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CSE-302: Mobile Computing Dr. R. B. Patel Dr. R. B. Patel 1 Breakthrough Technology • Wireless communication networks – multiple networks “covering” the globe – world- wide deregulation and spectrum auctions – standard communication systems and air link interfaces • Portable information appliances – laptops, notebooks, sub- notebooks, and MNCs – hand- held computers – PDAs and smart phones • Internet: – TCP/ IP& de- facto application protocols Dr. R. B. Patel 2 – ubiquitous web content New Forms of Computing Distributed Computing (Client/ Server) Wireless Computing Nomadic Computing Mobile Computing Ubiquitous Computing Pervasive Computing Invisible Computing Dr. R. B. Patel 3 Mobile Computing Mobile Computing • Using:– small size portable computers, handheld, MNC, and other small wearable devices, • To run stand- alone or network based applications via:– wireless networks: IR, BlueTooth, W- LANs, Cellular,W- Packet Data networks, SAT, etc. •By : – nomadic and mobile users (animals, agents, trains, cars, cell phones, ….) Dr. R. B. Patel 4 Mobile Computing • An important question to ask is which technology drove mobile computing to where it is today? • Is it the wireless network technology or the miniaturization and portable computing technology? • Unfortunately, there is no easy answer. An individual with a Palm Pilot will probably answer in favor of the portable technology, whereas a UPS package delivery worker will be more thankful to the wireless technology. • Whatever the right answer might be, more important questions need to be answered: where are we now? • And what are the challenges and impediments facing mobile computing? Dr. R. B. Patel 5 Mobile computing • Mobile computing represents a shift in the distributed systems paradigm. • The potential of decoupled and disconnected operation, location-dependent computation and communication, and powerful portable computing devices gives rise to opportunities for new patterns of distributed computation that require a revised view of distributed systems. • However, factors such as weak network connectivity, energy constraints, and mobility itself raise new concerns regarding the security, reliability, and even correct-ness of a mobile computing system. Dr. R. B. Patel 6 Mobile Computing • Migration is important for survival • Mobility originated from the desire to move either toward resource or away from scarcity • Mobile computing about both physical and logical computing entities that move • Physical entities are computers that change locations • Logical entities are instances of running user application or a mobile agent • Mobile agents can migrate any where over the Internet. • But applications can only move to a local cluster of computers Dr. R. B. Patel 7 Buzzwords • Mobile, ubiquitous, nomadic, un-tethered (unsecured), pervasive and any time, any where, any person computing are used by the researchers to refer to computing that uses small portable devices and wireless communication network. • Nomadic computing refer to limited migration – Migration is within a building at a pedestrian speed – Interleaved pattern of user relocation and indoor connections • In the same vein, users carrying laptop with Dialup modems are engaged in nomadic computing Dr. R. B. Patel 8 Buzzwords (contd...) • Mobile Computing requires: Wireless network to support outdoor mobility and handoff from one network to the next at a pedestrian or vehicular speed • Traveler in car using laptop connected with a GSM phoneengaged in mobile computing • Ubiquitous computing or pervasive computing refers to access to computer network all the time at any location by any person. • Ubiquitous computing cannot be realized unless mobile computing matures. Dr. R. B. Patel 9 Ubiquitous Computing = Nomadic Computing + Mobile Computing No Network Fixed Network Fixed Wireless Network Nomadic Computing Wireless Network (A) Wireless Network (B) Mobile Computing Ubiquitous computing Dr. R. B. Patel 10 Nomadic computing • It is another name for mobile computing, is the use of portable computing devices (such as laptop and handheld computers) in conjunction with mobile communications technologies to enable users to access the Internet and data on their home or work computers from anywhere in the world. • People using such a system are sometimes referred to as technomads, and their ability to use that system as nomadicity. Dr. R. B. Patel 11 Continued … • Nomadicity is the tendency of a person, or group of people, to move with relative frequency. • The need to support today's increasingly mobile workers with nomadic computing, the use of portable computing devices and, ideally, constant access to the Internet and data on other computers. • The goal of nomadic computing is to enable a consistent experience for users anywhere in the world, including as they travel from one place to another. Dr. R. B. Patel 12 Continued … • A nomadic environment is said to be one that is transparent to the user, regardless of location, the device and platform they're using, the available bandwidth, and whether or not they are in motion at any given time. • Standards such as the Internet Engineering Task Force’s (IETF) Mobile IPv6 standards and Dynamic Host Configuration Protocol (DHCP) can be said to support nomadic computing. Dr. R. B. Patel 13 Ubiquitous Computing • Ubiquitous computing names the third wave in computing, just now beginning. • First were mainframes, each shared by lots of people. Now we are in the personal computing era, person and machine staring uneasily at each other across the desktop. • Next comes ubiquitous computing, or the age of calm technology, when technology recedes into the background of our lives. • This is also called "Third Paradigm" computing. Dr. R. B. Patel 14 Sentient computing • Sentient computing is a form of ubiquitous computing which uses sensors to perceive its environment and react accordingly. • A common use of the sensors is to construct a world model which allows location-aware or context-aware applications to be constructed. Dr. R. B. Patel 15 Mobile Environment Wireless radio Cells Fixed host Fixed host Fixed host High-speed wireline network Fixed host Fixed host Fixed host Satellite link Wireless LAN Base station Mobile host Dr. R. B. Patel Wireless link Comm. cell 16 Wireless Networks Telecommunication Dr. R. B. Patel 17 Emerging Portable Information Devices The First Wrist PC: Ruputer The Nokia 9000 Communicator Motorola marco The Vadem Clio Subscriber Identification Module (SIM) The Power Ring The Pocket PC Motorola Envoy The Dr. Sharp R. Zaurus B. Patel 18 Fujitsu Stylistic 2300/ 3400 Japan’s PHS Phone, Year Wearable Computers Applications for mobile computing • There are several applications for mobile computing including wireless remote access by travelers and commuters, point of sale, stock trading, medical emergency care, law enforcement, package delivery, education, insurance industry, disaster recovery and management, trucking industry, intelligence and military. • Most of these applications can be classified into: (1) wireless and mobile access to the Internet, (2) wireless and mobile access to private Intranets, and (3) wireless and adhocly mobile access between mobile computers. Dr. R. B. Patel 19 Beneficiaries of ubiquitous computing Internet Education Insurance Emergency Trucking Intelligence Military Intranet Servers Commuters Travelers Stock traders Medical Law enforcement Ad-hoc network Dr. R. B. Patel Clients 20 Limitations of the Environment – – – – – – Mobile Limitations of the Wireless Network Heterogeneity of fragmented networks Frequent disconnections Limited communication bandwidth Limitations Imposed by Mobility Limitations of the Mobile Computer Dr. R. B. Patel 21 Continued… Frequent Disconnections – Handoff blank out (>1ms for most cellular system) – Drained battery disconnection – Battery recharge down time – Voluntary disconnection (turned off to preserve battery power, also off overnight) – Theft and damage (hostile environment) – Roam-off disconnections Dr. R. B. Patel 22 Continued… Limited Communication Bandwidth – Orders of magnitude slower than fixed network – Higher transmission bit error rates (BER) – Uncontrolled cell population – Difficult to ensure Quality of Service (QoS) – Asymmetric duplex bandwidth – Limited communication bandwidth exacerbates the limitation of battery lifetime. Dr. R. B. Patel 23 Continued… Limitations of the Mobile Computer – – Short battery lifetime (max ~ 5 hours) Subject to theft and destruction => unreliable – Highly unavailable (normally powered-off to conserve battery) – Limited capability (display, memory, input devices, and disk space) – Lack of de- facto general architecture: Handheld, communicators, laptops, and other devices Dr. R. B. Patel 24 Continued… Limitations Imposed by Mobility Lack of mobility- awareness by applications – inherently transparent programming model (object-,components- oriented, but not aspect- oriented) – lack of environment test and set API support Dr. R. B. Patel 25 Continued… Lack of mobility- awareness by the system – network: existing transport protocols are inefficient to use across heterogeneous mix of fixed/wireless networks – session and presentation: inappropriate for the wireless environment and for mobility – operating systems: lack of environment related conditions and signals – client/server: unless changed, inappropriate and inefficient Dr. R. B. Patel 26 Continued… Mobile and Wireless Networking Issues – Mobile IP – Wireless Transport – Ad- Hoc Networks – Location Management – Wireless Network Benchmarking – Ad- Hoc Network Simulation – Wireless Link Simulation Dr. R. B. Patel 27 Continued… Wireless and Mobile Computing Models – Mobility- aware Client/ Server using Proxies – Disconnected Operations – Application- aware Adaptations – Mobile Agents and Objects – Thin Client/ Server – Mobile Caching and Replication – Broadcast Disks – Service Advertisement and Brokering – Smart Pones Dr. R. B. Patel 28 Continued… Mobile file and Database Systems – Wireless File System Access – Disconnected File Systems – Mobile Access to C/ S or Distributed Databases – Ad- Hoc Database Systems – Checkpointing – Database recovery – Mobile Database Design Dr. R. B. Patel 29 Continued… Mobile Transaction and Workflow – ACID Relaxation – Mobile Transaction Models – Optimistic Data Replication – Semantic- based Conflict Resolution – Consensus in Mobile Environment Dr. R. B. Patel 30 Continued… Wireless and Mobile Applications and Services – Application Design for Wireless networks – Application Design for Mobility – Wireless WWW Access – Active Badges (Teleporting) – Wireless Classroom (Wireless Campus!) – Mobile Groupware – Location- sensitive Yellow Service – Pervasive Computing and Smart spaces – •..... Dr. R. B. Patel 31 Continued… Performance and QoS – QoS Measures in Wireless and Mobile Environments – QoS Guarantees – Simulators and Emulaors of Wireless Links – Simulators of Mobile and Ad- hoc Networks – Wireless Networking Benchmarking Dr. R. B. Patel 32 Continued… Emerging Standards – The 802.11b – The BlueTooth Standard – The Wireless Application Protocol (WAP) – The CompactHTML – The Network Computer Reference Specification – Telecom Standards: UMTS – … Dr. R. B. Patel 33 Continued… Commuters Travelers Stock traders Medical Law enforcement Internet Intranet Education Insurance Emergency Trucking Intelligence Military Intranet Ad-hoc network Servers Dr. R. B. Patel Clients 34 Challenges • • • • • • • Mobility/context aware applications Naming and locating Routing data and messages Reliability in presence of disconnection Data management Transaction models Security Dr. R. B. Patel 35 Continued… • Mobile computing affects entire spectrum of issues in computing • First of all it is distributed + mobile computing • Distributed computing as we know works on static wired network • Node may initiate computation somewhere and migrate to another place. • So two major problems that arise due to mobility – Searching for current location of a mobile node – To impose a communication structure among nodes Dr. R. B. Patel 36 Continued… • Physical location of mobile host is not the network address, so how do we route the message to a mobile host. • This question is being addressed by two different communities- Internet community and cellular community • Work of Internet community involves Mobile IP – Aims at standards that can extend IP in order to deal with location of mobile host – Mobile IP work assumes connectionless packet switching scenario Dr. R. B. Patel 37 Continued… • Cellular community’s effort based on location management of cellular phone users • It deals with connection-oriented communication, since it is motivated by issues in call-setup in telephony • Main problem in mobility management is to find an appropriate tradeoff between searching and informing • Searching is performed when address of the message recipient is not known- at least not known precisely Dr. R. B. Patel 38 Continued… • • Informing is a responsibility of the mobile host when it migrates Extreme situations can be 1. Mobile host never informs- works for hosts receiving few messages and for hosts which do not move during receiving 2. Always informs – works well for hosts receiving messages frequently Dr. R. B. Patel 39 Continued… • • Ad hoc network routing is the ultimate challenge Ad hoc networks arise in rapid development scenarios 1. 2. 3. • • Emergency disaster management Military operation in remote sites Business meeting venues without infrastructure support Many routing algorithms are designed: such as fisheye, state routing, dynamic source routing, ad hoc on demand routing, etc. There are interesting application of conventional graph theoretic problems in ad hoc network routing Dr. R. B. Patel 40 Continued… (b) Ad hoc network (a) Infrastructure-based wireless network Dr. R. B. Patel 41 Continued… • Main cause of loss of packets in wired network is congestion because error rates are very low • In wireless network congestion still remains a problem, but the situation is somewhat reversed • Wired and wireless network require different techniques to achieve reliability and flow control • TCP works is unsuitable for wireless network as it interprets errors packets loss Dr. R. B. Patel 42 Continued… ITCP (split/indirect TCP) splits TCP into two parts – One between sender and local MSS of the recipient – The other between local MSS and recipient – If MH switches cell during lifetime of a ITCP connection center point of connection moves to new MSS sender remains completely unaware about it Dr. R. B. Patel 43 Continued… • Disconnection/weak connection support is important • CODA file system provides support for this • It is implemented as client side cache management system • The issue concerns making a file system highly available while maintaining consistency • Caching in mobile environment is quite different. MSS cannot keep state information (due to scale) for all clients. So invalidation by notification Dr. R. B. Patel 44 Continued… • Categories of information dissemination 1. Wide area services – such as stock quotes on national scale 2. Macro services- such weather on a regional scale 3. Micro services- traffic condition is an immediate vicinity • Can be extend to even picocells – such finding a parking slot Dr. R. B. Patel 45 Continued… Proving services will require addressing of following new issues – Interoperability and adaptability to network environments ranging from high to low bandwidths and infrared communication links – Energy efficient data access – Support for mobility and disconnection – Support for active services, triggers (even notification), and periodic data delivery. Dr. R. B. Patel 46 Continued… • • • Two modes of information dissemination are 1. Publish 2. Provide on demand Publish data is filtered by client and server provides directory information for assisting the filtering Advantages of information dissemination by publishing are – Hot spots can be broadcast frequently-which saves energy at client, avoid congestion – Directory helps client to tune in selectively Dr. R. B. Patel 47 Continued… • Handoff management – an MH moves from one cell to another while being connected • Desirable features are – Probability of call dropping is minimized – Ping-pong handoffs avoided – Interruption is minimized Dr. R. B. Patel 48 Mobile Computing Models • The following models of computing in the mobile environment are currently being researched and investigated: – – – – – Client/Server Client/Proxy/server Disconnected Operation Mobile Agents The Thin Client Model Dr. R. B. Patel 49