draft-ietf-mmusic-img-framework-09.txt   rfc4435.txt 
MMUSIC Working Group Y. Nomura Network Working Group Y. Nomura
Internet-Draft Fujitsu Labs. Request for Comments: 4435 Fujitsu Labs.
Expires: June 23, 2006 R. Walsh Category: Informational R. Walsh
J-P. Luoma J-P. Luoma
Nokia Nokia
H. Asaeda H. Asaeda
INRIA Keio University
H. Schulzrinne H. Schulzrinne
Columbia University Columbia University
December 19, 2005 April 2006
A Framework for the Usage of Internet Media Guides
draft-ietf-mmusic-img-framework-09
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Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document defines a framework for the delivery of Internet Media This document defines a framework for the delivery of Internet Media
Guides (IMGs). An IMG is a structured collection of multimedia Guides (IMGs). An IMG is a structured collection of multimedia
session descriptions expressed using SDP, SDPng or some similar session descriptions expressed using the Session Description Protocol
session description format. This document describes a generalized (SDP), SDPng, or some similar session description format. This
model for IMG delivery mechanisms, the use of existing protocols and document describes a generalized model for IMG delivery mechanisms,
the need for additional work to create an IMG delivery the use of existing protocols, and the need for additional work to
infrastructure. create an IMG delivery infrastructure.
Table of Contents Table of Contents
1 Introduction ........................................ 3 1. Introduction ....................................................3
2 Terminology ......................................... 3 2. Terminology .....................................................3
2.1 New Terms ........................................... 4 2.1. New Terms ..................................................4
3 IMG Common Framework Model .......................... 5 3. IMG Common Framework Model ......................................5
3.1 IMG Data Types ...................................... 5 3.1. IMG Data Types .............................................5
3.1.1 Complete IMG Description ............................ 5 3.1.1. Complete IMG Description ............................5
3.1.2 Delta IMG Description ............................... 6 3.1.2. Delta IMG Description ...............................6
3.1.3 IMG Pointer ......................................... 6 3.1.3. IMG Pointer .........................................6
3.2 IMG Entities ........................................ 6 3.2. IMG Entities ...............................................6
3.3 Operation Set for IMG Delivery ...................... 7 3.3. Operation Set for IMG Delivery .............................7
3.3.1 IMG ANNOUNCE ........................................ 7 3.3.1. IMG ANNOUNCE ........................................7
3.3.2 IMG QUERY ........................................... 8 3.3.2. IMG QUERY ...........................................8
3.3.3 IMG RESOLVE ......................................... 8 3.3.3. IMG RESOLVE .........................................8
3.3.4 IMG SUBSCRIBE ....................................... 8 3.3.4. IMG SUBSCRIBE .......................................8
3.3.5 IMG NOTIFY .......................................... 9 3.3.5. IMG NOTIFY ..........................................9
3.3.6 Binding Between IMG Operations and Data Types ....... 9 3.3.6. Binding between IMG Operations and Data Types .......9
3.4 Overview of Protocol Operations ..................... 9 3.4. Overview of Protocol Operations ...........................10
4 Deployment Scenarios for IMG Entities ............... 10 4. Deployment Scenarios for IMG Entities ..........................10
4.1 Intermediary Cases .................................. 10 4.1. Intermediary Cases ........................................10
4.2 One-to-many Unidirectional Multicast ................ 12 4.2. One-to-Many Unidirectional Multicast ......................12
4.3 One-to-one Bi-directional Unicast ................... 12 4.3. One-to-One Bidirectional Unicast ..........................12
4.4 Combined Operations with Common Metadata ............ 14 4.4. Combined Operations with Common Metadata ..................13
5 Applicability of Existing Protocols to the 5. Applicability of Existing Protocols to the Proposed
Proposed Framework Model ............................ 14 Framework Model ................................................14
5.1 Existing Standard Fitting the IMG Framework Model ... 14 5.1. Existing Standard Fitting the IMG Framework Model .........14
5.2 IMG Mechanism Needs Not Yet Met ..................... 16 5.2. IMG Mechanism Needs Which Are Not Met by Existing
5.2.1 A Multicast Transport Protocol ...................... 16 Standards .................................................15
5.2.2 Usage of Unicast Transport Protocols ................ 17 5.2.1. A Multicast Transport Protocol .....................16
5.2.3 IMG Envelope ........................................ 17 5.2.2. Usage of Unicast Transport Protocols ...............16
5.2.4 Metadata Data Model ................................. 18 5.2.3. IMG Envelope .......................................17
6 Security Considerations ............................. 18 5.2.4. Metadata Data Model ................................18
7 IANA Considerations ................................. 19 6. Security Considerations ........................................18
8 Normative References ................................ 20 7. Normative References ...........................................19
9 Informative References .............................. 20 8. Informative References .........................................19
10 Acknowledgements .................................... 21 9. Acknowledgements ...............................................20
11 Authors' Addresses .................................. 21
1 Introduction 1. Introduction
Internet Media Guides (IMGs) provide and deliver structured Internet Media Guides (IMGs) provide and deliver structured
collections of multimedia descriptions expressed using SDP [2], collections of multimedia descriptions expressed using SDP [2], SDPng
SDPng [3] or other description formats. They are used to describe [3], or other description formats. They are used to describe sets of
sets of multimedia services (e.g., television program schedules, multimedia services (e.g., television program schedules, content
content delivery schedules) and refer to other networked resources delivery schedules) and refer to other networked resources including
including web pages. IMGs provide an envelope for metadata formats web pages. IMGs provide an envelope for metadata formats and session
and session descriptions defined elsewhere with the aim of descriptions defined elsewhere with the aim of facilitating
facilitating structuring, versioning, referencing, distributing, and structuring, versioning, referencing, distributing, and maintaining
maintaining (caching, updating) such information. (caching, updating) such information.
IMG metadata may be delivered to a potentially large audience, who IMG metadata may be delivered to a potentially large audience, which
use it to join a subset of the sessions described, and who may need uses it to join a subset of the sessions described and which may need
to be notified of changes to the IMG metadata. Hence, a framework for to be notified of changes to the IMG metadata. Hence, a framework
distributing IMG metadata in various different ways is needed to for distributing IMG metadata in various different ways is needed to
accommodate the needs of different audiences: For traditional accommodate the needs of different audiences: For traditional
broadcast-style scenarios, multicast-based (push) distribution of IMG broadcast-style scenarios, multicast-based (push) distribution of IMG
metadata needs to be supported. Where no multicast is available, metadata needs to be supported. Where no multicast is available,
unicast-based push is required. unicast-based push is required.
This document defines a common framework model for IMG delivery This document defines a common framework model for IMG delivery
mechanisms and their deployment in network entities. There are mechanisms and their deployment in network entities. There are three
three fundamental components in IMG framework model: data types, fundamental components in the IMG framework model: data types,
operation sets and entities. These components specify a set of operation sets, and entities. These components specify a set of
framework guidelines for efficient delivery and description of IMG framework guidelines for efficient delivery and description of IMG
metadata. The data types give generalized means to deliver and metadata. The data types give generalized means to deliver and
manage the consistency of application-specific IMG metadata. IMG manage the consistency of application-specific IMG metadata. IMG
operations cover broadcast, multicast distribution, event operations cover broadcast, multicast distribution, event
notification upon change, unicast-based push and interactive notification upon change, unicast-based push, and interactive
retrievals similar to web pages. retrievals similar to web pages.
Since we envision that any Internet host can be a sender and receiver Since we envision that any Internet host can be a sender and receiver
of IMG metadata, a host involved in IMG operations performs one or of IMG metadata, a host involved in IMG operations performs one or
more of the roles defined as the entities in IMG framework model. more of the roles defined as the entities in the IMG framework model.
The requirements for IMG delivery mechanisms and descriptions can be The requirements for IMG delivery mechanisms and descriptions can be
found in the IMG requirements document [4]. found in the IMG requirements document [4].
This document outlines the use of existing protocols to create This document outlines the use of existing protocols to create an IMG
an IMG delivery infrastructure. It aims to organize existing delivery infrastructure. It aims to organize existing protocols into
protocols into a common model and show their capabilities and a common model and show their capabilities and limitations from the
limitations from the viewpoint of IMG delivery functions. viewpoint of IMG delivery functions.
2 Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1]. document are to be interpreted as described in RFC 2119 [1].
2.1 New Terms 2.1. New Terms
Internet Media Guide (IMG): IMG is a generic term to describe Internet Media Guide (IMG): IMG is a generic term to describe the
the formation, delivery and use of IMG metadata. The formation, delivery, and use of IMG metadata. The definition of
definition of the IMG is intentionally left imprecise [4]. the IMG is intentionally left imprecise [4].
IMG Element: The smallest atomic element of metadata that can be IMG Element: The smallest atomic element of metadata that can be
transmitted separately by IMG operations and referenced transmitted separately by IMG operations and referenced
individually from other IMG elements [4]. individually from other IMG elements [4].
IMG Metadata: A set of metadata consisting of one or more IMG IMG Metadata: A set of metadata consisting of one or more IMG
elements. IMG metadata describes the features of multimedia elements. IMG metadata describes the features of multimedia
content used to enable selection of and access to media content used to enable selection of and access to media sessions
sessions containing content. For example, metadata may containing content. For example, metadata may consist of a media
consist of the URI, title, airtime, bandwidth needed, file object's URI, title, airtime, bandwidth needed, file size, text
size, text summary, genre and access restrictions [4]. summary, genre, and access restrictions [4].
IMG Description: A collection of IMG metadata with a data IMG Description: A collection of IMG metadata with a data type
type indicating a self-contained set or a subset of IMG indicating a self-contained set or a subset of IMG metadata, or a
metadata, or a reference to IMG metadata. reference to IMG metadata.
IMG Delivery: The process of exchanging IMG metadata both in IMG Delivery: The process of exchanging IMG metadata both in terms of
terms of large scale and atomic data transfers [4]. large-scale and atomic data transfers [4].
IMG Sender: An IMG sender is a logical entity that sends IMG IMG Sender: An IMG sender is a logical entity that sends IMG metadata
metadata to one or more IMG receivers [4]. to one or more IMG receivers [4].
IMG Receiver: An IMG receiver is a logical entity that receives IMG Receiver: An IMG receiver is a logical entity that receives IMG
IMG metadata from an IMG sender [4]. metadata from an IMG sender [4].
IMG Transceiver: An IMG transceiver combines an IMG receiver and IMG Transceiver: An IMG transceiver combines an IMG receiver and
sender. It may modify received IMG metadata or merge IMG sender. It may modify received IMG metadata or merge IMG metadata
metadata received from a several different IMG senders [4]. received from a several different IMG senders [4].
IMG Operation: An atomic operation of an IMG transport protocol, IMG Operation: An atomic operation of an IMG transport protocol, used
used between IMG sender(s) and IMG receiver(s) for the between IMG sender(s) and IMG receiver(s) for the delivery of IMG
delivery of IMG metadata and for the control of IMG metadata and for the control of IMG sender(s)/receiver(s) [4].
sender(s)/receiver(s) [4].
IMG Transport Protocol: A protocol that transports IMG metadata IMG Transport Protocol: A protocol that transports IMG metadata from
from an IMG sender to IMG receiver(s) [4]. an IMG sender to IMG receiver(s) [4].
IMG Transport Session: An association between an IMG sender and IMG Transport Session: An association between an IMG sender and one
one or more IMG receivers within the scope of an IMG or more IMG receivers within the scope of an IMG transport
transport protocol. An IMG transport session involves a protocol. An IMG transport session involves a time-bound series
time bound series of IMG transport protocol interactions of IMG transport protocol interactions that provide delivery of
that provide delivery of IMG metadata from the IMG sender IMG metadata from the IMG sender to the IMG receiver(s) [4].
to the IMG receiver(s) [4].
IMG Transfer: IMG Transfer: A transfer of IMG metadata from an IMG Transfer: A transfer of IMG metadata from an IMG sender to IMG
IMG sender to IMG receiver(s). receiver(s).
3 IMG Common Framework Model 3. IMG Common Framework Model
Two common elements are found in all of existing IMG candidate cases: Two common elements are found in all existing IMG candidate cases:
the need to describe the services and the need to deliver the the need to describe the services and the need to deliver the
descriptions. In some cases, the descriptions provide multicast descriptions. In some cases, the descriptions provide multicast
addresses and thus are part of the transport configuration. In other addresses and thus are part of the transport configuration. In other
cases, descriptions are specific to the media application and may be cases, descriptions are specific to the media application and may be
either meant for human or machine consumption. Thus, the technologies meant for either human or machine consumption. Thus, the
can be roughly divided into three areas: technologies can be roughly divided into three areas:
o Application-specific Metadata -- data describing the content o Application-specific Metadata: data describing the content of
of services and media which are both specific to certain services and media which are both specific to certain
applications and generally human readable. applications and generally human readable.
o Delivery Descriptions -- the descriptions (metadata) that are o Delivery Descriptions: the descriptions (metadata) that are
essential to enable (e.g., multicast) delivery. These include essential to enable (e.g., multicast) delivery. These include
framing (headers) for application-specific metadata, the framing (headers) for application-specific metadata, the
metadata element identification and structure, and fundamental metadata element identification and structure, and fundamental
session data. session data.
o Delivery Protocols -- the methods and protocols to exchange o Delivery Protocols: the methods and protocols to exchange
descriptions between the senders and the receivers. An IMG descriptions between the senders and the receivers. An IMG
transport protocol consists of two functions: carrying IMG transport protocol consists of two functions: carrying IMG
metadata from an IMG sender to an IMG receiver and controlling metadata from an IMG sender to an IMG receiver and controlling
an IMG transport protocol. These functions are not always an IMG transport protocol. These functions are not always
exclusive, therefore some messages may combine control exclusive; therefore, some messages may combine control messages
messages and metadata carriage functions to reduce the amount and metadata carriage functions to reduce the amount of the
of the messaging. messaging.
3.1 IMG Data Types 3.1. IMG Data Types
A data model is needed to precisely define the terminology and A data model is needed to precisely define the terminology and
relationships between sets, supersets and subsets of metadata. A relationships between sets, supersets, and subsets of metadata. A
precise data model is essential for the implementation of IMGs precise data model is essential for the implementation of IMGs,
although it is not within the scope of this framework and requires a although it is not within the scope of this framework and requires a
separate specification. However there are three IMG data types in separate specification. However, there are three IMG data types in
general: Complete IMG Descriptions, Delta IMG Descriptions and IMG general: Complete IMG Descriptions, Delta IMG Descriptions, and IMG
Pointers. Pointers.
3.1.1 Complete IMG Description 3.1.1. Complete IMG Description
A complete IMG description provides a self-contained set of metadata A Complete IMG Description provides a self-contained set of metadata
for one media object or service, i.e., it does not need additional for one media object or service, i.e., it does not need additional
information from any other IMG element. This is not to be confused information from any other IMG element. This is not to be confused
with "complete IMG metadata", which, although vaguely defined here, with "complete IMG metadata", which, although vaguely defined here,
represents the complete IMG metadata database of an IMG sender (or represents the complete IMG metadata database of an IMG sender (or
related group of IMG senders -- potentially the complete Internet IMG related group of IMG senders -- potentially the complete Internet IMG
knowledge). An IMG sender will generally deliver only subsets of knowledge). An IMG sender will generally deliver only subsets of
metadata from its complete database in a particular IMG transport metadata from its complete database in a particular IMG transport
session. session.
3.1.2 Delta IMG Description 3.1.2. Delta IMG Description
A Delta IMG Description provides only part of a Complete IMG A Delta IMG Description provides only part of a Complete IMG
Description, defining the difference from a previous version of the Description, defining the difference from a previous version of the
Complete IMG Description. Delta IMG Descriptions may be used to Complete IMG Description. Delta IMG Descriptions may be used to
reduce network resource usage, for instance when data consistency reduce network resource usage, for instance, when data consistency is
is essential and small and frequent changes occur to IMG elements. essential and small and frequent changes occur to IMG elements.
Thus, this description does not represent a complete set of metadata Thus, this description does not represent a complete set of metadata
until it is combined with other metadata that may already exist or until it is combined with other metadata that may already exist or
arrive in the future. arrive in the future.
3.1.3 IMG Pointer 3.1.3. IMG Pointer
An IMG pointer, typically a URI, identifies or locates metadata. This An IMG Pointer identifies or locates metadata. This may be used to
may be used to separately obtain metadata (Complete or Delta IMG separately obtain metadata (Complete or Delta IMG Descriptions) or
Descriptions) or perform another IMG management function such as data perform another IMG management function such as data expiry (and
expiry (and erasure). The IMG Pointer may be used to reference IMG erasure). The IMG Pointer may be used to reference IMG metadata
metadata elements within the IMG transport session and across IMG elements within the IMG transport session and across IMG transport
transport sessions. This pointer type does not include IMG metadata sessions. This pointer type does not include IMG metadata per se
per se (although it may also appear as a data field in Complete or (although it may also appear as a data field in Complete or Delta IMG
Delta IMG descriptors). Descriptions).
3.2 IMG Entities 3.2. IMG Entities
There are several fundamental IMG entities that indicate the There are several fundamental IMG entities that indicate the
capability to perform certain roles. An Internet host involved in IMG capability to perform certain roles. An Internet host involved in
operations may adopt one or more of these roles, which are defined in IMG operations may adopt one or more of these roles, which are
more detail in Section 3.3. defined in more detail in Section 3.3.
IMG Announcer: sends IMG ANNOUNCE IMG Announcer: sends IMG ANNOUNCE
IMG Listener: receives IMG ANNOUNCE IMG Listener: receives IMG ANNOUNCE
IMG Querier: sends IMG QUERY to receive IMG RESOLVE IMG Querier: sends IMG QUERY and receives IMG RESOLVE
IMG Resolver: receives IMG QUERY then send IMG RESOLVE
IMG Subscriber: sends IMG SUBSCRIBE then receive IMG NOTIFY IMG Resolver: receives IMG QUERY then sends IMG RESOLVE
IMG Notifier: receives IMG SUBSCRIBE then send IMG NOTIFY IMG Subscriber: sends IMG SUBSCRIBE then receives IMG NOTIFY
IMG Notifier: receives IMG SUBSCRIBE then sends IMG NOTIFY
Figure 1 shows the relationship between IMG entities and the IMG Figure 1 shows the relationship between IMG entities and the IMG
sender and receiver. sender and receiver.
+--------------------------------------------------------+ +--------------------------------------------------------+
| IMG Sender | | IMG Sender |
+------------------+------------------+------------------+ +------------------+------------------+------------------+
| IMG Announcer | IMG Notifier | IMG Resolver | | IMG Announcer | IMG Notifier | IMG Resolver |
+------------------+------------------+------------------+ +------------------+------------------+------------------+
| ^ ^ | ^ ^
message | | | message | | |
direction v v v direction v v v
+------------------+------------------+------------------+ +------------------+------------------+------------------+
| IMG Listener | IMG Subscriber | IMG Querier | | IMG Listener | IMG Subscriber | IMG Querier |
+------------------+------------------+------------------+ +------------------+------------------+------------------+
| IMG Receiver | | IMG Receiver |
+------------------+------------------+------------------+ +------------------+------------------+------------------+
Figure 1: Relationship between IMG Entities, Senders and Receivers Figure 1: Relationship between IMG Entities, Senders, and Receivers
3.3 Operation Set for IMG Delivery 3.3. Operation Set for IMG Delivery
A finite set of operations both meets the IMG requirements [4] and A finite set of operations both meets the IMG requirements [4] and
fits the roles of existing protocols. These are crystallized in the fits the roles of existing protocols. These are crystallized in the
next few sections. next few sections.
3.3.1 IMG ANNOUNCE 3.3.1. IMG ANNOUNCE
When an IMG receiver participates in unidirectional communications When an IMG receiver participates in unidirectional communications
(e.g., over satellite, terrestrial radio and wired multicast (e.g., over satellite, terrestrial radio, and wired multicast
networks) an IMG receiver may not need to send any IMG message to an networks), an IMG receiver may not need to send any IMG message to an
IMG sender prior to IMG metadata delivery. In this case, an IMG IMG sender prior to IMG metadata delivery. In this case, an IMG
sender can initiate unsolicited distribution for IMG metadata and an sender can initiate unsolicited distribution for IMG metadata and an
IMG sender is the only entity which can maintain the distribution IMG sender is the only entity that can maintain the distribution
(this includes scenarios with multiple and co-operative IMG senders). (this includes scenarios with multiple and cooperative IMG senders).
This operation is useful when there is large numbers of IMG receivers This operation is useful when there are large numbers of IMG
or the IMG receivers do not have a guaranteed uplink connection to receivers or the IMG receivers do not have a guaranteed uplink
the IMG sender. The IMG sender may also include authentication data connection to the IMG sender. The IMG sender may also include
in the announce operation so that IMG receivers may check the authentication data in the ANNOUNCE operation so that IMG receivers
authenticity of the metadata. This operation can carry any of the may check the authenticity of the metadata. This operation can carry
IMG data types. any of the IMG data types.
There is no restriction to prevent IMG ANNOUNCE from being used There is no restriction to prevent IMG ANNOUNCE from being used in an
in an asynchronous solicited manner, where a separate operation asynchronous solicited manner, where a separate operation (possibly
(possibly out of band) enables IMG receivers to subscribe/register to out of band) enables IMG receivers to subscribe/register to the IMG
the IMG ANNOUNCE operation. ANNOUNCE operation.
3.3.2 IMG QUERY 3.3.2. IMG QUERY
If an IMG receiver needs to obtain IMG metadata, an IMG receiver can If an IMG receiver needs to obtain IMG metadata, an IMG receiver can
use an IMG QUERY operation and initiate a receiver-driven IMG use an IMG QUERY operation and initiate a receiver-driven IMG
transport session. The IMG receiver expects a synchronous response to transport session. The IMG receiver expects a synchronous response
the subsequent request from the IMG sender. This operation can be to the subsequent request from the IMG sender. This operation can be
used where a bi-directional transport network is available between used where a bidirectional transport network is available between the
the IMG sender and receiver. Some IMG receivers may want to obtain IMG sender and receiver. Some IMG receivers may want to obtain IMG
IMG metadata when network connectivity is available or just to avoid metadata when network connectivity is available or just to avoid
caching unsolicited IMG metadata. The IMG receiver must indicate the caching unsolicited IMG metadata. The IMG receiver must indicate the
extent and data type of metadata wanted in some message in the extent and data type of metadata wanted in some message in the
operation. The extent indicates the number and grouping of metadata operation. The extent indicates the number and grouping of metadata
descriptions. In some cases requesting an IMG sender's complete IMG descriptions. In some cases, it may be feasible to request an IMG
metadata collection, it may be feasible to request. sender's complete metadata collection.
3.3.3 IMG RESOLVE 3.3.3. IMG RESOLVE
An IMG sender synchronously responds, and sends IMG metadata, to an An IMG sender synchronously responds, and sends IMG metadata, to an
IMG QUERY which has been sent by an IMG receiver. This operation IMG QUERY that has been sent by an IMG receiver. This operation can
can be used where a bi-directional transport network is available be used where a bidirectional transport network is available between
between the IMG sender and receiver. If the IMG QUERY specifies a the IMG sender and receiver. If the IMG QUERY specifies a subset of
subset of IMG metadata (extent and data type) that is available to IMG metadata (extent and data type) that is available to the IMG
the IMG sender, the IMG sender can resolve the query; otherwise, it sender, the IMG sender can resolve the query; otherwise, it should
should indicate that it is not able to resolve the query. The IMG indicate that it is not able to resolve the query. The IMG sender
sender may authenticate the IMG receiver to investigate the IMG may authenticate the IMG receiver during the QUERY operation to
QUERY operation in order to determine whether the IMG receiver is determine if the IMG receiver is authorized to receive that metadata.
authorized to be sent that metadata. The sender may also include The sender may also include authentication data in the RESOLVE
authentication data in the resolve operation so that IMG receivers operation so that IMG receivers may check the authenticity of the
may check the authenticity of the metadata. This operation may metadata. This operation may carry any of the IMG data types.
carry any of the IMG data types.
3.3.4 IMG SUBSCRIBE 3.3.4. IMG SUBSCRIBE
If an IMG receiver wants to be notified when the IMG metadata it If an IMG receiver wants to be notified when the IMG metadata it
holds is stale, the IMG receiver can use the IMG SUBSCRIBE operation holds becomes stale, the IMG receiver can use the IMG SUBSCRIBE
in advance in order to solicit IMG NOTIFY messages from an IMG operation in advance in order to solicit IMG NOTIFY messages from an
sender. IMG sender.
This operation may provide the IMG sender with specific details of This operation may provide the IMG sender with specific details of
which metadata or notification services it is interested in in the which metadata or notification services it is interested in the case
case where the IMG sender offers more than the simplest "all data" where the IMG sender offers more than the simplest "all data"
service. This operation implicitly provides the functionality of service. This operation implicitly provides the functionality of
unsubscribing to inform an IMG sender that an IMG receiver wishes unsubscribing to inform an IMG sender that an IMG receiver wishes to
to stop getting certain (or all) notifications. It should be noted stop getting certain (or all) notifications. It should be noted that
that unsubscription may be provided implicitly by the expiry unsubscription may be provided implicitly by the expiry (timeout) of
(timeout) of a subscription before it is renewed. a subscription before it is renewed.
Since the IMG receiver does not know when metadata will be updated Since the IMG receiver does not know when metadata will be updated
and the notify message will arrive, this operation does not and the notify message will arrive, this operation does not
synchronize with the notify messages. The IMG receiver may wait for synchronize with the notify messages. The IMG receiver may wait for
notify messages for a long time. The IMG sender may authenticate the notify messages for a long time. The IMG sender may authenticate the
IMG receiver to check whether an IMG SUBSCRIBE operation is from an IMG receiver to check whether an IMG SUBSCRIBE operation is from an
authorized IMG receiver. authorized IMG receiver.
3.3.5 IMG NOTIFY 3.3.5. IMG NOTIFY
An IMG NOTIFY is used asynchronously in response to an earlier IMG An IMG NOTIFY is used asynchronously in response to an earlier IMG
SUBSCRIBE. An IMG NOTIFY operation indicates that updated IMG SUBSCRIBE. An IMG NOTIFY operation indicates that updated IMG
metadata is available or part of the existing IMG metadata is stale. metadata is available or part of the existing IMG metadata is stale.
An IMG NOTIFY may be delivered more than once during the time an IMG An IMG NOTIFY may be delivered more than once during the time an IMG
SUBSCRIBE is active. This operation may carry any of the IMG data SUBSCRIBE is active. This operation may carry any of the IMG data
types. The IMG sender may also include authentication data in the types. The IMG sender may also include authentication data in the
IMG NOTIFY operation so that IMG receivers may check the authenticity IMG NOTIFY operation so that IMG receivers may check the authenticity
of the messages. of the messages.
3.3.6 Binding Between IMG Operations and Data Types 3.3.6. Binding between IMG Operations and Data Types
There is a need to provide a binding between the various IMG There is a need to provide a binding between the various IMG
operations and IMG data types to allow management of each discrete operations and IMG data types to allow management of each discrete
set of IMG metadata transferred using an IMG operation. This binding set of IMG metadata transferred using an IMG operation. This binding
must be independent of any particular metadata syntax used to must be independent of any particular metadata syntax used to
represent a set of IMG metadata, as well as be compatible with any represent a set of IMG metadata, as well as be compatible with any
IMG transport protocol. The binding must uniquely identify the set of IMG transport protocol. The binding must uniquely identify the set
IMG metadata delivered within an IMG transfer, regardless of the of IMG metadata delivered within an IMG transfer, regardless of the
metadata syntax used. The uniqueness may only be needed within the metadata syntax used. The uniqueness may only be needed within the
domains the metadata is used but this must enable globally unique domains the metadata is used, but this must enable globally unique
identification to support Internet usage. Scope/domain specific identification to support Internet usage. Care should be taken that
identifications should not 'leak' outside of the scope, and always scope- and domain-specific identifiers do not leak outside the scope;
using globally unique identification (e.g., based on URIs) should using globally unique identifiers such as URLs avoids these problems.
avoid this error.
The binding must provide versioning to the transferred IMG metadata The binding must provide versioning to the transferred IMG metadata
so that changes can be easily handled and stale data identified, and so that changes can be easily handled and stale data identified, and
give temporal validity of the transferred IMG metadata. It must give temporal validity of the transferred IMG metadata. It must
invalidate the IMG metadata by indicating an expiry time, and may invalidate the IMG metadata by indicating an expiry time, and may
optionally provide a time (presumably in the future) from when the optionally provide a time (presumably in the future) from when the
IMG metadata becomes valid. Temporal validity of IMG metadata may be IMG metadata becomes valid. The temporal validity of a metadata
changeable for an IMG transfer, and even for specific versions of the object may need to be updated later. Furthermore, the binding must
IMG transfer. Furthermore, the binding must be independent of the be independent of any specific metadata syntax used for the IMG
metadata syntax(es) used for the IMG metadata, in the sense that no metadata, in the sense that no useful syntax should be excluded.
useful syntax should be excluded.
3.4 Overview of Protocol Operations 3.4. Overview of Protocol Operations
Figure 2 gives an overview of the relationship between transport Figure 2 gives an overview of the relationship between transport
cases, IMG Operations and IMG data types. It is not a protocol cases, IMG operations, and IMG data types. It is not a protocol
stack. Generalized multicast point-to-multipoint (P-to-M) and stack. Generalized multicast point-to-multipoint (P-to-M) and
unicast point-to-point (P-to-P) transports are shown. unicast point-to-point (P-to-P) transports are shown.
+--------------------------------------------------+ +--------------------------------------------------+
IMG | | IMG | |
Data types | Complete Desc., Delta Desc., Pointer | Data Types | Complete Desc., Delta Desc., Pointer |
| | | |
+-------------------+----------------+-------------+ +-------------------+----------------+-------------+
IMG | IMG ANNOUNCE | IMG SUBSCRIBE | IMG QUERY | IMG | IMG ANNOUNCE | IMG SUBSCRIBE | IMG QUERY |
Operations | | IMG NOTIFY | IMG RESOLVE | Operations | | IMG NOTIFY | IMG RESOLVE |
+--------------+----+----------------+-------------+ +--------------+----+----------------+-------------+
IMG | | | IMG | | |
Transport | P-to-M | P-to-P | Transport | P-to-M | P-to-P |
| | | | | |
+--------------+-----------------------------------+ +--------------+-----------------------------------+
Figure 2: IMG Transport, IMG Operations and IMG Data types Figure 2: IMG Transport, IMG Operations, and IMG Data Types
4 Deployment Scenarios for IMG Entities 4. Deployment Scenarios for IMG Entities
This section provides some basic deployment scenarios for IMG This section provides some basic deployment scenarios for IMG
entities that illustrate common threads from protocols to use cases. entities that illustrate common threads from protocols to use cases.
For the purposes of clarity, this document presents the simple For the purposes of clarity, this document presents the simple
dataflow from an IMG sender to an IMG receiver, as shown in Figure 3. dataflow from an IMG sender to an IMG receiver, as shown in Figure 3.
+-------------+ +---------------+ +-------------+ +---------------+
| IMG Sender | | IMG Receiver | | IMG Sender | | IMG Receiver |
| |--------------->| | | |--------------->| |
+-------------+ +---------------+ +-------------+ +---------------+
Figure 3: A Simple IMG Sender to IMG Receiver Relationship Figure 3: A Simple IMG Sender to IMG Receiver Relationship
4.1 Intermediary Cases 4.1. Intermediary Cases
Some IMG metadata may be distributed to a large number of IMG Some IMG metadata may be distributed to a large number of IMG
receivers, for example, when public metadata is distributed to all receivers, for example, when public metadata is distributed to all
IMG receivers of a certain group. This kind of IMG metadata may be IMG receivers of a certain group. This kind of IMG metadata may be
distributed from one IMG sender to multiple IMG receivers (Figure 4) distributed from one IMG sender to multiple IMG receivers (Figure 4)
or may be relayed across a set of IMG transceivers that receive the or may be relayed across a set of IMG transceivers that receive the
IMG metadata, possibly filter or modify its content, and then forward IMG metadata, possibly filter or modify its content, and then forward
it. it.
+----------+ +----------+ +----------+ +----------+
skipping to change at page 11, line 25 skipping to change at page 11, line 21
. -->|IMG |----- . . -->|IMG |----- .
. -->|Transceiver| \ . . -->|Transceiver| \ .
/ +-----------+ \ / +-----------+ \
+----------+ / \ +----------+ +----------+ / \ +----------+
| IMG | / ---->| IMG | | IMG | / ---->| IMG |
| Sender |---- | Receiver | | Sender |---- | Receiver |
+----------+ +----------+ +----------+ +----------+
Figure 4: A Relay Network with an IMG Transceiver Figure 4: A Relay Network with an IMG Transceiver
IMG senders and receivers are logical functions and it is possible IMG senders and receivers are logical functions, and it is possible
for some or all hosts in a system to perform both roles, as, for for some or all hosts in a system to perform both roles, as, for
instance, in many-to-many communications or where a transceiver is instance, in many-to-many communications or where a transceiver is
used to combine or aggregate IMG metadata for some IMG receivers. An used to combine or aggregate IMG metadata for some IMG receivers. An
IMG receiver may be allowed to receive IMG metadata from any number IMG receiver may be allowed to receive IMG metadata from any number
of IMG senders. of IMG senders.
IMG metadata is used to find, obtain, manage and play media content. IMG metadata is used to find, obtain, manage, and play media content.
IMG metadata may be modified during IMG Transfer. For example, a IMG metadata may be modified during IMG transfer. For example, a
server may use IMGs to retrieve media content via unicast and then server may use IMGs to retrieve media content via unicast and then
make it available at scheduled times via multicast, thus requiring a make it available at scheduled times via multicast, thus requiring a
change of the corresponding metadata. IMG transceivers may add or change of the corresponding metadata. IMG transceivers may add or
delete information or aggregate IMG metadata from different IMG delete information or aggregate IMG metadata from different IMG
senders. For example, a rating service may add its own content senders. For example, a rating service may add its own content
ratings or recommendations to existing metadata. An implication of ratings or recommendations to existing metadata. An implication of
changing (or aggregating) IMG metadata from one or more IMG senders changing (or aggregating) IMG metadata from one or more IMG senders
is that the original authenticity is lost. Thus, IMG metadata is that the original authenticity is lost. Thus, it may be
fragmented reasonably may be beneficial for the intermediary to beneficial to sign fragments so that the intermediary can replace a
replace a small fragment without changing the authenticity of the fragment without changing the authenticity of the remainder. For
remainder. For example, smaller fragments may be appropriate for more example, smaller fragments may be appropriate for more volatile
volatile parts, and larger ones may be appropriate for stable parts. parts, and larger ones may be appropriate for stable parts.
4.2 One-to-many Unidirectional Multicast 4.2. One-to-Many Unidirectional Multicast
One-to-many unidirectional multicast case implies many IMG receivers The one-to-many unidirectional multicast case implies many IMG
and one or more IMG senders implementing IMG ANNOUNCER and IMG receivers and one or more IMG senders implementing IMG announcer and
LISTENER operations as shown in Figure 5. IMG listener operations as shown in Figure 5.
Unidirectional +----------+ Unidirectional +----------+
---------------> | IMG | ---------------> | IMG |
downlink | Listener | downlink | Listener |
------------->| 1 | ------------->| 1 |
/ +----------+ / +----------+
+-----------+ / . +-----------+ / .
| IMG |-------- . | IMG |-------- .
| Announcer | \ . | Announcer | \ .
+-----------+ \ +----------+ +-----------+ \ +----------+
------------->| IMG | ------------->| IMG |
| Listener | | Listener |
| # | | # |
+----------+ +----------+
Figure 5: IMG Unidirectional Multicast Distribution Example Figure 5: IMG Unidirectional Multicast Distribution Example
Note, as defined in by the IMG requirements REL-4 [4], an IMG Note, as defined in the IMG requirement REL-4 [4], an IMG transport
transport protocol MUST support reliable message exchange. protocol MUST support reliable message exchange. This includes the
This includes the one-to-many unidirectional multicast case, one-to-many unidirectional multicast case; however, the mechanism to
however, the mechanism to provide this is beyond the scope of this provide this is beyond the scope of this document.
document.
4.3 One-to-one Bi-directional Unicast 4.3. One-to-One Bidirectional Unicast
In one-to-one bi-directional unicast case, both query/resolve In the one-to-one bidirectional unicast case, both query/resolve
(Figure 6) and subscribe/notify (Figure 7) message exchange (Figure 6) and subscribe/notify (Figure 7) message exchange
operations are feasible. operations are feasible.
+----------+ +----------+ +----------+ +----------+
| IMG | | IMG | | IMG | | IMG |
| Resolver | | Querier | | Resolver | | Querier |
+----------+ +----------+ +----------+ +----------+
| | | |
|<----------IMG QUERY -----------| |<----------IMG QUERY -----------|
| | | |
skipping to change at page 13, line 35 skipping to change at page 13, line 22
: : : :
|-----------IMG NOTIFY---------->| |-----------IMG NOTIFY---------->|
: : : :
(time passes) (time passes)
: : : :
|-----------IMG NOTIFY---------->| |-----------IMG NOTIFY---------->|
| | | |
Figure 7: Subscribe/Notify Sequence Example Figure 7: Subscribe/Notify Sequence Example
4.4 Combined Operations with Common Metadata 4.4. Combined Operations with Common Metadata
As shown in Figure 8, a common data model for multiple protocol As shown in Figure 8, a common data model for multiple protocol
operations allows a diverse range of IMG senders and receivers to operations allows a diverse range of IMG senders and receivers to
provide consistent and interoperable sets of IMG metadata. provide consistent and interoperable sets of IMG metadata.
IMG Metadata IMG Senders IMG Receivers IMG Metadata IMG Senders IMG Receivers
+--------------+ +--------------+
+-----------+ ---->| IMG Listener | +-----------+ ---->| IMG Listener |
| IMG | / +--------------+ | IMG | / +--------------+
skipping to change at page 14, line 26 skipping to change at page 14, line 5
+-------------+ | \ | Resolver | +-------------+ | \ | Resolver |
+-------------+ \ +-----------+<----\ +--------------+ +-------------+ \ +-----------+<----\ +--------------+
\ \--->| IMG Querier | \ \--->| IMG Querier |
\ +-----------+ | - - - - - - -| \ +-----------+ | - - - - - - -|
\| IMG |<--------->| IMG | \| IMG |<--------->| IMG |
| Notifier | | Subscriber | | Notifier | | Subscriber |
+-----------+ +--------------+ +-----------+ +--------------+
Figure 8: Combined System with Common Metadata Figure 8: Combined System with Common Metadata
5 Applicability of Existing Protocols to the Proposed Framework Model 5. Applicability of Existing Protocols to the Proposed Framework Model
5.1 Existing Standard Fitting the IMG Framework Model 5.1. Existing Standards Fitting the IMG Framework Model
SDP: The SDP format [2] could be used to describe session-level SDP: The SDP format [2] could be used to describe session-level
parameters (e.g., scheduling, addressing and the use of media codecs) parameters (e.g., scheduling, addressing, and the use of media
to be included in Complete IMG Descriptions. Although there are codecs) to be included in Complete IMG Descriptions. Although there
extension points in SDP allowing the format to be extended, there are are extension points in SDP allowing the format to be extended, there
limitations in the flexibility of this extension mechanism. However, are limitations in the flexibility of this extension mechanism.
SDP syntax cannot provide IMG Descriptions and IMG Pointers without However, SDP syntax cannot provide IMG Descriptions and IMG Pointers
significant overhead. It is expected that the information conveyed by without significant overhead. It is expected that the information
SDP is just a small subset of IMG metadata, thus, the use of SDP for conveyed by SDP is just a small subset of IMG metadata; thus, the use
other than session parameters may not be reasonable. of SDP for other than session parameters may not be reasonable.
SDPng [3]: Similar to SDP, this format could also be used for SDPng [3]: Similar to SDP, this format could also be used for
representing session-level parameters of IMG metadata. Compared to representing session-level parameters of IMG metadata. Compared to
SDP, the XML-based format of SDPng should be much more flexible and SDP, the XML-based format of SDPng should be much more flexible and
allow extensions and integration with other description formats. allow extensions and integration with other description formats.
MPEG-7: Descriptions based on the MPEG-7 standard [5] could provide MPEG-7: Descriptions based on the MPEG-7 standard [5] could provide
application-specific metadata describing the properties of multimedia application-specific metadata describing the properties of multimedia
content beyond parameters carried in SDP or SDPng descriptions. content beyond parameters carried in SDP or SDPng descriptions.
MPEG-7 provides a machine-readable format of representing content MPEG-7 provides a machine-readable format of representing content
categories and attributes, helping end-users or receiving software in categories and attributes, helping end-users or receiving software in
choosing content for reception. MPEG-7 is based on XML so it is well choosing content for reception. MPEG-7 is based on XML, so it is
suited to be combined with other XML-based formats such as SDPng. well suited to be combined with other XML-based formats such as
SDPng.
TV-Anytime Forum: The TV-Anytime Forum [6] provides descriptions TV-Anytime: The TV-Anytime Forum [6] provides descriptions based on
based on XML schema for TV-specific program guides. TV-Anytime uses XML schema for TV-specific program guides. TV-Anytime uses the
the MPEG-7 User description profile to a limited extent, only for MPEG-7 User description profile to a limited extent, only for user
user preferences and usage history, and also a TV-Anytime-specific preferences and usage history, and also a TV-Anytime-specific data
data model for other schema. These are optimised to describe model for other schema. These are optimized to describe broadcast
broadcast schedules, on-demand program guides and program events. schedules, on-demand program guides and program events.
HTTP: The HTTP protocol [7] can be used as a bi-directional unicast HTTP: The HTTP protocol [7] can be used as a bidirectional unicast
IMG transport protocol. Being a request-reply oriented protocol, HTTP IMG transport protocol. Being a request-reply-oriented protocol,
is well suited for implementing synchronous operations such as QUERY, HTTP is well suited for implementing synchronous operations such as
RESOLVE and even SUBSCRIBE. However, HTTP does not provide QUERY, RESOLVE, and even SUBSCRIBE. However, HTTP does not provide
asynchronous operations such as ANNOUNCE and NOTIFY and to implement asynchronous operations such as ANNOUNCE and NOTIFY and to implement
asynchronous operations using HTTP, IMG receivers should poll the IMG asynchronous operations using HTTP, IMG receivers should poll the IMG
sender periodically. Thus, by itself, HTTP is not sufficient to sender periodically. Thus, by itself, HTTP is not sufficient to
fulfill all of the IMG requirements [4] in a unicast deployment. fulfill all of the IMG requirements [4] in a unicast deployment.
SAP: The announcement mechanism provided by SAP [8] provides Session Announcement Protocol (SAP): The announcement mechanism
unidirectional delivery of session discovery information. Although provided by SAP [8] provides unidirectional delivery of session
SDP is the default payload format of SAP, the use of a MIME type discovery information. Although SDP is the default payload format of
identifier for the payload allows arbitrary payload formats to be SAP, the use of a MIME type identifier for the payload allows
used in SAP messages. Thus, SAP could be used to implement the arbitrary payload formats to be used in SAP messages. Thus, SAP
multicast and unicast IMG ANNOUNCE and IMG NOTIFY operations. could be used to implement the multicast and unicast IMG ANNOUNCE and
IMG NOTIFY operations.
However, SAP lacks scalable and efficient reliability, extensibility However, SAP lacks scalable and efficient reliability, extensibility
for payload size, congestion control, and only one description for payload size, and congestion control, and only one description is
allowed per SAP message due to lack of payload segmentation. allowed per SAP message due to lack of payload segmentation.
In principle, SAP could be extended to get around its limitations. In principle, SAP could be extended to get around its limitations.
However, the amount of changes needed in SAP to address all of the However, the amount of changes needed in SAP to address all of the
above limitations would effectively result in a new protocol. Due to above limitations would effectively result in a new protocol. Due to
these limitations, the use of SAP as an IMG transport protocol is NOT these limitations, the use of SAP as an IMG transport protocol is not
RECOMMENDED. recommended.
SIP: The SIP-specific event mechanism described in RFC 3265 [9] SIP: The SIP-specific event mechanism described in RFC 3265 [9]
provides a way to implement IMG SUBSCRIBE and IMG NOTIFY operations provides a way to implement IMG SUBSCRIBE and IMG NOTIFY operations
via a bi-directional unicast connection. However, there are via a bidirectional unicast connection. However, there are
scalability problems with this approach, as RFC 3265 currently does scalability problems with this approach, as RFC 3265 currently does
not consider multicast. not consider multicast.
RTSP: The RTSP protocol [10] defines a retrieval and update Real Time Streaming Protocol (RTSP): The RTSP protocol [10] defines a
notification mechanism, named DESCRIBE and ANNOUNCE, for the retrieval-and-update notification mechanism, named DESCRIBE and
description of a presentation or media object in order to initialize ANNOUNCE, for the description of a presentation or media object in
a streaming session. These methods are subset of the entire streaming order to initialize a streaming session. These methods are a subset
control operations in RTSP, thus these could not be available for of the entire streaming control operations in RTSP; thus, these could
individual mechanisms. However, the DESCRIBE method in RTSP could be not be available for individual mechanisms. However, the DESCRIBE
used to instantiate IMG QUERY, IMG RESOLVE and IMG SUBSCRIBE, and the method in RTSP could be used to instantiate IMG QUERY, IMG RESOLVE,
RTSP ANNOUNCE could be used to instantiate an IMG NOTIFY for a and IMG SUBSCRIBE, and the RTSP ANNOUNCE could be used to instantiate
streaming session controlled by RTSP. an IMG NOTIFY for a streaming session controlled by RTSP.
5.2 IMG Mechanism Needs Not Yet Met 5.2. IMG Mechanism Needs Which Are Not Met by Existing Standards
Several needs result from the IMG requirements, framework model and Several needs result from the IMG requirements, framework model, and
existing relevant mechanisms as already shown in this document. Four existing relevant mechanisms as already shown in this document. Four
specific groupings of work are readily apparent which are: (a) specific groupings of work are readily apparent: (a) specification of
specification of an adequate multicast and unidirectional capable an adequate multicast- and unidirectional-capable announcement
announcement protocol; (b) specification of the use of existing protocol; (b) specification of the use of existing unicast protocols
unicast protocols to enable unicast subscribe and to enable unicast subscribe and announcement/notification
announcement/notification functionality; (c) specification of the functionality; (c) specification of the metadata envelope that is
metadata envelope which is common to, and independent of, the common to, and independent of, the application metadata syntax(es)
application metadata syntax(es) used; (d) agreement on basic metadata used; and (d) agreement on basic metadata models to enable
models to enable interoperability testing of the above. The following interoperability testing of the above. The following sections
sections describe each of these. describe each of these.
5.2.1 A Multicast Transport Protocol 5.2.1. A Multicast Transport Protocol
SAP is currently the only open standard protocol suited to the SAP is currently the only open standard protocol suited to the
unidirectional/multicast delivery of IMG metadata. As discussed, it unidirectional/multicast delivery of IMG metadata. As discussed, it
fails to meet the IMG requirements in many ways and, since it is not fails to meet the IMG requirements in many ways and, since it is not
designed to be extensible, we recognize that a new multicast designed to be extensible, we recognize that a new multicast
transport protocol for announcements needs to be specified to meet transport protocol for announcements needs to be specified to meet
IMG needs. This protocol will be essential to IMG delivery for IMG needs. This protocol will be essential to IMG delivery for
unidirectional and multicast deployments. unidirectional and multicast deployments.
The Asynchronous Layered Coding (ALC) [11] protocol from the IETF The Asynchronous Layered Coding (ALC) [11] protocol from the IETF
Reliable Multicast Transport (RMT) working group is very interesting Reliable Multicast Transport (RMT) working group is very interesting
as it fulfills many of the requirements, is extensible and has the as it fulfills many of the requirements, is extensible, and has the
ability to 'plug-in' both FEC (Forward Error Correction -- for ability to 'plug-in' both FEC (Forward Error Correction, for
reliability) and CC (Congestion Control) functional blocks -- it is reliability) and CC (Congestion Control) functional blocks. It is
specifically designed for unidirectional multicast object transport. specifically designed for unidirectional multicast object transport.
ALC is not fully specified, although RMT working group had a fully ALC is not fully specified, although the RMT working group had a
specified protocol using ALC called FLUTE (File Delivery over fully specified protocol using ALC called FLUTE (File Delivery over
Unidirectional Transport) [12]. FLUTE seems to be the only fully Unidirectional Transport) [12]. FLUTE seems to be the only fully
specified transport and open specification on which a new IMG specified transport and open specification on which a new IMG
announcement protocol could be designed. Thus, we recommend that ALC announcement protocol could be designed. Thus, we recommend that ALC
and FLUTE be the starting points for this protocol's design. and FLUTE be the starting points for this protocol's design.
Developing a new protocol from scratch, or attempting to improve SAP, Developing a new protocol from scratch, or attempting to improve SAP,
is also feasible, although it would involve repeating many of the is also feasible, although it would involve repeating many of the
design processes and decisions already made by the IETF for ALC. design processes and decisions already made by the IETF for ALC. In
particular, any announcement protocol must feature sufficient
In particular, any announcement protocol must feature sufficient scalability, flexibility, and reliability to meet IMG needs. Also,
scalability, flexibility and reliability to meet IMG needs. Also, the the IMG ANNOUNCE operation must be supported and IMG NOTIFY
IMG ANNOUNCE operation must be supported and IMG NOTIFY capability capability could be investigated for both hybrid unicast-multicast
could be investigated for both hybrid unicast-multicast and and unidirectional unicast systems.
unidirectional unicast systems.
5.2.2 Usage of Unicast Transport Protocols 5.2.2. Usage of Unicast Transport Protocols
A thorough description of the use of existing unicast protocols is A thorough description of the use of existing unicast protocols is
essential for the use of IMGs in a unicast point-to-point essential for the use of IMGs in a unicast point-to-point
environment. Such a specification does not currently exist, although environment. Such a specification has not been published, although
several usable unicast transport protocols and specifications can be several usable unicast transport protocols and specifications can be
harnessed for this (SIP [13], SIP events [9], HTTP [7], etc.) In harnessed for this (SIP [13], SIP events [9], HTTP [7], etc.). In
particular, both IMG SUBSCRIBE-NOTIFY and IMG QUERY-RESOLVE operation particular, both IMG SUBSCRIBE-NOTIFY and IMG QUERY-RESOLVE operation
pairs must be enabled. We anticipate that the IMG QUERY-RESOLVE pairs must be enabled. We anticipate that the IMG QUERY-RESOLVE
operation can be achieved using HTTP, although other transport operation can be achieved using HTTP, although other transport
protocol options may be beneficial to consider too. protocol options may be beneficial to consider too.
5.2.3 IMG Envelope 5.2.3. IMG Envelope
An IMG envelope provides binding between IMG Operations and data An IMG envelope provides the binding between IMG operations and data
types. Such a binding can be realized by defining a common minimal types. Such a binding can be realized by defining a common minimal
set of information needed to manage IMG metadata transfers, and by set of information needed to manage IMG metadata transfers, and by
including this information with any set of IMG metadata delivered to including this information with any set of IMG metadata delivered to
IMG receivers. IMG receivers.
Four options for IMG metadata transfer envelope delivery are Four options for IMG metadata transfer envelope delivery are
feasible: feasible:
1. Embedding in a transport protocol header. This can be done 1. Embedding in a transport protocol header. This can be done
with either header extensions of existing protocols, or with either header extensions of existing protocols, or newly
newly defined header fields of a new (or new version of a) defined header fields of a new (or new version of a) transport
transport protocol. However, multiple methods for the protocol. However, multiple methods for the variety of
variety of transport protocols would hinder transport protocols would hinder interoperability and
interoperability and transport protocol independence. transport protocol independence.
2. A separate envelope object, which points to the IMG 2. A separate envelope object, which points to the IMG metadata
metadata 'object', delivered in-band with the metadata 'object', delivered in-band with the metadata transport
transport protocol session. This might complicate protocol session. This might complicate delivery as the
delivery as the envelope and 'service' metadata objects envelope and 'service' metadata objects would have to be
would have to be bound, e.g., by pairing some kind of bound, e.g., by pairing some kind of transport object numbers
transport object numbers (analogous to port number pairs (analogous to port number pairs sometimes used for RTP and
sometimes used for RTP and RTCP [14]). This would also RTCP [14]). This would also enable schemes that deliver
enable schemes which deliver enveope and metadata envelope and metadata 'objects' by different media, also using
'objects' on by different media, also using more than a more than a single transport protocol.
single transport protocol.
3. A metadata wrapper which points to and/or embeds the 3. A metadata wrapper that points to and/or embeds the service
service metadata into its 'super-syntax'. For example, an metadata into its 'super-syntax'. For example, XML would
XML would enable embedding generic text objects. enable embedding generic text objects.
4. Embedding in the metadata itself. However, this requires 4. Embedding in the metadata itself. However, this requires a
new field in many metadata syntaxes and would not be new field in many metadata syntaxes and would not be feasible
feasible if a useful syntax were not capable of if a useful syntax were not capable of extensibility in this
extensibility in this way. It also introduces a larger way. It also introduces a larger 'implementation
'implementation interpretation' variety which would hinder interpretation' variety, which would hinder interoperability.
interoperability. Thus this option is not recommended. Thus, this option is not recommended.
It is likely that more than one of these options will fulfill the It is likely that more than one of these options will fulfill the
needs of IMGs so the selection, and possibly optimization, is left needs of IMGs, so the selection, and possibly optimization, is left
for subsequent specification and feedback from implementation for subsequent specification and feedback from implementation
experience. Such a specification is essential for IMG delivery. experience. Such a specification is essential for IMG delivery.
When there are superset/subset relations between IMG descriptions, When there are superset/subset relations between IMG Descriptions, it
it is assumed that the IMG descriptions of the subset inherit the is assumed that the IMG Descriptions of the subset inherit the
parameters of the superset. Thus, an IMG metadata transfer envelope parameters of the superset. Thus, an IMG metadata transfer envelope
carrying the IMG descriptions of a superset may implicitly define carrying the IMG Descriptions of a superset may implicitly define
parameters of IMG descriptors belonging to its subset. The parameters of IMG Descriptions belonging to its subset. The
relations between IMG descriptions may span from one envelope to relations between IMG Descriptions may span from one envelope to
another according to a data model definition. another according to a data model definition.
5.2.4 Metadata Data Model 5.2.4. Metadata Data Model
A structured data model would allow reuse and extension of the set of A structured data model would allow reuse and extension of the set of
metadata and may enable use of multiple syntaxes (SDP, MPEG-7, etc.) metadata and may enable use of multiple syntaxes (SDP, MPEG-7, etc.)
as part of the same body of IMG metadata. as part of the same body of IMG metadata.
Further work may be needed to meet application-specific requirements For the successful deployment of IMGs in various environments,
at defining metadata and data models for the successful deployment of further work may be needed to define metadata and data models for
IMGs in various environments. Existing (and future) work on these application-specific requirements. Existing (and future) work on
would need to be mapped to the IMG data types and use of the IMG these would need to be mapped to the IMG data types and use of the
transfer envelope concept as described above. IMG transfer envelope concept as described above.
This document is a framework for the delivery of IMG metadata and This document is a framework for the delivery of IMG metadata and
thus further discussion on the definition data models for IMGs is thus further discussion on the definition data models for IMGs is
beyond its scope. beyond its scope.
6 Security Considerations 6. Security Considerations
The IMG framework is developed from the IMG requirements document [4] The IMG framework is developed from the IMG requirements document
and so the selection of specific protocols and mechanism for use with [4], and so the selection of specific protocols and mechanism for use
the IMG framework must also take into account the security with the IMG framework must also take into account the security
considerations of the IMG requirements document. This framework considerations of the IMG requirements document. This framework
document does not mandate the use of specific protocols. However, an document does not mandate the use of specific protocols. However, an
IMG specification would inherit the security considerations of IMG specification would inherit the security considerations of
specific protocols used. specific protocols used.
Protocol instantiations which are used to provide IMG operations will Protocol instantiations that are used to provide IMG operations will
have very different security considerations depending on their scope have very different security considerations depending on their scope
and purpose. However, there are several general issues which are and purpose. However, there are several general issues that are
valuable to consider and, in some cases, provide technical solutions valuable to consider and, in some cases, provide technical solutions
to deal with. These are described below. for. These are described below.
Individual and group privacy: Customized IMG metadata may reveal Individual and group privacy: Customized IMG metadata may reveal
information about the habits and preferences of a user and may thus information about the habits and preferences of a user and may thus
deserve confidentiality protection, even if the original information deserve confidentiality protection, even if the original information
were public. Snooping and protecting this IMG metadata requires the were public. Protecting this metadata against snooping requires the
same actions and measures as for other point-to-point and multicast same actions and measures as for other point-to-point and multicast
Internet communications. Naturally, the risk of snooping depends on Internet communications. Naturally, the risk of snooping depends on
the amount of individual or group personalization the snooped IMG the amount of individual or group personalization the IMG metadata
metadata contains. contains.
IMG authenticity: In some cases, the IMG receiver needs to be assured IMG authenticity: In some cases, the IMG receiver needs to be assured
of the sender or origin of IMG metadata or its modification history. of the sender or origin of IMG metadata or its modification history.
This can prevent denial of service or hijacking attempts which give This can prevent denial-of-service or hijacking attempts that give an
an IMG receiver incorrect information in or about the metadata, thus IMG receiver incorrect information in or about the metadata, thus
preventing successful access of the media or directing the IMG preventing successful access of the media or directing the IMG
receiver to the incorrect media possibly with tasteless material. receiver to the incorrect media possibly with tasteless material.
IMG receiver authorization: Some or all of any IMG sender's metadata IMG receiver authorization: Some or all of any IMG sender's metadata
may be private or valuable enough to allow access to only certain IMG may be private or valuable enough to allow access to only certain IMG
receivers and thus make it worth authenticating users. Encrypting the receivers and thus make it worth authenticating users. Encrypting
data is also a reasonable step, especially where group communications the data is also a reasonable step, especially where group
methods results in unavoidable snooping opportunities for communications methods results in unavoidable snooping opportunities
unauthorized nodes. for unauthorized nodes.
Unidirectional specifics: A difficulty that is faced by Unidirectional specifics: A difficulty that is faced by
unidirectional delivery operations is that many protocols providing unidirectional delivery operations is that many protocols providing
application-level security are based on bi-directional application-level security are based on bidirectional communications.
communications. The application of these security protocols in case The application of these security protocols in case of strictly
of strictly unidirectional links is not considered in the present unidirectional links is not considered in the present document.
document.
Malicious code: Currently, IMGs are not envisaged to deliver Malicious code: Currently, IMGs are not envisaged to deliver
executable code at any stage. However, as some IMG transport executable code at any stage. However, as some IMG transport
protocols may be capable of delivering arbitrary files, it is protocols may be capable of delivering arbitrary files, it is
RECOMMENDED that the IMG operations do not have write access to the RECOMMENDED that the IMG operations do not have write access to the
system or any other critical areas. system or any other critical areas.
7 IANA Considerations 7. Normative References
This document does not request any IANA action.
8 Normative References
[1] S. Bradner, "Key words for use in RFCs to indicate requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
levels," RFC 2119, Internet Engineering Task Force, March 1997. Levels", BCP 14, RFC 2119, March 1997.
9 Informative References 8. Informative References
[2] M. Handley and V. Jacobson, "SDP: session description protocol," [2] Handley, M. and V. Jacobson, "SDP: Session Description
RFC 2327, Internet Engineering Task Force, April 1998. Protocol", RFC 2327, April 1998.
[3] D. Kutscher, J. Ott, and C. Bormann, "Session description and [3] Kutscher, D., Ott, J., and C. Bormann, "Session description and
capability negotiation," Internet Draft draft-ietf-mmusic-sdpng-07, capability negotiation", Work in Progress, October 2003.
Internet Engineering Task Force, October 2003. Work in progress.
[4] Y. Nomura, R. Walsh, J-P. Luoma, J. Ott, and H. Schulzrinne, [4] Nomura, Y., Walsh, R., Luoma, J-P., Ott, J., and H. Schulzrinne,
"Requirements for Internet Media Guides," Internet Draft "Requirements for Internet Media Guides", Work in Progress,
draft-ietf-mmusic-img-req-08, Internet Engineering Task Force, December 2005.
December 2005. Work in progress.
[5] "Multimedia content description interface -- Part 1: Systems", [5] "Multimedia content description interface -- Part 1: Systems",
ISO/IEC 15938-1, July 2002. ISO/IEC 15938-1, July 2002.
[6] TV-Anytime Forum, "Broadcast and On-line Services: Search, [6] TV-Anytime Forum, "Broadcast and On-line Services: Search,
select, and rightful use of content on personal storage systems select, and rightful use of content on personal storage systems
("TV-Anytime Phase 1"); Part 2: System description," ETSI-TS 102 ("TV-Anytime Phase 1"); Part 2: System description," ETSI-TS 102
822-2: System Description, V1.1.1, October 2003. 822-2: System Description, V1.1.1, October 2003.
[7] R. Fielding, J. Gettys, J. C. Mogul, H. Frystyk, L. Masinter, P. [7] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach and T. Berners-Lee, "Hypertext transfer protocol -- HTTP/1.1," Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
RFC 2616, Internet Engineering Task Force, June 1999. HTTP/1.1", RFC 2616, June 1999.
[8] M. Handley, C. E. Perkins, and E. Whelan, "Session announcement [8] Handley, M., Perkins, C., and E. Whelan, "Session Announcement
protocol," RFC 2974, Internet Engineering Task Force, October 2000. Protocol", RFC 2974, October 2000.
[9] A. B. Roach, "Session initiation protocol (sip)-specific event [9] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
notification," RFC 3265, Internet Engineering Task Force, June 2002. Notification", RFC 3265, June 2002.
[10] H. Schulzrinne, A. Rao, and R. Lanphier, "Real Time Streaming [10] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming
Protocol (RTSP)", RFC 2326, Internet Engineering Task Force, Protocol (RTSP)", RFC 2326, April 1998.
April 1998.
[11] M. Luby, J. Gemmell, L. Vicisano, L. Rizzo, and J. Crowcroft, [11] Luby, M., Gemmell, J., Vicisano, L., Rizzo, L., and J.
"Asynchronous layered coding (ALC) protocol instantiation," RFC 3450, Crowcroft, "Asynchronous Layered Coding (ALC) Protocol
Internet Engineering Task Force, December 2002. Instantiation", RFC 3450, December 2002.
[12] T. Paila, M. Luby, R. Lehtonen, V. Roca, R. Walsh, "FLUTE - [12] Paila, T., Luby, M., Lehtonen, R., Roca, V., and R. Walsh,
file delivery over unidirectional transport," RFC 3926, "FLUTE - File Delivery over Unidirectional Transport", RFC 3926,
Internet Engineering Task Force, October 2004. October 2004.
[13] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. R. Johnston, J. [13] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP: session Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
initiation protocol," RFC 3261, Internet Engineering Task Force, June Session Initiation Protocol", RFC 3261, June 2002.
2002.
[14] H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson, "RTP: [14] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
a transport protocol for real-time applications," RFC 3550, Internet "RTP: A Transport Protocol for Real-Time Applications", STD 64,
Engineering Task Force, July 2003. RFC 3550, July 2003.
10 Acknowledgements 9. Acknowledgements
The authors would like to thank Spencer Dawkins, Jean-Pierre Evain, The authors would like to thank Spencer Dawkins, Jean-Pierre Evain,
Ted Hardie, Petri Koskelainen, Joerg Ott, Colin Perkins, Toni Paila, Ted Hardie, Petri Koskelainen, Joerg Ott, Colin Perkins, Toni Paila,
Magnus Westerlund, and for their excellent ideas and input to this and Magnus Westerlund for their excellent ideas and input to this
document. document.
11 Authors' Addresses Authors' Addresses
Yuji Nomura Yuji Nomura
Fujitsu Laboratories Ltd. Fujitsu Laboratories Ltd.
4-1-1 Kamikodanaka, Nakahara-ku, Kawasaki 211-8588 4-1-1 Kamikodanaka, Nakahara-ku, Kawasaki 211-8588
Japan Japan
Email: nom@flab.fujitsu.co.jp
EMail: nom@flab.fujitsu.co.jp
Rod Walsh Rod Walsh
Nokia Research Center Nokia Research Center
P.O. Box 100, FIN-33721 Tampere P.O. Box 100, FIN-33721 Tampere
Finland Finland
Email: rod.walsh@nokia.com
EMail: rod.walsh@nokia.com
Juha-Pekka Luoma Juha-Pekka Luoma
Nokia Research Center Nokia Research Center
P.O. Box 100, FIN-33721 Tampere P.O. Box 100, FIN-33721 Tampere
Finland Finland
Email: juha-pekka.luoma@nokia.com
EMail: juha-pekka.luoma@nokia.com
Hitoshi Asaeda Hitoshi Asaeda
INRIA Keio University
PLANETE Research Team Graduate School of Media and Governance
2004, Route des Lucioles, BP93, 5322 Endo, Fujisawa, 252-8520 Kanagawa,
06902 Sophia Antipolis, Japan
France
Email: Hitoshi.Asaeda@sophia.inria.fr EMail: asaeda@wide.ad.jp
Henning Schulzrinne Henning Schulzrinne
Dept. of Computer Science Dept. of Computer Science
Columbia University Columbia University
1214 Amsterdam Avenue 1214 Amsterdam Avenue
New York, NY 10027 New York, NY 10027
USA USA
Email: schulzrinne@cs.columbia.edu
Intellectual Property Statement EMail: schulzrinne@cs.columbia.edu
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Internet Society. Administrative Support Activity (IASA).
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