ISO/IEC 16512-2:2011
(Main)Information technology — Relayed multicast protocol: Specification for simplex group applications — Part 2:
Information technology — Relayed multicast protocol: Specification for simplex group applications — Part 2:
ISO/IEC 16512-2:2011 specifies the relayed multicast protocol for simplex group applications (RMCP-2), an application-layer protocol, which constructs a multicast tree for data delivery from one sender to multiple receivers over the Internet where IP multicast is not fully deployed. It defines a basic RMCP-2 protocol without security features, and a secure RMCP-2 protocol that adds security features to the basic protocol. Both protocols specify a series of functions and procedures for multicast agents to construct a one-to-many relayed data path and to relay simplex data. They also specify the operations of the session manager to manage multicast sessions. These protocols can be used for applications that require one-to-many data delivery services, such as multimedia streaming services or file dissemination services. ISO/IEC 16512-2:2011 also defines a membership authentication procedure for use with the secure RMCP-2 protocol and provides informative material related to the protocols.
Technologies de l'information — Protocole de multidiffusion relayé: Spécification relative aux applications de groupe simplex — Partie 2:
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INTERNATIONAL ISO/IEC
STANDARD 16512-2
Second edition
2011-12-01
Information technology — Relayed
multicast protocol: Specification for
simplex group applications
Technologies de l'information — Protocole de multidiffusion relayé:
Spécification relative aux applications de groupe simplex
Reference number
ISO/IEC 16512-2:2011(E)
©
ISO/IEC 2011
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ISO/IEC 16512-2:2011(E)
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ii © ISO/IEC 2011 – All rights reserved
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ISO/IEC 16512-2:2011(E)
CONTENTS
Page
1 Scope . 1
2 Normative references . 1
2.1 Identical Recommendations | International Standards . 1
2.2 Additional references . 1
3 Definitions . 2
4 Abbreviations . 3
5 Overview . 4
5.1 RMCP-2 entities . 4
5.2 RMCP-2 protocol block . 5
5.3 Simplex delivery model of RMCP-2 . 6
5.4 Types of RMCP-2 messages . 6
6 Protocol operation . 7
6.1 SM's operation . 7
6.2 MA's operation . 9
7 RMCP-2 message format . 19
7.1 Common format of RMCP-2 message . 19
7.2 Control data format . 20
7.3 Messages . 21
8 Parameters . 52
8.1 Data forwarding profile . 52
8.2 Parameters used in RMCP-2 . 53
8.3 Encoding rules to represent values used in RMCP-2 . 54
9 Overview of secure RMCP-2 . 57
9.1 Conventions . 57
9.2 Secure RMCP-2 entities . 58
9.3 Protocol blocks . 60
9.4 Types of secure RMCP-2 protocol messages . 61
9.5 Structure of regional security management . 62
10 Protocol operation . 63
10.1 SM operation . 63
10.2 MA operation . 67
11 Format of secure RMCP-2 messages . 73
11.1 Common format for secure RMCP-2 messages . 73
11.2 Secure RMCP-2 messages . 73
12 Parameters . 86
12.1 Secure RMCP-2 node types and code values . 86
12.2 Secure RMCP-2 message types and code values . 86
12.3 Secure RMCP-2 control types and code values . 87
12.4 Code values related to the RMCP-2 security policy . 88
12.5 Miscellaneous code values . 89
Annex A – Tree configuration algorithm . 91
A.1 Bootstrapping rule . 91
A.2 Neighbour discovering rule . 92
A.3 HMA selection rule . 93
A.4 CMA acceptance rule . 93
A.5 Parent decision rule . 94
A.6 Tree improvement rule . 95
A.7 PMA's kicking-out rule . 95
Annex B – Real-time data delivery scheme . 96
B.1 Overview . 96
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ISO/IEC 16512-2:2011(E)
Page
B.2 IP-IP tunnel mechanism for RMCP-2 real-time data delivery . 96
Annex C – Reliable data delivery scheme . 98
C.1 Overview . 98
C.2 Operation . 98
C.3 Data encapsulation format . 100
C.4 Data profile . 100
Annex D – RMCP-2 API . 101
D.1 Overview . 101
D.2 RMCP-2 API functions . 102
Annex E – Membership authentication mechanism . 105
E.1 Overview . 105
E.2 Authentication procedure . 105
Annex F – Bibliography . 107
F.1 Informative references . 107
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ISO/IEC 16512-2:2011(E)
Foreword
ISO (the Internation al Organization for Standardizati on) and IEC (the Internationa l Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are members of
ISO or IEC parti cipate in the d evelopment of International Standards through technical committees
established by the respective organization to deal with particular fields of technical activity. ISO and IEC
technical committees collaborate in fields of mutual interest. Other international organizations, governmental
and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information
technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as
an International Standard requires approval by at least 75 % of the national bodies casting a vote.
Attention is drawn to t he possibility that some of the elements of this document may be the subject of patent
rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.
ISO/IEC 16512-2 was prepared by Joint Te chnical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 6, Telecommunications and information exchange between systems, in collaboration with
ITU-T. The identical text is published as ITU-T Rec. X.603.1 (03/2010).
This second edition cancels and replaces the first edition (ISO/IEC 16512-2:2008), which has been technically
revised.
ISO/IEC 16512 consists of the following parts, under the general title Information technology — Relayed
multicast protocol:
Part 1: Framework
Part 2: Specification for simplex group applications
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ISO/IEC 16512-2:2011(E)
Introduction
Introduction Relayed MultiCast Protocol Part 2 (RMCP-2) is an application-layer relayed multicast protocol for simplex
group applications. RMCP-2 can construct an optimized and robust one-to-many relayed multicast delivery path over a
unicast network with the help of RMCP entities defined by Rec. ITU-T X.603 | ISO/IEC 16512-1.
An RMCP-2 session consists of one SM and one or more MAs; SM initiates and terminates RMCP-2 session and
manages RMCP-2 session and participated MAs; MA configures an RMCP-2 tree to deliver group data by exchanging a
series of RMCP-2 control messages.
Along the relayed multicast delivery path, several types of data delivery channels can be constructed according to the
requirement of application services.
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ISO/IEC 16512-2:2011 (E)
INTERNATIONAL STANDARD
RECOMMENDATION ITU-T
Information technology – Relayed multicast protocol:
Specification for simplex group applications
1 Scope
This Recommendation | International Standard specifies the Relayed MultiCast Protocol for simplex group applications
(RMCP-2), an application-layer protocol, which constructs a multicast tree for data delivery from one sender to multiple
receivers over the Internet where IP multicast is not fully deployed.
Clauses 5-8 define a basic RMCP-2 protocol without security features, and clauses 9-12 define a secure RMCP-2
protocol that adds security features to the basic protocol. Both protocols specify a series of functions and procedures for
multicast agents to construct a one-to-many relayed data path and to relay simplex data. They also specify the
operations of the session manager to manage multicast sessions.
These protocols can be used for applications that require one-to-many data delivery services, such as multimedia
streaming services or file dissemination services.
Annex E defines a membership authentication procedure for use with the secure RMCP-2 protocol. Annexes A-D
provide informative material related to these protocols. Annex F contains an informative bibliography.
2 Normative references
The following Recommendations and International Standards contain provisions which, through reference in this text,
constitute provisions of this Recommendation | International Standard. At the time of publication, the editions indicated
were valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this
Recommendation | International Standard are encouraged to investigate the possibility of applying the most recent
edition of the Recommendations and Standards listed below. Members of IEC and ISO maintain registers of currently
valid International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of currently
valid ITU-T Recommendations.
2.1 Identical Recommendations | International Standards
– Recommendation ITU-T X.603 (2004) | ISO/IEC 16512-1:2005, Information technology – Relayed
multicast protocol: Framework.
2.2 Additional references
– ISO/IEC 9797-2:2002, Information technology – Security techniques – Message Authentication Codes
(MACs) – Part 2: Mechanisms using a dedicated hash-function.
– ISO/IEC 9798-3:1998, Information technology – Security techniques – Entity authentication –
Part 3: Mechanisms using digital signature techniques.
– ISO/IEC 18033-2:2006, Information technology – Security techniques – Encryption algorithms – Part 2:
Asymmetric ciphers.
– ISO/IEC 18033-3:2010, Information technology – Security techniques – Encryption algorithms – Part 3:
Block ciphers.
– ISO/IEC 18033-4:2005, Information technology – Security techniques – Encryption algorithms – Part 4:
Stream ciphers.
– IETF RFC 2094 (1997), Group Key Management Protocol (GKMP) Architecture.
– IETF RFC 3546 (2003), Transport Layer Security (TLS) Extensions.
– IETF RFC 3830 (2004), MIKEY: Multimedia Internet KEYing.
– IETF RFC 4279 (2005), Pre-Shared Key Ciphersuites for Transport Layer Security (TLS).
– IETF RFC 4346 (2006), The Transport Layer Security (TLS) Protocol Version 1.1.
– IETF RFC 4535 (2006), GSAKMP: Group Secure Association Key Management Protocol.
Rec. ITU-T X.603.1 (03/2010) 1
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ISO/IEC 16512-2:2011 (E)
3 Definitions
For the purposes of this Recommendation | International Standard, the following definitions apply:
3.1 multicast: A data delivery scheme where the same data unit is transmitted from a single source to multiple
destinations over a single invocation of service.
3.2 IP multicast: A multicast scheme in an IP network supported by multiple multicast-enabled IP routers.
3.3 relayed multicast: A multicast data delivery scheme that can be used in unicast environments; the scheme is
based on intermediate multicast agents that relay multicast data from a media server to media players over a tree
hierarchy.
3.4 relayed multicast protocol (RMCP): A protocol that supports and manages the relayed multicast data
transport.
3.5 RMCP-2 session: An MA set that uses the RMCP to configure the data delivery path.
3.6 multicast agent (MA): An intermediate data transport entity used to relay the multicast application data.
Depending on the deployment, an MA may be installed in the same system as a receiving client.
3.7 sender multicast agent (SMA): The MA attached to the sender in the same system or local network.
3.8 receiver multicast agent (RMA): The MA attached to the receiver in the same system or local network.
3.9 head multicast agent (HMA): A representative of the MA inside a local network where the multicast is
enabled.
3.10 session manager (SM): An RMCP entity that is responsible for the overall RMCP operations; it may be
located in the same system as the media server or located separately from the media server.
3.11 parent multicast agent (PMA): The next upstream MA in the RMCP-2 data delivery path.
3.12 child multicast agent (CMA): The next downstream MA in the RMCP-2 data delivery path.
3.13 RMCP-2 protocol: A relayed multicast protocol for simplex group applications.
3.14 basic RMCP-2 protocol: The relayed multicast protocol for simplex group application defined in clauses 5-8.
3.15 secure RMCP-2 protocol: The relayed multicast protocol supporting security features for simplex group
applications defined in clauses 9-12.
3.16 dedicated multicast agent (DMA): An intermediate MA pre-deployed as a trust server by the Session
Manager (SM) in an RMCP session.
3.17 security policy: The set of criteria for the provision of security services, together with the set of values for
these criteria, resulting from agreement of the security mechanisms defined in 10.1.4.
3.18 TLS_CERT mode: A mode of the TLS defined in IETF RFC 4346 for the authentication of MAs using a
certificate.
3.19 TLS_PSK mode: A mode of the TLS defined in IETF RFC 4279 for the authentication of MAs using a pre-
shared key for the TLS key exchange.
3.20 relayed multicast region; RM region: A management zone defined by the use of the session key Ks.
3.21 member multicast region; MM region: A management zone defined by the use of one or more group
keys Kg.
3.22 member multicast group; MM group:
1) (in a multicast disabled area) a group consisting of one DMA and multiple RMAs sharing the same
group key Kg.
2) (in a multicast enabled area) a group consisting of one HMA, multiple RMAs together with one or more
candidate HMAs sharing the same group key Kg.
3.23 candidate HMA: A DMA that is able to assume the role of an HMA, should the original HMA leave or be
terminated from a multicast-enabled MM group.
3.24 group attribute (GP_ATTRIBUTE): An attribute that defines whether or not the Content Provider controls
the admission of RMAs to the secure RMCP-2 session.
3.25 closed group: An MM group in which all the RMAs have been allocated a service user identifier from the
Content Provider before subscribing to the secure RMCP-2 session.
2 Rec. ITU-T X.603.1 (03/2010)
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ISO/IEC 16512-2:2011 (E)
3.26 open group: An MM group in which none of the RMAs require a service user identifier before subscribing to
the secure RMCP-2 session.
3.27 regular HB message: An HB message that is relayed without interruption along the path of the RMCP-2 tree
from the SMA to the receiver of the message. The originator of a regular HB message is the SMA.
3.28 pseudo-HB message: An HB message that indicates a fault in the delivery path of the RMCP-2 tree. The
originator of a pseudo-HB message is the MA that discovers this fault.
4 Abbreviations
For the purposes of this Recommendation | International Standard, the following abbreviations apply:
ACL Access Control List
AUTH Authentication
CEK Contents Encryption Key
CMA Child Multicast Agent
CP Content Provider
DMA Dedicated Multicast Agent
HANNOUNCE HMA announce message
HB Heartbeat message
HLEAVE HMA leave message
HMA Head Multicast Agent
HRSANS Head Required Security Answer
HRSREQ Head Required Security Request
HSOLICIT HMA solicit message
IP-IP IP in IP
KEYDELIVER Key Delivery
LEAVANS Leave answer message
LEAVREQ Leave request message
MA Multicast Agent
MAID Multicast Agent Identification
PMA Parent Multicast Agent
PPROBANS Parent probe answer message
PPROBREQ Parent probe request message
RELANS Relay answer message
RELREQ Relay request message
RMA Receiver Multicast Agent
RMCP Relayed MultiCast Protocol
SDP Session Description Protocol
SECAGANS SECurity AGreement ANSwer
SECAGREQ SECurity AGreement REQuest
SECALGREQ SECurity ALgorithms REQuest
SECLIST Selected sECurity LIST
SID RMCP-2 Session Identification
SMA Sender Multicast Agent
STANS Status report answer message
STCOLANS Status report collect answer message
STCOLREQ Status report collect request message
STREQ Status report request message
Rec. ITU-T X.603.1 (03/2010) 3
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ISO/IEC 16512-2:2011 (E)
SUBSANS Subscription answer message
SUBSREQ Subscription request message
T/TCP TCP extensions to Transactions
TCP Transmission Control Protocol
TERMANS Termination answer message
TERMREQ Termination request message
TLS Transport Layer Security
UDP User Datagram Protocol
5 Overview
The RMCP-2 is an application-level protocol that uses multicast agents (MAs) and a session manager (SM) to support
and manage a relayed multicast data transport over a unicast-based Internet. With the help of the SM, the RMCP-2
begins by constructing a relayed multicast control tree that consists of MAs. Consequently with the preconfigured
control tree, each MA connects appropriate data channels with each other.
The RMCP-2 entities for a simplex delivery model are described in clause 5.1.
5.1 RMCP-2 entities
The RMCP-2 entities are the same as those described in RMCP Part 1. As shown in Figure 1, each RMCP-2 session
constructs a relayed multicast data delivery model with the following entities:
a) one SM;
b) one sender multicast agent (SMA) per sender application;
c) one or more receiver multicast agents (RMAs);
d) one or more sending or receiving group applications.
An SM, which can handle one or multiple sessions simultaneously, can be implemented separately or as a part of other
entities in an RMCP-2 session.
Sending
app.
SMA
Session
manager
RMAs
RMA RMA RMA
X.603.1(07)_F01
Receiving Receiving Receiving
app. app. app.
Figure 1 – RMCP-2 service topology
An SM can provide the following functionalities:
a) session initialization;
b) session release;
c) session membership management;
d) session status monitoring.
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ISO/IEC 16512-2:2011 (E)
An MA, which refers to both the SMA and the RMA, constructs a relayed multicast delivery path from one sender to
many receivers and then forwards data along the constructed path, can provide the following functionalities:
a) session initialization;
b) session join;
c) session leave;
d) session maintenance;
e) session status reporting;
f) application data relay.
5.2 RMCP-2 protocol block
An SM should exchange control messages with other MAs to control and manage RMCP-2 session. The control
messages used by SM should be delivered reliably; otherwise, RMCP-2 session becomes unrecoverable. Figure 2 shows
a protocol stack of an SM.
Control module of RMCP-2 SM
TCP
IP (unicast)
Figure 2 – Protocol stack of SM
An MA, which refers to both the SMA and the RMA, constructs a relayed multicast delivery path from one sender to
many receivers and then forwards data along the constructed path. An MA consists of an RMCP-2 control module and a
data transport module. The control module establishes the relayed data delivery path. The data transport module sets up
a data channel along the path constructed by the control module and then relays data through the channel.
The MA's control module configures the control tree from the SMA to every leaf MAs by exchanging control messages
with other MAs. Also the control module is used for session control and management by SM. Figure 3 shows the
protocol stack of an MA's control module.
Control module of RMCP-2 MA
TCP
IP (unicast)
Figure 3 – Protocol stack of MA's control module
The MA's data module relays application data along the tree configured by the control module. Figure 4 shows the
protocol stack of RMCP-2 data module. Any kind of transport mechanism can be inserted, if needed, because RMCP-2
imposes no restrictions on the type of application data to be delivered.
To ensure that RMCP-2 can adopt any kind of data transport mechanism, two MAs (namely, the parent multicast agent
(PMA) and the child multicast agent (CMA)) construct a data delivery path on the control tree by exchanging the data
profiles described later.
Rec. ITU-T X.603.1 (03/2010) 5
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ISO/IEC 16512-2:2011 (E)
Data module of RMCP-2 MA
TCP, UDP, IP-IP, SCTP, etc.
IP (unicast or multicast)
Figure 4 – Protocol stack of RMCP-2 data module
The topologies of the two paths for control and data delivery are usually the same, because a data delivery path is
constructed along the RMCP-2 control tree. Along the data delivery path, the application data from the SMA can be
delivered to each leaf MAs. For more information, Annexes B and C present two feasible real-time and reliable data
delivery schemes.
5.3 Simplex delivery model of RMCP-2
The target services of RMCP-2 are simplex broadcasting services, such as Internet live TV and software dissemination.
In those service models, building an optimal data delivery path from a sender to multiple receivers is important.
RMCP-2 can support a simplex data delivery model by using the MA's control and data module.
The data delivery path that RMCP-2 considers is a per-source relayed multicast tree. Along the per-source relayed
multicast path, a unidirectional real-time or reliable data channel can be constructed. Figure 5 shows one of the
possible relayed multicast trees configured by RMCP-2 for simplex real-time or reliable applications.
Sending
app.
Simplex relayed
multicast network
SMA
Reliable | Real-time
unicast
and unidirectional
RMA RMA
transport connection
Reliable | Real-time
multicast
and unidirectional
Receiving Receiving Receiving
transport connection
app. app. app.
X.603.1(07)_F05
Figure 5 – Relayed multicast tree configured by RMCP-2
5.4 Types of RMCP-2 messages
To construct and maintain a relayed multicast tree, several control messages are exchanged between RMCP-2 peers in a
request-and-answer manner. Table 1 lists the RMCP-2 control messages according to the appropriate functions.
Table 1 – RMCP-2 messages
Messages Descriptions RMCP operations
SUBSREQ Subscription request
Session initialization
SUBSANS Subscription answer
PPROBREQ Parent probe request
MAP discovery
PPROBANS Parent probe answer
HSOLICIT HMA solicit
HANNOUNCE HMA announce HMA election
HLEAVE HMA leave
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ISO/IEC 16512-2:2011 (E)
Table 1 – RMCP-2 messages
Messages Descriptions RMCP operations
RELREQ Relay request
Data delivery
RELANS Relay answer
STREQ Status report request
STANS Status report answer
Session monitoring
STCOLREQ Status collect request
STCOLANS Status collect answer
LEAVREQ Leave request
Session leave
LEAVANS Leave answer
HB Heartbeat Session heartbeat
TERMREQ Termination request
Session termination
TERMANS Termination answer
6 Protocol operation
This clause describes the RMCP-2 protocol functions and their operations in details. All the components described in
this clause follow the definitions of Rec. ITU-T X.603 | ISO/IEC 16512-1.
6.1 SM's operation
6.1.1 Session initiation
To make the SM create a new session, a content provider (CP) should provide a session profile, which includes details
to create a session such as the session name, media characteristics, and the group address. To distinguish the sessions
from each other, the SM creates a globally unique session identification (SID). After a successful session creation, the
SM returns the SID to the CP. The CPs may announce the session creation by using a web server or email. But the way
of session announcement is out of scope this Specification.
After the successful session creation, the SM waits for a subscription request from the MAs. When the SM receives a
subscription request from an MA, the SM decides whether to ac
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