01 - Introduction€¦ · Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme 1 Chapter...
14
Distributed Systems Lehrstuhl für Informatik IV RWTH Aachen Prof. Dr. Otto Spaniol Dipl.-Inform. Dirk Thißen Organisation • about all 14 days • Room AH V, RWTH Aachen • Teacher-centred exercises Exercises Dirk Thißen Lehrstuhl für Informatik IV, Room 4226 (Building E1) Phone: 0241 / 80 - 21450 eMail: [email protected] Contact 10. May 2004 24. May 2004 14. June 2004 28. June 2004 12. July 2004 26. July 2004 Available on our homepage: http://www-i4.informatik.rwth-aachen.de/teaching/lectures/sub/vs/vsSS04 Slide copies and Video records to the lecture At the end of the summer term Written exam Literature Available in the library, section DiS • A.S. Tanenbaum, M. van Steen: Distributed Systems – Principles and Paradigms. Prentice-Hall, 2002. • G. Coulouris, J. Dollimore, T. Kindberg: Distributed Systems - Concepts and Design. Addison-Wesley, 2001. • Z. Tari, O. Bukhres: Fundamentals of Distributed Object Systems – The CORBA Perspective. Wiley Interscience, 2001. Further literature • S. Baker: CORBA Distributed Objects using Orbix. Addison-Wesley & acm Press, 1997. • C. Popien: Verteilte Systeme, Skript zur Vorlesung 1996. Verlag der Augustinus Buchhandlung, Aachener Beiträge zur Informatik, Band 16, 1996. Current (related) events: → Lecture ”Dependable Distributed Systems“, Prof. Gärtner Classification of the lecture Following events: → Seminar “Data Communications and Distributed Systems” → Diploma Theses at Informatik 4 → Several lectures, e.g. Multimedia Systems, Security in Communication Networks, … Useful prerequisites: → Lecture on Data Communication or Internet Technology
Transcript of 01 - Introduction€¦ · Lehrstuhl für Informatik 4 Kommunikation und verteilte Systeme 1 Chapter...
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
1C
hap
ter
1:
In
trodu
cti
onDis
trib
ute
dS
yste
ms
Lehr
stuh
l für
Info
rmat
ik IV
RW
TH
Aac
hen
Pro
f. D
r. O
tto
Sp
anio
l
Dip
l.-In
form
. Dir
k T
hiß
en
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
2C
hap
ter
1:
In
trodu
cti
on
Org
anis
atio
n
•ab
out a
ll 14
day
s•
Roo
m A
H V
, RW
TH
Aac
hen
•T
each
er-c
entr
ed e
xerc
ises
Exe
rcis
es
Dirk
Thi
ßen
Lehr
stuh
l für
Info
rmat
ik IV
, Roo
m 4
226
(Bui
ldin
g E
1)P
hone
: 02
41 /
80 -
2145
0eM
ail:
this
sen@
info
rmat
ik.r
wth
-aac
hen.
de
Co
nta
ct
10.
May
200
4
24.
May
200
4
14.
June
200
4
28.
June
2004
12.
July
200
4
26.
July
2004
Ava
ilabl
e on
our
hom
epag
e:ht
tp://
ww
w-i4
.info
rmat
ik.r
wth
-aac
hen.
de/te
achi
ng/le
ctur
es/s
ub/v
s/vs
SS
04
Slid
e co
pie
s an
d V
ideo
rec
ord
s to
th
e le
ctu
re
At t
he e
nd o
f the
sum
mer
term
Wri
tten
exa
m
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
3C
hap
ter
1:
In
trodu
cti
on
Lit
erat
ure
Ava
ilab
le in
th
e lib
rary
, sec
tio
n D
iS
•A
.S. T
anen
baum
, M. v
an S
teen
: Dis
trib
uted
Sys
tem
s –
Prin
cipl
es a
nd
Par
adig
ms.
Pre
ntic
e-H
all,
2002
.
•G
. Cou
lour
is, J
. Dol
limor
e, T
. Kin
dber
g: D
istr
ibut
ed S
yste
ms
-C
once
pts
and
Des
ign.
Add
ison
-Wes
ley,
200
1.
•Z
. Tar
i, O
. Buk
hres
: Fun
dam
enta
ls o
f Dis
trib
uted
Obj
ect S
yste
ms
–T
he
CO
RB
A P
ersp
ectiv
e. W
iley
Inte
rsci
ence
, 200
1.
Fu
rth
er li
tera
ture
•S
. Bak
er: C
OR
BA
Dis
trib
uted
Obj
ects
usi
ng O
rbix
. Add
ison
-Wes
ley
& a
cmP
ress
, 199
7.
•C
. Pop
ien:
Ver
teilt
eS
yste
me,
Skr
iptz
urV
orle
sung
1996
. Ver
lag
der
Aug
ustin
usB
uchh
andl
ung,
Aac
hene
rB
eitr
äge
zur
Info
rmat
ik, B
and
16, 1
996.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
4C
hap
ter
1:
In
trodu
cti
on
Cu
rren
t (r
elat
ed)
even
ts:
→Le
ctur
e ”D
epen
dabl
eD
istr
ibut
edS
yste
ms“
, Pro
f. G
ärtn
er
Cla
ssif
icat
ion
of
the
lect
ure
Fo
llow
ing
eve
nts
:
→S
emin
ar “
Dat
a C
omm
unic
atio
ns a
nd D
istr
ibut
ed S
yste
ms”
→D
iplo
ma
The
ses
at In
form
atik
4
→S
ever
al le
ctur
es, e
.g. M
ultim
edia
Sys
tem
s, S
ecur
ity in
Com
mun
icat
ion
Net
wor
ks, …
Use
ful p
rere
qu
isit
es:
→Le
ctur
e on
Dat
a C
omm
unic
atio
nor
Inte
rnet
Tec
hnol
ogy
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
5C
hap
ter
1:
In
trodu
cti
on
Wh
at is
a D
istr
ibu
ted
Sys
tem
?
Def
initi
on:
A D
istr
ibu
ted
Sys
tem
is a
sys
tem
with
spa
tially
dis
trib
uted
co
mpo
nent
s, w
hich
do
not u
se s
hare
d m
emor
y an
d w
hich
are
m
anag
ed in
a d
ecen
tral
ised
man
ner.
For
rea
lisin
g co
mm
on g
oals
, aco
oper
atio
n of
thes
e co
mpo
nent
sis
pos
sibl
e. [P
opie
n]
The
re a
re s
ever
al (
diffe
rent
) de
finiti
ons
for
Dis
trib
uted
Sys
tem
s.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
6C
hap
ter
1:
In
trodu
cti
on
... M
ore
Def
init
ion
s...
Or
som
etim
es:
“A d
istr
ibut
edsy
stem
ison
ein
whi
chth
efa
ilure
of a
com
pute
rw
hich
you
didn
‘tev
enkn
owex
iste
dca
nre
nder
your
own
com
pute
run
usab
le.“
(Les
lie L
ampo
rt)
orA
Dis
trib
ute
d S
yste
mis
a c
olle
ctio
n of
inde
pend
ent c
ompu
ters
that
ap
pear
s to
its
user
s as
a s
ingl
e co
here
nt s
yste
m. [
Tan
enba
um]
orA
Dis
trib
ute
d S
yste
mis
a s
yste
m in
whi
ch h
ardw
are
or s
oftw
are
com
pone
nts
loca
ted
at n
etw
orke
d co
mpu
ters
com
mun
icat
e an
d co
ordi
nate
th
eir
actio
nson
ly b
y pa
ssin
g m
essa
ges.
[Cou
lour
is]
orA
Dis
trib
ute
d S
yste
mis
a c
olle
ctio
n of
aut
onom
ous
com
pute
rslin
ked
by a
ne
twor
k an
d eq
uipp
ed w
ith d
istr
ibut
ed s
yste
m s
oftw
are.
[...]
The
dist
ribut
ed
syst
em s
oftw
are
enab
les
the
com
pris
ing
com
pute
rs to
coo
rdin
ate
thei
r ac
tiviti
esan
d to
sha
re s
yste
m r
esou
rces
. [T
ari]
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
7C
hap
ter
1:
In
trodu
cti
on
Co
nte
nts
1. In
tro
du
ctio
n:
Cla
ssif
icat
ion
an
d c
har
acte
rist
ics
of
Dis
trib
ute
d
Sys
tem
s
Typ
es o
f M
idd
lew
are
for
Dis
trib
ute
d S
yste
ms
Co
mm
un
icat
ion
in D
istr
ibu
ted
Sys
tem
s:
Clie
nt/
Ser
ver-
Mo
del
, Rem
ote
Pro
ced
ure
Cal
l, R
emo
te
Met
ho
d In
voca
tio
n, M
essa
ge-
Ori
ente
d S
yste
ms
2. P
roce
sses
an
d T
hre
ads,
(M
ob
ile)
Ag
ents
3. B
asic
pri
nci
ple
s:
Nam
ing
, Co
ncu
rren
cy, S
ynch
ron
isat
ion
, T
ran
sact
ion
s, R
eplic
atio
n, C
on
sist
ency
4. M
idd
lew
are:
DC
OM
, Jav
a R
MI,
CO
RB
A
5. T
he
Co
mm
on
Ob
ject
Req
ues
t B
roke
r A
rch
itec
ture
6. S
ervi
ces
and
Co
mp
on
ents
: th
e W
eb S
ervi
ces
con
cep
t
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
8C
hap
ter
1:
In
trodu
cti
on
Cla
ssif
icat
ion
of
Dis
trib
ute
d S
yste
ms
loos
e co
uplin
g
netw
ork
with
inde
pend
ent
PC
s/w
orks
tatio
ns a
nd s
hare
d se
rver
s
tight
ly c
oupl
ing
dist
ribut
ed a
pplic
atio
n on
se
vera
l hom
ogen
eous
co
mpu
ters
tight
ly c
oupl
ing
mul
ti-pr
oces
sor
syst
ems
loos
e co
uplin
g
colle
ctio
n of
co
mpu
ters
in a
ne
twor
k
Cla
ssifi
catio
n by
•H
ardw
are:
com
putin
g po
wer
(tig
htly
res
p. lo
ose
coup
ling)
•S
oftw
are:
ope
ratin
g sy
stem
s an
d ap
plic
atio
ns (
tight
ly r
esp.
loos
e co
uplin
g)
Har
dwar
eSof
twar
e
--no
t sui
tabl
e --
mul
ti-pr
oces
sor
oper
atin
g sy
stem
s
net
wo
rk o
per
atin
g s
yste
ms
(mos
t use
d co
ncep
t: ne
twor
k w
ith in
depe
nden
t com
pute
rs
but s
hare
d re
sour
ces)
dist
ribut
ed o
pera
ting
syst
ems
(for
a u
ser,
the
netw
ork
look
s lik
e a
sing
le c
ompu
ter)
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
9C
hap
ter
1:
In
trodu
cti
on
Dis
trib
ute
d O
per
atin
g S
yste
ms
Exa
mpl
e: C
lust
er o
f wor
ksta
tions
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
10
Ch
ap
ter
1:
In
trodu
cti
on
Net
wo
rk O
per
atin
g S
yste
m
Exa
mpl
e: th
eIn
tern
et
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
11
Ch
ap
ter
1:
In
trodu
cti
on
Evo
luti
on
of
Dis
trib
ute
d S
yste
ms
Sin
ce th
e 19
80s
a ge
nera
l tre
nd to
rej
ectio
n fr
om c
entr
alis
ed s
yste
ms
can
be
seen
.
The
dev
elop
men
t of d
istr
ibut
ed s
yste
ms
was
sup
port
ed b
y
•H
ardw
are:
exp
losi
on in
the
perf
orm
ance
of s
emic
ondu
ctor
chi
ps
�in
crea
sing
per
form
ance
whi
lepr
ices
and
dim
ensi
ons
wer
ede
crea
sed
�us
age
of m
ore
com
plex
sof
twar
e on
mor
e an
d m
ore
com
pute
rs
•C
omm
unic
atio
n: d
evel
opm
ent o
f fas
t loc
al n
etw
orks
�re
duct
ion
of a
cces
s tim
es
�fo
reru
nner
Eth
erne
t
•S
oftw
are
engi
neer
ing:
mod
ules
, int
erfa
ces,
obj
ects
�R
emot
e P
roce
dure
Cal
l, ob
ject
-orie
nted
mod
ellin
g
•A
uton
omy
of o
rgan
isat
ions
: Dec
entr
alis
atio
n
�no
mor
e st
rict h
iera
rchi
cally
org
anis
atio
n fo
rms
in e
nter
pris
es
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
12
Ch
ap
ter
1:
In
trodu
cti
on
Wh
y D
istr
ibu
ted
Sys
tem
s?
Ad
van
tag
es
•A
dapt
atio
n of
cap
aciti
es
�A
dapt
atio
n of
sys
tem
siz
e to
cur
rent
req
uire
men
ts
•In
tegr
atio
n of
exi
stin
g so
lutio
ns
�U
sage
of l
egac
y sy
stem
s by
new
sys
tem
com
pone
nts
(it is
not
nec
essa
ry to
dev
elop
a n
ew s
yste
m w
ith th
e sa
me
func
tiona
litie
s)
•R
isk
min
imis
atio
n
�B
y ex
pand
ing
the
syst
em,t
he r
isk
of o
verlo
adin
g so
me
syst
em c
ompo
nent
s is
min
imis
ed
•F
lexi
bilit
y, a
dapt
abili
ty
�Lo
wer
cos
ts b
y m
anag
eabl
e st
ruct
ures
•A
uton
omy
�T
oler
ance
of s
ingl
e fa
ilure
s by
oth
er c
ompo
nent
s
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
13
Ch
ap
ter
1:
In
trodu
cti
on
... b
ut.
..D
isad
van
tag
es a
nd
pro
ble
ms
•T
echn
olog
y�
mor
e co
mpl
exity
by
dist
ribut
ion
and
syst
em h
eter
ogen
eity
•C
ompl
ex in
fras
truc
ture
s
�m
anag
emen
t of t
he w
hole
sys
tem
•La
ck o
f sof
twar
e
�no
exp
erie
nce
inde
velo
ping
dis
trib
uted
sof
twar
e
•S
ecur
ity r
isks
�ne
w s
ourc
es o
f fai
lure
s by
new
com
pone
nts
�da
ta p
rote
ctio
n: e
asie
r ac
cess
as
in s
epar
ated
dat
a st
orag
e
•P
aral
lel e
vent
s
�or
derin
g of
eve
nts
occu
rrin
g on
diff
eren
t com
pute
rs
•P
robl
ems
with
con
sist
ency
�ac
cess
to d
istr
ibut
ed d
ata
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
14
Ch
ap
ter
1:
In
trodu
cti
on
Req
uir
emen
ts t
o D
istr
ibu
ted
Sys
tem
s
•O
penn
ess:
inte
rope
rabi
lity
and
port
abili
ty o
f a a
sys
tem
•In
tegr
atio
n: h
andl
ing
the
hete
roge
neity
•F
lexi
bilit
y: a
dapt
to th
e ev
olut
ion
•M
odul
arity
: for
ach
ievi
ng fl
exib
ility
•F
eder
atio
n: c
onne
ctio
n of
aut
onom
ous
syst
ems
•M
anag
eabi
lity:
han
dlin
g th
e co
mpl
exity
•S
ervi
ce q
ualit
y: g
uara
ntee
of u
ser
requ
irem
ents
to s
peci
al s
ervi
ces
•S
ecur
ity: p
rote
ctio
n ag
ains
t una
utho
rised
acc
esse
s
•T
ran
spar
ency
: hid
e im
plem
enta
tion
deta
ils a
nd c
ompl
exity
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
15
Ch
ap
ter
1:
In
trodu
cti
on
Tra
nsp
aren
cies
Tra
nspa
renc
y: h
ide
impl
emen
tatio
n de
tails
Impo
rtan
t in
dist
ribut
ed s
yste
ms:
di
strib
utio
n tr
ansp
aren
cy(h
ide
the
com
plex
ity o
f a d
istr
ibut
ed s
yste
m)
•ea
ses
the
usag
e of
dis
trib
uted
sys
tem
sso
ftwar
e
•hi
des
inte
rnal
eve
nts
from
a u
ser
•su
ppor
ts a
n ap
plic
atio
n pr
ogra
mm
er
som
e tr
ansp
aren
cies
:
•A
cces
s tr
ansp
aren
cy•
Loca
tion
tran
spar
ency
•R
eplic
atio
n tr
ansp
aren
cy•
Con
curr
ency
tran
spar
ency
•M
igra
tion
tran
spar
ency
•F
ailu
re tr
ansp
aren
cy•
Res
ourc
e tr
ansp
aren
cy
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
16
Ch
ap
ter
1:
In
trodu
cti
on
Tra
nsp
aren
cies
Hid
e w
heth
er a
(so
ftwar
e) r
esou
rce
is in
mem
ory
or o
n di
skP
ersi
sten
ce
Hid
e th
e fa
ilure
and
rec
over
y of
a r
esou
rce
Fai
lure
Hid
e th
at a
res
ourc
e m
ay b
e sh
ared
by
seve
ral
com
petit
ive
user
sC
oncu
rren
cy
Hid
e th
at a
res
ourc
e m
ay b
e ru
n in
sev
eral
inst
ance
s R
eplic
atio
n
Hid
e th
at a
res
ourc
e m
ay b
e m
oved
to a
noth
er lo
catio
n w
hile
in u
seR
eloc
atio
n
Hid
e th
at a
res
ourc
e m
ay m
ove
to a
noth
er lo
catio
nM
igra
tion
Hid
e w
here
a r
esou
rce
is lo
cate
dLo
catio
n
Hid
e di
ffere
nces
in d
ata
repr
esen
tatio
n an
d ho
w a
re
sour
ce is
acc
esse
dA
cces
s
Des
crip
tio
nT
ran
spar
ency
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
17
Ch
ap
ter
1:
In
trodu
cti
on
Han
dlin
g D
istr
ibu
tio
n:
Mid
dle
war
eF
or h
andl
ing
the
larg
e se
t of t
rans
pare
ncie
s, a
spe
cial
dis
trib
utio
n in
fras
truc
ture
is
need
ed.
Thi
s in
fras
truc
ture
is c
alle
d D
istr
ibu
tio
n P
latf
orm
(or:
Mid
dle
war
e). T
he
func
tiona
litie
s ca
n be
com
pare
d w
ith th
e hi
gher
laye
rs o
f the
OS
I ref
eren
ce m
odel
fo
r co
mm
unic
atio
n pr
otoc
ols:
The
mid
dlew
are
is b
uild
upo
n di
ffere
nt
oper
atin
g sy
stem
s, n
etw
orks
, and
co
mm
unic
atio
n pr
otoc
ols
(laye
r 1-
4).
The
app
licat
ions
can
be
prog
ram
med
in
diffe
rent
lang
uage
s.
... a
nd th
e m
iddl
ewar
e re
alis
es th
e co
oper
atio
n be
twee
n th
e so
ftwar
e co
mpo
nent
s.
•M
anag
emen
t of d
ialo
gs (
laye
r 5)
, •
Inde
pend
ent t
rans
fer
synt
ax (
laye
r 6)
,
•S
ecur
ity, t
rans
actio
ns, s
ynch
roni
satio
n, ..
.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
18
Ch
ap
ter
1:
In
trodu
cti
on
So
ftw
are
Co
nce
pts
Pro
vide
di
strib
utio
n tr
ansp
aren
cy
Add
ition
al la
yer
atop
of N
etw
ork
Ope
ratin
g S
yste
ms
impl
emen
ting
gene
ral-p
urpo
se s
ervi
ces
Mid
dlew
are
Offe
r lo
cal
serv
ices
to
rem
ote
clie
nts
Loos
ely-
coup
led
oper
atin
g sy
stem
for
hete
roge
neou
s m
ultic
ompu
ters
(LA
N a
nd
WA
N)
Net
wor
k O
pera
ting
Sys
tem
Hid
e an
d m
anag
e ha
rdw
are
reso
urce
s
Tig
htly
-cou
pled
ope
ratin
g sy
stem
for
mul
ti-pr
oces
sors
and
hom
ogen
eous
m
ultic
ompu
ters
Dis
trib
uted
O
pera
ting
Sys
tem
Mai
n G
oal
Des
crip
tio
nS
yste
m
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
19
Ch
ap
ter
1:
In
trodu
cti
on
Rel
atio
n t
o O
SI r
efer
ence
mo
del
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
20
Ch
ap
ter
1:
In
trodu
cti
on
OS
I lay
ers
Laye
rD
escr
iptio
nE
xam
ples
App
licat
ion
Pro
toco
ls th
at a
re d
esig
ned
to m
eet t
he c
omm
unic
atio
n re
quire
men
ts o
fsp
ecifi
c ap
plic
atio
ns, o
ften
defin
ing
the
inte
rfac
e to
a s
ervi
ce.
HT
TP
, FT
P, S
MT
P,
CO
RB
A II
OP
Pre
sent
atio
nP
roto
cols
at t
his
leve
l tra
nsm
it da
ta in
a n
etw
ork
repr
esen
tatio
n th
at is
inde
pend
ent o
f the
rep
rese
ntat
ions
use
d in
indi
vidu
al c
ompu
ters
,whi
chm
ay d
iffer
. Enc
rypt
ion
is a
lso
perf
orm
ed in
this
laye
r, if
req
uire
d.
Sec
ure
Soc
kets
(SS
L),C
OR
BA
Dat
aR
ep.
Ses
sion
At t
his
leve
l rel
iabi
lity
and
adap
tatio
n ar
e pe
rfor
med
, suc
h as
det
ectio
n of
failu
res
and
auto
mat
ic r
ecov
ery.
Tra
nspo
rtT
his
is th
e lo
wes
t lev
el a
t whi
ch m
essa
ges
(rat
her
than
pac
kets
)ar
e ha
ndle
d.M
essa
ges
are
addr
esse
d to
com
mun
icat
ion
port
s at
tach
ed to
pro
cess
es,
Pro
toco
ls in
this
laye
r m
ay b
e co
nnec
tion-
orie
nted
or
conn
ectio
nles
s.
TC
P, U
DP
Net
wor
kT
rans
fers
dat
a pa
cket
s be
twee
n co
mpu
ters
in a
spe
cific
net
wor
k. In
a W
AN
or a
n in
tern
etw
ork
this
invo
lves
the
gene
ratio
n of
a r
oute
pas
sing
thro
ugh
rout
ers.
In a
sin
gle
LAN
no
rout
ing
is r
equi
red.
IP, A
TM
virt
ual
circ
uits
Dat
a lin
kR
espo
nsib
le fo
r tr
ansm
issi
on o
f pac
kets
bet
wee
n no
des
that
are
dire
ctly
conn
ecte
d by
a p
hysi
cal l
ink.
In a
WA
N tr
ansm
issi
on is
bet
wee
n pa
irs o
fro
uter
s or
bet
wee
n ro
uter
s an
d ho
sts.
In a
LA
N it
is b
etw
een
any
pair
of h
osts
.Eth
erne
t MA
C,
AT
M c
ell t
rans
fer,
PP
PP
hysi
cal
The
circ
uits
and
har
dwar
e th
at d
rive
the
netw
ork.
It tr
ansm
its s
eque
nces
of
bina
ry d
ata
by a
nalo
gue
sign
allin
g, u
sing
am
plitu
de o
r fr
eque
ncy
mod
ulat
ion
of e
lect
rical
sig
nals
(on
cab
le c
ircui
ts),
ligh
t sig
nals
(on
fibr
e op
tic c
ircui
ts)
or o
ther
ele
ctro
mag
netic
sig
nals
(on
rad
io a
nd m
icro
wav
e ci
rcui
ts).
Eth
erne
t bas
e-ba
ndsi
gnal
ling,
IS
DN
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
21
Ch
ap
ter
1:
In
trodu
cti
on
Mid
dle
war
e an
d O
pen
nes
s
In a
n op
en m
iddl
ewar
e-ba
sed
dist
ribut
ed s
yste
m, t
he p
roto
cols
use
d by
ea
ch m
iddl
ewar
e la
yer
shou
ld b
e th
e sa
me,
as
wel
l as
the
inte
rfac
es th
ey
offe
r to
app
licat
ions
.
1.23
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
22
Ch
ap
ter
1:
In
trodu
cti
on
Co
mp
aris
on
bet
wee
n S
yste
ms
Ope
nO
pen
Clo
sed
Clo
sed
Ope
nnes
s
Var
ies
Yes
Mod
erat
ely
No
Sca
labi
lity
Per
nod
eP
er n
ode
Glo
bal,
dist
ribut
edG
loba
l, ce
ntra
lR
esou
rce
man
agem
ent
Mod
el
spec
ific
File
sM
essa
ges
Sha
red
mem
ory
Bas
is fo
r co
mm
unic
atio
n
NN
N1
Num
ber
of c
opie
s of
O
S
No
No
Yes
Yes
Sam
e O
S o
n al
l nod
es
Hig
hLo
wH
igh
Ver
y H
igh
Deg
ree
of
tran
spar
ency
Mu
ltic
om
.M
ult
ipro
c.
Mid
dle
war
e-b
ased
OS
Net
wo
rk
OS
Dis
trib
ute
d O
SIt
em
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
23
Ch
ap
ter
1:
In
trodu
cti
on
Mid
dle
war
e -
Ap
pro
ach
esD
istr
ibu
ted
file
sys
tem
s•
Dis
trib
utio
n tr
ansp
aren
cies
for
files
•P
opul
ar b
ecau
se o
f its
sca
labi
lity
Dis
trib
ute
d d
ocu
men
ts•
Exa
mpl
e W
orld
Wid
e W
eb•
Info
rmat
ion
are
seen
as
docu
men
ts, a
ddre
ssed
by
an U
RL
Rem
ote
Pro
ced
ure
Cal
l (R
PC
)•
Ear
ly m
iddl
ewar
e ap
proa
ch fo
r tr
ansp
aren
cy in
com
mun
icat
ion
Dis
trib
ute
d o
bje
cts
•E
nhan
cem
ents
of R
PC
to a
cces
s to
rem
ote
obje
cts
•O
nly
the
inte
rfac
e ca
n be
see
n fr
om o
utsi
de, t
he im
plem
enta
tion
deta
ils a
re
tran
spar
ent
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
24
Ch
ap
ter
1:
In
trodu
cti
on
File
Sys
tem
Bas
ed M
idd
lew
are
•B
ases
on
file
exch
ange
•T
rans
fer
Mod
els
(a)
uplo
ad/d
ownl
oad
mod
el(b
) re
mot
e ac
cess
mod
el
(a)
(b)
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
25
Ch
ap
ter
1:
In
trodu
cti
on
Do
cum
ent-
Bas
ed M
idd
lew
are
•E
xam
ple
Wor
ld W
ide
Web
(W
WW
)
�a
big
dire
cted
gra
ph o
f doc
umen
ts�
Tra
nspa
renc
y fo
r do
cum
ents
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
26
Ch
ap
ter
1:
In
trodu
cti
on
Co
mm
un
icat
ion
in D
istr
ibu
ted
S
yste
ms
Pro
blem
in d
istr
ibut
ed s
yste
ms:
•
Hig
h ov
erhe
ad c
ause
d by
pro
toco
l sta
ck
•N
eed
for
an e
asy
mod
el fo
r ef
ficie
nt c
omm
unic
atio
n
Idea
: •S
truc
turin
g of
the
oper
atin
g sy
stem
as
a se
t of c
oope
ratin
g pr
oces
ses
(Ser
vers
)•
Ser
vers
offe
r se
rvic
es fo
r us
ers
(Clie
nts
)
•C
omm
unic
atio
n by
usi
ng e
asy
prim
itive
s
Clie
nt/
Ser
ver
Mo
del
Rem
ote
Pro
ced
ure
Cal
l
Com
mun
icat
ion
betw
een
proc
esse
s is
a c
entr
al p
art o
f eac
h di
strib
uted
sys
tem
.W
ithou
t com
mun
icat
ion,
onl
y a
colle
ctio
n of
aut
onom
ous
proc
esse
sw
ithou
t a
poss
ibili
ty o
f coo
pera
tion
wou
ld e
xist
.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
27
Ch
ap
ter
1:
In
trodu
cti
on
Clie
nt/
Ser
ver
Mo
del
Clie
ntS
erve
r
netw
ork
Ker
nel
Ker
nel
requ
est
repl
y
•C
omm
unic
atio
n m
odel
with
low
man
agem
ent o
verh
ead
•C
onne
ctio
n-le
ss r
eque
st/r
eply
pro
toco
l (si
mpl
est c
ase:
onl
y ne
ed fo
r la
yer
1, 2
,
and
5)
•D
irect
add
ress
ing
of th
e se
rver
by
a cl
ient
:
�no
rmal
ly, t
he c
lient
kno
ws
the
serv
er's
add
ress
�si
mpl
e ad
dres
sing
: machine.process
�co
uld
by w
ritte
n(f
orpr
oces
s 42
26 o
n ho
st 1
37.2
26.1
2.22
1):
137.226.12.221.4226
or
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
28
Ch
ap
ter
1:
In
trodu
cti
on
Co
mm
un
icat
ion
Seq
uen
ce
Com
mun
icat
ion
ism
ade
byus
ing
two
syst
em c
alls
:
send(a, &mp)
tran
smits
a m
essa
ge r
efer
ence
d by
mp
to p
roce
ss a
.
The
cal
ler
is b
lock
ed w
hile
sen
ding
the
mes
sage
.
receive(a, &mp)
stor
es a
mes
sage
s re
ceiv
ed a
t add
ress
ain
a b
uffe
r re
fere
nced
by
mp
. The
cal
ler
is b
lock
ed w
hile
rec
eivi
ng th
e m
essa
ge.
Nee
ded:
syn
chro
nisa
tion
of send
and receive
.
wor
king
bloc
ked
send
receive
bloc
ked
wor
king
send
receive
Beg
inof
tr
ansm
issi
on
Clie
ntS
erve
r
Beg
inof
tr
ansm
issi
on
End
of
tran
smis
sion
End
of
tran
smis
sion
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
29
Ch
ap
ter
1:
In
trodu
cti
on
Exa
mp
le -
Ser
ver
head
er.h
con
tain
s co
mm
on
type
def
initi
ons
for
clie
nt a
nd
serv
er
Ser
ver:
cre
ates
a m
essa
ge m
2 ba
sed
on th
e co
nten
ts o
f mes
sage
m1
bloc
king
, wai
t
→fo
r in
com
ing
mes
sage
s fo
r F
ILE
_SE
RV
ER
Sen
d re
sult
to th
e ca
lling
clie
nt
→
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
30
Ch
ap
ter
1:
In
trodu
cti
on
Exa
mp
le -
Clie
nt
Sen
ding
of
the
requ
est
and
→
bloc
king
whi
le
wai
ting
for
the
repl
y
Clie
nt: u
ses
FIL
E_S
ER
VE
R,
to c
opy
a fil
e
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
31
Ch
ap
ter
1:
In
trodu
cti
on
Nam
e S
erve
r
Clie
ntS
erve
r
netw
ork
Ker
nel
Ker
nel
Nam
e S
erve
r
Ker
nel
netw
ork
3. r
eque
st
4. r
eply
1. r
eque
st
2. r
eply
Enh
ance
men
t of C
lient
/Ser
ver
Mod
el (
com
mon
met
hod)
:U
sing
a N
ame
serv
er
1. R
eque
st fo
r de
stin
atio
n ad
dres
s of
sea
rche
d se
rver
2. R
eply
with
ser
ver
addr
ess
3. R
eque
st to
ser
ver
4. R
eply
by
serv
er
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
32
Ch
ap
ter
1:
In
trodu
cti
on
Blo
ckin
g in
Clie
nt/
Ser
ver
Sys
tem
s
A d
istin
ctio
n is
mad
e be
twee
n b
lock
ing
and
no
n-b
lock
ing
prim
itive
s.T
he a
pplic
atio
n pr
ogra
mm
er c
an c
hoos
e fr
om th
em.
Blo
ckin
g pr
imiti
ves
•B
lock
s a
proc
ess
whi
le s
endi
ng a
mes
sage
•F
urth
er o
pera
tions
are
wor
ked
on o
nly
afte
r se
ndin
g th
e co
mpl
ete
mes
sage
•In
the
sam
e w
ay: r
ecei
ving
a m
essa
ge
Non
-blo
ckin
g pr
imiti
ves
•T
he m
essa
ge is
cop
ied
in a
buf
fer
man
aged
by
the
oper
atin
g sy
stem
•A
fter
the
copy
ope
ratio
n th
e se
nder
is u
nblo
cked
•S
peed
-up
by s
endi
ng th
e m
essa
ge a
nd w
orki
ng o
n th
e fu
rthe
r op
erat
ions
in
para
llel
•D
isad
vant
age:
the
send
er d
oes
not k
now
whe
n th
e tr
ansm
issi
on is
fini
shed
and
th
e bu
ffer
can
be u
sed
agai
n.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
33
Ch
ap
ter
1:
In
trodu
cti
on
Bu
ffer
ing
Ano
ther
dis
tinct
ion
of p
rimiti
ves
can
be m
ade
by b
uff
ers
Prim
itive
s w
ithou
t buf
fers
•W
ith receive(a, &mp)
the
kern
el is
info
rmed
that
the
calli
ng p
roce
ss w
ants
to
liste
n on
add
ress
afo
ra
mes
sage
to b
est
ored
at &mp
.•
Pro
blem
s:
1. M
essa
ge lo
st fo
r la
te receive
(the
ker
nel d
oes
not k
now
whe
re to
sto
re th
e m
essa
ge)
2. U
sage
of s
ame
addr
ess
by s
ever
al p
roce
sses
Prim
itive
s w
ith b
uffe
rs•
The
ker
nel s
tore
s th
e re
ceiv
ed m
essa
ge fo
r a
cert
ain
time
•P
robl
em: t
he k
erne
l has
to p
rovi
de a
nd m
anag
e ow
n bu
ffers
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
34
Ch
ap
ter
1:
In
trodu
cti
on
Clie
nt/
Ser
ver
Arc
hit
ectu
res
The
sep
arat
ion
of c
lient
and
ser
ver
can
take
pla
ce a
t diff
eren
t poi
nts
in th
e w
hole
app
licat
ion,
con
side
ring
stru
ctur
e an
d ta
sks
of th
e w
hole
sys
tem
.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
35
Ch
ap
ter
1:
In
trodu
cti
on
Mu
lti-
leve
l Sys
tem
s
The
ser
ver
itsel
f can
del
egat
e pa
rts
of it
s ta
sks
to o
ther
ser
vers
. In
doin
g so
, the
se
rver
bec
omes
a c
lient
for
the
new
ser
ver.
Thi
s se
para
tion
by a
reas
of r
espo
nsib
ilitie
s is
cal
led
vert
ical
dis
trib
uti
on
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
36
Ch
ap
ter
1:
In
trodu
cti
on
Oth
er a
rch
itec
ture
sH
oriz
onta
l dis
trib
utio
nar
ises
, whe
n se
rver
(or
clie
nt)
are
split
ted
into
sev
eral
eq
uiva
lent
par
ts (
e.g.
a w
eb s
erve
r fa
rm).
... a
nd th
ere
are
othe
r or
gani
satio
n m
odel
s fo
r cl
ient
/ser
ver
syst
ems
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
37
Ch
ap
ter
1:
In
trodu
cti
on
Rem
ote
Pro
ced
ure
Cal
lB
ase
para
digm
for
com
mun
icat
ion
(esp
ecia
lly fo
r lo
cal i
nvoc
atio
ns):
In
pu
t an
d o
utp
ut
of d
ata
By
calli
ng c
omm
unic
atio
n pr
imiti
ves send
and receive
expl
icitl
y:E
xch
ang
eof
dat
a
Nee
d fo
r an
othe
r m
echa
nism
: Le
t dis
trib
uted
com
puta
tions
look
like
cen
tral
ised
one
s
Sol
utio
n (B
irell
and
Nel
son,
198
4):
A p
rogr
am c
alls
a s
ubro
utin
e lo
cate
d on
an
othe
r co
mpu
ter.
Kno
wn
as R
emo
te P
roce
du
re C
all,
RP
C
Prin
cipl
e:
Whe
n a
prog
ram
loca
ted
on h
ost A
calls
a s
ubro
utin
e lo
cate
d on
hos
t B, t
he c
allin
g pr
oces
s on
hos
t Ais
sus
pend
ed w
hile
the
subr
outin
e on
hos
t Bis
exe
cute
d. T
he
exch
ange
of p
aram
eter
s an
d m
essa
ges
is in
visi
ble
for
the
user
.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
38
Ch
ap
ter
1:
In
trodu
cti
on
Rem
ote
Pro
ced
ure
Cal
l
Net
zwer
k
Clie
ntre
ques
t
resu
lt
Mec
hani
sm is
tr
ansp
aren
t for
the
calli
ng c
lient
Clie
ntre
ques
t
resu
lt
Put
dat
aon
sta
ck
Get
dat
afr
om s
tack
subr
outin
eco
mpu
tatio
n
a) L
ocal
cal
l to
subr
outin
e
b) R
emot
e P
roce
dure
Cal
l
Stu
b:
Act
s as
a p
roxy
for
the
subr
outin
e an
d pa
sses
the
requ
est t
o th
e fit
ting
serv
er
Mar
shal
ling:
tr
ansl
ates
dat
a in
to a
n in
depe
nden
t tr
ansp
ort f
orm
at
Ker
nel
Mec
hani
sm is
tran
spar
ent f
or th
e ca
lling
clie
nt
Unm
arsh
allin
g
Mar
shal
ling
Mar
shal
ling
Unm
arsh
allin
g
Ser
ver
stub
Clie
nt s
tub
resu
ltS
erve
r
requ
est
netw
ork
Ker
nel o
n se
rver
hos
tK
erne
l on
clie
nt h
ost
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
39
Ch
ap
ter
1:
In
trodu
cti
on
RP
C -
Pro
cess
Adv
anta
ge:
-th
e di
strib
uted
exe
cutio
n w
orks
with
out e
xplic
itly
calli
ng th
e co
mm
unic
atio
n pr
imiti
ves
by c
lient
res
p. s
erve
r.
-D
etai
ls a
re h
idde
n by
stu
bs.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
40
Ch
ap
ter
1:
In
trodu
cti
on
Rem
ote
Pro
ced
ure
Cal
l -E
xam
ple
Clie
nt:
•C
alls
the
proc
edur
e add(2,4)
•T
he d
ata
are
push
ed o
nto
the
stac
k•
The
clie
nt li
brar
y co
ntai
ns a
ref
eren
ce
to th
e cl
ien
t st
ub
inst
ead
refe
renc
ing
a lo
calp
roce
dure
dire
ctly
•
Tra
nsm
issi
on o
f con
trol
to th
e st
ub
Clie
nt s
tub:
•G
ener
ates
a m
essa
ge fr
om th
e re
ques
t w
hich
can
be
sent
to th
e se
rver
•M
arsh
allin
g of
the
data
, i.e
. the
dat
a ar
e tr
ansf
orm
ed in
a g
iven
mes
sage
st
ruct
ure
•T
he send
prim
itive
initi
ates
the
tran
smis
sion
of t
he m
essa
ge•
The
stu
b ca
lls receive
and
bloc
ks
Clie
nt:
x = add(2,4)
42add
Stu
b:add 2 4
mp
:
Clie
nt s
tack
send(ServerAdr, &mp)
receive(ClientAdr, &mp)
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
41
Ch
ap
ter
1:
In
trodu
cti
on
Rem
ote
Pro
ced
ure
Cal
l -E
xam
ple
Ser
ver
host
:•
The
ser
ver
wai
tsfo
r in
com
ing
requ
ests
by e
xecu
ting receive
.•
The
ker
nel p
asse
s th
e m
essa
ge to
the
serv
er s
tub.
•T
he s
tub
extr
acts
the
data
, pus
hes
them
ont
o th
e se
rver
sta
ck a
nd
calls
the
(loca
l) su
brou
tine.
•W
hen
the
com
puta
tion
is fi
nish
ed,
the
serv
er c
alls
its
stub
. The
stu
b m
arsh
als
the
resu
lt an
d se
nds
a
mes
sage
bac
k to
the
calli
ng c
lient
.
Stu
b:
add 2 4
42addS
erve
r st
ack
6
Ser
ver:
Stu
b:6
mp:
send(ClientAdr, &mp)
receive(ServerAdr, &mp)
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
42
Ch
ap
ter
1:
In
trodu
cti
on
Rem
ote
Pro
ced
ure
Cal
l -E
xam
ple
Clie
nt h
ost:
•T
he c
lient
stu
bw
aits
for
the
repl
y
perf
orm
ing
the receive
•T
he m
essa
ge is
writ
ten
in a
buf
fer
•T
he c
lient
stu
b is
unb
lock
ed•
The
stu
b ex
trac
ts th
e re
sult
and
push
es it
ont
o th
e cl
ient
sta
ck•
The
clie
nt is
giv
en b
ack
cont
rol a
n ge
ts
–lik
e in
the
loca
l cas
e –
the
data
from
its s
tack
6C
lient
:
Stu
b:6
x = 6
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
43
Ch
ap
ter
1:
In
trodu
cti
on
Pro
ble
ms
wit
h R
PC
The
com
mun
icat
ion
betw
een
iden
tical
com
pute
rs c
ause
s no
pro
blem
s.
In h
eter
ogen
eous
sys
tem
s, th
ere
can
be s
ome
prob
lem
s:
•D
iffer
ent c
hara
cter
rep
rese
ntat
ions
(A
SC
II -
ED
CD
IC)
•D
iffer
ent r
epre
sent
atio
n of
inte
gers
(lit
tle e
ndia
n-
big
endi
an)
Ano
ther
pro
blem
are
non
-sca
lar
data
type
s:
•T
here
is n
o sh
ared
add
ress
spa
ce –
how
to tr
ansm
it po
inte
rs a
nd r
efer
ence
s?
•N
orm
ally
: cop
y/re
stor
e, i.
e. tr
ansm
it re
fere
nced
dat
a di
rect
ly
•B
ut th
is w
orks
onl
y fo
r si
mpl
e st
ruct
ures
and
arr
ays;
for
mor
e co
mpl
ex s
truc
ture
s w
hich
are
def
ined
by
the
prog
ram
mer
, the
ser
ver
cann
ot u
nder
stan
d th
e st
ruct
ure.
Con
clus
ion:
clie
nt a
nd s
erve
r ha
ve to
agr
ee o
n a
com
mon
dat
a fo
rmat
whi
ch
can
be tr
ansm
itted
with
the
RP
C.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
44
Ch
ap
ter
1:
In
trodu
cti
on
Gen
erat
ion
of
Stu
bs
For
def
inin
g co
mm
on d
ata
form
ats
and
supp
ortin
gth
e im
plem
enta
tion
of s
tubs
, ve
ry o
ften
only
the
inte
rfac
es a
re d
efin
ed. T
he s
tubs
are
gen
erat
ed fr
om th
ese
defin
ition
aut
omat
ical
ly, c
onta
inig
the
who
le tr
ansf
er s
ynta
x w
hich
can
be
used
.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
45
Ch
ap
ter
1:
In
trodu
cti
on
En
han
cem
ents
of
RP
C
RP
C: d
e-fa
cto-
Sta
ndar
d fo
r co
mm
unic
atio
n in
dis
trib
uted
sys
tem
s
The
RP
C c
an b
e op
timis
ed fo
r sp
ecia
l sce
nario
s. S
ome
varia
nts
are
•Li
ghtw
eigh
t RP
Cfo
r in
ter-
proc
ess
com
mun
icat
ion
in th
e sa
me
addr
ess
spac
e
•A
sync
hron
ous
RP
Cfo
r de
coup
ling
clie
nt a
nd s
erve
r
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
46
Ch
ap
ter
1:
In
trodu
cti
on
Ber
shad
'sL
RP
C
The
dur
atio
n of
a R
PC
dep
ends
on
seve
ral p
aram
eter
s (s
ever
al c
opy
oper
atio
ns
on th
e pa
ram
eter
s, n
etw
ork
dela
y) a
nd c
an ta
ke s
igni
fican
t tim
e. F
or s
ome
circ
umst
ance
s, th
e ex
ecut
ion
can
be s
peed
ed u
p:
→U
se o
f sha
red
mem
ory
for
inte
r-pr
oces
s co
mm
unic
atio
n on
the
sam
e ho
st
•O
nly
one
copy
ope
ratio
n fo
r pa
ram
eter
pas
sing
(in
stea
d of
four
cop
y op
erat
ions
like
in R
PC
)
•T
he c
lient
can
acc
ess
the
serv
er c
ode
usin
g de
fined
acc
ess
poin
ts
•S
peed
-up
up to
thre
e tim
es
→N
ame:
Lig
htw
eigh
t RP
C, L
RP
C(li
ghtw
eigh
t mea
ns e
asie
r an
d fa
ster
)
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
47
Ch
ap
ter
1:
In
trodu
cti
on
Lig
htw
eig
ht
Rem
ote
Pro
ced
ure
Cal
l
2. R
eque
st
4. E
xecu
tion
of p
roce
dure
and
st
orin
g th
e re
sult
Clie
nt
Use
rS
tub
Ser
ver
Ker
nel
Stu
b 3. U
p ca
ll5.
Ret
urn
A
Com
mon
sta
ck
1. C
opyi
ng th
e ar
gum
ents
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
48
Ch
ap
ter
1:
In
trodu
cti
on
•T
he c
lient
can
wor
k on
oth
er ta
sks
till t
he r
esul
t fro
m th
e se
rver
com
es in
•T
he c
lient
get
s ba
ck n
o re
sult
Asy
nch
ron
ou
s R
PC
RP
C: s
ynch
ron
ou
s, i.
e. th
e cl
ient
blo
cks
till t
he s
erve
r re
ques
t com
es in
. But
in
som
e si
tuat
ions
, thi
s w
aitin
g is
not
nec
essa
ry:
In th
ese
case
s: a
syn
chro
no
us
RP
C, i
.e. t
he c
lient
doe
s no
t blo
ck, b
ut is
abl
e to
w
ork
on o
ther
task
s, ti
ll th
e se
rver
inte
rrup
ts it
with
the
resu
lt:
one-
way
RP
C: d
o no
t wai
t for
an
ackn
owle
dgem
ent,
but w
ork
on d
irect
ly
defe
rred
syn
chro
nous
RP
C: r
eque
st a
nd r
eply
bot
h ar
e us
ing
asyn
chro
nous
RP
C
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
49
Ch
ap
ter
1:
In
trodu
cti
on
Rem
ote
Met
ho
d In
voca
tio
nB
ase
prin
cipl
e of
RP
C: a
clie
nt c
alls
a s
ubro
utin
e/pr
oced
ure
in a
sep
arat
e se
rver
pr
oces
s.
Rem
ote
Met
ho
d In
voca
tio
n(R
MI)
:bui
lds
upon
the
sam
e pr
inci
ple:
an
obje
ct c
alls
a
met
hod
of a
noth
er o
bjec
t. T
he p
rinci
ple
is th
e sa
me,
but
the
unde
rlyin
g m
odel
is
chan
ged
(and
enh
ance
d w
ith s
ome
mor
e fu
nctio
nalit
y).
Pro
xy: c
lient
sid
e st
ub
for
invo
king
rem
ote
obje
cts
Ske
leto
n: s
erve
r si
de
stub
for
rece
ivin
g pr
oxy
requ
ests
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
50
Ch
ap
ter
1:
In
trodu
cti
on
Pee
r-to
-Pee
rco
mp
uti
ng
•W
eake
ning
of c
lient
and
serv
erro
les
•C
onne
ctio
nbe
twee
nan
ypa
ir of
com
pute
rs
•F
elxi
ble
netw
ork
of c
oope
ratio
ns
•W
ell k
now
nex
ampl
e: F
ile S
harin
g, e
.g. N
apst
er
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
51
Ch
ap
ter
1:
In
trodu
cti
on
Mes
sag
e-b
ased
Co
mm
un
icat
ion
Mes
sag
e-b
ased
(or
even
t-b
ased
) co
mm
unic
atio
n: o
bjec
ts a
re s
endi
ng
info
rmat
ion
to th
e re
ceiv
ers
by u
sing
mes
sage
s. T
hese
mes
sage
s ar
e se
nt
asyn
chro
nous
ly(in
con
tras
t to
the
basi
c pr
inci
ples
of t
he c
omm
unic
atio
n fo
rms
show
n be
fore
). T
he c
omm
unic
atio
n sy
stem
is r
espo
nsib
le fo
r de
liver
ing
the
mes
sage
s
Dis
tinct
ion
betw
een
two
kind
s of
sys
tem
s:
•P
ersi
sten
t com
mun
icat
ion
The
com
mun
icat
ion
syst
em s
tore
s m
essa
ges
till i
t is
able
to d
eliv
er th
em to
the
rece
iver
. Sen
der
and
rece
iver
are
dec
oupl
ed c
ompl
etel
y, th
e re
ceiv
ing
obje
ct is
al
low
ed to
be
not a
vaila
ble
whe
n th
e m
essa
ge is
sen
t.
•T
rans
ient
com
mun
icat
ion
The
com
mun
icat
ion
syst
em o
nly
stor
es th
e m
essa
ge w
hile
sen
der
and
rece
iver
ar
e up
and
run
ning
. If a
mes
sage
can
not b
e de
liver
ed b
ecau
se th
ere
ceiv
er
cann
ot r
each
ed, t
he m
essa
ge is
del
eted
.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
52
Ch
ap
ter
1:
In
trodu
cti
on
Mes
sag
e-q
ueu
ing
Sys
tem
s
Per
sist
ent,
asyn
chro
nous
com
mun
icat
ion:
the
send
er is
gua
rant
eed
that
its
mes
sage
rea
ches
the
rece
iver
. Onl
y w
hen
the
mes
sage
is d
eliv
ered
(and
if th
e re
ceiv
er r
eads
it)
is u
nkno
wn.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
53
Ch
ap
ter
1:
In
trodu
cti
on
Gen
eral
Arc
hit
ectu
re o
f a
Mes
sag
e-Q
ueu
ing
Sys
tem
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
54
Ch
ap
ter
1:
In
trodu
cti
on
Mes
sag
e B
roke
r
For
inte
grat
ing
seve
ral a
pplic
atio
ns in
a d
istr
ibut
ed in
form
atio
n sy
stem
, som
e m
ore
is n
eces
sary
: the
se a
pplic
atio
ns c
an u
se d
iffer
ent m
essa
ge fo
rmat
s (li
ke in
RP
C).
A
so-c
alle
d m
essa
ge
bro
ker
suits
for
conv
ertin
gm
essa
ges
in o
ther
form
ats.
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
55
Ch
ap
ter
1:
In
trodu
cti
on
Str
eam
-bas
ed C
om
mu
nic
atio
n
The
com
mun
icat
ion
mod
el lo
oked
at a
re n
ot c
onsi
derin
g sp
ecia
l req
uire
men
ts in
in
form
atio
n de
liver
y. B
ut fo
r m
ultim
edia
app
licat
ions
, tim
e re
stric
tions
are
ver
y im
port
ant.
→Le
ctur
e M
ultim
edia
Sys
tem
s
Leh
rstu
hl fü
r I
nfo
rm
ati
k 4
Kom
mu
nik
ati
on
un
d v
erte
ilte
Syste
me
56
Ch
ap
ter
1:
In
trodu
cti
on
Gro
up
Co
mm
un
icat
ion
If a
mes
sage
can
be
sent
to a
gro
up o
f rec
eive
rs, g
roup
com
mun
icat
ion
is n
eede
d fo
r ef
ficie
nt c
omm
unic
atio
n:
•F
ault
tole
ranc
e/av
aila
bilit
yA
serv
ice
is r
eplic
ated
, i.e
. rea
lised
on
seve
ral h
osts
. A c
lient
can
send
its
requ
est t
o al
l mem
bers
of t
he s
erve
r gr
oup.
All
of th
em a
re p
erfo
rmin
g th
e re
ques
t. E
ven
if so
me
of th
e se
rver
s cr
ash,
the
serv
ice
is a
lread
y av
aila
ble.
•P
erfo
rman
ce in
crea
se
Whe
n us
ing
repl
icat
ed s
erve
rs, e
.g. f
or p
laci
ng d
ata
near
to a
clie
nt a
nd th
us
impr
ove
its a
cces
s to
the
data
, all
data
base
s of
the
serv
ers
have
to b
e in
a
cons
iste
nt s
tate
. Whe
n a
data
cha
nge
occu
rs, t
he n
ew d
ata
have
to b
e tr
ansm
itted
to
all
mem
bers
of t
he s
erve
r gr
oup.
•E
vent
not
ifica
tion
One
serv
ice
type
is a
dis
trib
utio
n se
rvic
e: if
a c
erta
in e
vent
occ
urs,
a c
erta
inus
er
grou
p ha
s to
be
info
rmed
. One
exa
mpl
e fo
r su
ch a
ser
vice
is a
new
s sy
stem
, whe
re
a ne
w in
com
ing
new
s is
rep
orte
d to
a u
ser
grou
p.
Nee
ded:
mu
ltic
ast
com
mu
nic
atio
n
