CIS 6930: Mobile Computing Introduction Sumi Helal 1

References 4 1.1: G. H. Forman, J. Zahorjan, "The Challenges of Mobile Computing," IEEE Computer, Vol. 27, No. 4, (April 1994), pp : T. Imielinski and H. Korth, "Introduction to Mobile Computing", in Mobile Computing, edited by T. Imielinski and H. Korth, Kluwer Academic Publishers, 1996, pp : M. Satyanarayanan, "Fundamental challenges of mobile computing," ACM Symposium on Principles of Distributed Computing, 1995 (PODC'95 invited lecture) 4 1.4: M. Weiser, "The Computer for the Twenty-First Century", Scientific American, Vol. 265, No. 3, (September 1991), pp

Mobile Computing 4 Using: –small size portable computers, hand-helds, MNC, and other small wearable devices, 4 To run stand-alone applications and access remote ones via: –wireless networks: IR, W-LANs, Cellular, W-Packet Data networks and SAT. 4 By : –nomadic and mobile users

Nomadic, Mobile & Ubiquitous No Network Mobile Computing Nomadic Computing Wireless Network (B) Fixed Network Wireless Network (A) Fixed Wireless Network Ubiquitous Computing

Another View of Ubiquitous Computing 4 Mark Weiser’s views 4

Today’s Technology 4 Wireless communication networks –multiple networks “covering” the globe –wold-wide deregulation and spectrum auctions –standard communication systems and air link interfaces 4 Portable information appliances –laptops, notebooks, sub-notebooks, and MNCs –hand-held computers –PDAs and smart phones 4 Internet: –TCP/IP & de-facto application protocols –ubiquitous web content

Wireless Communication Technology (IMT-2000)

Wireless Communication Infrastructure Satellite Macro-Cell Micro-Cell Urban In-Building Pico-Cell Global Suburban dik ©

GSM Base Stations in Europe Nokia PrimeSite Ericsson RBS 2000

Wireless Network Convergence 2G/3G Mobility-Bandwidth Trade-off Mobility Bandwidth 10K 100K 1M 10M 100M 1G Room GlobalGSM D-AMPS/IS-95 DECT WLAN UMTS National Regional Metropolitan Campus Office 1-7 GHz GHz GHz 2-4 GHz 2-7 GHz >2 GHz GHz

UMTS: Universal Mobile Telecomm. Standard 4 Global seamless operation in multi-cell environment (SAT, macro, micro, pico) 4 Global roaming: multi-mode, multi-band, low-cost terminal, portable services & QoS 4 High data rates at different mobile speeds: 144kbps at vehicular speed (80km/h), 384 kbps at pedestrian speed, and 2Mbps indoor (office/home) 4 Multimedia interface to the internet 4 Based on core GSM, conforms to IMT Deployment as early as UMTS ETSI SMG ITU IMT-2000 FPLMTS IMT

Portable Information Appliances Subscriber Identification Module (SIM) CDPD Modem Car Stereo-Phone

Beneficiaries of Ubiquitous Computing Commuters Travelers Stock traders Medical Law enforcement Package delivery Education Insurance Emergency Trucking Intelligence Military Clients Adhoc network Servers Intranet Internet

Limitations of the Mobile Environment  Limitations of the Wireless Network  heterogeneity of fragmented networks  frequent disconnections  limited communication bandwidth  Limitations Imposed by Mobility  Limitations of the Mobile Computer

Heterogeneity of Fragmented Network Infrastructures Randy Katz’ heterogeneous network overlay vision (also: DARPA’s GloMo) Satellite Macro-Cell Micro-Cell Urban In-Building Pico-Cell Global Suburban dik ©

Frequent Disconnections  Handoff blank out (>1ms for most cellulars)  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

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.

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  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 env. related conditions and signals  client/server: unless changed, inappropriate and inefficient

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: hand- helds, communicators, laptops, and other devices

Caesar and Brutus