Mobile Computing

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Mobile Computing:

Mobile Computing

Computer Science:

Computer Science The discipline of Designing, Creating, and Maintaining Computer Software

Why Mobile Computing ?:

Why Mobile Computing ? People are mobile Devices are mobile

Goal of Wireless and Mobile Computing :

Goal of Wireless and Mobile Computing “People and their machines should be able to access information and communicate with each other easily and securely, in any medium or combination of media –voice, data, image, video, or multimedia –anytime, anywhere, in a timely, cost-effective way.”

What is Mobility?:

What is Mobility? A person who moves Between different geographical locations Between different networks Between different communication devices Between different applications A device that moves Between different geographical locations Between different networks

Mobile Computing Devices:

Mobile Computing Devices

Wireless Networks:

Wireless Networks

Disconnected Operation:

Disconnected Operation Offline feature Automated Predictive Use Friendly Windows Linux OS/2 Let’s see… what should I do next?

Research Issues in Mobile Computing :

Research Issues in Mobile Computing • Wireless Communications – Quality of connectivity – Bandwidth limitations • Mobility – Location transparency – Location dependency • Portability – Power limitations – Display, processing, storage limitations

Wireless Communications:

Wireless Communications • Harsh communications environment: – Lower bandwidth/higher latency: good enough for videoconferencing? – Higher error rates – More frequent disconnection – Performance depends on density of nearby users but inherent scalability of cellular/frequency reuse architecture helps • Connection/Disconnection – Network failure is common – Autonomous operation is highly desirable » Caching is a good idea, e.g., web cache – Asynchronous/spool-oriented applications, like mail or printing » Trickle back data when bandwidth is available – Disconnected file systems: CODA (CMU), Ficus (UCLA)

Wireless Communications Contd..:

Wireless Communications Contd.. • Low Bandwidth – Orders of magnitude differences between wide-area, in- building wireless • Variable Bandwidth – Applications adaptation to changing quality of connectivity » High bandwidth, low latency: business as usual » High bandwidth, high latency: aggressive prefetching » Low bandwidth, high latency: asynchronous operation, use caches to hide latency, predict future references/trickle in, etc. etc. • Heterogeneous Networks – “Vertical Handoff” among colocated wireless networks

Wireless Communications:

Wireless Communications • Security Concerns – Authentication is critical » Normal network point of attachment is a wall tap » Wireless access makes network attachment too easy – Exposure to over-the-air wiretapping » Any transmitter can also be a receiver! » Some wireless networks provide secure airlinks (e.g., CDPD) » Made more difficult by spread spectrum technologies


Mobility • Address Migration – Existing applications send packets to a fixed network address – Need to support dynamically changing “local” addresses as mobile device moves through network – Mobile IP specification: home environment tracks mobile device’s current location through registration procedure – Route optimization: exploit local caches of <global destination node addresses, current care-of address> – Location updates: » Forwarding » Hierarchical mobility agents – Other routing issues: e.g., multicast

Mobility Contd..:

Mobility Contd.. • Location Dependent Services – Discovery: What services exist in my local environment? e.g., printers, file and compute services, special local applications, etc. – Follow me services: “Route calls to my current location,” “Migrate my workstation desktop to the nearest workstation screen” – Information services: » Broadcast/“push” information (e.g., “Flight 59 will depart from Gate 23”) » “Pull” information (e.g., “What gate will Flight 59 depart from?”) – Service migration: computations, caches, state, etc. follow mobile device as it moves through the network – Privacy: what applications can track user locations?


Portability • Low Power – Limited compute performance – Low quality displays • Loss of Data – Easily lost – Must be conceived as being “network-integrated” • Small User Interface – Limited real estate for keyboards – Icon intensive/handwriting/speech • Small Local Storage – Flash memory rather than disk drive

Portability Issues:

Portability Issues • It’s the power, stupid!! • Batteries – Weight, volume determine lifetime » 20 W-hrs per pound » 2 pounds, 10 hours = 2 W power consumption! – Power consumption: CV2ƒ » Reduce C by increased VLSI integration and MCM technology » Reduce V to lower operating voltages: 5 V to 3.3V to 2.5V and below » Reduce ƒ by reducing clock frequency, standby and suspend power modes » Intelligent operation: spin-down disk drives

Putting It All Together: Concepts in Mobile Computing :

Putting It All Together: Concepts in Mobile Computing • Identification – Subscriber mobility: 700 phone number – Terminal mobility: mobile phone # or IP address – Application mobility • Registration – Authentication: who are you? – Authorization: what can you do? – Allocation: how much will I give you? • Call/Connection Establishment – Mobile Routing: Mobile IP, Cellular System HLR/VLR – Resource Reservations: Reserve channels in advance – Location Update: forward vs. hierarchy

Putting It All Together: Concepts in Mobile Computing Contd..:

Putting It All Together: Concepts in Mobile Computing Contd.. • Mobility – Handoff: when to do it, choice of network – Process Migration: application support infrastructure that follows the mobile • Privacy and Security – Authentication – Authorization – Encryption: over-the-air security

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