Mobile Computing - Bnrg.cs.berkeley.edu - University of California

Mobile Computing - Bnrg.cs.berkeley.edu - University of California

23 Pages · 1996 · 608 KB · English

1. CS 294-7: Challenges of Mobile. Computing. Professor Randy H. Katz. Computer Science Division. University of California, Berkeley. Berkeley, CA 94720- 

Mobile Computing - Bnrg.cs.berkeley.edu - University of California free download


1 CS 294-7: Challenges of Mobile Computing Professor Randy H. Katz Computer Science Division University of California, Berkeley Berkeley, CA 94720-1776 ? 1996 2 Natural Evolution of Computing Single User OSBatchTimesharingNetworkingLANs + WSsMobile Computing Freedom from Collocation More Flexible Resource Usage 3 Research Issues in Mobile Computing ?Wireless Communications ?Quality of connectivity ?Bandwidth limitations ?Mobility ?Location transparency ?Location dependency ?Portability ?Power limitations ?Display, processing, storage limitations 4 Classes of Mobile Devices ?Display Only ?InfoPad model: limited portable processing ?Constrained to operation within prepared infrastructure, like a cordless phone ?Advantages with respect to power consumption, upgrade path, lightweight, impact of lost/broken/stolen device ?Laptop Computer ?Thinkpad model: significant portable processing, operates independently of wireless infrastructure ?Disadvantages: power consumption, expensive, significant loss exposure, typically greater than 5 pounds ?Personal Digital Assistant ?Somewhere between these extremes 5 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) 6 Wireless Communications ?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 7 Heterogeneous ?Wireless Overlay? NetworksIn-BuildingCampus-Area Packet Relay Metropolitan-Area Regional-Area Remote Clinics Emergency Dispatch Hospital Campus Hospital Operating Room Emergency Room 8 Wireless Communications Bandwidths and Latencies Contrast with 100 mbps Fast Ethernet or 155 mbps ATM Plus these bandwidths are SHARED among colocated users! Immediate future: 20 mbps wireless in-building (European HiperLAN) 64 kbps wide area (European GSM) InfoPad: 200 mbps CDMA radio/2 mbps per user Type of Network Bandwidth Latency Mobility Typ Video Performance Typ Audio Performance In-Building >> 1 Mbps Comm?l RF: 2 Mbps Research IR: 50 Mbps < 10 ms Pedestrian 2-Way ?ractive Full Frame Rate (Comp) High Quality 16-bit Samples 22 Khz Rate Campus-Area Packet Relay Network » 64 Kbps » 100 ms Pedestrian Med. Quality Slow Scan Med. Quality Reduced Rate Wide-Area 19.2 Kbps > 100 ms Vehicular Freeze Frame Asynchronous ?Voice Mail? Regional-Area (LEO/DBS/VSAT) 4.8 kbps?10+ Mbps (asymmetric) > 100 ms Vehicular Stationary Seconds/Frame Freeze Frame Asynchronous ?Voice Mail? 9 Wireless Communications ?Security Concerns ?Authentication is critical ?Normal network point of attachment is a wall

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