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Title

テクチャに関する研究

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for mobile computing environment

Hiroki Morikawa

Scho ol of Information Science,

Japan Advanced Institute of Science and Technology

February 15, 1999

Keywords: Mobile Computing, Network,System Software.

Recently, network connectivity has been wide by developping network technology.

Carriyng a computer has been possible by developping p ortable computer(ex. PDA,

note bo ok computer), that made possib e to use computers in place of movement where

not only inside such as a laboratory but outside. PC Card Interfaces (Formerly called

PCMCIA interface)are widely used inp ortable computers sothat the conguration of a

mobile computer can be dynamically changed by replacing such devices while executing

applications. ByusingthesetechnologysuchasportablecomputersandPCCards,ithas

been possible toconnecttonetworkatany timefromeverywhereand touseservices and

resorces onnetwork and computing powercontain other computers.

In such environment called a mobile computing environment, a case that must dy-

namicallychangethenetworkmediaandselectab estnetworkmediainmanymediaswill

happen. The new network media which had been made for mobile computing environ-

mentsuchaswirelessLAN andPIAFShavedierentcharacteristicfromcurrentnetwork

media. Because of this, performance of communication may be declineextremely.

Moving computers and changing network medias cause changing IP address. Comu-

nication with other computers can not be possible if IP address changes. In current

network system IP address is assigned for network media, so changing network media

causes changing IP address. And movementcauses changing IP address, too.

For improving these problems, new network protocols such as IETF Mobile IP and

SONY CSL VIP are suggested. These methods oerhost migration transparency. IETF

Mobile IP makes p ossible to move computers by using servers called home agent and

foreign agent on network. IP address of mobile computer is used not identier of con-

necting point to network but identier of that computer. It makes p ossible to identify

the computernotdependingtoconnectingp ointofnetwork. Butcurrentsystemsoftware

Copyright c

1999byHirokiMorikawa

Compared with this method, VIP separateconnecting point of network and identier of

computer by separating network layer to two layers. Also VIP use propagating cache

methodthatcan makeroutingbest. Thesemethodcanoerhostmigrationtransparency

andconnectnetworkifcomputermoves,butcharacteristicofcurrentmediathatcomputer

is using maycause declineof communicationperformance.

Inthisresearch,wefoucusfourproblemsofmobilecomputingenvironmentandsuggest

JAIST Mobile IP that realize exible mobile computing environment by solving these

problems as following.

corresponding of various network media

lackof denite identier of computers

timingof changing networkmedia

changeof communicationcharacteristicby changing networkmedia

JAIST Mobile IP have some organizationsas follow,

easy change of network media by oering virtual network media

Virtualnetworkmediaconcealthedierenceofcharacteristicbetweennetwork

mediasuchas Ethernet orPPP by abstractinterface. By this network media

arechangedindep endentlyfromprotocolstackandchangingnetworkmediais

maskedfromhigher layer.

oer of denite identier of computers

Identier of connecting p oint to network and identier of that computer are

separatedbyassign homeaddress ofIETF Mobile IP tovirtualnetworkinter-

faceand assign IP address invisited networkmedia that manage.

smooth change of network media by hand-o controller

Hand-o controller that can select adapt network media by information from

environmentserverisplaced. Environmentserverisdatabasethathasresource

informationsincomputerandoerstheseinformationtoapplication. Hand-o

controllermakesp ossibletochangenetworkmediasmoothlybetweenwireand

wirelessmedia.

adapt to characteristic of network media by snooper

Foreign agent in IETF Mobile IP extend. It is called proxy agent. Proxy

agent has sno oper that makes possible adaptive communication with mobile

computer and function of foreign agent. Mobile computer also has snooper.

Bycorrespondingboth of snoopersinproxyagentand mobilecomputer,com-

municationthat adaptcharacteristicof currentnetwork mediaused bymobile

computerbecomespossible.

JAISTMobile IP asaframe workfor realizeexible mobilecomputingenvironment. We

discuss the useful of this system by comparing with other systems about functions, and

discuss the p erformance of this system by comparing communication performance with

Mobile IP built in CMU.