CS 501: Software EngineeringAdministrationQuiz 2, Question 2Slide 4PowerPoint PresentationSlide 6Slide 7Slide 8Distributed Computing: General ProblemNetwork ChoicesQuality of Network ServicesFirewallDistributed Computing Example 1: Distributed DatabaseDistributed Data and ReplicationSlide 15Slide 16Stateless Protocol v. StatefulSlide 18Distributed Computing Example 4: The Domain Name SystemSlide 20Distributed Computing Example 4: Domain Name SystemDistributed Computing Example 5: Web ServerTime-Critical SystemsTime-Critical System Example 1: Autonomous Land VehicleTime-Critical System Example 2: Routers and Other Network ComputingTechniques: Software DevelopmentTime-Critical System Example 3: CD ControllerTime-Critical System Example 4: Embedded Real-time SystemsSlide 29Time-Critical System Example 5: Shared SystemsTime-Critical System Example 4: Dartmouth Time Shared SystemTechniquesTechniques: Multi-ThreadingTechniques: Real Time ExecutiveTechniques: TimingTechniques: Software ConsiderationsContinuous Operation1CS 501 Spring 2002CS 501: Software EngineeringLecture 14System Architecture II2CS 501 Spring 2002Administration3CS 501 Spring 2002Quiz 2, Question 2A microwave oven has the following buttons:clear Clear all settingshigh-power Set high-power cooking (default)low-power Set low-power cookingrun Run until time expirespause Pause without changing settingsopen door Pause and open doorand a rotary dial:set-clock Set the clock (default is zero)4CS 501 Spring 2002Quiz 2, Question 2•Initially and after clear the microwave is set for high-power cooking and the clock is set to zero. •The microwave is ready to run when the clock is set to a value greater than zero and the door is closed. •The user can then hit the run button to begin cooking until time expires. •While cooking, opening the door or hitting the pause button suspends operation without changing any settings; the user can then hit clear, change settings, or hit run to continue. •Settings can be changed while the door is open; it is not possible to run with the door open.5CS 501 Spring 2002Initial Ready RunDoor openQuiz 2, Question 2Hint. It is possible to model this system with only 4 states, but there are correct answers with more states.States6CS 501 Spring 2002Initial Ready RunDoor open[ok_to_run]run[time_up]open_doorclose_doorQuiz 2, Question 2Major transitionsNote use of automatic transitions. ok_to_run is triggered when all settings complete.7CS 501 Spring 2002Initial Ready RunDoor openclear[ok_to_run]run[time_up]open_doorpauseclose_doorclearQuiz 2, Question 2Pause and clear transitionsNote. The question does not fully specify these transitions.8CS 501 Spring 2002Initial Ready RunDoor openclear[ok_to_run]run[time_up]open_doorpauseclose_doorset_clockset_clockset_clockhigh/lowhigh/lowhigh/lowclearQuiz 2, Question 2SettingsNote. These settings do not change state, but may trigger ok_to_run9CS 501 Spring 2002Distributed Computing: General ProblemAn application that is running on one computer wishes to use data or services provided by another:• Network connectionprivate, public, or virtual private networklocation of firewalls• Protocolspoint-to-point, multicast, broadcastmessage passing, RPC, distributed objectsstateful or stateless• Performancequality of service10CS 501 Spring 2002Network ChoicesPublic Internet:Ubiquitous -- worldwideLow costPrivate network:Security / reliabilityPredictable performanceChoice of protocols (not constrained to TCP/IP)11CS 501 Spring 2002Quality of Network ServicesCriteriaPerformanceMaximum throughputVariations in throughputReal-time media (e.g., audio)BusinessSuppliersTrouble shooting and maintenance12CS 501 Spring 2002FirewallPublic networkPrivate networkFirewallA firewall is a computer at the junction of two network segments that:• Inspects every packet that attempts to cross the boundary• Rejects any packet that does not satisfy certain criteria, e.g.,an incoming request to open a TCP connectionan unknown packet typeFirewalls provide security at a loss of flexibility and a cost of system administration.13CS 501 Spring 2002Distributed ComputingExample 1: Distributed Databasetwo copies of the same data14CS 501 Spring 2002Distributed Data and ReplicationDistributed DataData is held on several computer systems. A transaction may need to assemble data from several sources.ReplicationSeveral copies of the data are held in different locations. Mirror: Complete data set is replicated Cache: Dynamic set of data is replicated (e.g., most recently used)With replicated data, the biggest problems are concurrency and consistency.15CS 501 Spring 2002Distributed ComputingExample 2: Broadcast SearchUser interfaceserverUserDatabasesThis is an example of a multicast protocol.The primary difficulty is to avoid troubles at one site degrading the entire system (e.g., every transaction cannot wait for a system to time out).16CS 501 Spring 2002Distributed ComputingExample 3: UseNetThis is an example of an epidemic protocol. Such protocols are especially useful in networks with intermittent connectivity, e.g., mobile computing.The biggest problem is ensuring that the data is distributed effectively.17CS 501 Spring 2002Stateless Protocol v. StatefulStateless protocol Example: http Open connectionSend message Return replyClose connectionState in http must be sent with every message (e.g., as parameter string)Cookies are a primitive way of retaining some state18CS 501 Spring 2002Stateless Protocol v. StatefulStateful (session) protocolExample: Z39.50Open connectionBegin sessionInteractive sessionEnd sessionClose connectionServer remembers the results of previous transactions (e.g., authentication, partial results) until session is closed.19CS 501 Spring 2002Distributed ComputingExample 4: The Domain Name System.edu servercornell.edu servercs.cornell.edu serverFirst attempt to resolve www.cs.cornell.edu12320CS 501 Spring 2002Distributed ComputingExample 4: The Domain Name System.edu servercornell.edu servercs.cornell.edu serverBetter method 31almaden.ibm.comcornell.eduece.cmu.eduibm.comacm.org.edu2Localcachelocal DNS server21CS 501 Spring 2002Distributed ComputingExample 4: Domain Name SystemFor details of the actual protocol read:Paul Mockapetris, "Domain Names - Implementation and Specification". IETF Network Working Group, Request for Comments: 1035, November 1987. http://www.ietf.org/rfc/rfc1035.txt?number=103522CS 501 Spring 2002Distributed
View Full Document
Unlocking...