ISSC 2004, Bel as , June 30 - July 2
Examining Use Pe o mance in he p esence o La ency and
Ji e in Dis ibu ed In e ac i e Applica ions
Declan Delaney
φ
, Paul Meeneghan
φ
, Tomás Wa d* and Séamus Mc Loone*
φ
Depa men o Compu e Science,
NUI Maynoo h
Co. Kilda e, I eland
E-mail:
φ
[email p o ec ed]ay.ie
* Depa men o Elec onic Enginee ing,
NUI Maynoo h
Co. Kilda e, I eland
E-mail: * oma[email p o ec ed]
__________________________________________________________________________________________
Abs ac – La ency and ji e inhe en ly limi he main enance
o consis ency in Dis ibu ed In e ac i e Applica ions such as
compu e games, dis ibu ed whi eboa ds and eal- ime,
collabo a i e en i onmen s. Al hough he e has been much
esea ch in o me hods o main aining consis ency, he e is a
dis inc lack o esea ch explo ing he connec ion be ween la ency,
ji e and he end use expe ience in Dis ibu ed In e ac i e
Applica ions. We ha e de eloped an applica ion ha allows us o
conduc ials unde con olled la ency and ji e condi ions. This
p o ides da a, which can be analysed o cha ac e ise how people
adap o a ious deg ees o la ency and ji e . We p esen esul s
ha highligh how an inc ease in la ency and ji e a ec he end-
use expe ience, hus con i ming he need o echniques o comba
la ency and ji e in Dis ibu ed In e ac i e Applica ions. We alsoe
no e ha he e ec s o ji e a e signi ican ly g ea e han hose o
la ency.
Keywo ds – Dis ibu ed In e ac i e Applica ions, Ji e , La ency.
__________________________________________________________________________________________
I INTRODUCTION
Dis ibu ed In e ac i e Applica ions (DIAs) a e a
class o compu e p og ams in ol ing eal- ime use s
ac ing in a i ual en i onmen o execu e some
collabo a i e, coope a i e o in e ac i e ask. The
dis ibu ed na u e o such applica ions means ha a
consis en wo ld iew ac oss all pa icipan s is
impossible o achie e. This esul s in each
pa icipan seeing sligh ly di e en e en s a
di e en imes. In such a case he end-use
expe ience can be des oyed.
Al hough he e a e a numbe o issues ha a ec he
consis ency o a dis ibu ed applica ion, he ul ima e
limi a ion is imposed by la ency e ec s.
La ency has been de ined in a ious ways [1-3]. In
his pape we de ine i as he ime aken om s a o
ansmission o he i s bi o a da a packe a he
applica ion laye o one pa icipa ing node o he
eceip o he las bi o he same packe a he
applica ion laye o a second pa icipa ing node. A
numbe o delays combine o cause la ency. The e
a e queuing and p ocessing delays a ou e s, b idges,
ga eways and a packe sou ce and des ina ion;
delays in anscoding he da a (enc yp ion /
dec yp ion and comp ession / decomp ession);
p opaga ion and ansmission delays due o he speed
o ligh and he speed o he communica ions link.
The e has been a lo o esea ch ca ied ou in o
echniques and mechanisms o comba he e ec s o
la ency. Mos o hese echniques seek o educe he
numbe o packe s ha need o be ansmi ed
be ween pa icipan s. By so doing, he la ency
associa ed wi h queuing, p ocessing and anscoding
is educed. Some echniques include he ollowing:
• Clien -side p edic ion con ac mechanisms:
These include echniques such as dead
eckoning [4, 5] and s a egy-based
modelling [6, 7].
• Rele ance Fil e ing echniques: da a is
il e ed based on c i e ia such as
geog aphical p oximi y o a e o change
[8]. Ano he o m o ele ance il e ing is
isibili y culling [9].
• Ne wo k ansmission p o ocol:
Mul icas ing o g oups o pa icipan s wi h
he same da a equi emen s. The In e ne
o e s e y limi ed suppo o mul icas ing
p o ocols [10].
• Packe bundling: Inc ease he packe size by
sending mul iple packe s unde he one
heade . This may also in oduce la ency i
no used wi h ca e [8].
• Da a Comp ession: Reduce he size o he
in o ma ion packe being ansmi ed, using
o example, del a comp ession [8].
• Time Managemen : Synch onize e en s o
wall clocks among pa icipan s. E en s can
be p e-emp ed o delayed o main ain
consis ency [11, 12].
• P io i y Scheduling: Da a essen ial o
main aining consis ency is sen wi h he
highes p io i y [13].
• Quali y o Se ice (QoS) Techniques:
ne wo k pa ame e s such as bandwid h and
la ency a e gua an eed by he se ice
p o ide [14, 15].
Despi e he esea ch ca ied ou on sol ing he
la ency p oblem, e y li le wo k has been ca ied ou
on he e ec s o la ency a ia ion o ji e on use s o
dis ibu ed applica ions. An in e es ing sui e o
expe imen s was pe o med by Vaghi e al. in which
hey examined he e ec s o g adually inc easing
la ency on he in e ac ion o wo pa icipan s in a
i ual ball game [16]. Thei esul s indica ed ha
he use s modi y hei playing s a egies as hey a emp
o cope wi h la ency and hey iden i ied se e al ypes o
adap a ion s a egies. The ocus o his pape is on
examining he accu acy o use pe o mance in he
p esence o la ency. Fu he mo e, we ex end ou wo k
o also include he e ec s o ji e . We in end o show
ha hese e ec s can’ be simply igno ed.
In he ollowing sec ion we de ail he de elopmen o
he applica ion ha will be used o conduc expe imen s
unde con olled la ency and ji e condi ions. The
expe imen s pe o med a e ou lined in sec ion 3, while
he esul s a e p esen ed and analysed in sec ion 4. The
inal sec ion indica es ou conclusions and he u u e
di ec ion o he esea ch.
II TEST PLATFORM
The es pla o m was designed o measu e he abili y
o use s o pe o m a single ask in he p esence o
a ying deg ees o la ency and ji e and a di e en
speeds o ope a ion. The applica ion was de eloped
in Ja a e sion 1.4.2 (ja a.sun.com), employing a
Ja a class lib a y o gene a ing cha s called
JF eeCha e sion 0.9.16 (j ee.o g/j eecha /). The
Eclipse In eg a ed De elopmen En i onmen (IDE)
e sion 2.1 was used o de elop he applica ion.
The choice o ja a was made so ha he applica ion
would be independen o he unde lying ope a ing
sys em, hus allowing he applica ion o be made
a ailable o mul iple pla o ms o e he In e ne .
The g aphical use in e ace (GUI) was designed
Figu e 1: G aphical Use In e ace ha is in ui i e and allows he expe imen al
pa ame e s o be se .
Use sees
his en i y
Loca ion o en i y ha he
use does no see.
Di e ence in loca ion is
due o la ency and ji e .
Mo emen
T ajec o y
wi h wo objec i es in mind: (1) o allow he
expe imen e se he expe imen al pa ame e s easily
and hide hem om he use and (2) o p o ide an
easily na igable layou and game-like en i onmen
wi h bo h audio and isual eedback. The GUI is
shown in Figu e 1.
The main ea u es o he so wa e a e:
• T ajec o y, la ency and ji e alues can be
se using slide ba s;
• Feedback o he use can be u ned on/o ;
• All expe imen al da a is sa ed o a ime-
s amped di ec o y in ex o ma o acili a e
expo o o he applica ions;
• A se ies o 15 plo s a e au oma ically
gene a ed when he use exi s he
applica ion. A sample o one o hese plo s
is shown in Figu e 2.
The expe imen al pla o m simula es he local
ende ing o a emo e en i y ( ep esen ed as a disk),
which is mo ing along one o se e al possible
ajec o ies. The use can only see he posi ion o he
disk compu ed locally, al hough he ue posi ion o
he emo e en i y can also be shown i desi ed. The
ask pe o med by he pa icipan s in each
expe imen is o a emp o p edic he ac ual loca ion
o he emo e en i y’s posi ion unde a ying deg ees
o la ency and ji e . All mouse clicks a e eco ded
and when a co ec ‘hi ’ is made he applica ion
p o ides audio and isual eedback, as well as
inc emen ing a hi coun e . Al hough he e is no
limi o he numbe o mouse clicks ha can be
made, a hi can only be sco ed once o each
simula ion ime uni .
The da a p oduced by each expe imen is eco ded in
ASCII o ma in a unique ime s amped olde . In all
15 di e en a iables a e eco ded such as ime
sample, hi coun , ji e alue, la ency alue,
cumula i e e o and o al mouse clicks.
The es pla o m was used o eco d da a om a
numbe o use s. De ails o hese expe imen s a e
gi en in he ollowing sec ion.
III EXPERIMENTS
The es pla o m was employed o pe o m an
expe imen in ol ing a o al o eigh olun ee s.
Each olun ee pe o med a single expe imen
consis ing o a se ies o i e a ions du ing which he
la ency and ji e alues we e a ied au oma ically by
he applica ion acco ding o he pa ame e s de ined.
The ec angula ajec o y was employed. Use s
began a he op le -hand co ne o he ec angle and
mo ed in a clockwise di ec ion. The la ency and
ji e alues emained in a ian o each i e a ion o
he ec angle. A o al o 12 indi idual i e a ions o
he ec angle we e pe o med wi h di e en se ing
o la ency and ji e – see he lis o i e a ions o he
expe imen in Table 1. Bo h audio and isual
eedback we e u ned on bu use s we e unawa e o
he la ency and ji e pa ame e s. The objec i es o
he i e a ions a e desc ibed in he ollowing
pa ag aphs.
I e a ions La ency Ji e
1 0 0
2 1 0
3 2 0
4 3 0
5 4 0
6 5 (max) 0
7 3 0
8 3 10
9 3 15
10 3 20
11 3 25
12 3 30 (max)
Table 1: A se ies o 12 i e a ions we e pe o med.
Ji e and la ency we e a ied each ime he use
passed h ough he op le -hand co ne o he
ec angle.
I e a ion 1: Du ing his i e a ion we measu e he
pa icipan ’s pe o mance when he e is no ji e o
la ency. Bo h he local and emo e posi ions a e
iden ical and he use only has o mo e he mouse
cu so o e he mo ing a ge and click. Each mouse
click should esul in a sco e wi h any e o s being a
esul o use inaccu acy and no a esul o la ency
o ji e . An e o alue o 11 o unde esul s in a
‘hi ’ o sco e. This alue co esponds o he size o
he objec on he sc een. This p o ides a benchma k
o baseline measu emen , agains which o he
measu emen s can be accu a ely compa ed.
I e a ions
2 o 6: He e ji e was kep a a cons an
alue o ze o and la ency was inc eased in s eps om
Figu e 2: A se ies o g aphs a e au oma ically
gene a ed when he use exi s he p og am – a
sample g aph is shown he e.
ze o o i s maximum alue o he gi en applica ion
on e e y i e a ion o he ec angle. This p o ides a
measu e o he e ec s o la ency in he absence o
ne wo k ji e .
I e a ion 7: This i e a ion is pe o med wi h a
medium alue o la ency and ze o ji e . This la ency
alue will be main ained in he subsequen i e a ions.
This i e a ion is iden ical o i e a ion 4 and ma ks he
ansi ion om la ency- a ying o ji e - a ying
i e a ions.
I e a ions 8 o 12: In hese i e a ions, la ency is
main ained a a medium alue o 3 and use
pe o mance unde p og essi ely inc easing ji e is
measu ed. This p o ides da a ela ing o he e ec s
o ji e unde condi ions o cons an la ency.
An analysis o he esul s a e p esen ed in he
ollowing sec ion.
IV ANALYSIS OF RESULTS
The p esen ed esul s a e p elimina y and o m he
basis o unde s anding he beha iou o use s unde
con olled condi ions o la ency and ji e . The
esul s a e shown o a ypical use ha is
ep esen a i e o all pa icipan s in he i e a ion.
Figu es 3(a)-(d) illus a e a ep esen a i e
pe o mance o one o he pa icipan s in e ms o hi
coun sco e as la ency and ji e inc ease om 0 o
hei maximum alues. Figu es 3(b) and 3(d) a e he
no malized e sion o Figu es 3(a) and 3(c)
espec i ely. The no maliza ion is pe o med wi h
espec o he o al numbe o mouse clicks made by
he use . As la ency inc eases, Figu es 3(a) and 3(b)
show a all o in he sco e he use achie es,
educing om an absolu e alue o abou 30 o unde
15 when la ency is a i s maximum alue. Wi h
la ency main ained a a cons an alue, ji e ends o
esul in a poo e o e all use pe o mance wi h all
sco es lying be ween 10 and 20. In addi ion Figu e
3(c) shows ha he a ia ion in sco es is mo e
andom, compa ed o he g adual all o in
pe o mance wi h inc easing la ency. I ’s o in e es
o no e ha in Figu e 3(a) when la ency is 3 and ji e
is ze o, he hi coun is 24. In Figu e 3(c) when
la ency is educed o 3 and ji e is s ill ze o, he hi
coun is only 12. This was o be expec ed because
he use would be expec ing he end o inc easing
la ency o con inue and he adjus men in la ency was
g ea e han be ween any o he p e ious i e a ions.
The ins an aneous e o e e s o he sum o he
absolu e dis ance om he posi ion he mouse was
clicked a o he ac ual posi ion o he emo e en i y –
see Figu e 4. The cumula i e e o e e s o he sum
o he ins an aneous e o wi h ime. A ypical plo
o cumula i e e o agains ime is shown in Figu e 5
o h ee scena ios: (1) Ji e and la ency bo h se o
ze o; (2) la ency se o i s maximum alue and ji e
se o ze o and (3) la ency a a medium alue and
ji e se o maximum. In scena io (1) he cu e may
be app oxima ed as a s aigh line, indica ing ha he
accumula ion in e o is a linea p ocess. The o he
scena ios illus a e he a e o accumula ion o e o
in he p esence o high la ency is mo e han doubled
Figu e 4: The ins an aneous e o is compu ed
be ween he mouse click posi ion and he ac ual
posi ion o he emo e en i y.
Figu e 5: As ime p og esses he cumula i e
absolu e e o inc eases bu does so mo e apidly
in he p esence o ji e han ha o la ency.
Figu e 3(a)-(d): As la ency is inc eased, he
pa icipan ’s success a sco ing a hi educes.
In oducing ji e also esul s in a signi ican
educ ion.
(x
1
,y
1
)
(x
3
,y
3
)(x
2
,y
2
)
mouse click
posi ion
Local ende ing o
emo e posi ion
Ac ual emo e
posi ion
E o , ∆E
2
= (x
2
-x
1
)
2
+(y
2
-y
1
)
2
(x
1
,y
1
)
(x
3
,y
3
)(x
2
,y
2
)
mouse click
posi ion
Local ende ing o
emo e posi ion
Ac ual emo e
posi ion
E o , ∆E
2
= (x
2
-x
1
)
2
+(y
2
-y
1
)
2
Ze o la ency, ze o ji e
Max la ency, ze o ji e
La ency = 3, Max ji e
Hi Coun
Time
Ze o la ency, ze o ji e
Max la ency, ze o ji e
La ency = 3, Max ji e
Hi Coun
Time
La ency Value
Hi coun sco e
La ency Value
Ji e Value
(a) (b)
(c) (d)
Hi coun sco e
Hi coun sco e Hi coun sco e
Ji e Value
La ency Value
Hi coun sco e
La ency Value
Ji e Value
(a) (b)
(c) (d)
Hi coun sco e
Hi coun sco e Hi coun sco e
Ji e Value
compa ed o he case o ze o la ency and ze o ji e .
Finally we also no e ha he e was a u he inc ease
in cumula i e e o due o he addi ion o ji e .
Typical plo s o he ins an aneous e o s as a
unc ion o ime a e shown in Figu es 6(a)-(d).
Figu e 6(a) shows ha wi h no la ency o ji e he
ins an aneous e o is low, usually below he
expe imen al e o le el o 11. As la ency and ji e
a e in oduced he ampli ude o e o a ia ion
inc eases, wi h he wo se case scena io being he
case o medium la ency and high ji e in Figu e 6(d).
An examina ion o he dis ibu ion o ins an aneous
e o s clea ly demons a es he e ec s o ji e and
la ency on use pe o mance - see Figu e 7. The
dis ibu ions become wide as la ency and ji e a e
in oduced. The dis ibu ion o ze o la ency and
ze o ji e has a maximum sp ead o abou 20. In he
case o medium la ency and maximum ji e his
inc eases o a sp ead o almos 100.
The a e age ins an aneous e o o each i e a ion
was calcula ed oge he wi h he a iance. These
alues we e plo ed and a e shown in Figu e 8. The
a e age e o inc eases s eadily and becomes e a ic
when ji e is in oduced. The a iance is also much
less p edic able when ji e is in oduced. I is wo h
obse ing ha use s ind i easie o adap o
cons an ly inc easing la ency bu s uggled o cope
wi h he e ec s o ji e as indica ed in Figu e 8.
I is also in e es ing o no e he impo ance o
eedback o he use du ing he expe imen . A low
alues o la ency and ji e , use s adap ed o hei
p esence by elying on he audio eedback.
Howe e , a high alues o ji e hey elied mo e on
he isual eedback mechanism illus a ed in Figu e 9
because hey could hea ha hey we en’ making
any hi s and hey needed some addi ional
in o ma ion o help hem compensa e. Visual
eedback is p o ided in a small indica o sc een
showing he posi ion o he use ’s ac ual mouse click
and a line om he e o he co ec sco ing posi ion.
I is ob ious ha eedback becomes mo e impo an
a high la ency and ji e alues, bu his is o be
expec ed as he use ’s ask becomes mo e di icul as
la ency and ji e a e in oduced. These indings
con i m ou in ui ion and a e no al oge he
unexpec ed.
V CONCLUSIONS and FUTURE
WORK
A es pla o m and an expe imen designed o allow
us de e mine he e ec s o la ency and ji e on use
pe o mance ha e been desc ibed. While he esul s
p esen ed in his pape a e o one use only, i was
ound ha all eigh use s showed simila beha iou .
They illus a e ha use pe o mance, e en in a
ela i ely simple applica ion, de e io a es apidly in
Figu e 8: The a ia ion in a e age e o alue
and a iance o each expe imen
Figu e 9: The Visual Feedback Mechanism.
Figu e 7: The dis ibu ion o e o s inc eases
wi h inc easing la ency and ji e .
Figu e 6(a)-(d): Plo s o ins an aneous e o o
di e en la ency/ji e combina ions
Va iance Value
A e age Value
Expe imen no. Expe imen no.
(a) A e age o e o s (b) Va iance in e o s
Va iance Value
A e age Value
Expe imen no. Expe imen no.
(a) A e age o e o s (b) Va iance in e o s
local
posi ion
mouse click
posi ion
line connec ing
o co ec
posi ion
local
posi ion
mouse click
posi ion
line connec ing
o co ec
posi ion
(a) No la ency
o ji e
(b) Maximum
la ency, No ji e
(c) Medium
la ency, No ji e
(d) Medium la ency,
maximum ji e
Coun
E o Value
E o Value
E o Value
E o Value
Coun
Coun
Coun
(a) No la ency
o ji e
(b) Maximum
la ency, No ji e
(c) Medium
la ency, No ji e
(d) Medium la ency,
maximum ji e
Coun
E o Value
E o Value
E o Value
E o Value
Coun
Coun
Coun
Coun
E o Value
E o Value
E o Value
E o Value
Coun
Coun
Coun
(a) No la ency o ji e (b) Maximum la ency,
No ji e
(c) Medium la ency, No
ji e
(d) Medium la ency,
maximum ji e
Time
Time
Time
Time
E o
E o
E o
E o
(a) No la ency o ji e (b) Maximum la ency,
No ji e
(c) Medium la ency, No
ji e
(d) Medium la ency,
maximum ji e
Time
Time
Time
Time
E o
E o
E o
E o

he p esence o la ency and ji e and hus hese
ac o s canno be simply igno ed. The inc ease in
esea ch o la ency masking echniques he e o e
needs o be ma ched by esea ch in o comba ing he
e ec s o ji e .
The expe imen s conduc ed o da e indica e a numbe
o new a enues o explo e. Se e al ea u es will be
added o he es pla o m such as eco ding o use
mouse click coo dina es, use o a sc ip ing language
o se up he expe imen s and inc eased size o he
isual eedback sc een. Ou objec i e is o
de e mine accep able le els o ji e and la ency
alues so ha he use ’s psycho-pe cep ual
expe ience emains accep able.
R
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