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CS514: Intermediate Course in Operating Systems

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Title: CS514: Intermediate Course in Operating Systems


1
CS514 Intermediate Course in Operating Systems
  • Professor Ken Birman
  • Ben Atkin TA

2
Perspectives on Computing Systems and Networks
  • CS314 Hardware and architecture
  • CS414 Operating Systems with a focus on
    single-processor and multi-processor systems
  • CS513 A course on security for operating systems
    and networks
  • CS514 Emphasis on middleware networks,
    distributed computing, technologies for building
    reliable applications over the middleware
  • CS614 A survey of current research frontiers in
    the operating systems and middleware space
  • CS444, CS476, CS644, CS676 networks, routers,
    theory of network protocols, not offered recently

3
Styles of Course
  • CS514 tries to be practical in emphasis
  • We look at the tools used in real products and
    real systems
  • The focus is on technology one could build / buy
  • But not specific products
  • CS614 emphasis is on research opportunities
  • We try to understand the state of the art
  • Idea is to find good research topics
  • Both have projects, but
  • CS514 builds on popular middleware components
  • CS614 tries to break new ground

4
Recent Trends
  • Massive network rollout
  • Larger and larger numbers of small devices,
    web-compatible cell phones
  • Object orientation and components emerge as
    prevailing structural option
  • Widespread use of transactions for reliability
    and atomicity
  • XML The web-ization of everything
  • Java/Jini, .NET code can run on anything
  • Client-server yielding to scalable replication

5
Understanding Trends
  • Basically two options
  • Study the fundamentals
  • Then apply to specific tools
  • Or
  • Study specific tools
  • Extract fundamental insights from examples

6
Understanding Trends
  • Basically two options
  • Study the fundamentals
  • Then apply to specific tools
  • Or
  • Study specific tools
  • Extract fundamental insights from examples

7
Kens bias
  • I work on reliable, secure distributed computing
  • Air traffic control systems
  • Stock exchanges
  • Next generation electric power grid
  • To me, the question is
  • How can we build systems that do what we need
    them to do, reliably, accurately, and in a secure
    manner?

8
Butler Lampsons Insight
  • Why computer scientists didnt invent the web
  • CS researchers would have wanted it to work
  • The web doesnt really work
  • But it doesnt really need to!
  • Gives some reason to suspect that Kens bias
    isnt widely shared!

9
World Wide Web
  • A seductive pass-time, but increasingly seen as a
    serious business model
  • Idea would be to put information you need at your
    fingertips to enable better, more informed, more
    intelligent actions
  • The Web can also replace paper entirely a
    world-wide tool for sharing knowledge

10
Relying on the Web Banking
  • Companies and individuals will need to rely on
    the Web for this model to work
  • Broker will rely upon up-to-the minute stock
    quotes and investment data and advice
  • Back office will trade stocks based on what the
    broker currently wants
  • Criminals will try and violate security/privacy
    to steal funds or manipulate trades

11
Relying on the Web Medicine
  • Web-style interface in a hospital
  • Doctor relies on accuracy of patient status
    records to make treatment decisions
  • Nurse relies on accuracy of drug dosage and
    frequency data to administer treatment
  • Hospital legally obligated to provide for
    security and privacy of the data

12
Relying on the Web Publisher
  • More and more publications will go electronic in
    coming years (so will movies, MTV videos,
    classical music, etc)
  • Publishers edge quality of authors, quality of
    material. Will sell information
  • But for this to work, need reliable ways to
    charge for access and to limit access to
    authorized individuals!

13
Air Traffic Control on the Web
  • Web interface could easily show planes, natural
    for controller interactions
  • But clearly need to know that trajectory and
    flight data is current and consistent
  • Also need help with routing options
  • Continuous availability is vital. Security and
    privacy also needed

14
New Air Traffic Control System AAS
  • Started by FAA in 1989 to replace existing ATC
    system
  • Current system has video display of radar for
    controllers to use
  • Database has information about each flight
  • Telephones to talk to the planes

15
ATC systems divide country up
16
More details on ATC
  • Each sector has a control center
  • Centers may have few or many (50) controllers
  • Data comes from a radar system that broadcasts
    updates every 10 seconds
  • Database keeps other flight data
  • Controllers each own smaller sub-sectors

17
Current System has Problems!
  • Overloaded computers that often crash
  • Getting slow as volume of air traffic rises
  • Inconsistent displays a problem phantom planes,
    missing planes, stale information
  • Some major outages recently (Newark down for 1/2
    hour, LA down for 1 hour in 1995). One near-miss
    associated with LA outage

18
Concept of New System
  • Replace video terminals with workstations
  • Build a highly available real-time system
    guaranteeing no more than 3 seconds downtime per
    year
  • Offer much better user interface to ATC
    controllers, with intelligent course
    recommendations and warnings about future course
    changes that will be needed

19
ATC Architecture
NETWORK INFRASTRUCTURE
DATABASE
20
Technologies Used
  • Base on standard, off-the-shelf workstations
    (easier to maintain, upgrade, manage)
  • IBM proposed software for fault-tolerance and
    consistent system implementation
  • Fancy graphical user interface much like the Web,
    pop-up menus for control decisions, etc.

21
Project Was a Fiasco!!
  • IBM unable to implement a fault-tolerant software
    architecture! Problem was much harder than they
    expected.
  • Even a non-distributed interface turned out to be
    very hard, major delays, scaled back goals
  • Resulting system is unsatisfactory even before
    delivery

22
Free Flight
  • Many think this is the next step in aviation
  • Planes use GPS receivers to track own location
    accurately
  • Combine radar and a shared database to see each
    other
  • Each pilot makes own routing decisions
  • ATC controllers only act in emergencies

23
Free Flight (cont)
  • Now each plane is like an ATC workstation
  • Each pilot must make decisions consistent with
    those of other pilots
  • ... but if FAAs project failed in 1994, why
    should free flight succeed in 2010?
  • Something is wrong with the distributed systems
    infrastructure!

24
Other critical applications
  • Banking, stock markets, stock brokers
  • Heath care, hospital automation
  • Control of power plants, electric grid
  • Telecommunications infrastructure
  • Electronic commerce and electronic cash on the
    Web (very important emerging area)
  • Corporate information base a companys memory
    of decisions, technologies, strategy
  • Military command, control, intelligence systems

25
We depend on distributed systems!
  • If these critical systems dont work
  • When we need them
  • Correctly
  • Fast enough
  • Securely and privately
  • ... then revenue, health and safety, and national
    security may be at risk!

26
Signs of a Crisis in Computing
  • Highly visible fiascos ATC project, Denver
    lug-gage handling system, London Stock Exchange.
  • Hackers pose an increasingly serious threat
    dis-rupted telephone services, breakins to
    critical computing systems
  • Vendors offering little in the way of reliability
    (security situation is better)

27
Critical Needs of Critical Applications
  • Security Can tell who is doing what and can use
    this to enforce authorization
  • Privacy Intruders cant see data or user ids
  • Availability System is continuously up
  • Recoverability Can restart failed components
  • Consistency Actions of system at different
    locations are consistent with each other.

28
Web Brownouts
  • Domain name service (DNS) can overload (1-3)
  • Server or proxies can overload, crash (4-9)
  • Communication lines can overload or break
  • DNS or proxy can return stale data

29
Infrastructure Needs to Change
  • To avoid brownouts need to make more use of
    replicated (cached) data
  • DNS replication caching of host addresses
  • Web proxies replicate copies of documents
  • Creates a new challenge
  • Coherence guarantee that a cached copy of an
    object is up to date

30
What this course is really about
  • Distributed computing is rapidly transforming the
    way we work, live, the way that companies do
    business.
  • Increasingly, distributed computing systems are
    the only ones you can buy.
  • The challenge build distributed systems which
    can be relied upon in critical settings

31
Whats the Story Today?
  • Few distributed systems or Web applications
    consider reliability issues
  • The ones that do worry about reliability are
    often naive about what they are getting into,
    leading to highly visible failures
  • But we do have technical answers to many of the
    basic problems and some exciting initial options

32
Goals for this course?
  • Understand the basic technologies from which
    distributed systems are constructed
  • Maintain a degree of emphasis on reliability
    issues throughout how reliable are the standard
    technologies? Can they be used reliably despite
    their limitations?
  • Look at advanced technologies in context of real
    systems built in standard ways

33
Trends are changing
  • More and more pressure on industry
  • When the network is down, your company wont make
    money
  • Clients want tools they can rely on
  • This is creating pressure on vendors who offer
    middleware
  • Result is a new emphasis on scalability and
    reliability
  • We want reliability, as long as we can have
    performance and scalability too.

34
Technologies we will cover
  • RPC and client-server computing Streams
  • Internet technologies (email, news, msg. bus) and
    trends (the next generation Internet)
  • DCE, Corba, COM Object-Oriented and Component
    Environments
  • Web technologies (HTTP, XML), how the popular
    scalable architectures work
  • Process group computing and scalability issues
  • Transactions and reliability
  • Just a Taste of Security
  • System Management, Clusters, Realtime

35
Course Overview 24 lectures
  • Intro Basic technologies 4 lectures
  • Web and Internet 2 lectures
  • Reliability technologies
  • Distributed group solutions 6 lectures
  • Security options 2 lectures
  • Real-time issues 2 lectures
  • Transactional systems 2 lectures
  • Management 3 lectures
  • Other topics 3 lectures

36
Project
  • CS514 has
  • Homeworks, from time to time
  • A reasonably ambitious software project (can be
    used to satisfy your MEng project requirement)
  • Projects can be done in groups
  • Usually involve tackling reliability or
    scalability with some popular technology
  • This semester, hoping to use two Java-oriented
    b2b technologies
  • HPs eSpeak
  • BEA Systems WebLogic
  • Youll teach yourself how to use them

37
Major Themes?
  • Modularity (also known as object-orientation).
    Better structured systems are more reliable.
  • Performance. Technologies need to be fast to be
    perceived as working well
  • Exploiting group structures. These are common in
    reliable distributed systems
  • Rigor. We want to know why a technique works
    ad-hoc solutions often break under stress

38
Scalability
  • Suddenly the hot issue for industry
  • Basically, customers expect solutions that
  • Can be developed on a small scale
  • Continue to work during prime-time
  • Scalability and stability can be considered from
    many dimensions
  • Today, most of the most popular solutions scale
    poorly!

39
The Prevailing Mindset
  • Many developers believe that reliable systems are
    clumsy, overengineered, slow
  • Image a robust bridge. Sounds like some sort
    of ugly, heavy eyesore
  • The Web and the Net are about elegant,
    light-weight, fast systems antithesis of
    robust ones
  • Reliability is also at odds with using standard
    components and packages

40
Insights From Course?
  • Reliability techniques are often very elegant
  • Complexity is a challenge modularity used to
    control these costs
  • Can achieve high performance in reliable
    distributed systems
  • ... but they sometimes are hard to combine with
    standard technologies

41
Lightweight but Resilient Bridges, Secure
Computing Enclaves
42
Lightweight but Resilient Bridges, Secure
Computing Enclaves
  • A good way to imagine the technology we seek
  • Our job is to build those enclaves
  • Trick is to use the technical tools the right
    way!
  • In CS514, we wont study the security aspects of
    the problem in more than a shallow manner

43
Recommended Reading
  • Textbook read the Introduction
  • While surfing the Web, think about outages
  • Keep a count over half an hour of surfing the
    net how often did you have problems? What sorts
    of problems?
  • Find the University of Michigan Web pages on
    internet availability. What does this data tell
    you?
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