INTERNATIONAL ORGANIZATION FOR
STANDARDIZATION
ORGANISATION INTERNATIONAL NORMALISATION
ISO/IEC JTC1/SC29/WG11
CODING OF MOVING PICTURES AND ASSOCIATED AUDIO
ISO/IEC JTC1/SC29/WG11 N1559
MPEG97
21 February 1997
Source: DSM-CC Sub-Group
Status: Approved
Title: Answers to the DSM-CC FAQ Version 1.0
DSM-CC FAQ Version 1.0
1. About DSM-CC (overall)
1.1 Are there any articles or
tutorial kits about DSM-CC ?
1.2 I'm confused. Isn't DSM-CC a video
stream VCR-like control protocol?
1.3 What organizations have adopted
DSM-CC?
1.4 What's the difference
between DSM-CC and DAVIC protocol?
1.5 Is there a reference
implementation of DSM-CC (U-N, U-U, download, carousel)?
1.6 Can I use just one element of the
standard, or must I implement all the protocols and interfaces?
1.7 Why is the DSM-CC specification
document so large?
1.8 What are the different
connection types required in DSM-CC? How is low bandwidth
accommodated for each of the connections?
1.9 Is DSM-CC applicable to
markets other than video dialtone? What are the applications that
can take advantage of DSM-CC?
1.10 Is DSM-CC only used with set top
boxes?
1.11 What is the relation
between DSM-CC and TINA?
1.12 Does Internet make DSM-CC
redundant with RSVP, RTSP, RTP and SCP?
1.13 What companies are developing
DSM-CC implementations?
1.14 The Session Resource
Manager is a key element of DSM-CC and a single point of failure.
What kind of back-up precautions can be taken on the SRM to
secure safe operation of the system?
1.15 What is the minimum system
setup when using DSM-CC? (Low bandwidth system, no upstream
channel etc.)
1.16 What are the procedures
for conformance testing DSM-CC?
2. About DSM-CC U-N Session
Control
2.1 What is the scope of the session
protocol?
2.2 What is DSM-CC session ?
What is the purpose of DSM-CC session control?
2.3 What is the
difference between the DSM-CC session control and the call
control in telecommunication networks?
2.4 What set of problems does it
solve that aren't solved by other protocols such Q.2931, RSVP,
H.245?
2.5 What is
the relation between the DSM-CC AddResource operation and the
set-up/connection operation of existing resource control
protocols e.g., (Q.2931, RSVP)?
2.6 What is meant by DSM-CC allows the
use of heterogeneous networks?
2.7 There is only one SRM in the
DSM-CC U-N reference model. The situation where the Client and
the Server reside in domains of different SRMs seems to be
ignored. Can DSM-CC U-N globally scale up?
2.8 Is the session protocol
valid for broadcast scenarios?
3. About DSM-CC U-N
Configuration
3.1 What is the
difference between BOOTP or DHCP and DSM-CC UN Config?
4. About DSM-CC U-U
4.1 What is meant by DSM-CC allows the
use of heterogeneous networks?
4.2 Why does DSM-CC U-U use CORBA?
Do all the DSM-CC protocols require CORBA, IDL, RPC?
4.3 What is the
relationship of the object classes of the Service Domain
(User-User) to specific object domains like CORBA, Java, and COM?
Does the client have to implement a complete Object Request
Broker?
4.4 What is the scope
of the Service Domain interfaces? What functions does it provide?
4.5 Is the interfaceof the Service
Domain valid for broadacst scenarios?
5. About DSM-CC Download
5.1 How does the
download protocol differ from download protocols such as Trivial
File Transfer Protocol?
6. About DSM-CC SDB-CCP
6.1 What is
the relation between the DSM-CC SDB-CCP protocol and the DAVIC
ZAP protocol?
7. About DSM-CC Section (Transport)
Are there any articles or tutorial kits about DSM-CC ?
<In English>
Vahe Balabanian et al, Digital Storage of Media Command and
Control Protocol Applied to ATM IEEE JSAC Vol. 14 No. 6, August
1996
Vahe Balabanian et al, An
Introduction to Digital Storage Media Command and Control
Protocol (DSM-CC) IEEE Communication, November 1996.
DSM-CC Tutorial
<In Japanese>
Masa Kawashima, ITE Mag. (reference to be made available)
Masa, Kawashima IEICE-J Mag. (reference to be made available)
I'm confused. Isn't DSM-CC a video stream VCR-like control protocol?
DSM-CC (Digital Storage Media Command
and Control) work began early on to provide VCR like functions as
an annex to MPEG-2 TS ISO/IEC 13818-1. However, it subsequently
expanded in MPEG-2 ISO/IEC 13818-6 to provide a
Client-Network-Server paradigm for selection, access and control
of distributed video sources. The ISO/IEC 13818-6 now includes
VCR like functions in the Stream Control within a larger set of
function shown below: - User-Network Client Configuration
- User-Network Session protocol
- User-User Directory, Stream control, File access
- Interactive and broadcast download
- Broadcast object carousel
- Switched digital broadcast channel change protocol
While all the above functions can be
implemented together with some obvious synergism, a subset of the
functions can also be implemented with other non-DSM-CC
functions. In other words DSM-CC IS is a tool-kit.
What organizations have adopted DSM-CC?
Since DSM-CC IS is a tool-kit, an industry consortium can choose to implement any subset of DSM-CC IS. The solutions of the problems in those organizations are mirrored in the functions selected from DSM-CC.
What's the difference between DSM-CC and DAVIC protocol?
DAVIC is a consumer of standards, that selects specific pieces and provides restrictions for interoperability. DSM-CC IS as a standard covers the needs of a universe of DSM-CC implementers through:
DAVIC as a group of implementers that seek interoperability has chosen a set of options from the DSM-CC IS specification, e.g., carriage of DSM-CC U-N session commands over UDP and TCP. DAVIC also extended the resource descriptors in DSM-CC IS and added network dependent variables. For example DAVIC Client ID, specified in DSM-CC IS as any 20 byte ISAP field, to be E.164 NSAP with the HO-DSP containing the IP address for the stream control. The preceding are just but few examples.
Is there a reference implementation of DSM-CC (U-N, U-U, download, carousel)?
No reference implementations exist at the present time, however an example implementation has been graciously made available as shown below:
In Jan. 24, 1997, GCL (Graphics
Communication Laboratories) announced that it is offering free
Distribution of DSM-CC Software, compliant to the ISO/IEC 13818-6
International Specification. The software is in executable binary
files, without source codes. The following can be downloaded free
of charge from the GCL web page:
- DSM-CC Server System Software,
- DSM-CC Client Lib. + MHEG-5 Engine Software
The ensuing conditions apply:
- Expire on April 24, 1997
- No warranty
- No reverse engineering etc.
Please visit http://www.gctech.co.jp/
Can I use just one element of the standard, or must I implement all the protocols and interfaces?
The ISO/IEC 13818-6 DSM-CC IS has
assembled together a number of highly synergistic functional
groups. Although each one can be implemented separately, value
can be gained from their synergy in terms of reduced cost of
implementation, interoperability and portability. The functional
groups are:
- User-Network Client Configuration
- User-Network Session protocol
- User-User Directory, Stream control, File access
- Interactive and broadcast download
- Broadcast object carousel
- Switched digital broadcast channel change protocol
Why is the DSM-CC specification document so large?
Many other standards have each of the equivalent parts to DSM-CC specified in separate specifications. If all of these specifications are brought together which may take considerable effort by the user, the user not only is left with a bigger document but may encounter potential duplications and controversies that need to be resolved. It is left to implementers to find his/her way through the multiplicity of the standards in order to integrate the specifications into one implementation and ensure interoperability with other such vendors who use the same specifications. The experts that specified DSM-CC spent their time and effort in order to bring all aspects of multimedia services into one specification and facilitate the work of the potential DSM-CC implementers.
What are the different connection types required in DSM-CC? How is low bandwidth accommodated for each of the connections?
There are three types of connections required in DSM-CC, a) for Session control messages, b) for video streams c) for control of the video streams and access to other applications. The U-U messages on the other hand could cover a range based on the application used and the QoS chosen by the end-user.
Is DSM-CC applicable to markets other than video dialtone? What are the applications that can take advantage of DSM-CC?
The DSM-CC IS was targeted to meet the
video dialtone market. However, the concepts used in DSM-CC
satisfy a wider range of multimedia services.
The applications that can take advantage of DSM-CC are:
Video on Demand
Data broadcast
Broadband Internet access
AudioVideoGraphic Conferencing using ITU-T T.120 recommendations
And others
The DSM-CC work was extended as part of the MPEG-4 activity ISO/IEC 14496-6, with the DSM-CC Multimedia Integration Framework (DMIF). DMIF will expand upon the current DSM-CC standard (ISO/IEC 13818-6) to enable the convergence of interactive, broadcast and conversational multimedia into one specification which will be applicable to set tops, desktops and mobile stations. DMIF encompasses the following directions:
Is DSM-CC only used with set top boxes?
The benefits realized by DSM-CC for set top boxes such as, U-N Configuration, small footprint session control and lightweight download, in order to cope with their limited resources, can equally benefit PC desktops or PCTVs, devices such as Network Computers and devices such as Web-TVs. DSM-CC adds negligible overhead to such devices.
DSM-CC is also used in cable modems as defined in DAVIC 1.2 specification for broadband Internet access.
What is the relation between DSM-CC and TINA?
Although there is no formal relationship between DSM-CC and TINA, DSM-CC and TINA are built on similar precepts. DSM-CC U-U and TINA use IDL for common object concepts defined by OMG. The session concepts in DSM-CC U-N and TINA are similar, however TINA does not provide the protocol specifics or the state machines.
Does Internet make DSM-CC redundant with RSVP, RTSP, RTP and SCP?
No, DSM-CC is not made redundant. DSM-CC
works in conjunction with these protocols.
There are two main components of DSM-CC,
U-N and U-U. Equivalence can be drawn between U-N and RSVP on the
one hand and U-U and RTSP, RTP and SCP on the other hand.
RSVP is not able to account for the
stacks above which IP packets are carried. DSM-CC U-N on the
other hand accounts for the layers of transport above which IP
packets are carried as network connection resources. In addition
DSM-CC can account for network processing resources which are
used, such as multicast servers and translators. Since DSM-CC U-N
can be implemented independently from DSM-CC U-U it can operate
with RTSP, RTP and SCP.
RTSP provides the equivalent of the DSM-CC U-U directory resolve and stream control while RTP and SCP provide the equivalent of MPEG-2 TS and allows for the selection of a transport within the confines of connections between the sender and the receiver (or receivers for multicast). In comparison DSM-CC U-U allows for far more capable stream control through the use of Normal Play Time (NPT) state diagrams. DSM-CC also allows for a request for transport connection between the receiver and any sender it identifies for reasons of geographical proximity to the receiver or for load balancing with off hour traffic troughs in less used locations. The result of both leads to an efficient use of underlying connection resources and video server ports.
What companies are developing DSM-CC implementations?
The companies that are developing DSM-CC
implementations are:
Bellcore
What is the minimum system setup when using DSM-CC? (Low bandwidth system, no upstream channel etc.)
This question can be answered in many parts. First of all DSM-CC consists of several functional groups. While all the functions can be implemented together with some obvious synergism, a subset of the functions can also be implemented with other non-DSM-CC functions. For example the SDB (Switched Digital Broadcast) CCP (Channel Change Protocol) can be implemented with or without DSM-CC U-N Session messages. In the latter case it may be considered a minimal implementation while in the former it is a more DSM-CC involved implementation.
The minimal implementation consists of the core consumer portion.
What are the procedures for conformance testing DSM-CC?
The conformance testing document ISO/IEC
13818-10 for DSM-CC IS is being prepared by
the DSM-CC group. The Preliminary Working Draft (PWD) is targeted
for February 21, 1997 and the International Standard (IS) is
targeted for July 1998. Organizations that have shown interest in
conformance testing are Bellcore, Columbia University, Jupiter
and NIST.
About DSM-CC U-N Session Control
What is the scope of the session protocol?
A DSM-CC session groups all the
resources used in an instance of a service. This is accomplished
by tagging the resources with the network wide unique session ID.
Consequently, the logging of all the resources for later use in
billing is made possible. The session ID tag also facilitates the
disposal of the resources when the session is released so that
they can be made available to other service instances.
Occasionally the resources are disposed off when a service is
suspended in an active session and reestablished when it is
resume later. In some situations when a service is changed by a
Client, the release of some critical resources may be delayed for
a short time to allow for the resources to be used by the Client
in the new service without incurring the penalties for a new
connection establishment. This occurs in situations where a
Client suspends a given service and moves to another service. A
connection is reused if the resourceís QoS matches or is larger
than the QoS required by the new service.
To a user DSM-CC allows the delivery of
multimedia over a guaranteed end-to-end QoS irrespective of the
transport technology the user is using. Thus it allows the
end-user the choice of the transport technology and media within
the locality the service is provided which best suits his/her
budget.
At an age where multiplicity of
transport networks dominate, DSM-CC becomes an essential
component of multimedia business. Each user chooses the level of
service and pays for what he/she needs, each service provider
gets paid for the resources used within a session.
What is a DSM-CC session ? What is the purpose of DSM-CC session control?
DSM-CC session is an instance of network service which has, as attributes, the parties (users) involved with the service and the resources used for the service.
The DSM-CC session control may sound similar to the call control in B-ISDN because a call has a cap-ability of grouping connections. However we would highlight the following two major differences.
What set of problems does it solve that aren't solved by other protocols such Q.2931, RSVP, H.245?
As the purpose of DSM-CC session control is to associate resources for the same service, the actual protocols used for the allocation/de-allocation of each resource are outside the scope of DSM-CC. The DSM-CC AddResource operation is used just to bind (or register) resources to a session. The actual allocation of resource should be deferred to resource-specific protocols such as Q.2931 and RSVP. Resource descriptors are used DSM-CC U-N to describe the connections required. These resources are extendible to other networks than presently specified in the DSM-CC U-N specification.
What is meant by DSM-CC allows the use of heterogeneous networks?
DSM-CC relies on end-to-end significant
association tags to preserve the thread of continuity of a stream
across networks of different transport technologies. Thus the
Server view of a transport represented by its stacks can be
entirely different from the Clientís. This is exemplified by
different resource types and IDs at each end. By having the same
association tag at both ends, a server can indicate which
resource the Clientís application interface must be connected
to. This method is called Tap (application
interface)-to-associationTag (connection resource interface)
binding.
The Tap identifies the application interface and the associationTag identifies the connection resource interface. These two are joined together through the ConnBinder. A given DSM-CC U-U object may have a number of Tap-associationTag couplings specified in a ConnBinder. This is sent from the Server to the Client in order for it to perform the necessary bindings with the applications required at both ends of connections before the application operation begins.
Two DSM-CC concepts come into play.
Yes the SRM domain can be globally scaled up. The DSM-CC U-N reference model has SRM as one logical entity. It is possible to distribute agents terminating messages from users and let them interwork to form the one logical SRM. DSM-CC IS treats this interworking as implementation details of SRM. But there is an activity to specify this interworking in the MPEG/DSM group, which will realize the networking of SRMs of different network providers. This specification will form a part of the next version of DSM-CC, called DMIF (DSM-CC Multimedia Integration Framework)
In the DSM-CC IS specification SRM is identified as a set of functions covering Session and Resource Management and User configuration. The DSM-CC IS also specifies interfaces between the Client and the Server to the SRM and uses the Specification and Description Language (SDL) to provide an exhaustive representation of their use, including exception cases. The realization of the SRM functions is left to a particular vendor or implementers group. For example assuming that the SRM functions are implemented through SRM nodes, it is possible to reroute traffic from a node which has failed to another node with a minimum impact on the service.
Is the session protocol valid for broadcast scenarios?
Yes, through carousel, under download in section 5.
About DSM-CC U-N Configuration
What is the difference between BOOTP or DHCP and DSM-CC U-N Config?
The config protocol, like BOOTP and DHCP, is a protocol which
configures other protocols. The protocols differ in scope. The
BOOTP and DHCP protocols configure state for other Internet
protocols, such as for IP itself. The DSM-CC config protocol
initializes the state of the DSM-CC session protocol.
The role of the DSM-CC U-N config protocol is to create the precondition for session set-up. Any other configuration protocol is equally acceptable as long as the first session preconditions can be met.
Why does DSM-CC U-U use CORBA? Do all the DSM-CC protocols require CORBA, IDL, RPC?
The Service Domain (User-User) section of the standard adopts
CORBA concepts. The other sections of the standard, for example
config, session, and download, are protocols which do not adopt
object concepts. The specifications of the Object Management
Group provide three elements on which the design of the Service
Domain builds. The three elements are:
Since the service interfaces are specified in Interface Definition Language, the process to create the client side object which is the surrogate for the remote service is to:
The client does not have to provide a full Object Request Broker. It provides a package, in its favorite implementation language, which emits interoperable protocol.
What is the scope of the Service Domain interfaces? What functions does it provide?
The key service objects visible to the consumer Client are:
There is also a Generic Service class on which applications can build. It provides functions, such as access control and life cycle, common to all services. There are also interfaces within the Service Domain to install new services or content.
Is the interface of the Service Domain valid for broadacst scenarios?
Since the object interfaces do not expose the transport
mechanism, the same interfaces are valid for broadcast scenarios
and interactive scenarios. (The client discovers the mechanism
through the protocol state found inside the object references.
The object reference, however, does not expose the state.) The
architecture anticipates the design of applications which scale
to both scenarios.
The object design, to be specific the Interface Definition
Language, automates the protocol design. It provides, after
compilation, both the (implementation language specific)
interface which encapsulates the protocol, plus the protocol
itself. The application can program to the interface, in the
application implementation language, rather than the protocol.
The protocol itself is simple, as the functions it transports are
simple.
The objective was also to support simple application development. The application treats invocations on the service objects just like subroutine calls. This requires Remote Procedure Call semantics. If other protocols were to support these semantics, it would be necessary to interpose code between the interface and the protocol stack, such as TCP/IP or UDP/IP, below. This would yield protocol design stacks with comparable footprints to the object design stacks.
Compared to other download protocols, DSM-CC Download is designed for lightweight and fast operation in order to meet the needs of devices that contain limited memory. The DSM-CC download operates over heterogeneous connections and is applied to a number of network models one of which is the broadcast model with no upstream channel. The mechanisms used in download are:
What is the relation between the DSM-CC SDB-CCP protocol and the DAVIC ZAP protocol?
The DAVIC ZAP protocol is one instance of the DSM-CC SDB-CCP protocol. As SDB-CCP does not assume any specific transport network, a SDB-CCP message has a field to carry some transport network specific parameters. DAVIC ZAP details the format of this field to use SDB-CCP in a baseband ATM access network.
About DSM-CC Section (Transport)
(To be provided)