1. Mobile OS and Mobile Service Architectures Prabhaker Mateti CEG4361

2. What is an OS? An OS controls all the hardware of a computer, and every program currently running. All computer systems, by definition, include an OS. Several modern day gadgets, such as cell phones, MP3 players, wrist watches, PDAs, video game consoles, TiVO, … are specialized computer systems. Many appliances, such as microwave ovens, dishwashers and TVs, contain embedded computer systems. CEG4362

3. OS Definition by Functionality From the book by Silbershatz and others: "What are the three main purposes of an operating system? Answers: (i) To provide an environment for a computer user to execute programs on computer hardware in a convenient and efficient manner. (ii) To allocate the separate resources of the computer as needed to solve the problem given. The allocation process should be as fair and efficient as possible. (iii) As a control program it serves two major functions: (a) supervision of the execution of user programs to prevent errors and improper use of the computer, and (b) management of the operation and control of I/O devices." CEG4363

4. OS Definition by Components OS = … + … VM Virtual Memory Management File System Process Management Network Layer (TCP/IP) Input/Output System User Management (OS Boot Loader) [System Programs] an OS does not include GUI, nor CLI CEG4364

5. OS as a Collection of … System Calls – Libraries – APIs Program and Configuration Files – /boot/vmlinuz, /boot/initrd – /etc/password, …, /etc/udev/* – /sbin/init, … Processes – Resident Kernel – Device Drivers – Interrupt Handlers CEG4365

6. An Operating System in Action CPU loads boot program from ROM (e.g. BIOS in PC’s)‏ Boot program: – Examines/checks machine configuration (number of CPU’s, how much memory, number & type of hardware devices, etc.)‏ – Builds a configuration structure describing the hardware – Loads the operating system, and gives it the configuration structure Operating system initialization: – Initialize kernel data structures – Initialize the state of all hardware devices – Creates a number of processes to start operation (e.g. getty in UNIX, the Windowing system in NT, e.g.)‏ CEG4366

7. O.S. in Action (Cont’d) After basic processes have started, the OS runs user programs, if available, otherwise enters the idle loop In the idle loop: – OS executes an infinite loop (UNIX)‏ – OS performs some system management & profiling – OS halts the processor and enter in low-power mode (notebooks)‏ OS wakes up on: – Interrupts from hardware devices – Exceptions from user programs – System calls from user programs Two modes of execution – User mode: Restricted execution mode (applications)‏ – Supervisor mode: Unrestricted access to everything (OS)‏ CEG4367 ‏

8. 8 Control Flow in an OS Operating System Modules Idle Loop From boot Initialization RTI Interrupt System call main() ‏ Exception Supervisor Mode Return to user mode Return to user mode

9. On Interrupts Hardware calls the operating system at a pre-specified location Operating system saves state of the user program Operating system identifies the device and cause of interrupt Responds to the interrupt Operating system restores state of the user program (if applicable) or some other user program Execute an RTI instruction to return to the user program User program continues exactly at the same point it was interrupted. Key Fact: None of this is visible to the user program CEG4369

10. 10 On Exceptions Hardware calls the operating system at a pre-specified location Operating system identifies the cause of the exception (e.g. divide by 0)‏ If user program has exception handling specified, then OS adjust the user program state so that it calls its handler Execute an RTI instruction to return to the user program If user program did not have a specified handler, then OS kills it and runs some other user program, as available Key Fact: Effects of exceptions are visible to user programs and cause abnormal execution flow

11. CEG43611 On System Calls User program executes a trap instruction (system call)‏ Hardware calls the operating system at a pre-specified location Operating system identifies the required service and parameters (e.g. open(filename, O_RDONLY))‏ Operating system executes the required service Operating system sets a register to contain the result of call Execute an RTI instruction to return to the user program User program receives the result and continues Key Fact: To the user program, it appears as a function call executed under program control

12. High-level software architecture CEG43612 Operating System (process/device/memory management, file systems, interprocess communication, …) Memory Instruction Execution & Interrupt Processing User Applications Window System Command Interpreter I/O Devices “Middleware”

13. CEG43613 Operating System Structures Monolithic OS (e.g., Unix)‏Micro-kernel OS (e.g., Mach, Exokernel, …)‏ Memory Management CPU Scheduling Process Management Hardware Network Support Security File System Command Interpreter Device Management Network Support Network Support Memory Mgmt. Memory Mgmt. Window Server Window Server File Server File Server... Hardware CPU Scheduling CPU Scheduling Device Drivers Device Drivers Interrupt Handler Interrupt Handler Boot and Init. Boot and Init. Message Passing … … API

14. CEG43614 Microkernel architecture Microkernel assigns only a small number of essential processes to the kernel, such as address space management, inter- process communication and scheduling, and provides all other services in separate processes called servers

15. OS Summary An OS is just a “program”: – It has a main() function, which gets called only once (during boot)‏ – Like any program, it consumes resources (such as memory), can do silly things (like generating an exception), etc. But it is a very strange program: – It is “entered” from different locations in response to external events – It does not have a single thread of control, it can be invoked simultaneously by two different events (e.g. system call & an interrupt)‏ – It is not supposed to terminate – It can execute any instruction in the machine CEG43615

16. Abstraction Techniques in OS Operating systems offer a number of services to application programs and users – Applications access these services through APIs or system calls – By invoking these APIs, an application can request a service, pass parameters, receive results – Users interact with the OS using UI (CLI or GUI)‏ Achieved through abstraction - a process of bundling lower level instructions (machine code) to form high level instructions – reduces a complicated set of machine code instructions to a single, relatively simple high level expression that has meaning for the user CEG43616

17. Process/Thread Processes – A process is a program in execution – It is a single, sequential thread of execution, a current state, and an associated set of system resources A process refers to the program being run and the context it is running in The context refers to all services and utilities, working memory, file pointers, etc., that the program needs in order to run Executing a program involves the creation of a process by the OS by allocating some memory, loading the program code from a disk and starting it running CEG43617

18. Processes and Threads Process abstraction combines two concepts – Concurrency Each process is a sequential execution stream of instructions – Protection Each process defines an address space Address space identifies all addresses that can be touched by the program Threads – Key idea: separate the concepts of concurrency from protection – A thread represents a sequential execution stream of instructions – A process defines the address space that may be shared by multiple threads – Threads can execute on different cores on a multicore CPU (parallelism for performance) and can communicate with other threads by updating memory CEG43618

19. Threads vs. Processes Threads A thread has no data segment or heap A thread cannot live on its own, it must live within a process There can be more than one thread in a process, the first thread calls main & has the process’s stack If a thread dies, its stack is reclaimed Inter-thread communication via memory. Each thread can run on a different physical processor Processes A process has code/data/heap & other segments There must be at least one thread in a process Threads within a process share code/data/heap, share I/O, but each has its own stack & registers If a process dies, its resources are reclaimed & all threads die Inter-process communication via OS and data copying. Each process can run on a CEG43619

20. CEG436 Implementing Threads 20

21. Interrupts the basic form of time-sharing provide the computer with a way of automatically running specific code in response to events When an interrupt is received, the computer hardware automatically suspends running programs by pushing the current state on a stack and save registers and program counter The OS kernel decides how to deal with the event by running some code or ignoring it. The processing of hardware interrupts is a task that is delegated to software called “device drivers“ which is either part of the OS or another program or both CEG43621

22. Multi-tasking refers to the possibility of the CPU time to be divided equally between the different running applications, switching each one in and out of memory A multitasking OS can switch CPU time from an application waiting for an I/O operation to be completed to one needing CPU time and back again without the user being aware Multi-tasking needs clearly defined processes by allowing different processes to be swapped OS kernel contains a piece of software called „scheduler“ which determines how much time each program will spend executing, and in which order execution control is passed CEG43622

23. CEG43623 Multi-tasking challenges Improper synchronization –suspending and resuming execution requires signals to be sent to/from different processes –If these signals are lost or duplicated, the system crashes –„fault tolerance“ is needed to cope with interrupted communication in wireless communications Failed mutual exclusion –two or more procesess compete to use the same resource (e.g., data file)‏ Non-deterministic program operation (aka non-Atomic operation)‏ –interleaved programs sharing Deadlocks –two or more programs are waiting for each other to free a resource before continuing

24. CEG43624 Memory management Multi-tasking systems need to move processes in and out of memory effectively and efficiently (allocate memory dynamically to different programs as and when it is required) in order to avoid areas of memory being used by more than one program Process isolation –processes have their own memory and data and don not overlap or interfere with each other Automatic allocation and management –memory is allocated as and when required transperantly Support of modular programming –allowing programmers to define multiple program modules and to creat, modify, destroy them as required Protection and access control – allowing different programs to share memory locations as required by the application and specified by the programmer, and protecting programs from accidental or malicious access violations Long term storage –process information so that programs and data files can be restored when and as required

25. CEG43625 Memory management - Virtual memory Virtual memory is a mechanism that enables the programmer to address memory in a logical way without needing to overly concerned with how much memory is physically available at run time Virtual memory allows multiple programs to run concurrently. Paging systems allows processes to be composed of fixed-sized blocks of memory (called pages) A program uses a virtual address (page number and an offset within the page)‏ The paging system translates the virtual address into a real physical address in main memory The fixed size of pages allows them to be moved in/out memory

26. Information protection and security Operating systems can provide facilities to support better security – Access control means to restrict which processes can have access to different parts of the system/ different data based on the user profile – Information flow control means for controlling the flow of data within the system and its presentation to users – Certification means for ensuring that programs and data are authentic and have not been tampered with CEG43626

27. CEG43627 Scheduling and resource management Operating systems need to run multiple tasks concurrently without users being aware –All concurrently running processes need to share the processor and memory and other resources –Scheduling challenges Fairness: programs with similar priority and requirements profiles should have equal access to and time with any resource Differential responsiveness: at the same time, processes with different requirements need to be treated differently (priorities updated as program state change)‏ efficiency: OS need to maximize throughput and minimize response time, support multi-users

28. What Is Special About Mobile Operating Systems? A mobile OS need to support the effective and efficient functioning of a mobile device which is severely constrained. Physically constrained – battery-powered device – small screens of varying shapes, sizes, and resolutions – memory (clearly less than a laptop computer)‏ – storage space Working in Uncertainty – Networks come and go – Other devices appear and disappear – OS need to provide robust methods for handling connections and coping with service interruptions and ad hoc attempts to communicate Psychological affordance – Small devices, such as mobile phones, are most likely left unattended, forgotten or lost – It is not the job of the OS to provide a complete suit of security programs but it should offer a number of utilities and services for security applications CEG43628

29. CEG43629 What is special about mobile operating system (cont.) –Wireless networking capable Bluetooth (802.15)‏ 802.11x wireless LAN HiperLAN2 Telephony GSM GPRS 3G Data exchange using TCP/IP –Location dependent Utilities are needed for location and temporal awareness to support devices operating in different places and times GPS support clock and calender support user profile support

30. CEG43630 Mobile System requirements Processing power (energy) –Mobile devices need to be small, light, compact and easy to use –The heaviest part of mobile devices are batteries –Power consumption of the mobile devices needs to be minimal –Considerable improvements have been achieved in the size and longevity of batteries, increased battery life is mainly achieved by reducing the power demands of the device (power management)‏ power saving capabilities -> power-source profiling data storage -> access speed and capacity backlighting power consumption per pixel

31. CEG43631 Mobile Processors The ARM architecture (Advanced RISC Machine) is a 32-bit RISC processor architecture developed by ARM Limited that is widely used in embedded designs. Because of their power saving features, ARM CPUs are dominant in the mobile electronics market, where low power consumption is a critical design goal. Today, the ARM family accounts for approximately 75% of all embedded 32-bit RISC CPUs, Important branches in this family include Qualcomm Snapdragon, Marvell's XScale and the Texas Instruments OMAP series. Others include, e.g.,: –MIPS (Microprocessor without Interlocked Pipeline Stages) is a RISC microprocessor architecture developed by MIPS Technologies. Mainly used in embedded systems like TiVo, Playstation1 & 2 –Intel Atom Processors for netbooks

32. Sep-0532 A closer look at their processors, Droid The ARM instruction set architecture is surging to market prominence as the dominant standard for embedded CPU solutions CEG43632

33. Sep-0533 A closer look at these Systems CEG43633

34. CEG43634 Mobile System requirements Mobile devices need to be able to use a wide range of computer networks –Bluetooth –WLAN ( 802.11x or HiperLAN)‏ –2.5 G or 3 G (voice and data)‏ Ethernet access is achieved via some sort of docking station or cradle connected to the desktop computer

35. CEG43635 Mobile Memory The memory on the CPU for buffers and I/O management and stacks, the availability of the general purpose RAM and the memory of backing storage are all limited on mobile devices The better the memory management offered by the OS, the wider the options available to applications developers –Mobile devices have two types of memories –ROM for operating system and preinstalled programs –RAM for user information Types of RAMs –DRAM (Dynamic RAM): cheapest, used in mobile devices –EDO (Enhanced Data Output): more expensive but offers a speed increase of about 30% over DRAM (Windows CE)‏ –SDRAM (Synchronous Dynamic RAM): a further 50% speed (iPAQ)‏ –DDR (Double Data Rate) SDRAM is twice as fast as SDRAM –OUM (Ovonics Unified Memory): experimental

36. CEG43636 Mobile Storage Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed. –used in memory cards and USB flash drives for general storage and transfer of data in PDAs, laptop computers, digital audio players, digital cameras and mobile phones –a specific type of EEPROM (Electrically Erasable Programmable ROM) that is erased and programmed in large blocks; in early flash the entire chip had to be erased at once. –Flash memory costs far less than byte-programmable EEPROM and therefore has become the dominant technology wherever a significant amount of non-volatile, solid-state storage is needed. Compact Flash (CF) is a mass storage device format used in portable electronic devices. For storage, Compact Flash typically uses flash memory in a standardized enclosure. The format was first specified and produced by SanDisk in 1994.

37. CEG43637 Execute-in-place (XIP)‏ XIP is a method of executing programs directly from long term storage rather than copying it into RAM. It is an extension of using shared memory to reduce the total amount of memory required. Mobile devices reduces memory use and speed up program execution by using XIP

38. CEG43638 Multimedia Supports Data that contains combination of text, digital still and video images and audio information Processing multimedia relies on low level binary operations that are best handled by the operating system

39. CEG43639 Smartphone OS Competitive Landscape iPhone OS (Apple)‏BlackBerry OS (RIM)‏ Window Mobile (Microsoft)‏Android (Google)‏Symbian (Nokia)‏ PlatformClosed Open Source CodeClosed OpenOpen (in future)‏ Q2 WW Market Share (Gartner)‏ 2.8% (1)‏ 17.4%12.0%n/a57.1% Smartphone traffic share (AdMob)‏ WW: 4% US: 16% WW: 11% US: 31% WW: 13% US: 29% n/a WW: 64% US: 2% Pros Early momentum Data hungry early adopters Powerful distribution channel Strong reach (particularly in US)‏ Manufacturer / carrier agnostic Open source innovation Massive global reach Open source innovation IssuesApple dependant BB dependent Distribution Late to market Uncertain consumer demand Limited reach in US Distribution Application ecosystem >3K apps (~20% free)‏ More than 1M installs in only a few months Fewer free apps BB Application Center being developed for Storm >18K apps Skymarket to launch in 2009 Android Market announced $3.8MM awarded in Developer Challenge >10K apps Claims >90MM installs over last 2 years Notes: 1. Artificially low given the wait for the 3G iPhone (5.3% market share in Q1)‏

40. CEG43640 iPhone OS (Apple) – Starting with MAC OS X http://developer.apple.com/macosx/architecture/

41. CEG43641 iPhone OS Iphone uses streamlined (quite complete ) version of Mac os X. It uses a Mach kernel, Unix userland, Cocoa frameworks, Mac OS X application bundles, and other vestiges of Apple’s NeXTSTEP derived desktop version of the Mac operating system. A number of desktop oriented concepts have been stripped, simplified, cleaned up, or refigured to support the unique needs of a mobile device with limited resources The iPhone’s Mach kernel uses the same I/O Kit architecture as Mac OS X, allowing Apple to reuse a lot of the mature code that is already proven to work on the Mac. The I/O Kit in Mach uses kexts or kernel extensions to add low level hardware support.

42. CEG43642 Layers of iPhone OS Cocoa Touch –Multi-touch events and controls –Accelerometer support –View hierarchy –Localization (i18n)‏ –Camera support Media –OpenAL –Audio mixing and recording –Video playback –Image file formats –Quartz –Core Animation –OpenGL ES Core Services –Networking –Embedded SQLite database –GeoLocation –Threads OS X Kernel –TCP/IP –Sockets –Power management –File system –Security iPhone SDK http://developer.apple.com/iphone/

43. CEG43643 KERNEL EXTENSIONS: Apple has followed its own advice by using only two sets of kexts in the iPhone. –The first sets up USB input, specifically for a user human interface device, and more specifically the multitouch screen: IOUSBDeviceFamily IOHIDFamily AppleMultitouchSPI –The second pair of extensions relate to VPN or Virtual Private Networks. These extensions tie into the network stack to provide a way to securely tunnel encrypted traffic over a public network like the Internet. L2TP.ppp bPPTP.ppp

44. CEG43644 Kernel: MAC vs iPhone KERNEL FOR MAC OS X : Desktop Macs have kexts for the iSight camera, audio and video hardware, power and thermal management, and serial interfaces. Support for all hardware is implemented as a kext. On the Mac, different models have different hardware, so a modular set of plugin is required KERNEL FOR IPHONE: No equivalent kexts present. Support for all of the hardware in the iPhone is built into the iPhone’s kernel. Currently no variety in iphone hardware.

45. CEG43645 iPhone OS (Apple)‏ Pros: –Strong user growth and data-hungry user base More than 10 million iPhones sold 3.8% of worldwide smartphone web/data traffic and 7.8% in US (1)‏ –Application store creating a vibrant app ecosystem with great momentum More than 3K applications (~20% free)‏ More than 1 million downloads –Powerful technology enablers (e.g., multi-touch, GPS, accelerometer)‏ Issues: –App approval process is largely a black-box to developers –Apps viewed as competitive to Apple are often shut down –Downloads highly dependent on “featured” or “top download” promotion in store –App store is the only authorized distribution channel –Apple / hardware dependent Recent news / developments: –NDA requirement: Apple finally removed the onerous NDA requirement –Flash: signs pointing towards development of iPhone flash player Development resources: –http://developer.apple.com/iphone/index.actionhttp://developer.apple.com/iphone/index.action –http://iphoneincubator.com/blog/http://iphoneincubator.com/blog/ Notes: 1.Source: AdMob internal metrics

46. CEG43646 Android (Google)‏ Open software platform for mobile development A complete stack – OS, Middleware, Applications An Open Handset Alliance (OHA) project Powered by Linux operating system Fast application development in Java Open source under the Apache 2 license

47. CEG43647 Android – Starting with Linux

48. CEG43648 Linux Kernel Works as a HAL Device drivers Memory management Process management Networking

49. CEG43649 Libraries C/C++ libraries Interface through Java Surface manager – Handling UI Windows 2D and 3D graphics Media codecs, SQLite, Browser engine

50. CEG43650 Android Runtime Dalvik VM –Dex files –Compact and efficient than class files –Limited memory and battery power Core Libraries –Java 5 Std edition –Collections, I/O etc…

51. CEG43651 Symbian Symbian is a company created by a consortium of four mobile phone companies, Nokia, Ericsson (now Sony- Ericsson), Motorola and Matsushita (Panasonic), and Psion, a long established palm-top computer manufacrurer Symbian is driven from a mobile phone perspective Symbian emphasizes its non-properiatary, open platform for wireless communications with particular emphasis on 2G, 2.5G, and 3G networks Sybian OS small footprint, modular, object oriented design and good support for scalability, it is suitable for use in embeded systems Symbian OS is fully object-oriented and component based.

52. CEG43652 Symbian OS Architecture

53. CEG43653 Symbian OS Micro-kernel uses client/server session based IPC Servers mediate access to shared resources and services Kernel deals with memory allocation and IPCs Proactive defense mechanism – Platform Security Architecture – OS Services – Data Caging

54. CEG43654 Architectural Overview Core – Kernel, file server, memory management and device drivers System Layer – Communication and computing services e.g. TCP/IP, IMAP4, SMS and database management Application Engines User Interface Software Applications All layers communicate with each other using Client/Server Mechanism

55. CEG43655 Symbian (Nokia)‏ Pros –Massive global reach Leads WW market with 62% of smartphone traffic (1)‏ 57% market share of smartphones sold in Q2 ‘08 –Like Android, being open source could help accelerate pace of innovation Issues –Limited reach in the US –Application distribution more difficult today vs. iPhone’s app store Recent news / developments: –June ’08: Nokia announced plans to acquire full ownership of Symbian and start the Symbian Foundation, which will be an independent force for the future development of Symbian OS. They stated that Symbian OS (including the platforms S60, UIQ and MOAP(S)) will become open source in the first half of 2009 Developer resources: –http://www.forum.nokia.com/main/resources/technologies/symbian/http://www.forum.nokia.com/main/resources/technologies/symbian/ Notes: 1.Source: AdMob internal metrics

56. CEG43656 BlackBerry OS (RIM)‏ Pros: –Large reach and data-hungry user base Leads US market with 31% of smartphone traffic (1)‏ #2 in worldwide market with 11% of smartphone traffic (1)‏ –Developers not limited to single distribution channel Issues: –Developer momentum appears to be shifting to iPhone –Less reach outside of North America –Application distribution more difficult today vs. iPhone’s app store –Users more email focused vs. web consuming iPhone users –RIM / hardware dependent Recent news / developments: –BlackBerry Application Center scheduled to debut w/ BlackBerry Storm OS v4.7 –Speculation that Storm (i.e., touchscreen iPhone competitor) will be available in November Developer resources: –http://na.blackberry.com/eng/developers/http://na.blackberry.com/eng/developers/ –http://www.blackberrydeveloperconference.com/ (Oct. 20-22, Santa Clara)‏http://www.blackberrydeveloperconference.com/ –http://crackberry.com/http://crackberry.com/ Notes: 1.Source: AdMob internal metrics

57. CEG43657 Windows Mobile Pros –Strong user reach #2 in US market with 30% of smartphone traffic (1)‏ #2 in worldwide market with 13% of smartphone traffic (1)‏ –Manufacturer agnostic –>18K apps Issues –Current version in market (Windows Mobile 6) lacks support for some popular technology enablers (e.g., multi-touch, GPS, accelerometer)‏ –Next-gen version will be late to market –Less developer enthusiasm vs. that for iPhone and Android –Application distribution more difficult today vs. iPhone’s app store Recent news / developments: –Microsoft to launch “Skymarket” applications marketplace for Windows Mobile 7 (planned for launch in 2H ’09)‏ –Speculation that Windows Mobile 7 will support revamped UI and multi-touch Developer resources: –http://www.microsoft.com/windowsmobile/en-us/business/developers.mspxhttp://www.microsoft.com/windowsmobile/en-us/business/developers.mspx Notes: 1.Source: AdMob internal metrics

58. Models of Mobile and Distributed Systems CEG43658

59. What is a Mobile Distributed System Model? A MDS model addresses: – What are the main entities in the Computing System? – How do they interact? – What characteristics affect the individual & collective behavior? The purpose of the MDS model is to : – Make explicit all assumptions about the system – Enable generalizations about the system, based on these assumptions. CEG43659

60. CEG43660 Software and Hardware Service Layers

61. CEG43661 Distributed object management Spanning layers Network 1Network 2 TCPUDP Windows TCPUDP UNIX/Linux Application TCPUDP Mac OS Internet protocol Spanning layer Mobile TCPs UDP Wireless Network Mobile Platform MobileIP

62. Spanning layer Certain protocols are designed with the specific purpose of bridging differences at the lower layers, so that common agreements are not required there. Instead, the layer provides the definitions that permit translation to occur among a range of services or technologies used below. Thus, in somewhat abstract terms, at and above such a layer common standards contribute to interoperation, while below the layer translation is used. Real interoperation is achieved by the use of effective spanning layers. CEG43662

63. Software Layers Software architecture – the structure of software as layers or modules in terms of services offered and requested between processes located in the same or different computers. – Platform: the lowest-level hardware and software layers, i.e., Intel x86/Windows, Sun Sparc/SunOS, PowerPC/MacOS, Intel x86/Linux. – Middleware: a layer of software whose purpose is to mask heterogeneity and to provide a programming model to applications, CORBA, Java remote object invocation (RMI), Microsoft Distributed Component Object Model (DCOM). CEG43663

64. System Architecture: Client-Server Model CEG43664 Dual roles— A web server is often a client of a local file server. Web servers and other Internet servers are clients of the DNS server which translates Internet domain names to network addresses. A search engine is a server, but it runs programs called web crawlers that access web servers throughout the Internet for information inquiries.

65. Service Provided by Multiple Servers CEG43665 Servers may partition the set of objects maintain replicated copies of the entire set of objects on several hosts.

66. Client-Server Architecture – CEG43666 … invocation Results Clients Server … invocation Results Clients Service Single-ServerMultiple-Server

67. Web Proxy Server CEG43667 Web proxy servers provide a shared cache for client machines at a site or across several sites.

68. Peer Process Architecture CEG43668 All the processes play similar roles, interacting cooperatively as peers to perform tasks. For example, a distributed whiteboard application allows users to view and interactively modify a picture.

69. CEG43669 VM interpreter Java program Compilation JIT compiler Bytecode: low level but machine independent Native machine instructions Mobile code Java virtual machine

70. VM as a spanning layer The virtual machine addresses some problems in network distribution of applications: – Different instruction sets and operating systems (portability) – Network and GUI APIs (portability) – Security in downloading executables from untrusted sources (policies) A price that is paid: – 10X (perhaps down to 3X) performance hit for interpreted execution. This can be reduced using just-in-time (JIT) compilers and native Java processors. Typically applications are written in Java, which offers features (such as threading and garbage collection) coordinated with the VM definition. However, in principle an application could be written in a different language as long as an appropriate compiler is available. CEG43670 Java virtual machine Operating system Applications JavaBeans component framework

71. Thin Clients and Compute Servers CEG43671 Thin Client Application Process Network computer or PC Compute server network Thin client: a software layer that supports a window-based user interface on a local computer while executing application programs on a remote machine. Advantage: low management and hardware costs at the client Disadvantage: Delays are increased because of transfer of image and data between the thin client and the application process.

72. Conventional Example of Thin Clients – X-11 Window Systems X-11 server provides an extensive library of procedures for displaying and modifying graphical objects. X-11 client is the application program a user is interacting with. The client program communicates with the server by invoking procedures using the RPC mechanisms. CEG43672

73. New Example of Thin Clients – Mobile Smart Phone Systems Intending to provide a terminal for interaction with the Internet/Cloud. The client program communicates with the server by invoking procedures using the RPC mechanisms. CEG43673

74. Fundamental Models Fundamental Models address important aspects of a Mobile distributed system, in abstraction. Interaction Model – Addresses communication and coordination between processes Failure Model – Defines and classifies faults and methods of recovery or tolerance Security Model – Defines security threats and mechanisms for resisting them CEG43674

75. Interaction Model Communication Performance Latency – Propagation delay: the time it takes for the first bit of a message to reach the destination. – Transmission delay: the time interval between transmission of the first bit and the last bit of the message. – Processing delay: the time it takes for the OS to process/send/ receive the message. – Queueing delay: the time it takes a message to be queued either at end hosts or intermediate nodes waiting for transmission. Bandwidth: the total amount of information that can be transmitted over a given time. Jitter: the time difference between the delays incurred by different messages. CEG43675

76. Interaction Model Clocks & Timing events – No global notion of time – Clock drift rates: the relative rate at which a computer clock drifts away from a perfect reference clock. – Clock synchronization: Global positioning system (GPS): a few computers may use radio receivers to get time readings from GPS with an accuracy of 1 microsecond. They then send timing messages to other computers in their respective networks. Logical clocks: messages are time stamped with a sequence number that reflects their logical ordering. CEG43676

77. Real-time Ordering of Events CEG43677

78. Interaction Model Synchronous Distributed System – Each step in a process takes lb < time < ub – Each message is received within bounded time – Each local clock’s drift has a known bound Asynchronous Distributed System – No bounds on process execution – No bounds on message transmission delays – The drift rate of a clock is arbitrary – Internet is an asynchronous distributed system CEG43678

79. Failure Model Omission failures – Process omission failure Crash – a process halts and does not execute any further operations; can be detected by timeout in synchronous DS – In asynchronous systems, a timeout may be a consequence of process crash, extremely large message delays, or message losses. Fail-stop – a process crash is called fail-stop if other processes can detect certainly that the process has crashed. CEG43679

80. Failure Model Omission failures – Communication omission failures Send-omission: loss of messages between the sending process and the outgoing message buffer Channel omission: loss of message in the communication channel. Receive-omission: loss of messages between the incoming message buffer and the receiving process CEG43680

81. Processes and Channels CEG43681

82. Failure Model (cont’d) – Arbitrary failures Arbitrary process failure: arbitrarily omits intended processing steps or takes unintended processing steps. Arbitrary channel failures: messages may be corrupted, duplicated, delivered out of order, incurs extremely large delays; or non-existent messages may be delivered. – Timing failures Clock failure: the process’s local clock exceeds the bound on its drift rate from real time. Process-time failure: process exceeds the bound on the interval between two steps. Channel-time failure: message transmission time exceed the budgeted bound. CEG43682

83. Omission and Arbitrary Failures CEG43683 Class of failureAffectsDescription Fail-stopProcessProcess halts and remains halted. Other processes may detect this state. CrashProcessProcess halts and remains halted. Other processes may not be able to detect this state. OmissionChannelA message inserted in an outgoing message buffer never arrives at the other end’s incoming message buffer. Send-omissionProcessA process completes asend, but the message is not put in its outgoing message buffer. Receive-omission ProcessA message is put in a process’s incoming message buffer, but that process does not receive it. Arbitrary (Byzantine) Process or channel Process/channel exhibits arbitrary behaviour: it may send/transmit arbitrary messages at arbitrary times, commit omissions; a process may stop or take an incorrect step.

84. Timing Failures CEG43684 Class of FailureAffectsDescription ClockProcessProcess’s local clock exceeds the bounds on its rate of drift from real time. PerformanceProcessProcess exceeds the bounds on the interval between two steps. PerformanceChannelA message’s transmission takes longer than the stated bound.

85. Adaptations on Mobile Platforms CEG436: Mobile Computing (PM) 85

86. Mobile Applications must Adapt Need to adapt to heterogeneous, dynamic device/network status Need to optimize resource usage given that resources are often limited 86 Slides adapted from Wanghong Yuan, Klara Nahrstedt Richard Yang CEG436: Mobile Computing (PM)

87. Service Adaptation Service delivered should depend on – device status (e.g., display capability, input method, memory size, remaining battery level) – network status Adaptation needs the support of – the client, – the server, and/or – a third party (proxy or gateway) Server and third party adaptation is also called content adaptation 87 in-building campus-area packet radio metro-area regional-area CEG436: Mobile Computing (PM)

88. Adaptation: Client Responsibility Client informs server its device capability and connection status Client makes best use of – available resources and – available result data 88 CEG436: Mobile Computing (PM)

89. Content Adaptation Server/third party adapts service/content according to client capability 89 CEG436: Mobile Computing (PM)

90. Client Adaptation Client Capability Negotiation and Monitoring Make Best Use of Resources/Results – Adaptive CPU scheduling – Adaptive playout 90

91. Typical Power Usage 91

92. Power Management CEG436: Mobile Computing (PM) 92

93. Dynamic Voltage Scaling (DVS) Voltage to be dynamically adjusted DVS-enabled processors – StrongARM SA-2 (500mW at 600MHz; 40mW at 150MHz) – AMD (PowerNow!) http://www.amd.com/us- en/assets/content_type/DownloadableAssets/Power_ Now2.pdf – Intel (SpeedStep, XScale) – Texas Instrument – Transmeta 93

94. CPU Power Consumption Model When the supply voltage V is lower, charging/ discharging time is longer; thus frequency should be lower f  V The power consumption rate P of a CMOS processor satisfies P = kCV 2 f where k is a constant, C the capacitance of the circuit, f the CPU frequency, and V the voltage P  V 3 94

95. Voltage Scaling 95 throughput

96. Dynamic Voltage Scaling Basic idea: determining voltage according to program response time requirement For normal applications, give reasonable response time For multimedia applications, use the deadline to determine voltage 96

97. Architecture CEG436: Mobile Computing (PM) 97 CPU monitoring scheduling speed scaling demand distribution scheduler speed adaptor profiler multimedia applications requirements time constraint

98. Demand Prediction CEG436: Mobile Computing (PM) 98 Online profiling and estimation: count number of cycles used by each job cumulative probability b 1 b 2 C min =b 0 b r =C max 1 b r-1 CDF F(x) = P [X  x]

99. CPU Resource Allocation How many cycles to allocate to a multimedia job? Application should meet  percent of deadlines – each job meets deadline with probability  – allocate C cycles, such that F (C ) =P [X  C ]   CEG436: Mobile Computing (PM) 99 b 1 b 2 b 0 brbr 1 b r-1 cumulative probability F(x)F(x)  C

100. How Fast to Run the CPU? Assume the strategy is to run job i at a fixed speed Si Assume it needs Ci cycles during a time duration of Pi Fact: since power is a convex function of frequency, if a job needs C cycles in a period P, then the optimal frequency is C/P, namely the lowest constant frequency. CEG436: Mobile Computing (PM) 100

101. Why Not Uniform Speed? Intuitively, uniform speed achieves minimum energy if the allocated is used exactly However, jobs use cycles statistically – often complete before using up the allocated – potential to save more energy –  stochastic DVS CEG436: Mobile Computing (PM) 101

102. Stochastic DVS For each job – find speed Sx for each allocated cycle x time is 1/Sx and energy is (1 - F(x))S 3 x CEG436: Mobile Computing (PM) 102 such that

103. Example Speed Schedule CEG436: Mobile Computing (PM) 103 Job 1 2.5 x10 6 cycles speed (MHz) 100 400 200 Job 2 1.2 x10 6 cycles

104. DVS CEG436: Mobile Computing (PM) 104 speed A1 B1 A1 execution speed up within job context switch 1.Store speed for switched-out 2.New speed for switched-in switch back A2

105. Example: Deal with Variable Delay Consider multimedia applications Packets arrive with variable delay (why?) Variable delay does not work well for multimedia application CEG436: Mobile Computing (PM) 105

106. Client Playout Buffer Basic idea: delay playing out packets to accommodate delay jitter Question: how to determine the playout delay? 106 packets number time packets generated p p' delay 0 1 r packets received

107. An Example Client Architecture Application requests service – registers a resource descriptor and an upcall event handler with the OS Operating system maintains/monitors available resources – no need to have each application re-implement the monitoring OS notifies the application upon detecting resource changes Application adjusts requests to the server 107

108. Content Adaptation: Audio Send a lower resolution stream as the redundant information, e.g. nominal stream at 64 kbps and redundant stream at 13 kbps (such as GSM) 108 2 3

109. Content Adaptation: Video/Image Potentially many dimensions – frame rate (for video) – image size – quality of image Usage: e.g., data acceleration offered by many carriers 109

110. Block Transform Frame Encoding CEG436: Mobile Computing (PM) 110 DCT Zig-zag Quantize Run-length Code Huffman Code 011010001011101...

111. Example: MPEG Block Encoding CEG436: Mobile Computing (PM) 111 original image DCT DC component AC components Quantize zigzag run-length and Huffman encoding of the stream 10011011100011... coded bitstream < 10 bits (0.55 bits/pixel)

112. 112 Examples Uncompressed (262 KB) Compressed (22 KB, 12:1) Compressed (6 KB, 43:1) CEG436: Mobile Computing (PM)

113. Location Based Services (LBS)

114. Content-Centric LBS Current LBSs are content-oriented and lack the logic necessary for user interactivity (no user models captured in the service) Content could be boring! And has limited impact as compared to interactions Content-centricity was not by choice, it was more of a constraint. Downloading content was what is available, and was challenging enough (e.g. WAP performance) CEG436: Mobile Computing (PM) 114

115. Precision of the Localization subsystem Cellular triangulation useful for some applications but inadequate for others. On-board GPS (e.g., Assisted GPS) offers better accuracy, but does not work indoors. “Locate nearest Pizza place!” era of LBS – Does not need accuracy – Outdoor! CEG436: Mobile Computing (PM) 115

116. Telecom-centric LBS Localization based information provided by telco; telco partners with other content providers (such as Verizon and Microsoft MSN) The centricity and encumbrance by telecom proved to be non-scalable and actually an impedance to the much-anticipated proliferation of the elegant LBS concept CEG436: Mobile Computing (PM) 116

117. Redefining LBS to be a framework As an application, LBS, gets a location, passes it to an authoritative server (@telco), and then delivers back location relevant information to the target. This is one application – very limiting. As a framework, LBS gets a location, passes it to servers provided by third parties, and then delivers back location relevant services (applications) to the target. This is unlimited number of applications. This is very flexible and much more exciting! CEG436: Mobile Computing (PM) 117

118. Impromptu Delivery of Apps Middleware and intelligent markup languages should be developed to enable the development of compact size code that takes only a few seconds to download and to get interpreted on a mobile device. Code not content: compact code gets interpreted to native computations utilizing native resources. Net effect: – A few seconds instead of tens of seconds or minutes in delivery time – No installation, de-installation or management. – Applications appear & disappear. CEG436: Mobile Computing (PM) 118

119. Enable Indoor Localization More investment in indoor localization technology. Standardizations Solve Privacy issues Bluetooth Example: Through the creation of a new “Legalized Snooping” profile – Snoop protocol – Pay customer to snoop – Access to customer profile – On the fly tailored applications Technologies: Wi-Fi, Ultra wideband, or licensed frequencies. CEG436: Mobile Computing (PM) 119

120. Alter LBS Business Model Telco to sell and profit from basic services only (data pipe, SMS pipe,..and perhaps application pipe in the future). Telco no longer defines LBS. Empower third party to transact LBS directly with end users, using Telco basic services. This is B2C with B2B embedding. Any business should be allowed to participate and offer LBS. A business should be able to develop “LBSlets” using simple LBS development kits. Businesses can host their own LBSs either directly or through a web hosting service. User to own and sell his/her LBS user profile. CEG436: Mobile Computing (PM) 120

121. CEG436: Mobile Computing (PM) 121

122. Major Challenge: Positioning GPS – Good accuracy, 10m – short battery life, hours GSM – Poor accuracy, 200-400m – Long battery life, days WiFi / Skyhook – accuracy: 200-400m – battery: 16h E.g., SkyHook WiFi Location – Skyhook trucks war-drive a place Create map = Distribute map to phones – Phone user goes to a war- driven region, hears WiFi IDs Does a reverse Look Up – At the cost of Degraded location accuracy: walking paths ~ 60m Reliance on infrastructure (APs) War-driving ($$ + carbon footprint) NYTimes claims Skyhook has a fleet 500 trucks. CEG436: Mobile Computing (PM) 122

123. Assisted GPS (A-GPS) Typical in current cell phones. U.S. FCC's 911 mandate: location of a cell phone available to emergency call dispatchers911 mandate Time To First Fix – GPS: 40-80 sec – A-GPS: 30 sec A-GPS uses – radio signals from GPS satellites – precise coordinates of cell towers – AGPS assistance servers over cell/wi-fi network to utilize the satellites faster as well as better in poor signal conditions. CEG436: Mobile Computing (PM) 123

124. Skyhook Location Service skyhookwireless.com/ software-only location system that quickly determines device location with 10 to 20 meter accuracy. Skyhook Engine uses raw data from Wi-Fi access points, GPS satellites and cell towers and computes with advanced hybrid positioning algorithms. Skyhook maintains a worldwide database of cell tower locations, and Wi-Fi access points. – Skyhook trucks war-drive a place – Create map = – Distribute map to phones – 250 million wi-fi access points and covers 70 percent of population centers in the United States, Canada, Western Europe and Asia. Embedded into the MapQuest Android app Wi-Fi positioning performs best in urban areas and indoors. GPS provides accurate results in "open sky" environments. – indoors, tall buildings … block view of satellites – GPS or A-GPS cannot provide fast and accurate location results Cell tower triangulation provides generalized location results with only 200 - 1000 meter accuracy. CEG436: Mobile Computing (PM) 124 SkyhookGPSA-GPS Accuracy10 m 30 m Availability99.8%80.0%95% TT First-Fix1 sec65 sec30 sec

125. Other Approaches: CompAcc No War-Driving – Cannot drive walking paths (campus, parks, …) – Expensive / Environment unfriendly No reliance on WiFi infrastructure – Rural regions / developing countries Good accuracy (comparable to GPS) Improve energy-efficiency – Better than Skyhook, GPS CEG436: Mobile Computing (PM) 125

126. CompAcc: Basic Idea Direction(compass) + Displacement(accelerometer) = User’s directional trail Compute path signatures – Derived from a local electronic map (Google Maps) Compare directional trail with path signatures – Best match provides the user location CEG436: Mobile Computing (PM) 126 Directional Trail Path Signature …

127. … Directional Trail Correct location errors at turns CEG436: Mobile Computing (PM) 127

128. Path Signature … Directional Trail Correct location errors at turns Directional Trail Path Signature … CEG436: Mobile Computing (PM) 128

129. Advantages No war-driving No reliance on WiFi infrastructure – Maps available ubiquitously Improves battery lifetime – GPS ~10h – Skyhook ~16h – Accelerometer ~ 39h – Compass ~48h CEG436: Mobile Computing (PM) 129

130. CompAcc Architecture Tile Database Tile Database 6. Current location (lat A, long B) 2. Report initial location (lat X, long Y) Tile 4. Direction (Compass) 5. Displacement (Accelerometer) 1. Initial location GPS: (lat X, long Y) CompAcc Initial location Directional trail Current location 3. Obtain paths in the user vicinity CEG436: Mobile Computing (PM) 130

131. Directional trail: displacement displacement = Accelerometer-step-count * step-size CEG436: Mobile Computing (PM) 131

132. Directional trail: direction CEG436: Mobile Computing (PM) 132

133. Directional trail: direction CEG436: Mobile Computing (PM) 133

134. Path Signature Extract from Google Maps Geodesic formulas CEG436: Mobile Computing (PM) 134

135. Matching Directional Trail with Path Signatures Dissimilarity Metric: c i = compass readings p i = path computed direction N = directional trail size Directional Trail Path Signature CEG436: Mobile Computing (PM) 135

136. CompAcc Results CEG436: Mobile Computing (PM) 136

137. Results Average ALE GPS: 10m CompAcc: 11m WiFi-War-Walk: 30m Skyhook: 70m Energy GPS: 10h CompAcc: 23h WiFi-War-Walk:16h Skyhook:16h CEG436: Mobile Computing (PM) 137

138. g GPS, s Skyhook, c CompAcc CEG436: Mobile Computing (PM) 138 Assume GPS is absolute truth

139. CompAcc Today’s localization technologies limited – Energy- Efficiency – Coverage/Accuracy – Rely on simple localization mechanism – Need: Compass, Accelerometer and Maps Evaluation results: – ALE: 11m – Battery: 23h CompAcc scales to any mapped part of the world CEG436: Mobile Computing (PM) 139

140. References Constandache, Choudhury, Rhee, “CompAcc: Using Mobile Phone Compasses and Accelerometers for Localization”, IEEE Infocom, March 2010. Wanghong Yuan, Klara Nahrstedt, Energy- Efficient Soft Real-Time CPU Scheduling for Mobile Multimedia Systems CEG436: Mobile Computing (PM) 140