INTERNATIONAL TELECOMMUNICATION UNION
`
`)45 4
`
`TELECOMMUNICATION
`STANDARDIZATION SECTOR
`OF ITU
`
`4(cid:14)(cid:17)(cid:18)(cid:16)
`
`(07/96)
`
`SERIES T: TERMINAL EQUIPMENTS AND PROTOCOLS
`FOR TELEMATIC SERVICES
`
`$ATAPROTOCOLSFORMULTIMEDIACONFERENCING
`
`ITU-T Recommendation T.120
`
`(Previously CCITT Recommendation)
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 001
`
`

`

`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 — 002
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 002
`
`

`

`ITU-T RECOMMENDATION T.120
`
`DATA PROTOCOLS FOR MULTIMEDIA CONFERENCING
`
`Summary
`
`The T.120-Series of Recommendations collectively define a multipoint data communication service
`for use in multimedia conferencing environments. The purpose of this Recommendation is to provide
`an introduction and guide to the T.120-Series. This Recommendation defines the T.120 architectural
`model and shows
`the
`interrelationships between
`the constituent Recommendations. Each
`Recommendation in the Series is outlined and the requirements for T.120 compliance are specified.
`
`Source
`
`ITU-T Recommendation T.120 was prepared by ITU-T Study Group 8 (1993-1996) and was
`approved under the WTSC Resolution N°1 procedure on the 3rd of July 1996.
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 003
`
`

`

`FOREWORD
`
`ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of
`telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of
`the ITU. Some 179 member countries, 84 telecom operating entities, 145 scientific and industrial
`organizations and 38 international organizations participate in ITU-T which is the body which sets world
`telecommunications standards (Recommendations).
`
`The approval of Recommendations by the Members of ITU-T is covered by the procedure laid down in
`WTSC Resolution No. 1 (Helsinki, 1993). In addition, the World Telecommunication Standardization
`Conference (WTSC), which meets every four years, approves Recommendations submitted to it and
`establishes the study programme for the following period.
`
`In some areas of information technology which fall within ITU-T’s purview, the necessary standards are
`prepared on a collaborative basis with ISO and IEC.
`
`In this Recommendation, the expression “Administration” is used for conciseness to indicate both a
`telecommunication administration and a recognized operating agency.
`
`NOTE
`
`All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means,
`electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU.
`
` ITU 1996
`
`ii
`
`Recommendation T.120 (07/96)
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 004
`
`ª
`

`

`CONTENTS
`
`1
`
`2
`
`3
`
`4
`
`5
`
`6
`
`6.1
`
`6.2
`
`6.3
`
`6.4
`
`6.5
`
`7
`
`7.1
`
`7.2
`
`7.3
`
`8
`
`8.1
`
`8.2
`
`8.3
`
`8.4
`
`8.5
`
`8.6
`
`9
`
`Scope............................................................................................................................
`
`Normative references...................................................................................................
`
`Symbols and abbreviations ..........................................................................................
`
`Overview......................................................................................................................
`
`Introduction to multipoint multimedia communication...............................................
`
`The T.120 system model..............................................................................................
`
`User applications..........................................................................................................
`
`Application protocols...................................................................................................
`
`Node Controller ...........................................................................................................
`
`Communications infrastructure....................................................................................
`
`Networks......................................................................................................................
`
`T.120 infrastructure Recommendations.......................................................................
`
`Protocol stacks for audiographic and audiovisual conferencing –
`Recommendation T.123...............................................................................................
`
`Multipoint Communication Service (MCS) – Recommendations T.122, T.125.........
`
`Generic Conference Control (GCC – Recommendation T.124)..................................
`
`Application protocol Recommendations .....................................................................
`
`The Generic Application Template (GAT) – Recommendation T.121 .......................
`
`Multipoint Still Image and Annotation Protocol (MSIA) – Recommendation T.126 .
`
`Multipoint Binary File Transfer (MBFT) – Recommendation T.127..........................
`
`T.120 extensions For audiovisual control – For further study.....................................
`
`Proprietary extensions to standardized protocols ........................................................
`
`Non-standard application protocols .............................................................................
`
`T.120 compliance.........................................................................................................
`
`Annex A - T.120 channel and token allocations ....................................................................
`
`A.1
`
`A.2
`
`A.3
`
`Static channels .............................................................................................................
`
`Static tokens.................................................................................................................
`
`Standard application protocol session identifiers ........................................................
`
`Annex B - MCS domain parameters .......................................................................................
`
`Page
`
`1
`
`1
`
`1
`
`2
`
`3
`
`6
`
`7
`
`8
`
`8
`
`8
`
`9
`
`9
`
`9
`
`10
`
`11
`
`12
`
`12
`
`13
`
`13
`
`14
`
`14
`
`14
`
`14
`
`15
`
`15
`
`16
`
`16
`
`16
`
`Recommendation T.120 (07/96)
`
`iii
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 005
`
`

`

`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 — 006
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 006
`
`

`

`Recommendation T.120
`
`DATA PROTOCOLS FOR MULTIMEDIA CONFERENCING
`
`(Geneva, 1996)
`
`1
`
`Scope
`
`This Recommendation introduces a suite of standards, collectively referred to as the T.120-Series.
`
`This Recommendation describes the T.120 system model that provides an architecture for multipoint
`data communication in a multimedia conferencing environment. It provides an introduction and
`functional description of the Recommendations that go to make up the T.120 infrastructure. In
`addition it provides an overview to other Recommendations in the Series that provide standardized
`application protocol functionality.
`
`This Recommendation defines the criteria for compliance when the T.120 data protocols are used in
`a conferencing or group-working environment.
`
`This Recommendation only covers completed work contained in approved Recommendations. When
`new Recommendations are approved, supporting text will be generated for inclusion in this
`Recommendation at the next publication date.
`
`2
`
`Normative references
`
`The following Recommendations and other references contain provisions which, through reference
`in this text, constitute provisions of this Recommendation. At the time of publication, the editions
`indicated were valid. All Recommendations and other references are subject to revision: all users of
`this Recommendation are therefore encouraged to investigate the possibility of applying the most
`recent edition of the Recommendations and other references listed below. A list of the currently valid
`ITU-T Recommendations is regularly published.
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`3
`
`ITU-T Recommendation T.121 (1996), Generic application template.
`
`ITU-T Recommendation T.122 (1993), Multipoint communication service for audiographics
`and audiovisual conferencing service definition.
`
`ITU-T Recommendation T.123 (1994), Protocol stacks for audiographic and audiovisual
`teleconference applications.
`
`ITU-T Recommendation T.124 (1995), Generic conference control.
`
`ITU-T Recommendation T.125 (1994), Multipoint communication service protocol
`specification.
`
`ITU-T Recommendation T.126 (1995), Multipoint still image and annotation protocol.
`
`ITU-T Recommendation T.127 (1995), Multipoint binary file transfer protocol.
`
`Symbols and abbreviations
`
`For the purposes of this Recommendation, the following abbreviations are used.
`
`ASE
`
`ARM
`
`Application Service Element
`
`Application Resource Manager
`
`Recommendation T.120 (07/96)
`
`1
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 007
`
`

`

`APE
`
`Application Protocol Entity
`
`B-ISDN Broadband Integrated Services Digital Network
`
`CSDN
`
`Circuit Switched Data Network
`
`GAT
`
`GCC
`
`ISDN
`
`LAN
`
`Generic Application Template
`
`Generic Conference Control
`
`Integrated Services Digital Network
`
`Local Area Network
`
`MBFT
`
`Multipoint Binary File Transfer
`
`MCS
`
`MCU
`
`MSIA
`
`PDU
`
`PSDN
`
`PSTN
`
`QOS
`
`SI
`
`4
`
`Multipoint Communication Service
`
`Multipoint Control Unit
`
`Multipoint Still Image and Annotation
`
`Protocol Data Unit
`
`Packet Switched Data Network
`
`Public Switched Telephone Network
`
`Quality of Service
`
`Still Image (SI is a commonly used abbreviation for MSIA)
`
`Overview
`
`The T.120-Series of Recommendations collectively define a multipoint communication service for
`use in multimedia conferencing environments. The purpose of this Recommendation is to provide an
`introduction and guide for the T.120-Series, showing the interrelationships between the constituent
`Recommendations and to define the requirements for compliance to T.120 for conferencing.
`
`This Recommendation provides facilities to establish and manage interactive communications
`(conferences) involving two or more participants on and between a variety of different networks. It
`provides a comprehensive data communication service for those participants, which is independent
`of the underlying network. Within a conference it allows communications to be established between
`any combination of conference participants. This Recommendation also provides support for
`applications and their associated protocols, defining start-up mechanisms and capability exchange
`procedures, etc.
`
`This Recommendation makes provisions to ensure interoperability of commonly required
`functionality such as file transfer, still image exchange and shared whiteboards through the definition
`of standardized application protocols.
`
`The T.120 protocols provide a means of telecommunicating many forms of Data/Telematic
`information between two or more multimedia terminals and of managing such communication. They
`provide a multipoint data communication service that has a particular application in multimedia
`conferencing.
`
`The T.120 protocols are suitable for use on many types of network: PSTN, ISDN, CSDN, PSDN,
`B-ISDN, LANs. They provide the capability for seamless interworking of applications between
`terminals connected to different networks.
`
`2
`
`Recommendation T.120 (07/96)
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 008
`
`

`

`The T.120 protocols provide:
`•
`support for conference establishment among a group of network nodes (such as conference
`terminals and MCUs);
`mechanisms to identify the participating nodes and a comprehensive roster and capability
`exchange mechanism;
`flexible management of communication between any combination of these elements.
`
`•
`
`•
`
`The T.120 protocols can handle one or more simultaneous conferences. A terminal may participate in
`more than one of these if authorized to do so. The convenor of a conference may control the
`participation in that conference and the information which flows in that conference.
`
`In a conference that allows conductorship, the convenor may delegate part or all authority to the
`conductor. If a conference enters conducted mode, application protocols that are "conductor aware"
`modify their behaviour, as specified by their protocol for this mode of operation.
`
`This Recommendation imposes few inherent constraints on the configuration of connections between
`conference nodes (terminals and MCUs): but they must be arranged in a hierarchy, with a single node
`at the top of a tree. Nodes may be all connected to one star-point, or connected one to two others in a
`chain, or a chain of star-points, and so on, as long as it is clear for each connection, which direction
`is upward and there are no loops. The top node should be present from the beginning of a conference,
`since any change in the top can be disruptive.
`
`No constraint is placed on the rate or volume of information transmitted within the various media;
`the T.120 protocols have the capability to organize different rates of information flow, within the
`constraints imposed by the type of network and connections established thereon. They allow relative
`priorities to be set by the applications using the T.120 protocols.
`
`The structure of the T.120 protocols is described in clause 6. Not all of the T.120 protocol provisions
`are mandatory: T.123, T.122/125, and T.124 are mandatory for conferencing and group working
`environments. The remainder are conditional: where functionality covered by the standards is
`provided, the standard protocols of the T.120-Series must be implemented (see clause 9 for T.120
`compliance requirements). This ensures that it is always possible to achieve a basic level of
`interworking, and does not prohibit customized enhancements and negotiation of proprietary modes
`if (and only if) all participating elements are able to support such modes.
`
`5
`
`Introduction to multipoint multimedia communication
`
`Traditionally telephony services have been constrained to point-to-point operation. In order to
`support group activities such as meetings, conferences etc., involving physically separated
`participants, there is a requirement to join together more than two locations. The term multipoint
`communication simply describes the interconnection of multiple terminals. Normally a special
`network element, known as a Multipoint Control Unit (MCU), or more simply a bridge, is required
`in order to provide this function.
`
`A conference typically refers to a group of geographically dispersed nodes that are electronically
`joined together and that are capable of exchanging audiographic and audiovisual information across
`various communication networks.
`
`Conference participants may have access to various types of media handling capabilities such as
`audio only (telephony), audio and data, audio and video, or audio, video and data.
`
`The T.120-Series of Recommendations define the component which is used to provide both a data
`communications service, and a management service for any other media services present.
`
`Recommendation T.120 (07/96)
`
`3
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 009
`
`

`

`T.120 protocols provide the infrastructure required to provide data services for many types of
`conferencing and group working, making it suitable for a diverse range of application areas. It is
`expected to find use in videotelephony and audiographic conferencing as well as other forms of
`multipoint multimedia communication.
`
`This Recommendation regards point-to-point connections as the simplest form (a degenerate case) of
`a multipoint connection. Both forms of connection are supported by the T.120 protocols. Terminals
`with multiple communication ports (each with an appropriate T.120 transport stack) can act as T.120
`data bridges and allow multipoint connections to be established involving three or more nodes.
`Figure 1 b) shows a four site conference with multiport terminals acting as data bridges.
`
`MCUs are nodes that do not normally support terminal functionality. They act as bridging nodes,
`bridging data and other media streams present in the connections. Figure 1 c) shows an example of
`how three MCUs may be connected to bridge a group of terminals.
`
`4
`
`Recommendation T.120 (07/96)
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 010
`
`

`

`Terminal
`
`Terminal
`
`(The simplest case of a multipoint connection)
`
`A 0O INT TO POINT
`
`Terminal
`
`Multiport
`Terminal
`
`Multiport
`Terminal
`
`Terminal
`
`B #HAIN#ONNECT IONWITHTERMINALSACTINGASDATABRIDGES
`
`MCU
`
`Terminal
`
`MCU
`
`MCU
`
`Terminal
`
`Terminal
`
`Terminal
`
`Terminal
`
`Terminal
`
`C -ULTIPOINTTOPOLOGY
`3 MCUs providing connections to allow multiple terminals
`to participate in a conference
`
`T0826340-96
`
`FIGURE 1/T.120
`Examples of Multipoint conference configurations showing various
`connection topologies and Node types
`
`Figure 2 is an example of a conference that involves terminals of diverse capability, on multiple
`different networks and across administrations.
`
`Recommendation T.120 (07/96)
`
`5
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 011
`
`

`

`Corporate Network A
`
`Public Network
`
`LAN Gateway
`- Router -
`
`Terminal
`
`Terminal
`
`Terminal
`
`Terminal
`
`Terminal
`
`Corporate Network B
`
`LAN Gateway
`- Router -
`
`Terminal
`
`Terminal
`
`Terminal
`
`ISDN
`
`MCU
`
`MCU
`
`ISDN
`
`ISDN
`
`ISDN
`
`PSTN
`
`Multiport
`Terminal
`
`PSTN
`
`Multiport
`Terminal
`
`Terminal
`
`PSTN
`
`T0824960-95
`
`FIGURE 2/T.120
`Example of a mixed-network conference topology
`
`6
`
`The T.120 system model
`
`The T.120 model is comprised of a communications infrastructure and the application protocols that
`make use of it. Figure 3 shows the full model with both standardized and non-standardized
`applications. The model serves to show both the scope of the T.120 suite of Recommendations
`(indicated by the shaded background) and the relationship between each of the Recommendations
`and other components in the system.
`
`Generally, each layer provides services to the layer above and communicates to its peer(s) by sending
`Protocol Data Units (PDUs) via services provided by the layer below.
`
`This clause will address each of the major functional levels in Figure 3: User Applications,
`Application Protocols, Node Controller, Communications Infrastructure and Networks.
`
`6
`
`Recommendation T.120 (07/96)
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 012
`
`

`

`User Application(s)
`(Using Both Standard and Non-Standard Application Protocols)
`
`User Application(s)
`(Using Std. Appl. Protocols)
`
`Node
`Controller
`
`User Application(s)
`(Using Non-Std Protocols)
`
`Rec. T.127 (MBFT)
`
`Rec. T.126 (SI)
`Application Protocol Entity
`
`Rec. T.120
`Application Protocol
`Recommendations
`
`...
`
`...
`
`Non-Standard Application
`Protocol Entity
`
`Generic Conference Control (GCC)
`Rec. T.124
`
`Multipoint Communication Service (MCS)
`Rec. T.122/T.125
`
`Network Specific Transport Protocols
`Rec. T.123
`
`T.120 Infrastructure Recommendations
`
`T0826350-96
`
`FIGURE 3/T.120
`T.120 system model
`
`6.1
`
`User applications
`
`Applications per se are not the subject of standardization in the T.120-Series. Applications that use
`the services offered by the T.120-Series will generally be multipoint aware and designed to use the
`T.120 services provided by GCC and MCS. These applications are termed User Applications and
`they may use any combination of standardized and non-standard protocols to communicate with peer
`user applications. The T.120 environment supports multiple user applications concurrently operating
`in the same conference by providing mechanisms for the applications to coordinate the use of
`communications resources. The Generic Application Template (Recommendation T.121) provides
`guidance to user application developers on how to utilize the T.120 infrastructure in a coherent and
`consistent way. A user application addresses those tasks which have no direct effect on interworking
`(e.g. user interface) and which may thus be product and platform specific. The influence of the user
`application is felt at other sites through the application protocols it employs.
`
`Recommendation T.120 (07/96)
`
`7
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 013
`
`

`

`6.2
`
`Application protocols
`
`Application protocols comprise a set of Protocol Data Units (PDUs) and associated actions for
`application peer-to-peer(s) communication. These may be proprietary protocols or they may be
`standardized by the ITU-T or other international or national standards bodies. The T.120-Series
`includes a set of application protocols designed to meet the needs of multipoint conferencing. These
`protocols define minimum requirements in order to ensure interworking between different
`implementations. Recommendation T.127 provides simultaneous Multipoint
`file
`transfer.
`Recommendation T.126 provides still image viewing and annotation, shared whiteboard, and
`facsimile. A given application may use any combination of standardized and non-standard
`application protocols.
`
`An Application Protocol Entity is an instance of an Application Protocol. It may be considered as
`comprising of two functional components: the Application Resource Manager (ARM), that provides
`the generic functionality relevant to all protocols; and the Application Service Element (ASE), that
`provides the application specific functionality. Both of these are described further in the T.121
`Generic Application Template Recommendation. Recommendation T.121 presents templates and
`guidelines which may assist in the definition of new application protocols.
`
`6.3
`
`Node Controller
`
`The Node Controller is the element that provides the T.120 management role at a terminal or MCU.
`It issues primitives to the GCC provider which starts and controls the communication session. The
`node controller itself is outside the scope of the T.120-Series of Recommendations, and only where it
`communicates to GCC are its interfaces defined. However, correct interaction with GCC imposes
`some normative requirements on the Node Controller.
`
`6.4
`
`Communications infrastructure
`
`The communications infrastructure provides multipoint connectivity with reliable data delivery. It
`can accommodate multiple independent applications concurrently using the same multipoint
`environment. Connections between nodes can be any combination of circuit-switched
`telecommunications networks and packet based LANs and data networks. The T.120 infrastructure is
`composed of three standardized components: Generic Conference Control (GCC), the Multipoint
`Communication Service (MCS) and Transport Protocol Profiles for each of the supported networks.
`
`Generic Conference Control
`
`GCC provides a set of services for setting up and managing the multipoint conference. It provides
`access control and arbitration of capabilities. GCC facilities are used by applications to coordinate
`the use of MCS channels and tokens. GCC facilities can be used to query an MCU or multiport
`terminal node to find a desired conference. Multiple applications can be running on any given node
`and can be dynamically launched, used and shut down during a conference. As part of the
`management role, peer GCC providers exchange information about the applications present and their
`capabilities. GCC also makes a centralized registry facility available to applications in order to
`identify dynamically assigned resources such as channels and tokens.
`
`Multipoint Communication Service
`
`MCS provides a general purpose multipoint connection-oriented data service. It collects
`point-to-point Transport Connections and combines them to form a Multipoint Domain. Within that
`Domain a large number of logical channels are provided that can provide one-to-one, one-to-many
`and many-to-one data delivery. Nodes within an MCS Domain are hierarchically organized in a tree
`structure. Data delivery normally follows the most efficient path to the nodes that are to receive the
`
`8
`
`Recommendation T.120 (07/96)
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 014
`
`

`

`data, but a mechanism is provided to guarantee that data originating from different nodes is received
`in the same sequence at all nodes. MCS acts as a resource provider to the layers above, independent
`of the underlying network; providing channels and token resources on demand. Tokens are provided
`for applications to use for coordinating events and processes.
`
`Network specific transport protocols
`
`Recommendation T.123 provides reliable point-to-point sequenced data delivery of MCS PDUs and
`segmentation of that data if necessary. Recommendation T.123 specifies a protocol stack for each
`particular network supported. Recommendation T.123 presents a uniform OSI Transport Service
`interface to the MCS layer above.
`
`6.5
`
`Networks
`
`The T.120 suite provides for operation over the following networks:
`•
`ISDN - Integrated Services Digital Network as defined in the I-Series Recommendations.
`•
`CSDN - Other (switched or permanent) digital circuits.
`•
`PSDN - Packet Switched Data Network using Recommendation X.25.
`•
`PSTN - Public Switched Telephone Network (or compatible service).
`•
`Use of this Recommendation on other networks such as B-ISDN and LANs is currently
`under study. Alternative protocol stack profiles may be defined in the future.
`
`The approach taken with the T.120 architecture leads to the multipoint routing information being
`located in MCS above the transport stacks, this is the key to the network independence that can be
`achieved with this Recommendation.
`
`The various Recommendations that comprise the T.120 suite are described in greater detail in
`clauses 7 and 8.
`
`7
`
`T.120 infrastructure Recommendations
`
`The T.120 protocols are designed to operate over a wide range of networks and indeed to facilitate
`communication between endpoints on a mixture of networks. The differences in T.120 operation for
`the various networks are confined to the lowest layers as detailed in Recommendation T.123.
`
`7.1
`
`for
`stacks
`Protocol
`Recommendation T.123
`
`audiographic
`
`and
`
`audiovisual
`
`conferencing
`
`–
`
`Recommendation T.123 defines the network specific transport stacks for each supported network.
`Generally, existing link layer protocols appropriate to each network are selected and then mapped
`into a common interface layer, thus defining a transport profile for a given network. At Transport
`level the conference is seen as a group of point-to-point connected pairs (different pairs may be on
`different networks). The Multipoint Communication Service (MCS), takes the transport pairs from
`the layer below it and maps them into a multipoint domain. See Figure 4.
`
`Recommendation T.120 (07/96)
`
`9
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 015
`
`

`

`Network
`Independent
`Layer
`
`Network
`Dependent
`Transports
`
`T.125 - Multipoint Communication Service (MCS)
`
`ISDN
`Transport
`
`CSDN
`Transport
`
`PSDN
`Transport
`
`PSTN
`Transport
`
`B-ISDN
`Transport
`
`LAN
`Transport
`
`T0826360-96
`
`FIGURE 4/T.120
`Protocol stacks – defined in Recommendation T.123
`
`7.2
`
`Multipoint Communication Service (MCS) – Recommendations T.122, T.125
`
`The Multipoint Communication Service (MCS) is contained in two Recommendations: T.122
`defines the MCS service and T.125 the protocol which is mandatory.
`
`MCS is a key element in the infrastructure of T.120. It takes the point-to-point transport connections
`provided by the layers below it and combines them to form a multipoint domain. The T.120 protocol
`can handle a multiplicity of Domains - each effectively an independent conference or group activity.
`Nodes may participate in more than one domain.
`
`A domain with only two terminal nodes participating mirrors the traditional point-to-point
`communications model and is fully supported by MCS but with the potential of introducing more
`nodes as required.
`
`Each connected pair in an MCS domain is ordered, so that one node is higher than the other. The
`domain must rise hierarchically (without loops) to a top node. The MCS Provider at the top node is
`assigned the Top Provider role, acting as the resource server for the domain.
`
`The MCS provides transport of control and data streams from one terminal to any or all others in the
`conference. It does not need to know anything about the content of application data streams.
`
`MCS introduces the concept of channels to provide data distribution within a domain; an MCS
`channel connects all the nodes which have expressly joined it. It is not required that a channel be
`joined in order to send to it. Data sent to a channel will be conveyed to all other nodes which have
`joined that channel. MCS supports four types of channel.
`
`A "static" channel exists when a domain is established. MCS reserves a block of channel identifiers
`for static use. Static channels may be given preassigned roles by the protocols making use of MCS
`services (such roles are not of concern to MCS). Annex A defines the mapping of preassigned roles
`to channel identifiers. Any node may join a static channel, and there is no "owner".
`
`A "dynamic" channel is created on request by any node or application. Dynamic channels come in
`three forms: "Multicast", "Private" and "Single Member". Multicast (Assigned) channels are similar
`to static channels in that they are open access - any terminal may join them, and there is no owner.
`Private channels however are owned by their creator and are joined by invitation only, thus forming a
`private or closed-user-group. A "Single Member" channel is normally used to provide a User
`Identifier, giving the owner a unique address within the domain.
`
`There are two specified types of data: ordinary data is sent by the shortest route to its destinations -
`nothing governs the order in which information arrives from different source terminals, so it can
`
`10
`
`Recommendation T.120 (07/96)
`
`Zoho Corp. and Zoho Corp. Pvt., Ltd.
`Exhibit 1017 – 016
`
`

`

`happen that presentations to users may not be identical. Uniform sequenced data, on the other hand,
`is routed to a common point (the top MCU in the connection hierarchy, called the "top provider")
`and distributed thence to all relevant terminals in the same order; clearly this may take longer than
`for ordinary data.
`
`MCS supports four data priorities; according to the priority requested in the header of data primitives
`coming down into MCS, they are routed into one of up to four corresponding transport connections.
`
`MCS provides a token management service and is able to support the use of a range of tokens. In
`order to provide exclusivity, and thus consistency across a domain only the Top Provider is able to
`execute actions on tokens. MCS supports the following token actions; grab, inhibit, give, please and
`release. The role allocated to tokens is assigned by the layers above MCS (and is not the concern of
`MCS).
`
`Much of the power and flexibility of MCS derives from its provision of services in a manner that is
`independent of the underlying network connections. This allows portability across networks and an
`inherent capability to interwork between terminals on different networks.
`
`7.3
`
`Generic Conference Control (GCC – Recommendation T.124)
`
`The Generic Conference Control (GCC) service and protocol is defined in Recommendation T.124;
`it resides above MCS in the T.120 stack infrastructure. GCC is a mandatory component for
`peer-to-peer conferencing and group working environments, providing a high-level framework for
`management and control in support of a diverse range of terminals and MCUs.
`
`A GCC conference has a direct correspondence to an MCS Domain. GCC provides mechanisms for
`the creation, control and the termination of conferences. It also makes provision for building and
`distributing the conference and application databases.
`
`MCS supports four data priorities, one of which (top priority) is reserved for exclusive use by GCC
`for control and management. The remaining three priorities are available for application use.
`
`GCC reserves a block of MCS tokens and designates them to be static and thus assigned
`functionality by this Recommendation (Annex A). The remaining tokens are designated dynamic and
`their functionality is assigned in the registry and is valid only for the duration of a conference
`session.
`
`The conference roster contains a record of the conference configuration, that includes such things as
`the name of the conference, the types of participating nodes (terminal, MCU or Multiport terminal),
`and site and participant information for each node.
`
`When a node joins a conference it announces its presence to that conference. This causes the
`conference roster to be updated and distributed.
`
`GCC supports the enrolment in a conference of application protocols. Each GCC provider maintains
`a local application roster containing information and capabilities for its enrolled application
`protocols. The local rosters are sent to the top node of a conference where a Conference Application
`Roster is compiled and then distributed. In this way all nodes learn of the addi