Computer Science Technical Report Archive

USC Computer Science Technical Reports, no. 675 (1998)

(USC DC Other)

USC Computer Science Technical Reports, no. 675 (1998)

PDF

Download a page range

Download transcript

Copy asset link

Request this asset

Transcript (if available)

Content Exp eriences with Usercongurable Lo cationa w are Sc heduling
USC TR John Heidemann Dha v al Shah
April
Abstract
Mobile computers often b enet from soft w are whic h
adapts to its lo cation F or example a computer migh t
b e bac k ed up when at the oce or the default prin ter
migh t alw a ys be a nearb y one In man y existing
systems lo cationtriggered actions are only possible
for sp ecic applications or with sp ecial infrastructure
This pap er describ es lcr on a system whic h supp orts
userc ongur able actions triggered on change in lo c a
tion or other ev en ts common to mobile computers W e
describ e the design implemen tation and our exp eri
ences with this system fo cusing on use of existing clues
for computer lo cation suc h as net w ork connection
and mapping of lo wlev el lo cation in to usersensible
terms
In tro duction
T odayman y computer users nd a single laptop com
puter more con v enien t than t w o computers at home
andatw ork F or laptop users do c king stations pro vide
a con v enien t w a y to adapt their computers to hea vy
or wired computing and hence lo cationsp ecic hard
w are Surprisingly though to da y there has b een v ery
little exp erience with softwar e whic h reacts to its lo ca
tion
Sp ecialized applications suc h as mail and prin ting
often include some lo cation a w areness p erhaps queue
ing messages or printjobs un til a net w ork or serv er b e comes a v ailable These serv ers are usually custom de
signed though and ma yha v e duplicativ e or limited de
tection mec hanisms and rarely supp ort userc ontr ol le d
detection and actions
Some researc hers ha v e examined at systems to re
The authors can be con tacted at Admiralt y W a y Marina del Rey CA or b y electronic mail to
fjohnhdha v alshgisiedu John Heidemanns w ork w as partially
funded under the VINT pro ject D ARPAgran t ABTC
and the LSAM pro ject D ARP A gran t JFBI
lax these constrain ts The Xero x P ar cT ab supp orted
a customizable con texta w are system as do es the
ORL Activ e Badge system Although inuen tial
in exploring these ideas these systems ha veseen rel
ativ ely little widespread deplo ymen t p ossibly b ecause
of the o v erhead of building and main taining the re
quired infrastructure A system whic h uses existing
infr astructur e for lo cation detection w ould be m uc h
easier to deplo y This pap er examines lcr on a system whic h addresses
eac h of these p oin ts Lcron allo ws soft w are congura
tion in resp onse to lo cation c hanges and other kinds
of ev en ts It supp orts easy user conguration based
on the existing cron mo del widely used in Unix and
recen tly a v ailable in Microsoft Windo ws with pac k ages
suc h as the Norton Program Sc heduler and Microsoft
System Agen ts In this sense lcron is an example
of an answ er to the question raised b y the Dataman
pro ject at Rutgers what if lo cation w ere a rstclass
op eratingsystem concept m uchas time is no w Finally it tak es adv an tage of in trinsic sources of lo
cation information in existing wired and wireless net
w orks W e b eliev e that there is substan tial b enet
to adding a notion of lo cation to usercongurable
sc heduling
Lo cation and ev en ta w are sc heduling simplies a
n umberofcommontasks Reminders can b e senttoa
user when a lo cation is reac hed feed the cat when y ou
get home Lo cationa w are queueing is easy prin t
this job when Im at w ork System defaults can
be up dated when a locationisreac hed prin ttothe
prin ter in ro om when Im at w ork Replicated or
cac hed data can b e refreshed when con v enien t bac k
up m y hard disk when I ha v e a go o d net w ork connec
tion
Although w e see lo cationa w areness as the primary
application for our w ork lo cation is actually one in
stance of more general event awar eness In addition to
lo cation laptop users often wish to resp ond to other
system ev en ts suchas po w er constrains p o w er is lo w

so sh ut do wn the wireless net w ork and dont scan for
viruses no w Other ev en ts ma y arise from the in
teraction of systems remind me to ask whats new
when I next meet a particular colleague Our system
generalizes to supp ort actions triggered from arbitrary
ev en ts suc h as these
The main con tribution of this pap er is a descrip
tion of ho w to determine the kinds of lo cation relev an t
to mobile users from widely a v ailable sources In the
examples ab o v e w ork home and fast net w ork
ma y not directly corresp ond to sources of geographic
lo cation suc h as GPS The triggeredev en t mo del w e
describ e is actually more general supp orting actions
triggered on arbitrary ev en ts suc h as curren t po w er
status Finallyw e describ e our exp eriences using this
to ol
Using Lo cation Information
T o understand the requiremen ts of lcron this section
considers what tasks migh t b e simplied if they w ere
triggered based on lo cation and other ev en ts F rom
these tasks w e generalize what kinds of lo cation are
imp ortan t to users
In the in tro duction w e iden tied a n um ber of user
tasks that w ould b enet from lo cation information W e
b eliev e that man y of the tasks whic h w ould b enet
from lo cation a w areness require a m uc h more rened
denition of lo cation than simple ph ysical lo cation as
pro vided b y GPS T able breaks these examples in to
sev eral classes Although some tasks dep end on ph ysi
cal lo cation man y tasks dep end on hardw are or some
external computing capabilit y Other tasks should o c cur on when another user or other mo ving ob ject hap
pens to be presen t Finally across eac h of these cate
gories a task could dep end onaspecic or a generic
resource
Some examples mak e these dimensions clearer F or
a generic ph ysical lo cation one migh t w antto be re
minded to drop o a shirt when one is near the next
dry cleaners where an y cleaners is acceptable Later
one mightw anttobe reminded to pic k that shirt up
when near that particular cleaners
In to da ys mobile computing en vironmen t lo cation
a w are tasks are often hardw are or device sp ecic
Prin ting is one example Net w ork access to replicate
or bac k up data or send mail are common examples
Again these examples ma y be sp ecic bac kup m y
computer when connected b y a highsp eed net w ork to
our compan ys bac kup serv er or generic send mail
when next connected to the In ternet
Some ma y argue that ubiquitous wireless net w ork
ing ma y eliminate this class of jobs Wh y queue mail
if y oure alw a ys connected to the net w ork Although
w e b eliev e that connectivit y will reduce these needs
cost and esp ecially p o w er constrain ts ma y limit use of
otherwise a v ailable net w orking
Lcron is most useful for systems whic h connect to
sev eral dieren t net w orks but it is also useful for con
nection and disconnection to a single net w ork Detec
tion of net w ork reconnection can be used to trigger
ev en ts suc h as sending queued mail or sync hronization
of a disconnected le system Finally although w e ha v e fo cused on lo cation
a w are job sc heduling other ev en ts map w ell in to
the lcron mo del F or example computers often do
p erio dic housek eeping defragmen ting a disk c hec k
ing for viruses indexing mail on a p ossibly po w er
constrained laptop these tasks are b est sc heduled when
not running on battery po w er when at the A C
po w ered virtual lo cation W e are curren tly in v esti
gating ho w general an ev en t mo del is useful for lcron
System Lo cation
The rst step in lo cationa w areness is iden tifying
sources of lo cation information This section con
siders three p oten tial sources of lo cation information
the global p ositioning satellite GPS net w ork ph ysi
cal net w ork conditions and rep orts of basestations in
wireless net w orks
GPS receiv ers pro vide an ob vious source of lo cation
information With recen t price reductions at the time
of writing US receiv ers are not uncommon
GPS receiv ers seem increasingly attractiv e GPS re
ceiv ers w ork in most op en areas but they ha v e limited
use in buildings or other areas of limited reception
Unfortunatelypo w er consumption and an tenna space
maybe incon v enien t for some p ortable computer users
Also GPS accuracy is b oth a help and a hindrance On
one hand GPS lo cations are to o detailed for direct use
Howman y p eople kno w the latitude and longitude of
their oce On the other hand curren t accuracy of
GPS receiv ers is not sucien t to place a user in the
ro om of a building without additional pro cessing
F or computers whic h are frequen tly net w ork ed the
wired net w ork infrastructure itself can pro vide lo ca
tion information P ortable computers ma y b e assigned
dieren t IP addresses and routers or dieren tmobile
IP addresses dep ending on where they are By
monitoring the net w ork attac hmentw e can determine
where the computer is The opp osite of GPS accu
racy net w orks attac hmentonly v aguely sp ecify ph ys
ical lo cation somewhere a giv en Ethernet segmen t

constrain t uniqueness example
ph ysical lo cation sp ecic remind me to get shirts at the cleaners
ph ysical lo cation generic what will the w eather b e here tomorro w
device sp ecic prin t this do cumen t to the prin ter with m y letterhead
device generic send this message when connected to a net w ork
other users sp ecic remind me when I see a particular p erson
other users generic send the next meetings agenda to ev eryone inthisroom
other ev en ts scan for viruses when not running on battery p o w er
T able Sev eral classes of lo cationa w are tasks
Ho w ev er if lo cationdep enden t jobs often require the
net w ork for example computer bac kup net w ork at
tac hmen t ma y be more relev an t than GPSmeasured
ph ysical lo cation
Wireless net w orking to o can pro vide lo cation infor
mation Most wireless proto cols supp ort m ultiple base
stations or cells If these systems kno w their ph ysical
lo cation and can rep ort it to the system then b oth
net w ork connectivityand ph ysical lo cation can b e de
termined
One imp ortan t implemen tation issue mo derates lo
cation detection First although one w ould liketode tect lo cation c hanges exactly in some circumstances
polling is required Sometimes c hangeinlo cation is
imp ossible to detect at the device lev el for example
with GPS where the data is con tin uous There ma y
b e no driv er supp ort to trigger cron when a lo cation is
c hanged In these cases wem ust p oll lo cation p erio di
cally p ossibly using battery unnecessarily F ortunately
it is often p ossible to trigger cron only when lo cation
c hanges F or example PCCard insertion ev en ts corre
sp ond with net w ork c hanges
Mapping F rom System to
User Lo cation
Although weha veiden tied a n um ber of w a ys a sys
tem will directly measure lo cation these approac hes
are often to o lo wlev el for t ypical users W e believ e
that one k ey to useful lo cationa w areness is a mapping
from lo w to userlev el information m uc h as the do
main name system maps from bit IP addresses to
h umanfriendly hostnames
As examples of this mapping consider GPS and net
w ork lo cation GPS receiv ers rep ort latitude and lon
gitude Because of measuremen t accuracy a user m ust
sp ecify within m of this latlon instead of at
this latlon F or man y latlon are as dicult to man
age as IP addresses so another lev el of mapping should
allo w at ISI or near USC rather than within m
of N W Similar examples apply to
net w ork lo cation F ew users remem b er what net w ork
segmen t or router they use but on the net w ork I use
at USC is ob vious
Although highlev el mappings simplify lo cation de
scription it is also imp ortan t to matc h lo cation de
scription to the task mix A t ISI could mean when
connected to the highsp eed ISI net w ork to do bac k
ups when connected to anyISI net w ork to prin ta
do cumen t or when ph ysically near ISI to send a re
minder message A exible mapping mec hanism can
mak e these distinctions visible W e b eliev e a larger
userbase is required to understand ho w imp ortan t
these distinctions are
Lcron Implemen tation
This section summarizes sev eral asp ects of lcron im
plemen tation including ho w lo cation is sp ecied and
howc hanges are detected
Base cron
Lcron is implemen ted as a mo dication of an exist
ing cron implemen tation and sev eral help er programs
W e based lcron on Geo Kuennings implemen tation
xcr on ! Although other freely a v ailable cron imple
men tations are more widely used xcron had sev eral
features imp ortan t to us for mobile use Xcron is a w are
that computers ma y b e turned o or susp ended it op
tionally runs jobs sc heduled during do wntime when
the system next starts Xcron also includes in tegrated
supp ort for dela y ed oneshot jobs at jobs simpli
fying supp ort for lo cationa w are at services Finally xcron supp orts b oth the traditional cron tab format
table driv en with one column per eld and a new er
format without strict columns The new er format uses
con text to to in terpret the time sp ecication so means to run at am daily
m nethome setdefaultprinter homelp
nethome fetchmail
m network setdefaultprinter psdd
network fetchmail
m network fetchmail
m powerac network backupdisk
Figure A sample cron tab sp ecication with
lo cationsp ecic commands Unlik e standard
Unix cron lcrons rst eld is list of ags defaulted
elds ma y be omitted and the " eld sp ecies lo ca
tion constrain ts
Sp ecifying lo cation
Easy user conguration of ev en ttriggered actions is
a goal of lcron W e accomplish this b y adding an
ev en t eld to the existing cron tab le format A
users cron tab le lists the commands that are to be
executed on users b ehalf at sp ecied times on sp eci
ed dates The new eld sp ecies that ev en ts should
be executed when a particular lo cation is reac hed or
a particular ev en t o ccurs Actions can b e triggered ei
ther p erio dically when at a lo cation or only when that
lo cation is rst reac hed
A sample cron tab with lo cationtriggered jobs ap
pears in Figure The optional lo cation eld b egins
with the " sign In this example w e fetc h mail times a da y when at home but ev ery min utes when
at w ork and when w e rst connect to the w ork net w ork
W e set the default prin ter to v ary dep ending on where
w e are the m ag and lac k of a time sp ecication
indicate that this action is triggered once eac h time
that lo cation is reac hed Finally when w e connect to
the w ork net w ork and are p o w ered w e run a program
to bac k up the p ortable computer
Our implemen tation allo ws lo cation sp ecications
to be regular expressions matc hing sev eral possible
places W e plan to supp ort m ultiple lo cations as in
the when p o w ered at w ork example to allo w logical
ands w eha v e not y et implemen ted this facilit y Lo cation sources and detection
Our primary source of lo cation information is net
w ork connectivit y W e examined GPS receiv ers as an
additional source of information but most lo cation
a w are applications w e w an ted to sc hedule dep ended
on net w ork connectivit y so GPS receiv er cost size
and po w er requiremen ts limited its use W e ha v e
also planned mapping battery p o w er in to nonlo cation
ev en ts but ha venot y et done so
T o sense net w ork lo cation w e measure what net w orks
are curren tly congured and map either the gatew a y
host or the net w ork IP address and mask to a user
sensible lo cation as describ ed in the next section
Curren tly w e sense net w ork attac hmen ts with the net
stat rn command
W e can detect lo cation c hanges b oth b y p ol ling and
trigger e d notic ation T o implemen t p olling a non
lo cationsp ecic cron job periodically c hec ks the sys
tems lo cation noticing and acting an yc hanges The
polling in terv al can b e selected to tradeo resp onsiv e
ness and o v erhead b y default wepoll ev ery min utes
P olling is required for ev en ts whic h are con tin uous in
v alue suc h as GPS data and battery p o w er
T riggered notication a v oids the dela y and constan t
if lo w o v erhead of p olling W e use triggering as our
primary means of detecting discrete lo cations W e de
tect c hange to net w ork connectivit y with a oneline ad
dition to the PCCard and PPPconguration scripts
that are used with our system This line informs cron
of lo cation c hange after a new net w ork is initiated
Mapping from system to user
In addition to what actions are triggered based on
ev en ts ho w lo cation is dened should b e user cong
urable As discussed in Section systemmeasured
kinds of lo cation arent alw a ys appropriate for direct
user consumption Lcron therefore emplo ys a mapping
function from system to user lo cations
W e implemen t this mapping as a short P erl program
whic h lters ra w lo cations in to usersensible ones W e
c hose to implemen t mapping as program rather than
through a table to increase exibilit y Net w orks migh t
map gatew a y names in to lo cations while GPS data
migh t b e mapp ed based on ph ysical pro ximit y or more
detailed top ological understanding
Since mapping is userdep enden tw e plan on a sim
ple to ol whic h asso ciates the curren t system lo cation
based on one or more lo wlev el criteria with a user
lo cation This to ol w ould mo dify the mapping pro
gram adding st ylized co de Since this to ol is not y et
implemen ted wecurren tly add mappings byhand Fig
ure sho ws an example of curren t mapping co de Al
though this example maps only gatew a y information
to usersensible lo cation it could also aggregate m ulti
ple gatew a ys to a single lo cation or map one gatew a y
to sev eral logical lo cations as in the rst example
Similar mapping scripts are p ossible for other kinds of
ev en ts

usrlocalbinperl
openSTDIN netstat rn die netstat failuren
myf heads
while f split
parse headers to be portable across different netstats
if f desti foreach f headslcf! !
next
!
The next lines map gateway to multiple logical locations
print netisinnetisiwiredn if fheads"gateway"! eq "#$"
print netisinetwavennetisiwi rele ssn if fheads"gateway"! eq "##"
The remaining map onetoone
print netuscn if fheads"gateway"! eq "##%"
print nethomen if fheads"gateway"! eq "#"
print netpppn if fheads"gateway"! eq "#"
!
Figure A sample lo cation mapping program After initial pro cessing the net w ork gatew a y eld is mapp ed
to a usersensible lo cation
Exp eriences using lcron
Lcron has b een used b y a few researc hers at ISI since
Jan uary Our users ha v e dieren t lev els of net
w ork connectivit y A t the lo wend one users laptop is
either connected or disconnected to a single net w ork
A t the other end one user regularly uses four net
w orks in three dieren t ph ysical lo cations ISI USC
and home This section briey describ es our exp eri
ences dev eloping and using lcron
User en vironmen t
In Section w e describ ed and classied a n um ber of
lo cationdep enden t tasks W e ha v e considered lcron
for four classes of da ytoda y tasks
File replication and email transfer
Conguration of system en vironmen t
Alarm service
Aweakformofuserin terface telep orting
W e curren tly use lcron for rst three tasks on a daily
bases Weha v e exp erimen ted with userin terface tele
p orting automatically bringing up a copyofrunning
applications on a nearb y displa y but some further de
v elopmen t is still required
None of these applications are new le
replication automatic system congura
tion lo cationsp ecic alarms and
telep orting ha v e b een exp erimen ted with b efore
The adv an tage of lcron is that no w these applications
can b e casually deplo y ed b y users without substan tial
existing infrastructure
A common and eectiv e use of lcron is for le replica
tion and email transfer Since email is often timely it
is helpful to immediately send or fetc h queued messages
up on connection In addition p erio dic email retriev al
is easily congurable with lcron Usercustomization
is helpful here the imp ortance of timely email deliv
ery can b e w eighed against battery constrain ts when
connected b y a wireless net w ork and tolls when con
nected from home via a metered service This lev el of
conguration w ould b e dicult or imp ossible with the
simpler retriev al mo dels of most t ypical email pac k
ages
File replication p oses similar problems Automatic
le bac kup is imp ortan t to a safe en vironmen t Lcron
triggers this bac kup p erio dically when connected to a
fast net w ork
In b oth cases of email and le bac kup w e had pre
viously emplo y ed customized systems of p olling T o
a v oid draining laptop po w er w e previously p olled for
the laptop from a serv er mac hine Although feasible
this system w as not easy to c hange and required con
guration on m ultiple mac hines Replacing this system

with lcron simplied conguration and concen trated it
on the laptop under user con trol As a result of these
simplications w e automated case that b efore w ere not
considered imp ortan t enough to deplo y Examples of lo cationdep enden t system congura
tion are selecting a default prin ter and telephone di
aling W e wrote a small program whic h c hanges the
denition a particular prin ter en try when the laptop
arriv es at a new lo cation Users can th us set their de
fault prin ter to the prin ter called nearest to prin ttoa
lo cationdep enden tnearb y prin ter Similarly dieren t
lo cations ha v e dieren t con text for telephone dialing
area co des handling of extensions and telephone in
terface Our telephone autodialer supp orts these op
tions lcron allo ws us to automatically select b et w een
them as w e do for prin ters Other lo cationdep enden t
tasks similar to these can b e completed automatically
using lcron
A third example application w e exp erimen ted with is
a lo cationbased notication service Users can record
reminder messages whic h are repla y ed when a giv en
lo cation or time is reac hed Although w e ha v e found
this service v ery useful for timedep enden t messages
lo cationdep enden t message are curren tly v ery limited
b y our lac k of lo cationa w areness in the at program
W e are curren tly w orking to remo v e this limitation
W e also exp erimen ted with telep orting in lcron
T elep orting is the idea that a users existing applica
tions should mo v e transparen tly to the nearest most
capable display Although weha v e not deplo y ed a
full telep orting system suc h as has b een used at ORL
weha v e exp erimen ted with a w eak er form where new
sessions of a set of applications are automatically b e gunonanearb y displaywhen a net w ork connection is
made Although main taining application state w ould
b e desirable there is considerable v alue in simply ha v
ing new instances of the correct applications set up
F rom our exp erimen ts with lcron the primary ben et is the automation of da ytoda y tasks that w ere
dicult or not w arran ted b eforehand In some cases
of email retriev al lcron replaced man ual requests In
others it replaced older less capable and more com
plicated retriev al mec hanisms based on application
sp ecic p olling Finally the simplicit y of lcron con
guration supp orted additional uses Prior arrange
men ts required conguration on m ultiple mac hines to
a v oid p olling from the p o w erconstrained laptop lcron
simplied conguration b y allo wing all conguration
to tak e place on the laptop
Dev elopmen t en vironmen t
Lcron w as dev elop ed under SunOS and Lin ux Based
on xcron it inherits that systems p ortabilit y Small c hanges to the base op erating systems net
w ork conguration scripts allo w lcron to a v oid p olling
W e made lines of mo dication to RedHat Lin uxs
PCCard and PPP scripts
W e found one hardw are limitation w e detect net
w ork conguration based on PCCard insertion and re
mo v al One laptop included a builtin Ethernet adap
tor that lac k ed these ev en ts P olling the net w ork for
carrier can w ork around this problem another ap
proachw ould b e to mo dify the net w ork driv er to allo w
an application to blo ckun til c hange in carrier
Our exp eriences with lcron dev elopmen t suggest that
it should b e easily p ortable to other v ersions of Unix
P erio dic polling p erhaps at min ute in terv als can
b e used to detect net w ork c hange but w e exp ect that
direct detection with small c hanges will often b e a p os
sible optimization
Related w ork
Lcron builds on three areas of related w ork First
groups suc h as the Dataman pro ject Xero xP AR C and
and the Oliv etti and Oracle ResearchLab ha velook ed
at general w a ys lo cation a w areness c hanges system b e ha vior Second a n umberofgroups ha velook ed at ho w
to mo dify actions to consider lo cation information Fi
nally sev eral sp ecial purp ose systems ha v e dev elop ed
custom approac hes to w atc h for lo cation c hanges
Our w ork w as inspired b y the Dataman pro jects
question of ho ww ould system soft w are c hange if lo
cation w ere a rstclass op eratingsystem concept The Dataman pro ject has lo ok ed at ho w mobilityaf fects net w ork transp ort mobile IP and m ulticast ge
ographic messaging W e apply their prop osition in a
v ery real sense b y considering the use of lo cation in
existing approac hes to task sc heduling
Xero x P AR Cs w ork in ubiquitous computing through systems suc h as the P ar cT ab pioneered
lo cationa w are computing Their w ork in con text
a w are computing describ ed systems similar in function
to lcron Lcron builds up on this w ork b y de
scribing howm ultiple commonly a v ailable of lo cation
information suc h as net w ork connections and GPS in
formation can b e mapp ed to userrelev an t lo cations
Sc hilit Adams and W an t classify con texta w are
computing along t w o axes see Figure from
based on whether the task at hand is p erforming infor
mation retriev al or command execution and whether
!
man ual automatic
information pro ximate selectioncon textual info auto con textual recong
command con textual commands con textualtriggered actions
T able Sc hilit Adams and W an ts classication of con texta w are computing from it is done man ually or automatically By this clas
sication lcron is automatic not man ual and sup
ports commands not information th us falling in to
the con texttriggered actions quadran t Ho w ev er w e
ha vesho ws ho w con texttriggered actions in lcron allo w
us to implemen t allo w us to implemen t con textual com
mands for example prin ting to the nearest prin ter
and automatic con textual reconguration for exam
ple b y automatically replicating data th us pro viding
some supp ort for some kinds of con texta w are appli
cations whic h are not directly supp orted W e believ e
that the nal quadran t man ual information retriev al
is b est solv ed with other w ork suchas locationa w are
w ebbro wsers Lo cation dep enden t information suc h as nearest
restauran t a v ailabilit y of space in the nearest parking
lot or lo cal w eather information can b est b e retriev ed
ondemand basis b y lo cationa w are w ebbro wsers On
the con trary lcron mainly targets those lo cation dep en
den t tasks whose timely execution on lo cation c hange is
imp ortan t for prop er functioning of the system Ho w
ev er lcron could also b e used for automatic information
retriev al bysc heduling a information retriev al task to
be executed at dieren t lo cations Lcron th us giv es
users explicit con trol o v er the nature and con ten ts of
lo cationdep enden t information to b e retriev ed in con
trast to the limited set of information a v ailable to the
lo cationa w are w eb bro wser users
F uture w ork
There are sev eral directions for future w ork Our pri
mary sources of lo cation come from net w ork attac h
men ts additional exp erience with other sources w ould
be helpful Exp osing the cells of a cellular net w ork
migh t be attractiv e since that information is already
a v ailable Wider use of GPS information w ould also
b e useful
Impro v emen ts in mapping arbitrary ev en ts in to lcron
w ould also b e helpful W e are curren tly dev eloping and
exp erimen ting with mapping c hanges in po w er con
sumption to ev en ts More exp erience here w ould be
helpful
Curren tly lcron fo cuses on one v ariable what hap
p ens as the system c hanges state bymo ving around or
losing po w er Some lo cationa w are applications ha v e
more sophisticated requiremen ts F or example re
minders triggered when t w o p eople are colo cated as
sumes m ultiple mo ving ob jects W ork in activ e badges
suggests that these kinds of in teractions can be pro
vided b y p erio dically broadcasting presence informa
tion to the lo cal area Renemen t of this idea in lcron
remains future w ork
Lcron curren tly uses a tabledriv en approac h to sp ec
ify ev en t triggers This tabular approac h is easy for
users but can limit sp ecication exibilit y F or exam
ple its easy to tak e actions at particular times if con
nected but not easy to sc hedule a job at a connection
and then at regular in terv als after that time Whether
the limitations of this fairly rigid structure is a problem
in man y situations remains to b e seen Wew ork around
this example with hourly p olling through a help er pro
gram P ossibly a b etter solution is to sp ecify ev en ts
triggers through a programming language as w emap
from system to user lo cations and to use a fron tend
to construct program statemen ts for simple cases
Conclusions
W e ha v e describ ed lcron a system supp orting user
congurable actions in resp onse to lo cation and ev en t
triggers Ak ey feature of lcron is that it uses net w ork
information common to the existing wired and wire
less infrastructure to appro ximate lo cation and that
lo wlev el sources of lo cation and ev en ts are mapp ed
to usersensible terms through a congurable pro cess
Our exp eriences with lcron suggest that it ac hiev es its
aim of making these actions easy to use and that easy
userconguration allo ws m uc h broader automation of
lo cationtriggered actions than more static system
Ac kno wledgmen ts
The authors thank Geo Kuenning for use of the xcron
source co de discussions of lcronrelated issues and
a careful review of this pap er W e w ould also lik e
to thank Ramesh Go vindan and Joseph Bannister for
careful readings of the pap er

Soft w are Av ailabilit y
Weplantomak e the soft w are dev elop ed as part of this
pap er publicly a v ailable Please con tact the authors for
curren t status
References
Arup Ac hary a B R Badrinath T omasz Imielin
ski and Julio C Na v as A WWWbased lo cation
dep enden t information service for mobile clien ts
A t h ttpwwwcsrutgersedu na v asdataman
pap erslo c dep mosaicOv erviewh tml July
Mic Bo wman Larry L P eterson and Andrey
Y eatts Univ ers An attributebased name serv er
Softwar ePr actic e and Exp erienc e April John S Heidemann Thomas W P age Jr Ric h
ard G Guy and Gerald J P op ek Primarily dis
connected op eration Exp eriences with Ficus In
Pr o c e e dings of the Se c ond Workshop on Manage
ment of R eplic atedData pages Univ ersityof
California Los Angeles IEEE No v em ber T omasz Imielinski and B R Badrinath Wireless
mobile computing Challenges in data manage
men t Communic ations of the A CM
Octob er James J Kistler and Mahadev Sat y anara y anan
Disconnected op eration in the Co da le sys
tem A CM T r ansactions on Computer Systems ! Geo Kuenning Exp eriences with an extended
cron daemon Unpublished man uscript No v em ber
C P erkins IP mobilit y supp ort RF C In
ternet Request F or Commen ts Octob er !
T ristan Ric hardson F razer Bennett Glenford
Mapp and Andy Hopp er T elep orting in an x win
do w system en vironmen t IEEE Personal Com
munic ations Magazine ! July B Sc hilit N Adams and R W an t Con text
a w are computing applications In Pr o c e e dings of
the Workshop on Mobile Computing Systems and
Applic ations pages San ta Cruz CA USA
Decem b er IEEE
Bill Sc hilit Marvin Theimer and Bren t W elc h
Customizing mobile applications In Pr o c e e d
ings of the USENIX Symp osium on Mobile and
L o c ationIndep endent Computing pages
Cam bridge MA USA August USENIX
Georey M V o elk er and Brian N Bershad Mo
bisaic An information system for a mobile wire
less computing en vironmen t In Pr o c e e dings of the
Workshop on Mobile Computing Systems and Ap
plic ations pages San ta Cruz CA USA
Decem b er IEEE
Ro y W an t Andy Hopp er V eronica F alcao and
Jonathon Gibb ons The activ e badge lo cation sys
tem A CM T r ansactions on Information Systems Jan uary Ro y W an t Bill N Sc hilit Norman I Adams
Ric h Gold Karin P etersen Da vid Goldb erg
John R Ellis and Mark W eiser An o v erview
of the P ar cT ab ubiquitous computing exp eri
men t IEEE Personal Communic ations Magazine ! Decem b er
Mark W eiser Some computer science problems
in ubiquitous computing Communic ations of the
A CM ! July

Abstract (if available)

Linked assets

Computer Science Technical Report Archive

Conceptually similar

PDF

USC Computer Science Technical Reports, no. 677 (1998)

PDF

USC Computer Science Technical Reports, no. 688 (1998)

PDF

USC Computer Science Technical Reports, no. 687 (1998)

PDF

USC Computer Science Technical Reports, no. 667 (1998)

PDF

USC Computer Science Technical Reports, no. 695 (1999)

PDF

USC Computer Science Technical Reports, no. 876 (2006)

PDF

USC Computer Science Technical Reports, no. 645 (1997)

PDF

USC Computer Science Technical Reports, no. 692 (1999)

PDF

USC Computer Science Technical Reports, no. 764 (2002)

PDF

USC Computer Science Technical Reports, no. 827 (2004)

PDF

USC Computer Science Technical Reports, no. 699 (1999)

PDF

USC Computer Science Technical Reports, no. 788 (2003)

PDF

USC Computer Science Technical Reports, no. 968 (2016)

PDF

USC Computer Science Technical Reports, no. 682 (1998)

PDF

USC Computer Science Technical Reports, no. 681 (1998)

PDF

USC Computer Science Technical Reports, no. 548 (1993)

PDF

USC Computer Science Technical Reports, no. 661 (1997)

PDF

USC Computer Science Technical Reports, no. 660 (1997)

PDF

USC Computer Science Technical Reports, no. 686 (1998)

PDF

USC Computer Science Technical Reports, no. 646 (1997)

Description

John Heidemann and Dhaval Shah. "Experiences with user-configurable location-aware scheduling." Computer Science Technical Reports (Los Angeles, California, USA: University of Southern California. Department of Computer Science) no. 675 (1998).

Asset Metadata

Creator Heidemann, John (author), Shah, Dhaval (author)

Core Title USC Computer Science Technical Reports, no. 675 (1998)

Alternative Title Experiences with user-configurable location-aware scheduling (title)

Publisher Department of Computer Science,USC Viterbi School of Engineering, University of Southern California, 3650 McClintock Avenue, Los Angeles, California, 90089, USA (publisher)

Tag OAI-PMH Harvest

Format 8 pages (extent), technical reports (aat)

Language English

Unique identifier UC16271007

Identifier 98-675 Experiences with User-configurable Location-aware Scheduling (filename)

Legacy Identifier usc-cstr-98-675

Format 8 pages (extent),technical reports (aat)

Rights Department of Computer Science (University of Southern California) and the author(s).

Internet Media Type application/pdf

Source 20180426-rozan-cstechreports-shoaf (batch), Computer Science Technical Report Archive (collection), University of Southern California. Department of Computer Science. Technical Reports (series)

Access Conditions The author(s) retain rights to their work according to U.S. copyright law. Electronic access is being provided by the USC Libraries, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright.

Repository Name USC Viterbi School of Engineering Department of Computer Science

Repository Location Department of Computer Science. USC Viterbi School of Engineering. Los Angeles\, CA\, 90089

Repository Email csdept@usc.edu

Inherited Values

Title Computer Science Technical Report Archive

Coverage Temporal 1991/2017

Repository Email csdept@usc.edu

Repository Name USC Viterbi School of Engineering Department of Computer Science

Repository Location Department of Computer Science. USC Viterbi School of Engineering. Los Angeles\, CA\, 90089

Publisher Department of Computer Science,USC Viterbi School of Engineering, University of Southern California, 3650 McClintock Avenue, Los Angeles, California, 90089, USA (publisher)