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Location Management for Mobile Computing. Sandeep Gupta Arizona State University. Tutorial Outline. 1. Introduction - Technical Issues & Technologies - New (database) Applications 2. Location Information Services 3. Location Management 4. Location Based Queries 5. Summary.

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Location Management for Mobile Computing


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    1. Location Management for Mobile Computing Sandeep Gupta Arizona State University

    2. Tutorial Outline 1. Introduction - Technical Issues & Technologies - New (database) Applications 2. Location Information Services 3. Location Management 4. Location Based Queries 5. Summary CSE535 Mobile Computing

    3. Introduction

    4. Motivation • Information is the core of business success. • The Internet has changed the way information is accessed. • Wireless networks are in place. • Mobile devices are available in the market. • Users like to go mobile and get ubiquitous access of information. • New applications requiring data management Why do we care about mobile database management? CSE535 Mobile Computing

    5. Mobile Applications • Expected to create an entire new class of Applications • new massive markets in conjunction with the Web • Mobile Information Appliances - combining personal computing and consumer electronics • Applications: • Vertical: vehicle dispatching, tracking, point of sale, information service (yellow pages), Law enforcement • Horizontal: mail enabled applications, filtered information provision, collaborative computing… CSE535 Mobile Computing

    6. Medical Example • 911 Call • Ambulance arrives/departs • Closest hospital • Access patient records • Send vital signs • Update patient records • Page hospital personnel • Order medical supplies CSE535 Mobile Computing

    7. Party on Friday • Update Smart Phone’s calendar with guests names. • Make a note to order food from Dinner-on-Wheels. • Update shopping list based on the guests drinking preferences. • Don’t forget to swipe that last can of beer’s UPS label. • The shopping list is always up-to-date. CSE535 Mobile Computing

    8. Party on Friday • AutoPC detects a near Supermarket that advertises sales. • It accesses the shopping list and your calendar on the Smart Phone. • It informs you the soda and beer are on sale, and reminds you. that your next appointment is in 1 hour. • There is enough time based on the latest traffic report. CSE535 Mobile Computing

    9. Party on Friday • TGIF… • Smart Phone reminds you that you need to order food by noon. • It downloads the Dinner-on-Wheels menu from the Web on your PC with the guests’ preferences marked. • It sends the shopping list to your CO-OP’s PC. • Everything will be delivered by the time you get home in the evening. CSE535 Mobile Computing

    10. Wireless Networks • Cellular - GSM (Europe+), TDMA & CDMA (US) • FM: 1.2-9.6 Kbps; Digital: 9.6-14.4 Kbps (ISDN-like services) • Cellular Subscribers in the United States: • 90,000 in 1984; 4.4 million in 1990;13 million in 1994; 120 million in 2000; 187.6 million by 2004 (Cahner In-State Group Report). • Handheld computer market will grow to $1.77 billion by 2002 • Public Packet Radio - Proprietary • 19.2 Kbps (raw), 9.6 Kbps (effective) • Private and Share Mobile Radio • Paging Networks – typically one-way communication • low receiving power consumption • Satellites – wide-area coverage (GEOS, MEOS, LEOS) • LEOS: 2.4 Kbps (uplink), 4.8Kbps (downlink) CSE535 Mobile Computing

    11. Wireless Networks (Cont.) • Wireless Local Area Networks • IEEE 802.11 Wireless LAN Standard based systems, e.g., Lucent WaveLan. • Radio or Infrared frequencies: 1.2 Kbps-15 Mbps • Packet Data Networks • ARDIS • RAM • Cellular Digital Packet Data (CDPD) • Private Networks • Public safety, UPS. CSE535 Mobile Computing

    12. Wireless Local Area Network • Data services: IP packets • Coverage Area: Offices, buildings, campuses • Roaming: Within deployed systems • Internet access: via LAN. • Type of services: Data at near LAN speed. CSE535 Mobile Computing

    13. Wireless Data • Data can be everywhere: • Computers • LAN • Internet • Air! CSE535 Mobile Computing

    14. Recent History of Wireless Data • 1970s: First use of mobile data systems in police cars. • 1980s: IBM/Motorola build ARDIS data network. • 1990s: RAM Mobile Data Network. • 1990s: CDPD packet network. • 1990s: GSM cellular systems support circuit-switched data access. • 1998: CDMA PCS systems support 14.4 circuit-switched data access. CSE535 Mobile Computing

    15. If the history repeats itself Wireless data will be booming pretty soon! CSE535 Mobile Computing

    16. Mobile and Wireless Computing • Goal: Access Information Anywhere, Anytime, and in Any Way. • Aliases: Mobile, Nomadic, Wireless, Pervasive, Invisible, Ubiquitous Computing. • Distinction: • Fixed wired network: Traditional distributed computing. • Fixed wireless network: Wireless computing. • Wireless network: Mobile Computing. • Key Issues: Wireless communication, Mobility, Portability. CSE535 Mobile Computing

    17. Mobile Network Architecture CSE535 Mobile Computing

    18. Wireless characteristics • Variant Connectivity • Low bandwidth and reliability • Frequent disconnections • predictable or sudden • Asymmetric Communication • Broadcast medium • Monetarily expensive • Charges per connection or per message/packet • Connectivity is weak, intermittent and expensive CSE535 Mobile Computing

    19. Portable Information Devices • PDAs, Personal Communicators • Light, small and durable to be easily carried around • dumb terminals [InfoPad, ParcTab projects], palmtops, wristwatch PC/Phone, walkstations • will run on AA+ /Ni-Cd/Li-Ion batteries • may be diskless • I/O devices: Mouse is out, Pen is in • wireless connection to information networks • either infrared or cellular phone • specialized HW (for compression/encryption) CSE535 Mobile Computing

    20. Portability Characteristics • Battery power restrictions • transmit/receive, disk spinning, display, CPUs, memory consume power • Battery lifetime will see very small increase • need energy efficient hardware (CPUs, memory) and system software • planned disconnections - doze mode • Power consumption vs. resource utilization CSE535 Mobile Computing

    21. Portability Characteristics • Resource constraints • Mobile computers are resource poor • Reduce program size – interpret script languages (Mobile Java?) • Computation and communication load cannot be distributed equally • Small screen sizes • Asymmetry between static and mobile computers CSE535 Mobile Computing

    22. Mobility Characteristics • Location changes • location management - cost to locate is added to communication • Heterogeneity in services • bandwidth restrictions and variability • Dynamic replication of data • data and services follow users • Querying data - location-based responses • Security and authentication • System configuration is no longer static CSE535 Mobile Computing

    23. What Needs to be Reexamined? • Operating systems • File systems • Data-based systems • Communication architecture and protocols • Hardware and architecture • Real-Time, multimedia, QoS • Security • Application requirements and design • PDA design: Interfaces, Languages CSE535 Mobile Computing

    24. Query/Transaction Processing • Concern shifts from CPU time and network delays to battery power, communication costs, and tariffs • Updates may take the form of long-running transactions • nodes may continue in disconnected mode • need new transaction models [Chrysanthis 93, Satya 94] • Context (location) based query responses • Consistency, autonomy, recovery • Providing uniform access in a heterogeneous environment • Design of human-computer interfaces (pen-based computing) • Dynamic system info: Location information, user profiles CSE535 Mobile Computing

    25. Recurrent Themes • Handling disconnections (planned failures?) • caching strategies • managing inconsistencies • Delayed write-back and prefetch: use network idle times • increases memory requirements • Buffering/batching: allows bulk transfers • Partitioning and replication • triggered by relocation • Compression: increase effective bandwidth increases battery power requirements • Receiving needs less power than sending CSE535 Mobile Computing

    26. Everybody is ready! • End users: they want to access to data ubiquitously. • Wireless networks: there are many choices of digital wireless data networks. • Mobile devices: they are wireless-ready today. • Applications: Internet standards are in progress to facilitate developments of wireless applications. CSE535 Mobile Computing

    27. Location Information Services

    28. Location Information Services:Types • Location-Transparent • Location-Tolerant • Location-Aware CSE535 Mobile Computing

    29. Location-Transparent Services • Hides the effect of mobility to applications and users. • Network services and resources can be transparently accessed by means of a resource and service broker functions which map the application’s service type requests on adequate service provider instances. • Application defined quality-of-service (QoS) for the underlying network connections is sustained through a QoS manager. CSE535 Mobile Computing

    30. Location-Tolerant Services • Allows applications and users to tolerate the effects of mobility that can not be hidden by the platform. • A trader function allows the application to perform a service and service type re-negotiation to achieve a graceful degradation instead of dumb service termination. • A profile handler function allows to retrieve user and terminal characteristics to perform application adaptation according to terminal type currently being used. CSE535 Mobile Computing

    31. Location-Aware Services • Allows applications and users to be aware of their mobility and the absolute and real physicalpositions of real-world objects. • Applications can exploit this information for customizing their functionality and users can benefit from this information for navigation purposes. • This abstraction level is realized by the location information server (LIS) function that allows to query location information and to be notified about the occurrences of predefined location-related events. CSE535 Mobile Computing

    32. mobile application platform mobility manager APIs resource & service broker location manger server QoS manager profile handler application application locating infrastructure wired & wireless networks APIs APIs Platform for Mobile and Location-Aware Applications mobile and location-aware multimedia applications mobility-management services platform access protocols mobility management signalling protocol generic support functions Infrastructure and network interfaces Mobility Management Domain CSE535 Mobile Computing

    33. Acquires information about the – absolute or relative – physical location of real world objects in which an application is interested. Hides from applications which locating technology is being used. Has map and relationship knowledge to translate the low-level position information from the locating infrastructure into location information having meaningful abstraction level for application. Application can query the LIS about current location of objects (LIS directory database) or can request to be notified when certain location-related conditions between objects locations are fulfilled (LIS event handler). location-aware application location-aware application other APIs LIS API LIS API to remote platforms directory access protocol other midlleware components profile handler Location information server (LIS) directory database event handler locater Infrastructure to locate physical objects Location Information Server CSE535 Mobile Computing

    34. A Generic Locating Model • LIS locates objects (identified by object-ID) representing either persons or resources inside areas (identified by area-ID). • Objects have a tag (identified by tag-ID) attached to them that identifies and localizes them. • Resources can serve as tags e.g. badges, cordless telephones, PDAs, or laptops. • A LIS: • maintains relations between objects and tags. • provides graphical map in human-readable format and calculates shortest paths between areas. • finds objects that are nearest to a specified area and fulfill certain conditions. • supports both querying and notification services. • A locator provides the interface between locating infrastructure and LIS. CSE535 Mobile Computing

    35. location information server object  area application relations maps position  area object  tag sensor  area tag  sensor tag  position database/ event handler locator locator sensor sensor positioning system tag tag tag tag tag tag LIS Data Model Locating rules: • A tag is located within an area by means of sensors installed in that area. This information is collected by the locator and published to LIS, which uses a map to translate sensor-ID into area-ID. • A tag may determine its absolute geographical position (e.g. using GPS) and publish this through the locator to LIS, which uses map to translate geographical location into area-ID. CSE535 Mobile Computing

    36. LIS Service Types • Location retrieval service • Location-dependent object and area selection service • Event notification service • Map retrieval service • Identifier mapping service • Relationship service CSE535 Mobile Computing

    37. Location Retrieval Service • Provides physical location of static/mobile object with/without tags, e.g. • In which area is person A (and when was her last sighting)? • How many (or which persons) are present in area B? • Where is equipment C (e.g. printer) in area B? CSE535 Mobile Computing

    38. Location-dependent Object and Area Selection Service • Provides type or class oriented location information, e.g. • Which object of type D is present in area B? • Which one is the nearest object of type D (relative to my own location) and where it is located? • Which (nearest) area fulfils certain condition (e.g. which one is the nearest unoccupied meeting room)? CSE535 Mobile Computing

    39. Event Notification Service • Avoids repeated polling the LIS by an application. This functionality is, e.g., needed to start a function on a mobile device as soon as it enters a certain area. Examples of events are • Inform me when person A enters (or leaves) area B! • Inform me when area B is empty! • Inform me next time person A meets person B anywhere! CSE535 Mobile Computing

    40. Map Retrieval Service • To help users (of navigation based applications) in finding others persons, resources, or areas by providing maps and navigation instructions, e.g. • Provide me with with a (human-readable) map of area A! • Provide me with the shortest-path between area A and area B! CSE535 Mobile Computing

    41. Identifier Mapping Service • Provides mappings between identifiers of areas, sensors, and positions • to support internal LIS operations, • for other support functions of mobile application platform, and • for location-aware applications operating at tag-level. CSE535 Mobile Computing

    42. Relationship Service • Provides relationship information between objects and tags for applications operating at tag level instead of object level, or for applications that want to communicate with objects through its tag,e.g. • Which object is associated with tag A? • Which (if any) tag does object B posses ? • Associate tag A with objet B! CSE535 Mobile Computing

    43. LIS: Implementation Issues • DBMS-based or Directory-based (such as X.500 [Maas MONET 98]) • LIS do not require full functionality of DBMS • Should support distributed implementation on multiple platforms • Communication with external locator • Dramatically increases search time • Minimize the interaction with external locator using • Precise search filters • Location query optimization techniques • Event Monitoring • Active Databases CSE535 Mobile Computing

    44. Location Management Schemes

    45. Location Management: Context • Mobility Management: Enables users to support mobile users, allowing them to move, while simultaneously offering them incoming calls, data packets, and other services. • Types of mobility: • Terminal mobility: ability of terminal to retain connectivity with the network so that all on-going communication services remain active despite terminal’s migration. • Personal mobility: disassociates user from the terminal (e.g. in GSM a mobile station = mobile terminal + smart card with subscriber identification module (SIM)). • Service mobility: provides continuous service to mobile clients across multiple administrative domains. • Consists of: • Location management: tracking mobiles and locating them prior to establishing incoming calls (deliverying pending messages). • Handoff management (a.k.a. automatic link transfer): rerouting connections with minimal degradation of QoS. CSE535 Mobile Computing

    46. Location Management Problem • In static networks, a terminal’s network address serves two purposes: • End-point identifier • Location identifier • Mobility prevents using a single address for both purposes • Both end-point identifier and location identifier are needed. • Location management keeps mapping between an end-point identifier and its location identifier • Basically a directory problem. • Two primitive operations: • Lookup (a.k.a. search/find/paging/locating) operation: is the procedure by which the network finds the location of the mobile. • required when a call (message) to a user is placed (to be delivered) • Update (a.k.a tracking/move/registration) operation: is the procedure by which the network elements update information about the location of the mobile. • required when a user changes its “location” • The information gathered during updating/tracking is used during the locating operation CSE535 Mobile Computing

    47. Location Management: Issues • More precise location needs to be maintained as cell size shrink: • Wide area cells are 10’s – 100’s km in diameter • Macro-cells: 1-10 km • Micro-cells: 100’s m • Pico-cells: under 10 m • Database issues in tracking mobile users: • Maintaining update intensive location information • Strategies to reduce location query latency (such as replication) and traffic (such as caching) • Consistency between replicas; Cache management polices CSE535 Mobile Computing

    48. Location Management: Schemes • Several schemes have been developed which are motivated by fundamental trade-off between search operation cost and update operation cost. • Schemes which try to minimize one cost tend to increase the other cost • Try to optimize the aggregate cost or normalized cost. • Categorization: • Update Scheme: Static or Dynamic • Static update scheme: registration areas • Dynamic update scheme: distance/time/movement based strategy • Locating Scheme: Static or Dynamic • Static location scheme: page all the cells in the network • Dynamic location scheme: expanding ring search centered at last reported location of the the user • Database Architecture: Flat or Hierarchical CSE535 Mobile Computing

    49. Selection of LM Schemes • Cost of location updates and lookups • Maximum service capacity of each location database = • the maximum rate of updates and lookups that each database can service • Space restrictions (size of the location database) • Type and relative frequency of call to move operations (call-to-mobility ratio (CMR)) CSE535 Mobile Computing

    50. One-Tier Scheme • A home database, called Home Location Register (HLR) is associated with each mobile user. • The HLR of a user x maintains the current location of x as part of x’s profile. • To locate a user x, x’s HLR is identified and queried. • When a user x moves to a new cell, x’s HLR is updated. CSE535 Mobile Computing