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The Center for Distributed Object Computing
Research Synopsis
David L. Levinewww.cs.wustl.edu/ �levine/
Director, Center for Computer Science Dept.Distributed Object Computing Washington University, St. Louis
SponsorsNSF, DARPA, Bellcore/Telcordia, BBN, Boeing, CDI/GDIS, Comverse, Hughes,
Kodak, Lockheed, Lucent, Microsoft, Motorola, Nokia, Nortel, OCI,OTI, Raytheon, SAIC, Siemens SCR, Siemens MED, Siemens ZT, Sprint, USENIX
24 November 1999
DOC Center Washington University, St. Louis
Motivation: the Communication Software Crisis
www.arl.wustl.edu/arl/� Symptoms
Communication hardware getssmaller, faster, cheaper
– Communication software gets larger,slower, more expensive
� Culprits
– Inherent and accidental complexity
� Solution Approach
– Standard communicationmiddleware
1
DOC Center Washington University, St. Louis
DOC Center Research Focus
HighPerformance
Real-TimeCORBA
DistributedConfigurable
Systems
Adaptive Communication Environment (ACE)
The ACE Orb (TAO)
Patte
rns,
Pat
tern
Lan
guag
es, a
nd F
ram
ewor
ks
SimulationandEmbeddedSystems
MissionCritical
Communication
2
DOC Center Washington University, St. Louis
DOC Center Members� David L. Levine, Director
� Fred Kuhns, Associate Director
� Douglas C. Schmidt, Former Director
� Full-time staff: C. Gill, C. O’Ryan, J. Parsons, I. Pyarali, N. Wang
� PhD students: C. Gill, J. Hu, C. O’Ryan, O. Othman, I. Pyarali, N.Wang
� Masters students: L. Baker, D. Brunsch, P. Gore, V. Kachroo, Y.Krishnamurthy, B. Natarajan, K. Parameswaran, J. Parsons, M.Spivak
� Undergrads: K. Pathayapura
3
DOC Center Washington University, St. Louis
DOC Center Sponsors
Bellcore/Telcordia MotorolaBBN NokiaBoeing NortelCDI/GDIS NSFComverse OCIDARPA OTIHughes RaytheonKodak SAICLockheed Martin SiemensLucent SprintMicrosoft USENIX
4
DOC Center Washington University, St. Louis
Problem: Lack of QoS-enabled Middleware
HHOOSSTT IINNFFRRAASSTTRRUUCCTTUURREE MMIIDDDDLLEEWWAARREE
DDIISSTTRRIIBBUUTTIIOONN MMIIDDDDLLEEWWAARREE
CCOOMMMMOONN MMIIDDDDLLEEWWAARREE SSEERRVVIICCEESS
AAPPPPLLIICCAATTIIOONNSS
HHAARRDDWWAARREE DDEEVVIICCEESS
WWTTSSHHUUDD
NNaavv
AAVVIIOONNIICCSSRREEPPLLIICCAATTIIOONN
SSEERRVVIICCEEDDOOMMAAIINN--SSPPEECCIIFFIICC MMIIDDDDLLEEWWAARREE SSEERRVVIICCEESS
OOPPEERRAATTIINNGG SSYYSSTTEEMMSS && PPRROOTTOOCCOOLLSS
EEVVEENNTTCCHHAANNNNEELL
CCoonnssCCoonnss
CCoonnss
� Many applications require QoSguarantees
– e.g., avionics, telecom, WWW,medical, high-energy physics
� Building these applicationsmanually is hard
� Existing middleware doesn’tsupport QoS effectively
– e.g., CORBA, DCOM, DCE, Java� Solutions must be integrated
horizontally & vertically
5
DOC Center Washington University, St. Louis
Candidate Solution: CORBA
INTERFACE
REPOSITORY
IMPLEMENTATION
REPOSITORY
IDLCOMPILER
DII ORBINTERFACE
ORBORB CORECORE GIOPGIOP//IIOPIIOP//ESIOPSESIOPS
IDLIDLSTUBSSTUBS
operation()operation()in args
out args + return value
CLIENTOBJECT(SERVANT)
OBJ
REF
STANDARD INTERFACE STANDARD LANGUAGE MAPPING
ORB-SPECIFIC INTERFACE STANDARD PROTOCOL
INTERFACE
REPOSITORY
IMPLEMENTATION
REPOSITORY
IDLCOMPILER
IDLSKELETON
DSI
OBJECT
ADAPTER
www.cs.wustl.edu/�schmidt/corba.html
Goals of CORBA
� Simplify distributionby automating
– Object location &activation
– Parametermarshaling
– Demultiplexing– Error handling
� Provide foundationfor higher-levelservices
6 DO
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Cav
eat:
Req
uire
men
ts/L
imita
tions
ofC
OR
BA
for
QoS
-ena
bled
Sys
tem
s
NE
TW
OR
KN
ET
WO
RK
OP
ER
AT
ION
SO
PE
RA
TIO
NS
CE
NT
ER
CE
NT
ER
HSM
HSM
AR
CH
IVE
AR
CH
IVE
SE
RV
ER
SE
RV
ER
AG
EN
TA
GE
NT
INT
ER
AC
TIV
EIN
TE
RA
CT
IVE
AU
DIO
AU
DIO
//VID
EO
VID
EO
AG
EN
TA
GE
NT
AR
CH
ITE
CT
UR
EA
RC
HIT
EC
TU
RE
SP
CS
PC
HA
RD
WA
RE
HA
RD
WA
RE
EM
BE
DD
ED
EM
BE
DD
ED
TA
OT
AO
MIB
MIB
AG
EN
TA
GE
NT
ww
w.c
s.w
ustl.
edu/
�
schm
idt/R
T-O
RB
.ps.
gz
Req
uire
men
ts
�
Loca
tion
tran
spar
ency
�
Per
form
ance
tran
spar
ency
�
Pre
dict
abili
tytr
ansp
aren
cy
�
Rel
iabi
lity
tran
pare
ncy
Lim
itatio
ns
�
Lack
ofQ
oSsp
ecifi
catio
ns
�
Lack
ofQ
oSen
forc
emen
t
�
Lack
ofre
al-t
ime
prog
ram
min
gfe
atur
es
�
Lack
ofpe
rform
ance
optim
izat
ions
DOC Center Washington University, St. Louis
Problem: Optimizing Complex Software
DIAGNOSTIC STATIONSDIAGNOSTIC STATIONS
ATMATMMANMAN
ATM
LAN
ATM
LAN
MODALITIES
(CT, MR, CR) CENTRAL
BLOB STORE
CLUSTER
BLOB
STORE
DX
BLOB
STORE
www.cs.wustl.edu/�schmidt/JSAC-99.ps.gz
Common Problems !
� Optimizing complex softwareis hard
� Small “mistakes” can be costly
Solution Approach (Iterative) !
� Pinpoint overhead viawhite-box metrics– e.g., Quantify and
VMEtro
� Apply patterns and frameworkcomponents
� Revalidate via white-box andblack-box metrics
8
DOC Center Washington University, St. Louis
Solution 1: Patterns and Framework Components
ACCEPTORCONNECTOR
ABSTRACTFACTORY
SERVANTCLIENT
OS KERNELOS KERNEL
LEADER /FOLLOWERS
THREAD -SPECIFICSTORAGE
COMPONENTCONFIGURATOR
REACTOR
WRAPPER FACADES
STRATEGY
www.cs.wustl.edu/�schmidt/ORB-patterns.ps.gz
Definitions
� Pattern
– A solution to a problem ina context
� Framework
– A “semi-complete”application built withcomponents
� Components
– Self-contained, “pluggable”ADTs
9
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Sol
utio
n2:
OR
BO
ptim
izat
ion
Prin
cipl
eP
atte
rns
Defi
nitio
n
�
Opt
imiz
atio
npr
inci
ple
patte
rns
docu
men
tru
les
for
avoi
ding
com
mon
desi
gnan
dim
plem
enta
tion
prob
lem
sth
atca
nde
grad
eth
eef
ficie
ncy,
scal
abili
ty,a
ndpr
edic
tabi
lity
ofco
mpl
exsy
stem
s
Key
Prin
cipl
eP
atte
rns
Use
din
TAO
#P
rinci
ple
Pat
tern
1O
ptim
ize
for
the
com
mon
case
2R
emov
egr
atui
tous
was
te3
Rep
lace
inef
ficie
ntge
nera
l-pur
pose
func
tions
with
effic
ient
spec
ial-p
urpo
seon
es4
Shi
ftco
mpu
tatio
nin
time,
e.g.
,pre
com
pute
5S
tore
redu
ndan
tsta
teto
spee
d-up
expe
nsiv
eop
erat
ions
6P
ass
hint
sbe
twee
nla
yers
and
com
pone
nts
7D
on’t
betie
dto
refe
renc
eim
plem
enta
tions
/mod
els
8U
seef
ficie
nt/p
redi
ctab
leda
tast
ruct
ures
DOC Center Washington University, St. Louis
Patterns for Communication Middleware
EventPatterns
ConcurrencyPatterns
ExternalPolymorphism
WrapperFacade
Connector
Acceptor
ThreadPool
Thread-perSession
Thread-perRequest
AsynchronousCompletion
Token
ThreadSpecificStorage
ActiveObject
Half-Sync/Half-Async
Leader/Followers
ServiceConfigurator
Object LifetimeManager
Reactor
Proactor
DoubleCheckedLocking
Thread-Safe
Interface
ScopedLocking
StrategizedLocking
InitializationPatterns
SynchronizationPatterns
� Observation
– Failures rarely resultfrom unknown scientificprinciples, but fromfailing to apply provenengineering practicesand patterns
� Benefits of Patterns
– Facilitate design reuse– Preserve crucial design
information– Guide design choices
11
DOC Center Washington University, St. Louis
The ADAPTIVE Communication Environment (ACE)
PROCESSES/THREADS
DYNAMICLINKING
SHAREDMEMORY
SELECT/IO COMP
FILE SYSAPIS
WIN32 NAMEDPIPES & UNIXSTREAM PIPES
UNIXFIFOS
CCAAPPIISS
SOCKETS/TLI
CCOOMMMMUUNNIICCAATTIIOONNSSUUBBSSYYSSTTEEMM
VVIIRRTTUUAALL MMEEMMOORRYY && FFIILLEESSUUBBSSYYSSTTEEMM
GGEENNEERRAALL OOPPEERRAATTIINNGG SSYYSSTTEEMM SSEERRVVIICCEESS
PPRROOCCEESSSS//TTHHRREEAADDSSUUBBSSYYSSTTEEMM
FFRRAAMMEEWWOORRKKLLAAYYEERR
AACCCCEEPPTTOORR CCOONNNNEECCTTOORR
NNEETTWWOORRKKEEDDSSEERRVVIICCEE
CCOOMMPPOONNEENNTTSSLLAAYYEERR
NAMESERVER
TOKENSERVER
LOGGINGSERVER
GATEWAYSERVER
SOCK SAP/TLI SAP
FIFOSAP
LOGMSG
SSEERRVVIICCEEHHAANNDDLLEERR
TIMESERVER
CC++++WWRRAAPPPPEERRFFAACCAADDEELLAAYYEERR SPIPE
SAP
CCOORRBBAAHHAANNDDLLEERR
FILESAP
SHAREDMALLOC
THE ACE ORB(TAO)
JAWS ADAPTIVEWEB SERVER
SSTTAANNDDAARRDDSS--BBAASSEEDD MMIIDDDDLLEEWWAARREE
RREEAACCTTOORR//PPRROOAACCTTOORR
PROCESS/THREADMANAGERS
SSTTRREEAAMMSS
SSEERRVVIICCEECCOONNFFIIGG--UURRAATTOORR
SYNCHWRAPPERS
MEMMAP
OOSS AADDAAPPTTAATTIIOONN LLAAYYEERR
www.cs.wustl.edu/�schmidt/ACE.html
� ACE Overview– Concurrent OO
networkingframework
– Available for C++and Java
– Ported to POSIX,Win32, VxWorks,Chorus, PharLapTNT, et al.
12 DO
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The
AC
EO
RB
(TA
O)
and
ItsC
OR
BA
Obj
ectS
ervi
ces
SC
HE
DU
LIN
G
PR
OP
ER
TY
EV
EN
T/
NO
TIF
ICA
TIO
NT
RA
DIN
G
NA
MIN
GC
ON
CU
RR
EN
CY
TIM
E
A/V
ST
RE
AM
ING
NE
TW
OR
K
OR
B Q
OS
INT
ER
FA
CE
RID
LS
TU
BS
RID
LS
KE
LE
TO
N
CL
IEN
T
OS
KE
RN
EL
OS
I/
O S
UB
SY
ST
EM
NE
TW
OR
K A
DA
PT
ER
S
OS
KE
RN
EL
OS
I/
O S
UB
SY
ST
EM
NE
TW
OR
K A
DA
PT
ER
S
GIO
P/R
IOP
OB
JE
CT
(SE
RV
AN
T)
LO
GG
ING
CORBA SERVICES
IDL
CO
MP
ILE
R
RE
AL-T
IME
OR
B C
OR
E
AC
EC
OM
PO
NE
NT
S
LIF
EC
YC
LE
RE
AL-T
IME
OB
JE
CT
AD
AP
TE
R
DOC Center Washington University, St. Louis
ACE and TAO Statistics
� Over 30 person-years of effort
– ACE > 200,000 LOC– TAO > 125,000 LOC– TAO IDL compiler > 100,000 LOC– TAO CORBA Object Services >
150,000 LOC
� Ported to POSIX, Win32, VxWorks,et al.
� Large user community
– www.cs.wustl.edu/�schmidt/ACE-users.html
� Currently used by dozensof companies
– Bellcore, Boeing,Ericsson, Kodak,Lockheed, Lucent,Motorola, Nokia, Nortel,Raytheon, SAIC,Siemens, etc.
� Supported commercially
– ACE !
www.riverace.com– TAO !
www.theaceorb.com
14
DOC Center Washington University, St. Louis
Real-time Optimizations in TAO
NETWORKNETWORK
OS KERNELOS KERNEL
OS IOS I//O SUBSYSTEMO SUBSYSTEM
NETWORK INTERFACESNETWORK INTERFACES
ORBORBINTERFACEINTERFACE
ORBORBCORECORE
operation()operation()
IDLIDLSTUBSSTUBS
OBJECTOBJECT
ADAPTERADAPTER
IDLIDLSKELETONSKELETON
in argsin args
out args + return valueout args + return value
CLIENT
GIOP
OBJECT(SERVANT)
CONCURRENCY
MODELS
TRANSPORT
PROTOCOLS
I/OSUBSYSTEM
NETWORK
ADAPTER
PRESENTATION
LAYER
SCHEDULING,DEMUXING, &DISPATCHING
DATA COPYING
& MEMORY
ALLOCATION
CONNECTION
MANAGEMENT
OS KERNEL
OS I/O SUBSYSTEM
NETWORK INTERFACES
OBJ
REF
15
DOC Center Washington University, St. Louis
New TAO Features and Optimizations
STANDARD
SYNCHRONIZERS
END-TO-END
PRIORITY
PROPAGATION
ORB CORE
OBJECT
ADAPTER
CLIENTOBJECT(SERVANT)
THREAD
POOLS
EXPLICIT
BINDING
NETWORK
OS KERNEL
NETWORK INTERFACE
OS I/O SUBSYSTEM
OS KERNEL
NETWORK INTERFACE
OS I/O SUBSYSTEM
PLUGGABLEPROTOCOLS &
PROPERTIES
GIOP GIOP
� New Features
– Real-time CORBA– Minimum CORBA– CORBA Messaging– Fault Tolerance
� URL
– �schmidt/TAO-status.html
16
DOC Center Washington University, St. Louis
Integrating TAO with ATM I/O Subsystem
REACTOR
(20 HZ)
REACTOR
(10 HZ)
REACTOR
(5 HZ)
REACTOR
(1 HZ)
ORB CORE
APIC ATM DRIVER
I/OSUBSYSTEM
PER-VC
SOCKET
QUEUES
APIC PACING
QUEUES
Z
E
R
O
C
O
P
Y
B
U
F
F
E
R
S
�schmidt/RIO.ps.gz
Features
� Vertical integration of QoSthrough ORB, OS, and ATMnetwork
� Real-time I/O enhancementsto Solaris kernel
� Provides rate-based QoSend-to-end
� Leverages APIC features forcell pacing and zero-copybuffering
17
DOC Center Washington University, St. Louis
Strategized Scheduling Framework ssttrruucctt RRTT__IInnffoo {{ wwcc__eexxeecc__ttiimmee__;; ppeerr iioodd__;; ccrr iittiiccaalliittyy__;; iimmppoorr ttaannccee__;; ddeeppeennddeenncciieess__;; }};;
SSCCHHEEDDUULLIINNGG
SSTTRRAATTEEGGYY
RRTT__IINNFFOO
RREEPPOOSSII TTOORRYY
OOFFFF--LL II NNEE
SSTTRRAATTEEGGIIZZEEDD
SSCCHHEEDDUULLEERR
OOFFFF--LLIINNEE
OONN--LLIINNEE
RRTT__IINNFFOO
RREEPPOOSSII TTOORRYY
RRUUNN--TTIIMMEE
SSCCHHEEDDUULLEERR
11.. SSPPEECCIIFFYY RRTT__OOPPEERRAATTIIOONN
CCHHAARRAACCTTEERRIISSTTIICCSS AANNDD
DDEEPPEENNDDEENNCCIIEESS
55.. AASSSSEESSSS SSCCHHEEDDUULLAABBIILL IITTYY
33.. AASSSSII GGNN SSTTAATTIICC PPRRIIOORRIITTYY AANNDD SSTTAATTIICC SSUUBBPPRRIIOORRIITTYY
44.. MMAAPP SSTTAATTIICC PPRRIIOORRIITTYY,, DDYYNNAAMMII CC SSUUBBPPRRII OORRII TTYY,, AANNDD
SSTTAATTIICC SSUUBBPPRRIIOORRIITTYY II NNTTOO DDIISSPPAATTCCHHIINNGG PPRRIIOORRIITTYY
AANNDD DDIISSPPAATTCCHHIINNGG SSUUBBPPRRIIOORRIITTYY
66.. AASSSSIIGGNN DDIISSPPAATTCCHHIINNGG QQUUEEUUEE CCOONNFFIIGGUURRAATTIIOONN
22.. PPOOPPUULLAATTEE
RRTT__IINNFFOO
RREEPPOOSSIITTOORRYY
77.. SSUUPPPPLLYY DDIISSPPAATTCCHHIINNGG QQUUEEUUEE
CCOONNFFIIGGUURRAATTIIOONN TTOO TTHHEE OORRBB
RRTTOOppeerraattiioonn
RRTTOOppeerraattiioonn
RRTTOOppeerraattiioonn
II //OO SSUUBBSSYYSSTTEEMM
OORRBB CCOORREE
OOBBJJEECCTT AADDAAPPTTEERR
99.. SSUUPPPPLLYY SSTTAATTIICC PPOORRTTIIOONNSS OOFF
DDIISSPPAATTCCHHIINNGG PPRRIIOORRIITTYY AANNDD
DDIISSPPAATTCCHHIINNGG SSUUBBPPRRIIOORRIITTYY
TTOO TTHHEE OORRBB
((SSCCHHEEDDUULLEERR''SS OOUUTTPPUUTT
IINNTTEERRFFAACCEE))
((SSCCHHEEDDUULLEERR''SS IINNPPUUTT
IINNTTEERRFFAACCEE))
88.. CCOONNFFIIGGUURREE QQUUEEUUEESS BBAASSEEDD
OONN DDIISSPPAATTCCHHIINNGG QQUUEEUUEE
CCOONNFFIIGGUURRAATTIIOONN
1100.. DDYYNNAAMMIICC QQUUEEUUEESS AASSSSIIGGNN
DDYYNNAAMMIICC PPOORRTTIIOONNSS OOFF
DDIISSPPAATTCCHHIINNGG SSUUBBPPRRIIOORRIITTYY
((AANNDD PPOOSSSSIIBBLLYY
DDIISSPPAATTCCHHIINNGG PPRRIIOORRIITTYY)) OORRBB EENNDDSSYYSSTTEEMM
18 DO
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Use
-cas
esfo
rA
CE
and
TAO
' &
$ %' &
$ %
Dom
ains
�
Ele
ctro
nic
med
ical
imag
ing
�
Net
wor
km
anag
emen
t
�
Wire
less
pers
onal
com
mun
icat
ion
syst
ems
(PC
S)
�
Rea
l-tim
eav
ioni
csm
issi
onco
mut
ing
�
Mul
timed
iase
rvic
es
�
Dis
trib
uted
inte
ract
ive
sim
ulat
ion
DOC Center Washington University, St. Louis
Applying ACE and TAO to Medical Imaging
DIAGNOSTIC STATIONSDIAGNOSTIC STATIONS
ATMATMMANMAN
ATM
LAN
ATM
LAN
MODALITIES
(CT, MR, CR) CENTRAL
BLOB STORE
CLUSTER
BLOB
STORE
DX
BLOB
STORE
� Domain Challenges
– Large volume of “Blob”data
� e.g., 10 to 40 Mbps– “Lossy compression”
isn’t viable– Prioritization of
requests
� URLs
– �schmidt/COOTS-96.ps.gz
– �schmidt/av.ps.gz– �schmidt/NMVC.html
20
DOC Center Washington University, St. Louis
Applying ACE to Network Management
Session RouterModule
PresentationModule
Event FilterModule
Event AnalysisModule
PresentationModule
Switch RouterModule
Reactor
MD110MD110 ERICSSONERICSSON
TELECOMTELECOM
SWITCHESSWITCHES
SUPERSUPER
VISORSVISORS
MD110MD110 ERICSSONERICSSON
MD110MD110 ERICSSONERICSSON
SUPERSUPER
VISORSVISORS
SUPERSUPER
VISORSVISORS
Switch IO
Session IO
� Domain Challenges
– Low latency– Multi-platform– Family of related
services� URLs
– �schmidt/DSEJ-94.ps.gz
– �schmidt/ECOOP-95.ps.gz
21
DOC Center Washington University, St. Louis
Applying ACE to Global PCS
WIDE AREA
NETWORK
SATELLITESSATELLITESTRACKINGTRACKINGSTATIONSTATION
PEERSPEERS
STATUS INFO
COMMANDS BULK DATA
TRANSFER
LOCAL AREA NETWORK
GROUNDSTATION
PEERS
GATEWAY
� Domain Challenges
– Long latency satellite links– High reliability– Prioritization
� URL
– �schmidt/TAPOS-95.ps.gz
22
DOC Center Washington University, St. Louis
Applying TAO to Real-time Avionics
REPLICATION
SERVICE
OBJECT REQUEST BROKER
1: SENSORS
GENERATE
DATA
FLIRGPS IFF
3:PUSH (EVENTS)
2: SENSOR PROXIES DEMARSHAL DATA
& PASS TO EVENT CHANNEL
3:PUSH (EVENTS)
EVENT
CHANNEL
HUD NavAir
FrameWTS
4: PULL(DATA)
� Domain Challenges
– Real-time periodicprocessing
– Complexdependencies
– Very low latency
� URL
–�levine/research/JSAC-98.ps.gz
23
DOC Center Washington University, St. Louis
Open ATM Signaling & Control
MANAGE
MIBTAO
RIO
APIC
NETWORK OPERATIONS
CENTER - ENDSYSTEM
GET STATSRECONFIG
SWITCH STATUS
CHANGE
RIO
APIC
TAO objB
objA
LOW LATENCY
CONTROLHIGH - BANDWIDTH
VIDEO/AUDIO DATA
ENDSYSTEM A
ENDSYSTEM B
HIGH - BANDWIDTH
BULK DATA
ENDSYSTEM C
HIGH -BANDWIDTH
VIDEO/AUDIO
MULTICAST
NETWORK
SERVICE
PROCESSOR
SPC
WUGS
SPC
SPC
SPC
SPC
SPC
SC
CLASSIFIER /ROUTER
ACTIVE NETWORK
RESOURCE CONTROLLER
NATIVE ATM BYPASSES THROUGH APIC
ATM PORT INTERCONNECT CONTROLLER (APIC)
USER
KERNEL
NSP
HIGH -PERFORMANCE
NETWORK ELEMENT
WEIGHTED
FAIR
QUEUING
IP FLOW
CLASSIFICATION
AND ROUTING
TAO
WUGS
OBJECT
SIGNALING
SERVERTAO
RESOURE
MANAGER
SWITCH
MANAGER
SWITCH CONTROLLER
HIGH -PERFORMANCE NETWORK ELEMENT
QOSMANAGER
TAO
PORT
CONTROLLER
SMART
PORT
CARD
24 DO
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Aud
io/V
ideo
Str
eam
ing
End
-poi
ntFl
ow d
ata
Ada
ptor
Stre
am
(Sou
rce)
Flow
dat
a
Ada
ptor
Obj
ects
And
Man
agem
ent
Obj
ect
Con
trol
Inte
rfac
e
OR
B C
OR
E
POA
End
-poi
nt
Stre
am
Con
trol
Inte
rfac
e
Obj
ect
Stre
am
Stre
am POA
Con
trol
(Sin
k)
MU
LT
IME
DIA
STR
EA
M
Effi
cien
cy
�
Soc
kets
for
data
tran
sfer
toge
thig
hpe
rfor
man
ce
Fle
xibi
lity
�
Use
sC
OR
BA
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DOC Center Washington University, St. Louis
Concluding Remarks
� Researchers and developers of distributed, real-time applicationsconfront many common challenges
– e.g., service initialization and distribution, error handling, flow control,scheduling, event demultiplexing, concurrency control, persistence, faulttolerance
� Successful researchers and developers apply patterns,frameworks, and components to resolve these challenges
� Careful application of patterns can yield efficient, predictable,scalable, and flexible middleware
– i.e., middleware performance is largely an “implementation detail”
� Next-generation ORBs will be highly QoS-enabled, though manyresearch challenges remain
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