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Cellular Networks and Mobile Computing COMS 6998-11, Fall 2012

Cellular Networks and Mobile Computing COMS 6998-11, Fall 2012. Instructor: Li Erran Li ( lierranli@cs.columbia.edu ) http://www.cs.columbia.edu/~lierranli/coms6998-11Fall2012/ 12/11/2012: Course Summary. Syllabus. Mobile App Development (lecture 2,3)

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Cellular Networks and Mobile Computing COMS 6998-11, Fall 2012

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  1. Cellular Networks and Mobile ComputingCOMS 6998-11, Fall 2012 Instructor: Li Erran Li (lierranli@cs.columbia.edu) http://www.cs.columbia.edu/~lierranli/coms6998-11Fall2012/ 12/11/2012: Course Summary

  2. Syllabus • Mobile App Development (lecture 2,3) • Mobile operating systems: iOS and Android • Development environments: Xcode, Eclipse with Android SDK • Programming: Objective-C and android programming • System Support for Mobile App Optimization (lecture 4,7) • Mobile device power models, energy profiling and ebug debugging • Core OS topics: virtualization, storage and OS support for power and context management • Interaction with Cellular Networks (lecture 1,5, 8) • Basics of 3G/LTE cellular networks • Mobile application cellular radio resource usage profiling • Measurement-based cellular network and traffic characterization • Interaction with the Cloud (lecture 6,9) • Mobile cloud computing platform services: push notification, iCloud and Google Cloud Messaging • Mobile cloud computing architecture and programming models • Mobile Platform Security and Privacy (lecture 10,11,12) • Mobile platform security: malware detection and characterization, attacks and defenses • Mobile data and location privacy: attacks, monitoring tools and defenses Cellular Networks and Mobile Computing (COMS 6998-11)

  3. Mobile App Development: iOS iOS Overview Objective C Xcode Model-View-Controller Blocks and Multithreading Core Data and Location iCloud Cellular Networks and Mobile Computing (COMS 6998-11)

  4. Mobile App Development: Android • Android OS Overview • Eclipse and Android SDK • Application Framework • Activity, content provider, broadcast receiver, intent • Networking • Google Cloud Messaging (GCM) Cellular Networks and Mobile Computing (COMS 6998-11)

  5. System Support for Mobile App Optimization • Mobile device power models, energy profiler and ebug debugging • Core OS topics: • Virtualization • Storage Cellular Networks and Mobile Computing (COMS 6998-11)

  6. System Calls As Power Triggers Key observation: System call is the interface through which an application communicates with the underlying system (hardware) and outside world (Internet, GPS, etc.) Key Idea: Use System Calls as triggers in power modeling Advantages: • Encapsulates utilization based triggers • Parameters of system calls • Captures power behavior of ones that do notnecessarily imply utilization • Can be traced back to process, thread, function • Eases energy accounting Cellular Networks and Mobile Computing (COMS 6998-11) Courtesy: Pathak et al

  7. Finite-State-Machine (FSM) as Power Model Representation State 1 Transitions State 2 State 3 Use Finite-State-Machine (FSM) • Nodes: Power states • Base State: No activity on phone • Productive state: Actual utilization • Tail state: No-useful work • Edges: Transition rules • System calls (start/completion) • Workload (Ex: 50 pkts/sec) • Timeout Cellular Networks and Mobile Computing (COMS 6998-11) Courtesy: Pathak et al

  8. device namespaces VP 1 VP 2 VP 3 Linux Kernel Input Sensors Android... GPU Power Audio/Video RTC / Alarms Framebuffer WiFi Cell Radio ••• Virtualization: Device Namespace safely, correctly multiplex access to devices ••• Cellular Networks and Mobile Computing (COMS 6998-11) Courtesy: Jason Nieh et al.

  9. How Apps Use Storage? /data/data/com.necla.webview lib (empty) WebBench Storage Schema These files written to FS in write-behind cache webviewCache 6aaa3f00, 03051d8d, … many files (5.5MB) • Apps typically store some data in FS (e.g., cache files) and some in a SQLite database (e.g., cache map) • All data through SQLite is written synchronously  slow! • Apps often use SQLite oblivious to performance effects databases These files written to SQLite in sync webview.db (14KB) webviewCache.db (129KB) • Exactly what makes web browsing slow on Android? • Key lies in understanding how apps use SQLite and FS interface Cellular Networks and Mobile Computing (COMS 6998-11) Courtesy: NitinAgrawal et al.

  10. Interaction with Cellular Networks • Basics of 3G/LTE cellular networks • Impact of radio access network on mobile apps • Radio resource usage profiling (ARO) • Impact of cellular network core on mobile applications • In-depth study of middleboxes in cellular networks • Cellular network architecture characterization and Implication to CDN Cellular Networks and Mobile Computing (COMS 6998-11)

  11. LTE Infrastructure • UE: user equipment • eNodeB: base station • S-GW: serving gateway • P-GW: packet data network gateway • MME: mobility management entity • HSS: home subscriber server • PCRF: policy charging and rule function eNodeB 1 Cellular Core Network MME/PCRF/HSS eNodeB 2 S-GW 1 UE 1 P-GW Internet and Other IP Networks eNodeB 3 S-GW 2 UE 2 GTP Tunnels Cellular Networks and Mobile Computing (COMS 6998-11)

  12. LTE Architecture (Cont’d) Home Subscriber Server (HSS) Control Plane • eNodeB, S-GW and P-GW are involved in session setup, handoff, routing Data Plane Mobility Management Entity (MME) Policy Control and Charging Rules Function (PCRF) Packet Data Network Gateway (P-GW) Serving Station (eNodeB) Base Gateway (S-GW) User Equipment (UE) Cellular Networks and Mobile Computing (COMS 6998-11)

  13. Power Management: LTE • UE runs radio resource control (RRC) state machine • Two states: IDLE, CONNECTED • Discontinuous reception (DRX): monitor one subframe per DRX cylce; receiver sleeps in other subframes Courtesy:Morley Mao

  14. Power Management: UMTS Tail Time Delay: 1.5s Delay: 2s Tail Time State promotions have promotion delay State demotions incur tail times

  15. Example: RRC State Machinefor a Large Commercial 3G Network Tail Time Waiting inactivity timers to expire DCH: High Power State (high throughput and power consumption) FACH: Low Power State (low throughput and power consumption) IDLE: No radio resource allocated DCH Tail: 5 sec FACH Tail: 12 sec Promo Delay: 2 Sec Courtesy: Feng Qian Cellular Networks and Mobile Computing (COMS 6998-11)

  16. ARO: Mobile Application Resource Optimizer • Motivations: • Are developers aware of the RRC state machine and its implications on radio resource / energy? NO. • Do they need a tool for automatically profiling their prototype applications? YES. • If we provide that visibility, would developers optimize their applications and reduce the network impact? Hopefully YES. • ARO: Mobile Application Resource Optimizer • Provide visibility of radio resource and energy utilization. • Benchmark efficiencies of cellular radio resource and battery life for a specific application Cellular Networks and Mobile Computing (COMS 6998-11) Courtesy: Feng Qian et al.

  17. RRC State Machine Inference P1: IDLEFACH, P2:IDLEDCH P1: FACHDCH, P2:Keep on DCH Normal RTT < 300msRTT w/ Promo > 1500ms A packet of min bytes never triggers FACHDCH promotion (we use 28B) A packet of max bytes always triggers FACHDCH promotion (we use 1KB) • State promotion inference • Determine one of the two promotion procedures • P1: IDLEFACHDCH; P2:IDLEDCH • State demotion and inactivity time inference • See paper for details Cellular Networks and Mobile Computing (COMS 6998-11)

  18. ARO System Architecture Cellular Networks and Mobile Computing (COMS 6998-11)

  19. Example: Pandora Music Problem: High resource overhead of periodic audience measurements (every 1 min) Recommendation: Delay transfers and batch them with delay-sensitive transfers Cellular Networks and Mobile Computing (COMS 6998-11) Courtesy: Feng Qian

  20. Impact of Middleboxes Cellular Networks and Mobile Computing (COMS 6998-11)

  21. Impact of Architecture • Observation • All 4 major carriers cover the U.S. with only 4-8 clusters • Cellular DNS resolvers are placed at the same level as GGSN data centers • Implication • Mobile content providers should place their content close to GGSNs • Mobile content providers should select the content server closest to the GGSN Cellular Networks and Mobile Computing (COMS 6998-11)

  22. Interaction with Cloud Mobile cloud platform services: push notification, iCloud and Google Cloud Messaging Mobile cloud computing architecture and programming models Cellular Networks and Mobile Computing (COMS 6998-11)

  23. Mobile Cloud Platform Services • Social network services • Demo: add social feature to the calculator app • iCloud service • Demo: add iCloud feature to the calculator app • Push notification service • Apple push notification service • Demo: add push notification to the calculator app • Google GCM • Demo: add push notification to the calculator app • Thialfi: reliable push notification system • Track service Cellular Networks and Mobile Computing (COMS 6998-11)

  24. mCloud Programming Model • MAUI: RPC based offloading architecture • CloneCloud: tight synchronization between cloud and phone • Odessa: data-flow graph to exploit parallelism in perception applications • COMET: distributed shared memory • MAUI, CloneCloud , Odessa all have profiler, solver Cellular Networks and Mobile Computing (COMS 6998-11)

  25. Distributed Shared Memory • COMET is offloading + DSM • Offloading bridges computation disparity • DSM provides logically shared address space • DSM usually applied to cluster environments • Low latency, high throughput • Mobile relies on wireless communication Cellular Networks and Mobile Computing (COMS 6998-11) Courtesy: Mark Gordon et. al.

  26. Java Memory Model • Dictates which writes a read can observe • Specifies 'happens-before' partial order • Access in single thread totally ordered • Lazy Release Consistency locking • Fundamental memory unit is the field • Known alignment, known width Cellular Networks and Mobile Computing (COMS 6998-11)

  27. Field DSM • Track dirty fields locally • Need 'happens-before' established? • Transmit dirty fields! (mark fields clean) • Not clear it scales well past two endpoints • Not important to our motivation • Use classic cluster DSM on server Cellular Networks and Mobile Computing (COMS 6998-11)

  28. VM-Synchronization • Used to establish ‘happen-before’ relation • Directed operation between pusher and puller • Synchronizes • Bytecode sources • Java thread stacks • Java heap Cellular Networks and Mobile Computing (COMS 6998-11)

  29. Mobile Security • DroidRanger: Non-virtualization-based malware detection • Behavioral footprint matching for known malware • Dynamic execution monitoring for unknown malware • DroidScope Virtualization-based malware detection • Reconstruct OS, Dalvik VM and native view • Malware characterization • Installation • Activation • Malicious payloads • Evolution Cellular Networks and Mobile Computing (COMS 6998-11)

  30. Mobile Privacy Data privacy • Detecting and preventing privacy leaks • PiOSfor iOS • TaintDroid for Android • Limiting mobile data exposure with idle eviction [assume device prone to loss] • CleanOS • Stealthy information leaks through covert channels and prevention • Soundcomber Location privacy [after-class reading] • Quantifying location privacy Cellular Networks and Mobile Computing (COMS 6998-11)

  31. PiOS: Analysis (CFG) • Most iOS apps are written in Objective-C • Cornerstone: objc_msgSenddispatch function • Task: Resolve type of receiver and value of selector for objc_msgSend calls • Backwards slicing • Forward propagation of constants and types • Result: Inter and intra procedural CFG is constructed from successfully resolved objc_msgSend calls Cellular Networks and Mobile Computing (COMS 6998-11)

  32. PiOS: Finding Privacy Leaks • Inter and intra procedural Control Flow Graph • Reachability Analysis (find paths) • From interesting sources • To network sinks • Implicit interruption of CFG for user-input (e.g., dialog boxes, etc.) • Touch events are generated by the OS not in the developer's code Cellular Networks and Mobile Computing (COMS 6998-11) Courtesy: Egele et. al

  33. PiOS: Example ObjC to ASM • 1 LDR R0, =off_24C58 • 2 LDR R1, =off_247F4 • 3 LDR R0, [R0] • 4 LDR R1, [R1] • 5 BLX _objc_msgSend • 6 LDR R1, =off_247F0 • 7 LDR R1, [R1] • 8 BLX _objc_msgSend • … UIDevice currentDevice r0? r1? UIDevice ::currentDevice uniqueIdentifier r1? UIDevice ::uniqueIdentifier 9 STR R0, [SP,#0x60+var_34] 10 LDR R3, [SP,#0x60+var_34] … 11 BLX _objc_msgSend NSString ::initWithFormat:(fmt: "uniqueid=%@&username=%@&country=%@&email=%@") … 12 BLX _objc_msgSend POSTScore ::startPostingData:toURL: (0x1b478) Cellular Networks and Mobile Computing (COMS 6998-11)

  34. TaintDroidLeverage Android Platform Virtualization Message-level tracking Application code Application code msg Virtual machine Virtual machine Variable-level tracking native system libraries Method-level tracking Network interface Secondary storage File-level tracking Cellular Networks and Mobile Computing (COMS 6998-11) Courtesy: Byung-Gon et. al

  35. TaintDroid Android Architecture in Detail

  36. The End Questions and comments? Cellular Networks and Mobile Computing (COMS 6998-11)

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