REIHE INFORMATIK
1/93
MCAM: An Application Layer Proto col for
R. Keller und W. E elsb erg
Universitat Mannheim
Seminargebaude A5 68131 Mannheim
MCAM: An Application Layer Proto col for
Movie Control, Access, and Management
y
Ralf Keller and Wolfgang E elsb erg
Praktische Informatik IV
University of Mannheim, Germany
1 Intro duction
The aim of Op en System Interconnection OSI is to allow
the interconnection of heterogeneous and distributed com-
puter systems. The proto cols of layers 1-6 are now stan-
dardized, and several application layer proto cols have also
reached International Standard level, including X.400 for
electronic mail and FTAM for le transfer, access, and ma-
nagement [13]. What is still missing is a standard for the
control, access, and management of continuous media CM .
CM-streams suchasmovies have di erent requirements
than traditional discrete media e.g. text and graphics in
terms of bandwidth, delay, delay jitter, error control and
ow control. Every comp onent in a distributed multimedia
system has to guarantee these requirements. Considerable
work has to b e done to meet the challenge of multimedia
data streams. Examples of current research elds are mul-
Abstract
timedia le systems [23], op erating systems [2], synchroni-
zation [22], transmission proto cols [4], network supp ort [5],
Most of the recentwork on distributed multimedia sys-
and throughput improvement in upp er layers [9].
tems has concentrated on the transmission, synchronization
In this pap er we address the application layer layer 7
and op erating system supp ort for continuous media data st-
issues of continuous media data streams within the OSI fra-
reams. We consider the integrated control of remote multi-
mework. From our ongoing work on the XMovie pro ject [19]
media devices, such as cameras, sp eakers and microphones,
wehave gained exp erience in implementing CM-streams in
to b e an imp ortant part of a distributed multimedia system.
a network. Wehave learned from XMovie and other pro-
In this pap er we describ e MCAM, an application layer archi-
jects that low-level stream services can b e implemented on
tecture, service and proto col for Movie Control, Access, and
to day's computers successfully. Mo dern MAC proto cols for
Management in a computer network. The OSI Reference
high-sp eed networks, i.e. DQDB and ATM, allow iso chro-
Mo del is our framework. We present the proto col data units
nous transmission at high data rates [8]. Mo dern transp ort
and the Finite State Machine for our application proto col
proto cols employ rate-based ow control and forward er-
and outline the automatic generation of the implementation
ror correction in order to maintain the timing relationship
co de for layer 7 from our formal sp eci cation. MCAM al-
between sender and receiver [1], [26] . But application level
lows complete and integrated control of movie data streams
proto cols for CM streams are still missing.
and devices in a heterogeneous multimedia network.
Keywords: multimedia systems, digital movies, ISO/OSI,
CM streams have to b e enriched in layer7by supp ort ser-
application layer
vices. Wehave identi ed two such services: movie directory
and CM equipment control . Both services are absolutely
necessary for the realization of a multimedia service in a
y
distributed heterogeneous environment.
The movie directory is used as a rep ository for movie in-
Permission to copy without fee all or part of this material
formation, such as digital image format and storage lo cation.
is granted provided that the copies are not made or distri-
The equipment control service enables the user to control
buted for direct commercial advantage, the ACM copyright
CM equipment attached to remote computer systems, e.g.
notice and the title of the publicati on and its date app ear,
sp eakers, cameras, and microphones.
and notice is given that copying is by p ermission of the As-
In our mo del a user can access create, delete and select ,
so ciation for Computing Machinery.To copy otherwise, or
manage query and mo dify attributes , and control play-
to republish, requires a fee and/or sp eci c p ermission.
back or record movies .Thus we call our proto col MCAM
c
1993 ACM
for Movie Control, Access and Management.
Two other approaches to multimedia control in distribu-
vironments are the Lancaster Architecture and Bellco-
ted en source sink source sink
re's Touring Machine. An overview of the two architectures
hitectures make use of a rep o-
can b e found in [25]. Both arc FILE
sitory/name service, and in the Lancaster Architecture it is
also p ossible to control CM equipment. But there is one ma-
jor distinction b etween these two architectures and MCAM:
FILE SHM
We separate the control proto col from the CM stream proto-
col and include the two new services in the control proto col.
Our assumption is that name services and device control ha-
e requirements radically di erent from those of continuous
v LIVE
media streams and should thus b e carried over a di erent
proto col stack. unication Sys-
In IBM's \Heidelb erg Multimedia Comm source sink
tem" equipment control and stream control are also avai-
lable but separated from each other [3].
Figure 1: An example of the three movie typ es
None of these pro jects provides a formal description of
the control proto col, whichwe consider to b e an imp ortant
step towards standardization.
Directory System. We use the ISO/CCITT directory
This pap er is organized as follows. In Section 2, we pre-
service and proto col to store and access distributed movie in-
sent the mo del of the movie service. Section 3 describ es
formation [11]. The X.500 directory standard distingui shes
the service de nition. The proto col sp eci cation and use
twotyp es of entities: directory user agents DUAs and di-
of underlying services is outlined in Section 4. Section 5
rectory system agents DSAs . Arbitrary information can
concludes the pap er.
b e stored in the entries of an X.500 directory. Therefore its
use for digital movie services is straightforward.
A user interacts with the directory system via a DUA.
2 Mo del of the Movie Service
The directory information is stored by the DSAs. They
co op erate to guarantee the consistency of distributed data,
2.1 Streams and Movies
and to answer remote and distributed queries.
The directory entry for a movie contains at least the fol-
Amultimedia application has to handle streams of conti-
lowing attributes: a unique name, lo cation a host , typ e
nuous media data, e.g. video and/or stereo audio streams.
FILE, SHM, or LIVE , format audio or video format , and
In this pap er we concentrate on digital movies. Three typ es
compression metho d.
of movies can b e distinguish ed: FILE , SHM , and LIVE .At
A user can query the directory system using the MCAM
the b eginning of its lifetime a movie will b e pro duced bya
service. He can request information ab out a sp eci c movie
source, e.g. a camera LIVE movie . After this it can b e
or search for movies of a sp ecial typ e or format. If he has
stored on disk for later use FILE movie , transmitted as
the authorization he can create, mo dify or delete a movie
a data stream through a network or pip ed through shared
entry.
memory SHM movie . The last step of its career will b e
amovie consumer, e.g. a graphic display { a window from
Equipment Control System. Most of the CM equip-
the user p oint of view LIVE movie . We will see later that
ment attached to a computer will supp ort more op erations
the three typ es have di erent functions and requirements;
than play, pause, resume and stop basic stream op erations .
for example live sources cannot b e played backwards.
It may b e p ossible to turn, zo om and fo cus a camera, or to
The reason whyweintro duce the SHM typ e is for multi-
increase or to decrease the volume of a sp eaker. Therefore
cast distribution or lters. We can connect a movie source
we consider remote equipment control to b e an imp ortant
to a shared memory bu er SHM which in turn can b e
part of a distributed multimedia system.
connected to multiple sinks, implementing an application -
Our mo del provides an interface to device op erations.
controlled multicast. The SHM can also b e used for ltering,
MCAM transmits the user requests to an equipment user
compression, etc. An example is shown in Figure 1.
agent EUA . The requested op eration is p erformed byan
We call an entity reading from an input device and pro-
equipment control agent ECA , which is directly connec-
ducing a stream on a network a source of a movie and an
1
ted to the CM equipment . All ECAs form the equipment
entity consuming a stream by writing on an output device
control system ECS , which provides a lo cation-transparent
a sink ofamovie. Sources and sinks can b e of either of the
access to CM-equipment.
three movie typ es FILE, SHM or LIVE.
Stream Provider System. The stream provider system
2.2 Functional Mo del
SPS provides to MCAM a plain stream service. Such st-
ream services have b een prop osed in the literature e.g. [4],
The functional mo del of our system is shown in Figure 2. It
1
consists of four parts: Directory System, Equipment Control
MCAM can use the directory service to determine the lo ca-
tion of each ECA. System ECS , Stream Provider System SPS , and MCAM. 2 local system remote system
DSA X.500 DSA X.500 Directory DSA DSA DSA DSA level
MCAM MCAM MCAM User MCA DUA MCAM MCA DUA application SUA EUA SUA EUA protocol level
SPS CM stream CM stream SPA SPA protocol level SPS SPA
ECS ECA ECA equipment level ECA ECA ECS
DUA: Directory User Agent MCA: Movie Control Agent DSA: Directory System Agent MCAM: Movie Control Access Management
SUA: Stream User Agent EUA: Equipment User Agent SPA: Stream Provider Agent ECA: Equipment Control Agent
SPS: Stream Provider System ECS: Equipment Control System
Figure 2: MCAM functional mo del
[7], [19] , and several research pro jects rep ort successful im-
Parameter Typ e of source
plementations. The SPS provides
SHM LIVE FILE
a connection service b etween stream provider agents
Reliabil i ty
SPAs and
Sp eed
Mo de
a stream data interface with the op erations play, stop,
Quality
pause, and resume.
Section
One of the connected SPAs acts as the source and the
Direction
other as the sink of the stream. The role of each of the SPAs
is determined at connection establishment time and cannot
be changed until connection release, i.e. the direction of the
Table 1: Movie parameters
stream is xed.
Every play op eration creates a play context , and a stop
releases it. A play context determines which op erations are
archive for pro duction-qual i tymovies, or if medical data is
allowed and how they are p erformed on a sink. On a LIVE
involved, the movie transmission mighthave to b e error-free.
or SHM sink new data can only b e app ended, whereas on a
The default dep ends on the typ e of the source. The reliabi-
FILE sink new data can b e inserted or app ended, and old
lity parameter controls the error correction scheme used on
data can b e replaced or erased. The play context also car-
the CM data stream.
ries information ab out the currentvalue of the parameters
Eachmovie has a default data rate, called the real-time
for reliability , speed , mode , quality , section and direction .
rate. The initiator can request a speed presentation rate
Some of them can b e mo di ed by the user, others are xed
higher, lower, or equal to the real-time rate. E.g. an NTSC
see Table 1; a missing indicates that the corresp onding
video has a real-time rate of 30 frames/second; if the initia-
parameter is xed .
tor requests a presentation rate of 15, the movie is played
With the parameter reliability the initiator declares whe-
at half sp eed.
ther he demands error-free service or whether he accepts
transmission errors. Most of to day's multimedia applica- Scienti c and commercial application s often use slowor
tions do not require 100 reliable transmission b ecause the fast motion mode for sp ecial e ects. Whether this para-
errors are often not recognizable to human end users e.g. meter will haveany e ect dep ends on the typ e of source.
pixel errors in a video frame . But if the sink is a disk A FILE movie must b e recorded with 50 frames/second to 3
allow a 50 slow motion. Fast motion is easier b ecause The initiator and the resp onder b oth are Multiple Asso cia-
uniform skipping is sucient to create the desired e ect. tion Control Functions MACFs within layer 7. They cont-
rol an MCAM service element, a directory service element,
The ability to use the quality parameter dep ends on the
a stream control service element, and an equipment control
kind of source. Its main purp ose is to control the data com-
service element.
pression algorithms. The requested quality in uences the
Amovie transmission and management service is in many
resulting amount of data e.g. the quantization factor of
resp ects similar to a le transfer and management service.
JPEG [27] .
Therefore our MCAM service follows closely the FTAM ser-
If the source is a FILE then the initiator can request trans-
vice already standardized by ISO [13]. Similar to FTAM,
mission of only a section of the stream. The default value
the movie service is sub divided into regimes. Three typ es of
for this parameter is the whole movie. It is also p ossible
movie service regimes are de ned:
to cho ose b etween two directions ; the movie can b e trans-
mitted in the default direction forward or in the reverse
the MCAM regime which exists while the application
direction backwards .
asso ciation is used for the MCAM proto col, and
If the resp onder cannot guarantee either reliabli tyor
the movie connection regime during which one sink and
sp eed at connection establishment the request is rejected.
one source are asso ciated with the MCAM regime
In contrast, if the guarantees are violated during op eration
the movie control regime.
the resp onder can react in one of twoways: he can send
a noti cation to the initiator and continue or he can stop
The MCAM service provides for a sequence of movie
and issue a \provider stop". This option can b e selected at
connection regimes within a MCAM regime and a sequence
connection establishment time.
of movie control regimes within a movie connection regime.
Let us consider an example. A lab oratory assistantwants
Termination of a regime implies termination of all regimes
to observe a dangerous exp eriment with a remote camera.
nested within that regime. The nesting of MCAM regimes is
He uses his MCAM user agent to establish a connection
shown in Figure 3. The notion of regimes follows the FTAM
between the SPA of the remotely controllable camera LIVE
standard.
source and one of his windows on his screen LIVE sink ,
and starts the movie. If he wants to see the details of the
3.2 MCAM Service Primitives
exp eriment, he can turn and zo om the camera to the desired
p osition, using his mouse and the MCAM control proto col
This section provides a short description of the MCAM ser-
over the network.
vice primitives. For each service, the user of the service
i.e. the application service element that invokes the service
primitive is stated.
Movie Control, Access, and Management. All the
services provided by MCAM can b e accessed at the service
MCAM Regime Control. Three services are asso ciated
access p oint SAP of the MCAM layer. The movie control
with MCAM regime control. The MCAM regime establish-
agent MCA uses the directory, ECS, and SPS to provide
ment service M-INITIALIZE is used by the initiator to
the MCAM service to the initiator. MCAM itself uses the
create and bind a MCAM regime to the application asso cia-
directory service to obtain information. For example, let
tion linking the twomovie service users. It also establishes
us assume that a client requests to connect movie source A
MCAM sp eci c information such as authorization and ac-
with movie sink B . If MCAM has no cached information
counting data. The orderly MCAM regime termination ser-
ab out A or B , it sends a query to its DUA and uses the
vice M-TERMINATE is used by the initiator to dissolve
information received to ll in the parameters for the SPS
the MCAM regime and unbind it from the application asso-
call.
ciation b etween the movie service user and the movie service
provider. The abrupt MCAM regime termination service is
used by either one of the service users M-U-ABORT or
3 Service De nition
the service provider M-P-ABORT to dissolve the MCAM
regime and its binding to the application uncondition all y.
3.1 Movie Service Provider and Movie
Service User
CM Equipment control. The M-EQUIPMENT-CON-
TROL service primitive allows the integrated handling of
In order to provide remote connections b etween sources and
remote devices, e.g. to p erform a camera zo om, or to adjust sinks in a heterogeneous environment, the MCAM comp o-
the volume of sp eakers. This service is visible in every regi-
nent uses a well-de ned service and proto col.
me. It interfaces to the user on the initiator side and to the
Our MCAM service de nition uses the abstract mo del
ECS on the resp onder side.
and terminology de ned in the OSI Basic Reference Mo del
[12] and the OSI Upp er Layer Architecture [10 ]. Our mo-
del describ es the interactions b etween the twomovie service
Movie Management. The movie management primi-
users and the movie service provider. Information is passed
tives create and delete movie sources and sinks. With the
between a movie service user and the movie service provider
create sink service M-CREATE-SINK the initiator can
bymovie service primitives whichmay carry parameters.
create a new sink e.g. a new le for the storage of a mo-
vie or a movie window on his screen or select an existing One of the movie service users is de ned as the initiator
one e.g. a sp eaker at a workstation and register this new or the user side and the other is de ned as the responder . 4 MCAM regime
movie connection regime
movie control regime
M-PLAY M-U-STOP M-RESUME M-PAUSE M-P-STOP M-MOVIE-PARAMETER M-EQUIPMENT-CONTROL
M-EQUIPMENT-CONTROL M-MOVIE-PARAMETER M-P-ERROR M-CONNECT M-DISCONNECT
M-CREATE-SINK M-CREATE-SOURCE M-DELETE-SINK M-DELETE-SOURCE M-EQUIPMENT-CONTROL M-MOVIE-ATTRIB
M-INITIALIZE M-TERMINATE M-U-ABORT
M-P-ABORT
Figure 3: Nesting of movie service regimes
sink with the MCAM server and the directory service. The each of the parameters describ ed in Section 2.2. This ser-
create source service M-CREATE-SOURCE creates a new vice is visible in b oth movie connection and movie control
source or selects an existing one and registers it with the regime.
MCAM server and the directory service. Dep ending on the
lifetime parameter of the create source or create sink service,
Movie Control Regime. In order to control movies,
the movie ob ject will exist only for the duration of the asso-
MCAM de nes ve services. The play service M-PLAY
ciation or until an explicit delete is p erformed. The delete
is used by the initiator to start a stream; the source starts
source service M-DELETE-SOURCE enables the initiator
sending and the sink b egins to receiveinaway determined
to release the binding b etween the MCAM service and the
by the kind of source and sink. Also the play context is
sp eci ed sink in either of twoways: the sink ceases to exist
established. The pause service M-PAUSE enables the ini-
or only the registration of the sink at the MCAM service
tiator to stop the movie; the play context is preserved. The
is removed. In its functionality the delete sink service M-
resume service M-RESUME restarts a movie whichwas
DELETE-SINK corresp onds to the delete source service.
stopp ed by the pause service. With the user stop service
Both services remove the resp ective directory entry. If the
M-U-STOP the initiator can stop the movie and release
initiator wants to interrogate or to mo dify the attributes of
the play context. The provider stop service M-P-STOP is
the sp eci ed movie source/sink he can use the movie attri-
used by the provider to signal the initiator that the end of
bute service M-MOVIE-ATTRIB .
the movie has b een reached or that an unrecoverable error
has o ccurred and the movie has b een stopp ed.
Connection Regime. With the movie connect service
M-CONNECT the initiator can connect one movie source
Provider Error. The provider error service M-P-ER-
to one movie sink. This de nes the direction of the data
ROR is used by the resp onder or by the provider to signal
ow and establishes access rights for movie control. The
the initiator that an error o ccurred, without stopping the
disconnect service M-DISCONNECT enables the initiator
movie. This can happ en if the reliabil ity or sp eed parame-
to release the sp eci ed connection.
ters cannot b e met at runtime, and the initiator had stated
at connection establishment time that he wants the movie
to continue in such cases.
Movie Parameters. The adjustmentofmovie parame-
ters is p erformed by a single service: M-MOVIE-PARAME- Obviously, most of the services describ ed ab ove require
TER. The initiator can interrogate and mo dify the value of access control, e.g. a remote microphone can only b e turned 5
Service primitive MPDU Carried by Service primitive MPDU Carried by
M-INITIALIZEreq INIRQ A-ASSOCIATE M-CREATE-SINKreq CSIRQ P-DATA
M-INITIALIZEresp INIRP A-ASSOCIATE M-CREATE-SINKresp CSIRP P-DATA
M-TERMINATEreq TERRQ A-RELEASE M-CREATE-SOURCEreq CSORQ P-DATA
M-TERMINATEresp TERRP A-RELEASE M-CREATE-SOURCEresp CSORP P-DATA
M-U-ABORTreq UABRQ A-ABORT M-DELETE-SINKreq DSIRQ P-DATA
M-P-ABORTind UABRQ A-ABORT M-DELETE-SINKresp DSIRQ P-DATA
M-DELETE-SOURCEreq DSORQ P-DATA
M-DELETE-SOURCEresp DSORQ P-DATA
M-EQUIPMENT-CONTRO Lreq ECORQ P-DATA
Table 2: MCAM proto col data units { regime establishment
M-EQUIPMENT-CONTRO Lresp ECORP P-DATA
M-MOVIE-ATTRIBreq MATRQ P-DATA
M-MOVIE-ATTRIBresp MATRP P-DATA
on by authorized users. The details of the access control
M-CONNECTreq CONRQ P-DATA
and authenti cation mechanisms are b eyond the scop e of
M-CONNECTresp CONRP P-DATA
M-DISCONNECTreq DISRQ P-DATA
this pap er.
M-DISCONNECTresp DISRP P-DATA
M-MOVIE-PARAMETERreq PARRQ P-DATA
M-MOVIE-PARAMETERresp PARRP P-DATA
4 Proto col Sp eci cation
M-PLAYreq PLYRQ P-DATA
M-PLAYresp PLYRP P-DATA
The MCAM service is distributed in nature. In order to
M-PAUSEreq PAURQ P-DATA
op erate in a heterogeneous environment, wehave to de ne
M-PAUSEresp PAURP P-DATA
M-U-STOPreq USTRQ P-DATA
the MCAM proto col precisely.
M-U-STOPresp USTRP P-DATA
We are convinced that the new generation of high-sp eed
M-P-STOPreq PSTRQ P-DATA
networks, and in particular ATM, provides the technical
M-RESUMEreq RESRQ P-DATA
foundation for the transmission of digital movies in worldwi-
M-RESUMEresp RESRP P-DATA
de networks. But equipment is heterogeneous, and will pro-
M-P-ERRORreq PERRQ P-EXPEDI-
bably always b e so. In order to enable movie transmission
TED-DATA
in a heterogeneous network the standardization ofamovie
transmission and control proto col is of ma jor imp ortance.
Table 3: MCAM proto col data units { control, access, and
We therefore provide a formal de nition of our MCAM pro-
management
to col, using the widely accepted OSI conventions.
In this section we describ e each of the MCAM proto col
data units PDUs , their mappings to underlying services,
Presentation Service Mappings. All remaining MCAM
and give an example for a state/transition diagram for cor-
proto col data units are mapp ed to the OSI Presentation
rect sequencing.
Service [15]. Only one presentation context is active when
the MCAM regime is established. Rememb er that MCAM
handles only the interchange of control information b etween
4.1 MCAM Proto col Data Units
twomovie service users. No CM data are transferred on an
ISO has de ned a data description language for application
MCAM asso ciation. The transfer of MCAM PDUs has no
layer PDUs called ASN.1 Abstract Syntax Notation One
real-time or high-bandwid th requirements, and thus no sp e-
[16] . We are currently in the pro cess of de ning all MCAM
cial presentation context is needed. The mapping of MCAM
PDUs in ASN.1. This allows us to generate C/C++ da-
application PDUs to the Presentation Services is shown in
ta structures for our implementation automatically. The
Table 3.
ASN.1 sp eci cation can also b e used to automatically crea-
te an enco der/deco der for MCAM PDUs for our runtime
4.2 State Transition Diagram
implementation . ASN.1 to ols are now provided with many
ISO/OSI communication software packages; a well-known
In addition to de ning the exact PDU formats in ASN.1 and
example is ISODE [24]. The PDUs of MCAM Regime Cont-
their mapping to lower layer services, a proto col sp eci ca-
rol are mapp ed to the ACSE service primitives, all others
tion must state the allowable sequences of events. We use
are mapp ed directly to the Presentation Layer service.
a conventional state/transition diagram to sp ecify the dy-
namic b ehavior of the MCAM proto col. Since the diagrams
of the MCAM regime and the movie connection regime are
ACSE Mappings. The application asso ciation and rela-
relatively simple, only the more interesting diagram of the
ted application context for the movie proto col are establi-
movie control regime is presented in Figure 4.
shed by the Asso ciation Control Service Element ACSE
[14] . The service primitives used for initiali zi ng and ter-
minating the instance of the MCAM regime carry the pa-
4.3 Example
rameters of the asso ciation context and authorization and
A simple example of the usage of the movie service and the accounting information. The mapping of the MCAM ap-
corresp onding proto col ow is shown in Figure 5 in the form plication PDUs MPDUs to the ACSE service is shown in
of a time sequence diagram. An initiator establishes an asso- Table 2. 6 Connected
1 3 8 6
Outgoing Incoming Outgoing Incoming Play Play U-Stop U-Stop 22 21 Pending Pending Pending Pending 21 22
2 4 5 7 5 7
Outgoing Pause Outgoing Outgoing 17 Pending 18 EquipControl EquipControl 9 10 Pending Pending 18 Incoming 17 19 Playing Pause Pause 20 Incoming 11 12 Incoming Pending EquipControl 20 19 EquipControl Pending Pending 23 14 13 24 25 Outgoing 26 Outgoing 24 Incoming Resume 25 23 Regulate 26 Regulate 16 Pending 15 Pending Pending Incoming Outgoing 27 Regulate 27 Regulate Incoming Pending Pending Resume 28 28 Pending
1 M-PLAY request / PLYRQ 15 RESRQ / M-RESUME indication 2 PLYRP / M-PLAY confirm 16 M-RESUME response / RESRP 3 PLYRQ / M-PLAY indication 17 M-EQUIPMENT-CONTROL request / ECORQ 4 M-PLAY response / PLYRP 18 ECORP / M-EQUIPMENT-CONTROL confirm 5 M-U-STOP request / USTRQ 19 ECORQ / M-EQUIPMENT-CONTROL indication 6 USTRP / M-U-STOP confirm 20 M-EQUIPMENT-CONTROL response / ECORP 7 USTRQ / M-U-STOP indication 21 M-P-STOP request / PSTRQ 8 M-U-STOP response / USTRP 22 PSTRQ / M-P-STOP request 9 M-PAUSE request / PAURQ 23 M-MOVIE-PARAMETER request / PARRQ 10 PAURP / M-PAUSE confirm 24 PARRP / M-MOVIE-PARAMETER confirm 11 PAURQ / M-PAUSE indication 25 PARRQ / M-MOVIE-PARAMETER indication 12 M-PAUSE response / PAURP 26 M-MOVIE-PARAMETER response / PARRP 13 M-RESUME request / RESRQ 27 M-P-ERROR request / PERRQ
14 RESRP / M-RESUME confirm 28 PERRQ / M-P-ERROR indication
Figure 4: State transition diagram of the movie control regime 7
Extended Finite State Machine EFSM mo del. Compared
Initiator Responder to hand-written co de, an EFSM sp eci cation is more natural
M-INITIALIZE request
and easier to understand for the develop er. Using an FDT
y advantages: M-INITIALIZE indication sp eci cation and a co de generator has man
M-INITIALIZE response
the co de generated from an FDT has fewer bugs than
M-INITIALIZE confirm hand-written co de
M-CONNECT request
the co de is well structured and easy to understand
proto col machine asp ects are nicely separated from
M-CONNECT indication
unication system no de, suchas
M-CONNECT response other asp ects of a comm
bu er management, timer management, le I/O, etc.
M-CONNECT confirm and
M-PLAY request
the co de is more p ortable than hand-written co de.
M-PLAY indication t
M-PLAY response It is often claimed that generated co de is less ecien
than hand-written co de. We do not see a go o d reason for
ent ineciency in generated co de provided that the
M-PLAY confirm M-P-STOP request inher
co de generator is well implemented. In another pro ject our
M-P-STOP indication
research group is investigating p ossible p erformance enhan-
M-DISCONNECT request
cements by parallel execution. The overall sp eedup gained
y parallel execution is much higher than a p ossible sp eedup
M-DISCONNECT indication b
y manual co de optimization [9]. The parallel co de runs on
M-DISCONNECT response b OSF/1, and is also generated automatically from the same
M-DISCONNECT confirm Estelle sp eci cation [6].
ork is also in progress to re ne and improve our own CM
M-TERMINATE request W
stream proto col MTP [20] to provide the following services:
M-TERMINATE indication reliable and unreliable stream service using an adjus-
M-TERMINATE response
table forward error correction mechanism
M-TERMINATE confirm
supp ort for several uncompressed and compressed for-
2
mats for movies and
Figure 5: Time sequence diagram of a movie control example
rate-based ow control for iso chronous transmission.
The improved Movie Transmission Proto col MTP and
other parts of the XMovie pro ject form the basis of our
ciation and connects a FILE source and a LIVE sink. Then
SPS implementation at the University of Mannheim. The
he issues a play command. When the end of the FILE source
XMovie prototyp e currently allows the transmission of digi-
is reached, the movie automatically stops, and the resp onder
tal movies b etween RISC workstations from DEC, Sun and
sends a provider stop signal to the initiator. The initiator
IBM at up to 25 frames/s. The movies are displayed in an X
then disconnects the sink and the source and terminates the
window, using our own extension to the X Window System
asso ciation.
[18].
Wehave conducted initial exp eriments with QUIPU, the
5 Summary, Status and Outlo ok
X.500 implementation of ISODE, as a basis for our movie
directory service. Our movie directory prototyp e is not yet
Wehaveintro duced MCAM, a new OSI Application Layer
completed.
Services Element for the access, control, and managementof
In a joint pro ject with IBM's Europ ean Networking Cen-
digital movies in op en networks. The movie control service
ter in Heidelb erg wehave also develop ed a remote camera
is enriched by supp ort services for the storage and retrie-
control system. The camera op erator uses his mouse, scroll
val of movie information and the control of CM equipment
bars and push buttons on his window surface to control a
attached to multimedia computer systems. The functional
remote video camera [3].
mo del of MCAM was presented, and the main comp onents
As a nal goal, weenvision several SPAs, ECAs, and
and their interworking were describ ed.
MCAM entities in an ATM network to provide a digital
The formal MCAM service de nition and proto col sp eci-
movie service in a heterogeneous environment using stan-
cation were outlined. These formal de nitions can b e used
dardized transmission and control proto cols.
to derive an implementation automatically.
We are currently writing a complete formal description
2
With the exception of MPEG [21], no international or de fac-
of the MCAM proto col in Estelle, and an abstract syntax
to standard for the format of stored digital CM streams exists.
for the movie service using ASN.1. Estelle [17] is one of
Therefore wehave develop ed our own format to store sequences
three international ly standardized sp eci cation techniques
of audio samples or video frames in a great variety of b oth com-
pressed and uncompressed formats. Formal Description Techniques: FDTs . It is based on the 8
[12] Information pro cessing systems { Op en Systems In- Acknowledgement
terconnection { Basic Reference Mo del. International
Wewould like to thank Bernd Lamparter for his invaluable
Standard ISO 7498, 1984.
and ongoing contributions to the XMovie pro ject. The re-
[13] Information pro cessing systems { Op en Systems Inter-
mote camera control system would not have b een p ossible
connection { File Transfer, Acces and Management. In-
without the help of our colleagues at IBM ENC Heidelb erg,
ternational Standard ISO 8571, Decemb er 1988.
in particular Ralf Steinmetz.
[14] Information pro cessing systems { Op en Systems Inter-
connection { Service De nition and Proto col Sp eci ca-
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