throughput 10
• Response time 20
• Errors may exist in modeling phase or in the
  measurement phase

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State and Transitions of a CBMG
0.25
Search
0.25
0.35
Browse
0.2
Pay
1.0
0.3
0.2
0.15
0.2
0.3
0.3
0.1
0.1
0.1
0.7
0.05
Entry
Home
Login
Add to cart
Select
0.6
0.2
0.1
0.4
0.05
0.2
0.05
0.1
0.2
Register
0.5
0.3
0.2
0.1
0.15
0.35
Search
0.25
0.2
0.1
58
Capacity Planning

• Determining future load levels
• Natural evolution of existing workloads
• Deployment of new applications and services
• Changes in customer behavior
• Traffic surges due to new situations
• Changes in customer navigational patterns due to
  availability of new business functions
• Predictive patterns and not experimentation

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Definition of Adequate Capacity
e.g. response time lt 2 sec Availability gt 99.5
Service Level Agreements
Customers
Adequate capacity
Adequate capacity
Specified Technologies And standards
e.g. NT servers, Oracle DBMS, SSL, SET
Management
Cost constraints
e.g. startup cost lt 5.5 million Maintenance cost
lt 1.6 million/yr
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CBMG for Online Auto-Buying Service with Virtual
Buying feature
Select options
Select options
Select order
Select Svc contr
Enter data
Select car
Apply for financing
entry
home
Enter deliv data
View order
Hold car
Cancel order
61
Typical Multi-Tier E-Business Site Architecture
LAN 1
LAN 2
T3 link
App Servers
Router
Firewall
DB Servers
Web Server
MS windows NT server MS SQL server
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CSID for the Option Select E-Business Functions
1 2 3 4 5 6 7
1,200
1,320
1,400
1,1050
1,2400
1,2600
C
WS
AS
DB
AS
C
WS
(Int,LAN1)
(LAN1,LAN2)
(LAN2)
(LAN2)
(LAN1,LAN2)
(LAN1,Int)
SearchCarOptions
SendReply
LaunchShowOptions
DisplayCarOptions
DisplayCarOptions
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Performance Laws

• T observation period
• Bo system busy period
• Ao number of arrivals of requests
• Co number of completed requests
• Can then derive operational quantities

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Utilization Law

• Fraction of time the resource is busy
• Utilization, U Bi / T
• Average throughput from queue Xi Co / T
• Ui Bi / T Bi / (Co/Xi) (Bi/Co) X Xi Si X
  Xi

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Forced Flow Law

• Average number of visits, Vi each completing
  transaction has to pass Vi times on average by
  queue i
• Xo transaction complete per unit time
• Vi X Xo transactions visit queue I per unit time
• Xi Vi X Xo is the Forced Flow Law

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Service Demand Law

• Combine the Utilization and Forced Flow Laws
• Di Vi X Si (Xi / Xo) X (Ui / Xi) Ui / Xo

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Littles Law

• Simple and widely applicable to performance
  analysis of computing resources

N
Customers arrive at the black box, spend R
seconds in the black box and leave
X
R
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Littles Law
Number of customers in the black box at time t
n(t)
k
N
t
0
t
rk
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Littles Law

• Departure rate through black box is X
  customers/sec
• N average number of customers in the black box
  (at the web site)
• Show that N X X R
• Observation time is t
• Average number of customers in the interval can
  be calculated

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A Performance Modeling Question
Model ?
DB Servers (e.g.mainframes)
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Single Server Model
Arrival process
Resources
Queuing Space
Service process
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Single Queue Model
Model
Web server
Responses
Requests
Data Storage device
Single Queue
Requests/ responses
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Queuing Network Model
74
Queuing Network Model
75
Financial Site CSID for Show Portfolio
C
3
0.05,m2
2
7
8
1
4
6
5
WS
AS
DB
AS
WS
C
C
1,m1
0.95,m3
0.8,m6
1,m7
1,m8
1,m9
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Open QN of the Financial Site
6
disk
5
processor
Web server
App server
Database server
responses
77
Response Time of Financial Site
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Contention for Software in E-Business Sites

• WS is multithreaded (m threads)
• AS has n threads
• DS has p threads
• Queue for WS limited (requests may be rejected)
• Requests sent to AS and/or DS and are queued there

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S/W and H/W Queues
AS threads
DS threads
1
1
m
m
Rejected requests
80
Example of Zipfs Law
81
Traffic Volume to an E-Tailer Site
82
Historical Data Patterns
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So What is Being Done?
84
Technology Assessment

• Reduces the risk of using obsolete or unproven
  solutions and identifies available products and
  services with attractive price-performance
  profiles
• The thrust is to make full use of
  standards-based, leading edge technologies that
  are commercially available, plug-and-play
  components.

85
Prototyping, modeling, and simulation

• Techniques are used to evaluate alternative
  conceptual designs, predict performance, and
  conduct trade-off analyses
• Analysis tools to support workload forecasting,
  performance measurement, capacity management, and
  cost estimation
• Used to evaluate conceptual designs and select
  the system alternative that best meets current
  and future requirements

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Acquisition Phase

• Active support role, or assumes full
  responsibility in acquiring all the necessary
  products and services competitively to build the
  target system
• Prepare acquisition specifications, screen
  potential vendors, elicit proposals, evaluate
  offers, and select best-value solution

87
Implementation Phase

• Support clients in managing systems development,
  installation, and cut over activities to ensure
  quality performance by vendors
• Monitor work progress, conduct formal reviews at
  major milestones, identify risk areas, and devise
  corrective actions to ensure the delivery of
  reliable, maintainable systems, on schedule and
  within budget

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Job Description
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• Participate ..on a project team of engineers
  involved in development of systems and software
  for XX products.... Requires a strong background
  in Systems design...and system-level
  documentation, on projects that may include any
  of the following list of responsibilities
  Specify detailed product requirements,
  participate in the architecture and requirements
  of system software/hardware for optical products
  designed for the core of optical networks.
  Demonstrate a high degree of originality and
  innovation in defining product and project level
  architecture. Significantly influences the design
  of interfaces between products to ensure
  interoperability. Define new software product
  features. Champion new, improved design
  methodologies. Define Reliability, Availability,
  Servicability (RAS) goals for products. Strong
  interpersonal skills ...

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Summary

• The internet is here to stay (and becoming
  critical)
• Complexity of modern solutions requires a good
  systems engineering approach
• SMU is in a hotbed for this technology
• Educational opportunities