Information technology — Relayed Multicast Control Protocol (RMCP) — Framework — Part 1:

Relayed multicast protocol (RMCP) is a protocol which is used to realize a relayed multicast data transport scheme. Different from the conventional IP multicast, RMCP can configure a relayed multicast path that multicast traffic flows by using intermediate end-hosts. RMCP can be applied to the current unicast based IP network where IP multicast is not fully deployed. ISO/IEC 16512-1:2016 addresses the basic concepts needed to specify RMCP for relayed multicast. It defines the related terminology and proposes a framework for the future development of subsequent protocols. The framework covers network topology including network entities and the relationship among them, service scenarios, basic operations, and message format.

Technologies de l'information — Protocole de multidiffusion relayé (RMCP) — Cadre général — Partie 1:

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INTERNATIONAL ISO/IEC
STANDARD 16512-1
Second edition
2016-04-01
Information technology — Relayed
Multicast Control Protocol (RMCP) —
Framework
Technologies de l'information -- Protocole de multidiffusion relayé
(RMCP) — Cadre général
Reference number
ISO/IEC 16512-1:2016(E)
ISO/IEC 2016
---------------------- Page: 1 ----------------------
ISO/IEC 16512-1:2016(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2016

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any

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Permission can be requested from either ISO at the address below or ISO’s member body in the country of the requester.

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Published in Switzerland
ii © ISO/IEC 2016 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/IEC 16512-1:2016(E)
Foreword

ISO (the International Organization for Standardization) and IEC (the International Electrotechnical

Commission) form the specialized system for worldwide standardization. National bodies that are members of

ISO or IEC participate in the development 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.

The procedures used to develop this document and those intended for its further maintenance are described

in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of

document should be noted. This document was drafted in accordance with the editorial rules of the

ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the 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. Details of any

patent rights identified during the development of the document will be in the Introduction and/or on the ISO

list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,

as well as information about ISO's adherence to the WTO principles in the Technical Barriers to Trade (TBT),

see the following URL: Foreword — Supplementary information.

This second edition cancels and replaces firs edition of ISO/IEC 16512-1:2005 which has been technically

revised.

ISO/IEC 16512-1 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology, in

collaboration with ITU-T. The identical text is published as ITU-T X.603 (03/2012).

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
© ISO/IEC 2016 – All rights reserved ii-1
---------------------- Page: 3 ----------------------
CONTENTS
Page

1 Scope .............................................................................................................................................................. 1

2 Normative references...................................................................................................................................... 1

3 Definitions ...................................................................................................................................................... 1

3.1 Terms defined elsewhere ..................................................................................................................... 1

3.2 Terms defined in this Recommendation | International Standard ........................................................ 1

4 Abbreviations ................................................................................................................................................. 2

5 Conventions .................................................................................................................................................... 2

6 Framework of RMCP ..................................................................................................................................... 2

6.1 Introduction ......................................................................................................................................... 2

6.2 Basic concept of RMCP ...................................................................................................................... 3

6.3 RMCP data delivery model ................................................................................................................. 5

6.4 Security consideration in RMCP ......................................................................................................... 8

7 RMCP functions ............................................................................................................................................. 8

7.1 Session initiation ................................................................................................................................. 8

7.2 Session subscription and join .............................................................................................................. 9

7.3 Session leave ....................................................................................................................................... 9

7.4 Session termination ............................................................................................................................. 9

7.5 Session maintenance ........................................................................................................................... 9

7.6 Session monitoring .............................................................................................................................. 9

8 Messages ........................................................................................................................................................ 10

8.1 Basic message structure ...................................................................................................................... 10

8.2 Control format ..................................................................................................................................... 10

8.3 Sub-control format .............................................................................................................................. 10

Bibliography .............................................................................................................................................................. 12

Rec. ITU-T X.603 (03/2012) iii
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Introduction

This Recommendation | International Standard specifies the relayed multicast protocol (RMCP) used for realizing

relayed multicast. Relayed multicast, also known as an overlay multicast or an application-layer multicast, is a data-

delivery scheme for group communications applications over an IP-based network environment. RMCP employs

intermediate multicast agents for relaying application data from one or more senders to many receivers.

The design of RMCP has been motivated from the following observations:

In the marketplace, diverse group applications and services have been provisioned commercially all over the world.

Some of the examples include Internet TV, remote education, real-time media streaming applications, live broadcasting

of special events such as the Victoria’s Secret Fashion Show, stock-tickers, etc.

At present, most of the group applications mentioned above use a replicated IP unicast method to realize group services.

As a result, those applications have scalability problems due to the limitation in supporting a number of simultaneous

users. In terms of a business model, it would mean less revenue or profit.

IP multicast has been known as an effective transport technology for providing group communication services.

Nevertheless, the IP multicast has not been deployed widely over the Internet due to several reasons, including the

following:
– high deployment cost along with an uncertainty of return-on-investment (ROI)
– IP multicast alone cannot support all kinds of group applications.

Network services such as group file transfer or network games, need a reliable multicast transport mechanism.

However, even current reliable multicast transport mechanisms still have unresolved problems including scalability,

flow control, congestion control, etc. Until an appropriate multicast transport mechanism is laid down, group

communication applications requiring reliable data transfer will continue to depend on the server-based replicated

unicast method.

Although IP multicast is not deployed globally, various local networks have already been equipped with IP multicast

capability. For example, Ethernet-based LANs and private networks, such as corporate and campus networks,

substantially provide the multicast transport capability within their local subnet or administrative domains.

Recognizing these observations, there is a crucial need to develop an alternative group delivery scheme. RMCP is one

such scheme to realize group delivery over the IP-based network. RMCP utilizes existing unicast, multicast, and/or

multicast tunnelling schemes. In addition, RMCP is designed in separate forms to support any kind of group service

type. RMCP is expected to provide a substantial solution for group services over the IP-based network.

iv Rec. ITU-T X.603 (03/2012)
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ISO/IEC 16512-1:2016 (E)
INTERNATIONAL STANDARD
ITU-T RECOMMENDATION
Information technology – Relayed multicast protocol: Framework
1 Scope

Relayed multicast protocol (RMCP) is a protocol which is used to realize a relayed multicast data transport scheme.

Different from the conventional IP multicast, RMCP can configure a relayed multicast path that multicast traffic flows

by using intermediate end-hosts. RMCP can be applied to the current unicast based IP network where IP multicast is not

fully deployed.

This Recommendation | International Standard addresses the basic concepts needed to specify RMCP for relayed

multicast. It defines the related terminology and proposes a framework for the future development of subsequent

protocols. The framework covers network topology including network entities and the relationship among them, service

scenarios, basic operations, and message format.
2 Normative references
None.
3 Definitions
3.1 Terms defined elsewhere
None.
3.2 Terms defined in this Recommendation | International Standard

For the purpose of this Recommendation | International Standard the following definitions apply:

3.2.1 child multicast agent (CMA): A next downstream multicast agent (MA) in the relayed multicast protocol

(RMCP) data delivery path.

3.2.2 IP multicast: Realizes a multicast scheme in the IP network with the help of multicast-enabled IP routers.

3.2.3 multicast: A data delivery scheme where the same data unit is transmitted from a single source to multiple

destinations in a single invocation of service.

3.2.4 multicast agent (MA): An intermediate node which relays group application data.

3.2.5 N-plex: Wherein anyone can send something, and, if someone does so, all others may receive it.

3.2.6 parent multicast agent (PMA): A next upstream multicast agent (MA) in the relayed multicast protocol

(RMCP) data delivery path.

3.2.7 relayed multicast: A multicast data delivery scheme that can be used in unicast environments.

3.2.8 receiver multicast agent (RMA): A multicast agent (MA) other than sender multicast agent (SMA).

3.2.9 relayed multicast protocol (RMCP): A protocol to realize the relayed multicast scheme using end hosts.

3.2.10 relayed multicast protocol (RMCP) session: A set of multicast agents (MAs) which configures the data

delivery path using RMCP.

3.2.11 session identification (SID): Corresponds to group name and identifies relayed multicast protocol (RMCP)

session uniquely.

3.2.12 session manager (SM): A relayed multicast protocol (RMCP) entity that is responsible for the overall RMCP

operations.

3.2.13 sender multicast agent (SMA): A multicast agent (MA) attached to a sender in the same system or local

network.

3.2.14 simplex: Wherein only one sender is send-only and all others are receive-only.

Rec. ITU-T X.603 (03/2012) 1
---------------------- Page: 6 ----------------------
ISO/IEC 16512-1:2016 (E)
4 Abbreviations

For the purposes of this Recommendation | International Standard, the following abbreviations apply:

CMA Child Multicast Agent
IPC Inter-Process Communication
IPIP IP in IP encapsulation
MA Multicast Agent
PMA Parent Multicast Agent
RMA Receiver Multicast Agent
RMCP Relayed Multicast Protocol
RMT Reliable Multicast Transport
SID Session ID
SM Session Manager
SMA Sender Multicast Agent
T/TCP TCP extensions to Transactions
TCP Transmission Control Protocol
TP Transport Protocol
UDP User Datagram Protocol
5 Conventions
None.
6 Framework of RMCP
6.1 Introduction

Relayed multicast protocol (RMCP) is an application-level multicast protocol. It constructs and manages a relayed

multicast network to support the group communication services over the current unicast-based IP network. After a

series of RMCP control connections are established, a multicast data delivery path is constructed by using multiple

multicast agents (MAs). Along the delivery path, real-time or reliable data transport channels are inter-connected

between upstream and downstream MAs. Only after the data delivery path and data channel are established, group

communication applications can work as in the native IP multicast network.

RMCP aims to support various kinds of group-based applications and services. Table 1 categorizes the group

communication services with types of communications and characteristics of data delivery.

Table 1 – Considerable group communication services
Characteristics
Real-time data Reliable data
Type of
communications
Internet live TV, Stock-ticker, file dissemination,
Simplex
Internet live banner software live update
Distributed virtual environment,
Videoconference,
N-plex network game, data mirroring and
inter-domain multicast proxy
caching
2 Rec. ITU-T X.603 (03/2012)
---------------------- Page: 7 ----------------------
ISO/IEC 16512-1:2016 (E)
6.2 Basic concept of RMCP

Each RMCP session configures relayed multicast data delivery model with the following entities as shown in Figure 1:

a) One session manager (SM);
b) Sender multicast agent (SMA) per sender application;
c) One or more receiver multicast agents (RMAs);
d) Group communication applications sending or receiving group data.
Sending Sending
application application
SMA SMA
RMAsRMARMA
RMA RMA RMA
Receiving Receiving
Receiving
application application
application
Figure 1 – RMCP entities

The SM is involved in session configuration and maintenance. A single SM can handle one or multiple sessions,

simultaneously. Since the SM does not participate in data delivery, it has RMCP control module only. Figure 2 shows

the protocol stack of SM.
RMCP control module
Transport protocol for message delivery
IP (unicast)
Figure 2 – Protocol stack of SM
A session manager (SM) can prov
...

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