SQME OMPUT R SC|ENGG ISSUES IN m U biquitous computing enhances computer use by making many com puters available throughout the physical environment, while making them effectively invisible to the user. This article explains what is new and different about the com puter science involved i n ubiquitous computing. First, it provides a brief overview of ubiquitous computing, then elaborates through a series of examples drawn from various subdisciplines of com puter science: hardware com- ponents (e.g., chips), network protocols, interaction substrates (e.g., software for screens and pens), applications, privacy, and computational methods. Ubiquitous computing offers a framework for new and exciting research across the spectrum of computer science. Since we started this work at Xerox Palo Alto Research Center (PARC) in 1988 a few places have begun work on this possible next-generation computing environment in which each person is continually interacting with hundre ds of nearby wirelessly interconnected computers. The goal is to achieve the most effective kind of technology, that w hich is essentially invisible to the user. To bring computers to this point while retaining their power will require radically new kinds of com- puters of all sizes and shapes to be available to each person. I call this future world "Ubiquitous Computing" (Ubicomp) [27]. The research method for ubiquitous computing is stan- dard experimental computer science: the construction of wo rking prototypes of the necessai -y infrastructure in sufficient quantity to debug the viability of the systems in everyday use; ourselves and a few colleagues serving as guinea pigs. This is Reprinted with permission. Copyright c) 1993 by The A ssociati on or Computi ng Machinery, n c. All rights reserved. T his article ori ginally ap- peared in Comm unicati ons f the ACM , Vol. 36, No. 7 (July 1993), Pages 75-84. 12 Mobile Computing and Communications Review, Volume 3, Number 3
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8/8/2019 Weiser-Etal_2007_Some Computer Science Issues in Ubiquitous Computing
U b i q u i t o u s c o m p u t i n g e n h a n c e s c o m p u t e r u s e b y
m a k i n g m a n y c o m p u t e r s a v a il a bl e t h r o u g h o u t t h e
p h y s i c a l e n v i r o n m e n t , w h i l e m a k i n g t h e m e f fe c t iv e l y i n v is i b le
t o t h e u s e r. T h i s a r t ic l e e x p l a i n s w h a t i s n e w a n d d i f f e r e n t
a b o u t t h e c o m p u t e r s c ie n c e in v o lv e d in u b i q u i t o u s c o m p u t i n g .
F i rs t, i t p r o v i d e s a b r i e f o v e r v i e w o f u b i q u i t o u s c o m p u t i n g ,
t h e n e l a b o r a t e s t h r o u g h a s e ri e s o f e x a m p l e s d r a w n f r o m
v a r i o u s s u b d i s c ip l i n e s o f c o m p u t e r s c i en c e : h a r d w a r e c o m -
p o n e n t s ( e .g . , c h i p s ) , n e t w o r k p r o t o c o l s , i n t e r a c t i o n s u b s t r a t e s
( e . g . , s o f t w a r e f o r s c r e e n s a n d p e n s ) , a p p l i c a t i o n s , p r i v a c y ,
a n d c o m p u t a t i o n a l m e t h o d s . U b i q u i t o u s c o m p u t i n g o ff er s a
f r a m e w o r k f o r n e w a n d e x c i t i n g r e s e a r c h a c r o s s t h e s p e c t r u m
o f c o m p u t e r s c ie n c e.
S i n c e w e s t a r t e d t h i s w o r k a t X e r o x P a l o A l t o R e s e a r c h
C e n t e r ( P A R C ) i n 1 98 8 a f e w p l a c e s h a v e b e g u n w o r k o n t h is
p o s s i b l e n e x t - g e n e r a t i o n c o m p u t i n g e n v i r o n m e n t i n w h i c h
e a c h p e r s o n is c o n ti n u a l ly i n t e r a c t i n g w i t h h u n d r e d s o f n e a r b yw i r e l es s ly i n t e r c o n n e c t e d c o m p u t e r s . T h e g o a l i s t o a c h i e v e t h e
m o s t e f f e c t iv e k i n d o f t e c h n o l o g y , t h a t w h i c h i s e s s e n t i a l l y
i n v i s i b l e t o t h e u s e r . T o b r i n g c o m p u t e r s t o t h i s p o i n t w h i l e
r e t a i n i n g t h e i r p o w e r w i l l r e q u i r e r a d i c a l l y n e w k i n d s o f c o m -
p u t e r s o f a l l s iz e s a n d s h a p e s t o b e a v a i l a b l e to e a c h p e r s o n . I
c al l t h is f u t u r e w o r l d " U b i q u i t o u s C o m p u t i n g " ( U b i c o m p )
[ 27 ]. T h e r e s e a r c h m e t h o d f o r u b i q u i t o u s c o m p u t i n g i s s t a n -
d a r d e x p e r i m e n t a l c o m p u t e r s c i e n c e : t h e c o n s t r u c t i o n o f
w o r k i n g p r o t o t y p e s o f t h e n e c e ss a i- y i n f r a s t r u c t u r e i n s u f f i c ie n t
q u a n t i t y t o d e b u g t h e v i a b i li t y o f th e s y s t e m s i n e v e r y d a y u s e ;
o u r s e l v e s a n d a f e w c o l l e a g u e s s e r v i n g a s g u i n e a p i g s . T h i s i s
Reprinted with permission. Copyright c) 1993 by The A ssociation orComputing Machinery, n c. All rights reserved. This article originallyap-peared in Communications f the ACM , Vol. 36, No. 7 (July 1993), Pages75-84.
12 Mobile Computing and Communications Review, Volume 3, Number 3
8/8/2019 Weiser-Etal_2007_Some Computer Science Issues in Ubiquitous Computing
its OSI equivalent, CLNP, providessufficient iniYastructure 1or highly
mobile devices. Both interpret fields
in the network names of devices m
order to route packets to the device.
For instance, the "13" in IP name
13.2.0.45 is interpreted to mean net
13, and network routers anywhere in
the world are expected to know how
to get a packet to net 13, and all de-
vices whose name starts with 13 are
expected to be on that network. This
assum ption fails as soon as a user of a
net t 3 mobile device takes her device
on a visit to net 36 (Stanford).
Changing the device name dynami-cally dep end ing on location is no so-
lution: higher-level protocols such as
TCP assume that underlying names
will not change during the life of a
connection, and a n ame change must
be accompanied by informing the
entire network of the change so that
existing services can fin d the device.
A nu mbe r of solutions have been
proposed to this problem, among
them Virtual IP from Sony [24], and
Mobile IP from Col umbia University
[ 10]. "l'hese solutions p erm it existing
IP networks to interoperate trans-
pare ntly with roam ing hosts. The key
idea of all approaches is to add a sec-
ond layer of IP address, the "real"
address indicating kKadon, to the
existing fixed-device address. Special
routing nodes that forward packets
to the correct real address, and keep
track of where this address is, are
required for all approaches.*
In teract ion S ubstratesUbicomp has led us to explore new
substrates for interaction. Four such
substrates are men tioned here, span-
ning the space from virtual key-boards to protocols for window sys-
tems.
Tabs have a very small interaction
area~too small for a keyboard, too
small even for standard handprint-
* T h e I n t e r n e t c o m m u n i t y h a s a w o r k i n g g r o u pc o n s i d e r i n g s t a n d a r d s f o r t h i s a r e a ( c o n t a c td e e r i n g @ x e r o x . c o m f o r m o r e i n f o r m a t i o n ) .
ing recognition. Handprmting has
the further problem of requiring
looking at what is written. Improve-
ments in voice recognition are no
panacea, because when other people
are present, voice will often be inap-
propriate. As one possible solution,
we developed a method of touch-
printing that uses only a tiny areaand does trot require looking. A
drawback of our method is it re-
quires a new printing alphabet to be
memorized, and reaches only half
the speed of a fast typist [8].
Liveboards have a high intera ction
area, 400 times that of the tab. Using
conventional pull-down or pop-up
menus might require walking across
the room to the appropriate button,
a serious problem. We have devel-
oped methods of location-indepen-
dent interaction by which even coin-
plex interactions can be popped up
at any location. [13].The X-Window system, although
designed for network use, makes it
difficult for windows to move once
instantiate d at a given X server. This
is because the server retains consid-
erable state about individual win-
dows, and does not provide conve-
nient ways to move that state. For
instance, context and window IDs are
dete rmin ed solely by the server, and
cannot be transferred m a new
server, so applications that depend
on knowing their value (almost all)
will break if a window changes serv-
ers. However, in the ubiquitous corn-
puling world a user may move fre-
quently from device to device, and
want to bring windows along.
Christian Jacobi at PAR(; has im-
plemented a new X toolkit that facili-
tates window migration. Applications
need not be aware that they have
moved from one screen to another;
or if desired, the user can be so in-
forme d with an upcall. We have writ-
ten a numb er of applications on top
of this toolkit, all of which can be
"whistled up" over the network to
follow the user from screen toscreen. Th e a uthor, for instance, fre-
quently keeps a single program de-
velopment and editing environment
ope n for days at a time, migrating its
windows back and forth from home
to work and back each day.
A f inal window system problem is
bandwidth. The bandwidth available
to devices in ubiquitous computing
can vary front Kb/sec to Gb/sec, and
with window migration a single ap-
plication may have to dynamically
adjust to bandwidth over time. The
X-Window system protocol was pri-
marily developed for Ethernet
speeds, and most of the applications
written in it were similarly tested at10Mb/sec. To solve the problem of
efficient X-Window use at lower
bandwidth, the X consortium is
sponsoring a "Low Bandwidth X"
(LBX) working group to investigate
new methods of lowering bandwidth.
[7].
ApplicationsApplications are o f course the whole
point of ubiquitous computing. Two
examples of applications are locating
people and shared drawing.
Ubicomp permits the location of
people and objects in an environ-ment. This was first pioneered by
Olivetti Research la bs in Cambridge,
England, in their Active Badge sys-
tem [26]. In ubiquitous comp utin g
we continued to extend this work,
using it for video annotation and
updating dynamic maps. For in-
stance, Figure 2 shows a portion of
CSL early one morning, and the in-
dividual laces are the locations of
people. This map is updated every
few seconds, permitting quick locat-
ing of people, as well as quickly notic-
ing a meeting one might want to go
to (or where one can find a fresh pot
of coffee).
Xerox PARC, EuroPARC, and tile
Olivetti Research Center have built
several different kinds of locauon
servers. Generally these have two
parts: a central database of informa-
tion about location that can be
quickly queried and dumped, and a
group of servers that collect infor ma-
tion about location and update the
database. Inf orma tion about location
can be deduced from logins, or col-
lected directly from an active badge
system. The location database may beorganized to dynamically notify cli-
ents, or simply to facilitate frequent
polling.
Some example uses of location in-
formation are automatic phone for-
warding, locating an individual for a
meeting, and watching general activ-
ity in a bu ildin g to feel in touc h with
8 0 , ] u b 1993/Vot.36.N od C O , I A ~ U m ~ . A ~ O N ' m O ~ T ~
Mobile Computing and Communications Review, Volume3, Number 3 17
8/8/2019 Weiser-Etal_2007_Some Computer Science Issues in Ubiquitous Computing
p o s s i b l e d e s i g n p o i n t t h e c o m p r e s -
s i o n o f p a g e s i n a R A M : c a c h e , r a t h e r
t h a n w r i t i n g t h e m a l l t h e w a y b ac k
o v e r a s l o w l in k . T h e q u e s t i o n a r i se s
o f ~ h e o p t i m a l s t r a t e g y t 0 r p a r t i ti o n -
i n g m e m o r y b e tw e e n c o m p r e s s ed
a n d u n c o m p r e s s e d p a g e s .
T h i s p r o b l e m c a n b e g e n e r a li z e d
a s t o l l o w s [ 1 ] :
" I 'h e C a c h e S h a r i n g P r o b l e m . A
p r o b l e m i n s t a n c e i s g i v e n b y a s e -
q u e n c e o f p a g e r e q u e s ts . P a g e s a r e o f
t w o t y p e s , U a t td C ( f b r u n c o n t -
p r e s s e d a n d c o m p r e s s e d ) , a n d e a c h
p a g e i s e i t h e r I N o r O U T . A r e q u e s t
i s s e r v e d b y c h a n g i n g t h e r e q u e s t e d
p a g e t o I N i f i t i s c u r r e n t l y O U T . h f i -
t ia l ly al l p a g e s a r e O U T . T h e c o s t t o
c h a n g e a t y p e - U ( t y p e - C ) p a g e f r o m
O U T t o I N i s C u ( r e s p e c t i v e l y , C c ) .
W h e n a r e q u e s t e d p a g e i s O U T , w e
s a y t h a t t h e a l g o r i t h n t m i s s e d . R e -
m o v i n g a p a g e f r o m m e m o r y is f r e e .
L o w e r B o u n d T h e o r e m : N o de t er -
m i n i s fi c , o n - l i n e a l g o r i t h m f b r c a c h e
s h a r i n g c a n b e c - c o m p e t i t i v e f o r
c < M A X (1 + C t : / ( C t ~ + C c ) , 1 +
C c i ( C t ; + C c ) )
T h i s l o w e r b o u n d t o r c r a n g e s
f l - o m 1 . 5 t o 2 , a n d n o o n - l i n e a l g o -
r i t h m c a n a p p r o a c h c l o s e r t o th e o p -
t i m u m t h a n t h i s f a c t o r . B e r n e t a l . [ 11
a l s o c o n s t r u c t e d a n a l g o r i t h m t h a t
a c h i e v e s t hi s f a c to r , t h e r e t o r e p r o -
v i d i n g a n u p p e r b o u n d a s w el l. T h e y
f h r t h e r p r o p o s e a s et o f m o r e g e n -e r a l s y m b o li c p r o g r a m m i n g t o ol s f b r
s o l v i n g c o m p e t i t i v e a l g o r i t h m s o f th i s
s o r t .
Concluding R emarksA s w e s t a r t t o p u t t a b s , p a d s , a n d
b o a r d s i n t o u s e , t h e f i r s t p h a s e o f
u b i q u i t o u s c o m p u t i n g s h o u l d e n t e r
i ts m o s t p r o d u c t i v e p e r i o d . W i t h t h i s
s u b s t r a t e i n p l a c e w e c a n m a k e m u c h
m o r e p r o g r e s s b o t h i n e v a l u a t in g o u t
t e c h n o l o g i e s a n d i n c ht x > si n g o u r
n e x t s t e p s . A k e y p a r t o f t h i s e v a l u a -
t i o n i s u s i n g t h e a n a l y s e s o f p s y c h o l o -
g i st s , a n t h r o p o l o g i s t s , a p p l i c a t i o nw r i t e r s , a r t i s t s , m a r k e t e r s , a n d c u s -
t o m e r s . W e b e l i ev e t h e y w i l l f i n d
s o m e l i g a t u r e s w o r k w e l l ; w e k n o w
t h e y w i ll f i n d s o m e f e a t u r e s d o n o t
w o r k . T h u s w e w il l b e g i n a g a i n t h e
c y c l e o f c r o s s - d i s c i p l i n a r y f e r t i l iz a -
t i o n a n d l e a r n i n g . U b i c o m p i s l i ke l y
t o p r o v i d e a f r a n t e w o r k f o r i n te r e s t -
i n g a nd p r o d u c t i v e w o r k t b r m a n y
m o r e y e a r s o r d e c a d e s , b u t w e h a v e
m u c h t o l e a r n a b o u t t h e d e t a i ls .
A c k n o w l e d g m e n t s
T h i s w o r k w a s f u n d e d b y X e r o x
P A R C . P o r t i o n s o f " t h i s w o r k w e r e
s p o n s o re d u n d e r c o n t r ac t # D A B q
6 3 - 9 1 - 0 0 2 7 . U b i q u i t o u s c o m p u t i n g iso n l y a sm a l l p a r t o f t h e w o r k g o i n g
o n a t P A R C , a n d w e a r e g r a t e f t f l t b )
P A R C ' s r i c h , c o o p e r a t i v e , a n d f e r t i l e
e n v i r o m n e n t i n s u p p o r t o f th e d o c u -
m e n t c o m p a n y . []
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