Superseded by a more recent version
`
`ITU-T
`
`TELECOMMUNICATION
`STANDARDIZATION SECTOR
`OF ITU
`
`H.323
`
`(1 1/96)
`
`SERIES H: AUDIOVISUAL AND MUL Tl MEDIA SYSTEMS
`Infrastructure of audiovisual services - Systems and
`terminal equipment for audiovisual services
`
`Visual telephone systems and equipment for
`local area networks which provide a
`non-guaranteed quality of service
`
`ITU-T Recommendation H .323
`Superseded by a more recent version
`
`(Previously CCITT Recommendation)
`
`IPR2016-01710
`UNIFIED EX1011
`
`

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`3UPERSEDED BY A MORE RECENT VERSION
`
`ITU-T H-SERIES RECOMMENDATIONS
`!5$)/6)35!, !.$ -5,4)-%$)! 3934%-3
`
`Characteristics of transmission channels used for other than telephone purposes
`Use of telephone-type circuits for voice-frequency telegraphy
`Telephone circuits or cables used for various types of telegraph transmission or
`simultaneous transmission
`Telephone-type circuits used for facsimile telegraphy
`Characteristics of data signals
`CHARACTERISTICS OF VISUAL TELEPHONE SYSTEMS
`INFRASTRUCTURE OF AUDIOVISUAL SERVICES
`General
`Transmission multiplexing and synchronization
`Systems aspects
`Communication procedures
`Coding of moving video
`Related systems aspects
`3YSTEMS AND TERMINAL EQUIPMENT FOR AUDIOVISUAL SERVICES
`
`H.10–H.19
`H.20–H.29
`H.30–H.39
`
`H.40–H.49
`H.50–H.99
`H.100–H.199
`H.200–H.399
`H.200–H.219
`H.220–H.229
`H.230–H.239
`H.240–H.259
`H.260–H.279
`H.280–H.299
`((cid:14)(cid:19)(cid:16)(cid:16) ((cid:14)(cid:19)(cid:25)(cid:25)
`
`&OR FURTHER DETAILS(cid:12) PLEASE REFER TO )45 4 ,IST OF 2ECOMMENDATIONS(cid:14)
`
`

`
`3UPERSEDED BY A MORE RECENT VERSION
`
`)45 4 2%#/--%.$!4)/. ((cid:14)(cid:19)(cid:18)(cid:19)
`
`6)35!, 4%,%0(/.% 3934%-3 !.$ %15)0-%.4 &/2 ,/#!, !2%! .%47/2+3
`7()#( 02/6)$% ! ./. ’5!2!.4%%$ 15!,)49 /& 3%26)#%
`
`3UMMARY
`
`Recommendation H.323 describes terminals, equipment and services for multimedia communication
`over Local Area Networks (LAN) which do not provide a guaranteed quality of service. H.323
`terminals and equipment may carry real-time voice, data and video, or any combination, including
`videotelephony.
`The LAN over which H.323 terminals communicate, may be a single segment or ring, or it may be
`multiple segments with complex topologies. It should be noted that operation of H.323 terminals
`over the multiple LAN segments (including the Internet) may result in poor performance. The
`possible means by which quality of service might be assured on such types of LANs/internetworks is
`beyond the scope of this Recommendation.
`H.323 terminals may be integrated into personal computers or implemented in stand-alone devices
`such as videotelephones. Support for voice is mandatory, while data and video are optional, but if
`supported, the ability to use a specified common mode of operation is required, so that all terminals
`supporting that media type can interwork. This Recommendation allows more than one channel of
`each type to be in use. Other Recommendations in the H.323-Series include H.225.0 packet and
`synchronization, H.245 control, H.261 and H.263 video codecs, G.711, G.722, G.728, G.729, and
`G.723 audio codecs, and the T.120-Series of multimedia communications protocols.
`This Recommendation makes use of the logical channel signalling procedures of Recommendation
`H.245, in which the content of each logical channel is described when the channel is opened.
`Procedures are provided for expression of receiver and transmitter capabilities, so transmissions are
`limited to what receivers can decode, and so that receivers may request a particular desired mode
`from
`transmitters. Since
`the procedures of Recommendation H.245 are also used by
`Recommendation H.310 for ATM networks, Recommendation H.324 for GSTN, and V.70,
`interworking with these systems should not require H.242 to H.245 translation as would be the case
`for H.320 systems.
`H.323 terminals may be used in multipoint configurations, and may interwork with H.310 terminals
`on B-ISDN, H.320 terminals on N-ISDN, H.321 terminals on B-ISDN, H.322 terminals on
`Guaranteed Quality of Service LANs, H.324 terminals on GSTN and wireless networks, and V.70
`terminals on GSTN.
`
`3OURCE
`
`ITU-T Recommendation H.323 was prepared by ITU-T Study Group 15 (1993-1996) and was
`approved under the WTSC Resolution No. 1 procedure on the 8th of November 1996.
`
`2ECOMMENDATION ((cid:14)(cid:19)(cid:18)(cid:19)
`
`(cid:8)(cid:17)(cid:17)(cid:15)(cid:25)(cid:22)
`
`3UPERSEDED BY A MORE RECENT VERSION
`
`i
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`3UPERSEDED BY A MORE RECENT VERSION
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`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. The ITU-T is responsible for studying technical, operating and tariff questions and issuing
`Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
`
`The World Telecommunication Standardization Conference (WTSC), which meets every four years,
`establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations
`on these topics.
`
`The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in
`WTSC Resolution No. 1.
`
`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
`
`INTELLECTUAL PROPERTY RIGHTS
`
`The ITU draws attention to the possibility that the practice or implementation of this Recommendation may
`involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence,
`validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others
`outside of the Recommendation development process.
`
`As of the date of approval of this Recommendation, the ITU had/had not received notice of intellectual
`property, protected by patents, which may be required to implement this Recommendation. However,
`implementors are cautioned that this may not represent the latest information and are therefore strongly urged
`to consult the TSB patent database.
`
`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 1997
`
`ii
`
`2ECOMMENDATION ((cid:14)(cid:19)(cid:18)(cid:19)
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`(cid:8)(cid:17)(cid:17)(cid:15)(cid:25)(cid:22)
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`3UPERSEDED BY A MORE RECENT VERSION
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`ª
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`1
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`2
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`3
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`4
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`5
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`6
`6.1
`6.2
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`6.3
`6.4
`6.5
`6.6
`6.7
`6.8
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`#/.4%.43
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`Scope ..........................................................................................................................
`
`Normative references..................................................................................................
`
`Definitions ..................................................................................................................
`
`Symbols and abbreviations.........................................................................................
`
`Conventions................................................................................................................
`
`System description......................................................................................................
`Information streams....................................................................................................
`Terminal characteristics .............................................................................................
`6.2.1
`Terminal elements outside the scope of this Recommendation ....................
`6.2.2
`Terminal elements within the scope of this Recommendation .....................
`6.2.3
`LAN interface................................................................................................
`6.2.4 Video codec...................................................................................................
`6.2.5 Audio codec...................................................................................................
`6.2.6 Receive path delay ........................................................................................
`6.2.7 Data channel..................................................................................................
`6.2.8 H.245 control function ..................................................................................
`6.2.9 RAS signalling function ................................................................................
`6.2.10 Call signalling function .................................................................................
`6.2.11 H.225.0 layer .................................................................................................
`Gateway characteristics ..............................................................................................
`Gatekeeper characteristics ..........................................................................................
`Multipoint controller characteristics ..........................................................................
`Multipoint processor characteristics...........................................................................
`Multipoint control unit characteristics .......................................................................
`Multipoint capability ..................................................................................................
`6.8.1 Centralized multipoint capability ..................................................................
`6.8.2 Decentralized multipoint capability ..............................................................
`6.8.3 Hybrid multipoint – Centralized audio .........................................................
`6.8.4 Hybrid multipoint – Centralized video .........................................................
`6.8.5
`Establishment of common mode ...................................................................
`6.8.6 Multipoint rate matching...............................................................................
`6.8.7 Multipoint lip synchronization ......................................................................
`6.8.8 Multipoint encryption....................................................................................
`6.8.9 Cascading multipoint control units ...............................................................
`
`0AGE
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`2ECOMMENDATION ((cid:14)(cid:19)(cid:18)(cid:19)
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`(cid:8)(cid:17)(cid:17)(cid:15)(cid:25)(cid:22)
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`Call signalling.............................................................................................................
`Addresses....................................................................................................................
`7.1.1
`LAN address..................................................................................................
`7.1.2
`TSAP identifier .............................................................................................
`7.1.3 Alias address .................................................................................................
`Registration, Admissions and Status (RAS) channel .................................................
`7.2.1 Gatekeeper discovery ....................................................................................
`7.2.2
`Endpoint registration .....................................................................................
`7.2.3
`Endpoint location ..........................................................................................
`7.2.4 Admissions, bandwidth change, status, disengage........................................
`Call signalling channel ...............................................................................................
`7.3.1 Call signalling channel routing .....................................................................
`7.3.2 Control channel routing.................................................................................
`Call reference value....................................................................................................
`Conference ID and Conference Goal .........................................................................
`
`Call signalling procedures ..........................................................................................
`Phase A – Call set-up .................................................................................................
`8.1.1 Basic call set-up – Neither endpoint registered.............................................
`8.1.2 Both endpoints registered to the same Gatekeeper .......................................
`8.1.3 Only calling endpoint has Gatekeeper ..........................................................
`8.1.4 Only called endpoint has Gatekeeper............................................................
`8.1.5 Both endpoints registered to different Gatekeepers ......................................
`8.1.6 Call set-up via gateways................................................................................
`8.1.7 Call set-up with an MCU ..............................................................................
`8.1.8 Call forwarding .............................................................................................
`8.1.9 Broadcast call set-up .....................................................................................
`Phase B – Initial communication and capability exchange ........................................
`Phase C – Establishment of audiovisual communication...........................................
`8.3.1 Mode changes................................................................................................
`8.3.2
`Exchange of video by mutual agreement ......................................................
`8.3.3 Media Stream Address Distribution..............................................................
`Phase D – Call services ..............................................................................................
`8.4.1 Bandwidth changes .......................................................................................
`8.4.2
`Status .............................................................................................................
`8.4.3 Ad Hoc Conference Expansion .....................................................................
`8.4.4
`Supplementary services.................................................................................
`Phase E – Call termination .........................................................................................
`
`2ECOMMENDATION ((cid:14)(cid:19)(cid:18)(cid:19)
`
`(cid:8)(cid:17)(cid:17)(cid:15)(cid:25)(cid:22)
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`7
`7.1
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`7.2
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`7.3
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`7.4
`7.5
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`8
`8.1
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`8.2
`8.3
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`8.4
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`8.5
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`8.5.1 Call clearing without a Gatekeeper ...............................................................
`8.5.2 Call clearing with a Gatekeeper ....................................................................
`8.5.3 Call clearing by Gatekeeper ..........................................................................
`Protocol failure handling ............................................................................................
`
`Interoperation with other terminal types ....................................................................
`Speech only terminals.................................................................................................
`Visual telephone terminals over the ISDN (H.320) ...................................................
`Visual telephone terminals over GSTN (H.324) ........................................................
`Visual telephone terminals over mobile radio (H.324/M) .........................................
`Visual telephone terminals over ATM (H.321)..........................................................
`Visual telephone terminals over guaranteed quality of service LANs (H.322) .........
`Simultaneous voice and data terminals over GSTN (V.70) .......................................
`T.120 terminals on the LAN.......................................................................................
`
`8.6
`
`9
`9.1
`9.2
`9.3
`9.4
`9.5
`9.6
`9.7
`9.8
`
`10
`10.1
`
`Optional enhancements ..............................................................................................
`Encryption ..................................................................................................................
`
`Maintenance ...............................................................................................................
`11
`Loopbacks for maintenance purposes ........................................................................
`11.1
`11.2 Monitoring methods ...................................................................................................
`
`Annex A – H.245 messages used by H.323 endpoints ............................................................
`
`Appendix I – Processing of Q.931 messages in Gateways......................................................
`
`0AGE
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`70
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`2ECOMMENDATION ((cid:14)(cid:19)(cid:18)(cid:19)
`
`(cid:8)(cid:17)(cid:17)(cid:15)(cid:25)(cid:22)
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`3UPERSEDED BY A MORE RECENT VERSION
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`v
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`

`
`

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`3UPERSEDED BY A MORE RECENT VERSION
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`2ECOMMENDATION ((cid:14)(cid:19)(cid:18)(cid:19)
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`6)35!, 4%,%0(/.% 3934%-3 !.$ %15)0-%.4 &/2 ,/#!, !2%! .%47/2+3
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`(cid:8)’ENEVA(cid:12) (cid:17)(cid:25)(cid:25)(cid:22)
`
`(cid:17)
`
`3COPE
`
`This Recommendation covers the technical requirements for narrow-band visual telephone services
`defined in H.200/AV.120-Series Recommendations, in those situations where the transmission path
`includes one or more Local Area Networks (LAN), which may not provide a guaranteed Quality of
`Service (QOS) equivalent to that of N-ISDN. Examples of this type of LAN are:
`–
`Ethernet (IEEE 802.3);
`–
`Fast Ethernet (IEEE 802.10);
`–
`FDDI (non-guaranteed quality of service mode);
`–
`Token Ring (IEEE 802.5).
`This Recommendation covers the case of visual telephone services in those situations where the
`transmission path includes one or more Local Area Networks (LAN), which are configured and
`managed to provide a guaranteed Quality of Service (QOS) equivalent to that of N-ISDN such that
`no additional protection or recovery mechanisms beyond those mandated by Recommendation
`H.320 need to be provided in the terminals. Pertinent parameters are the data error and loss
`properties and variation of transit delay. An example of a suitable LAN is: Integrated Services (IS)
`LAN: IEEE 802.9A Isochronous services with Carrier Sense Multiple Access with Collision
`Detection (CSMA/CD) Media Access Control (MAC) service.
`H.323 terminals may be used in multipoint configurations, and may interwork with H.310 terminals
`on B-ISDN, H.320 terminals on N-ISDN, H.321 terminals on B-ISDN, H.322 terminals on
`Guaranteed Quality of Service LANs, H.324 terminals on GSTN and wireless networks, and V.70
`terminals on GSTN. See Figure 1.
`The scope of this Recommendation does not include the LAN itself, or the transport layer which
`may be used to connect various LANs. Only elements needed for interaction with the Switched
`Circuit Network (SCN) are within the scope of this Recommendation. The combination of the H.323
`Gateway, the H.323 terminal, and the out-of-scope LAN appears on the SCN as an H.320, H.310,
`H.324, or V.70 terminal.
`This Recommendation describes the components of an H.323 system. This includes Terminals,
`Gateways, Gatekeepers, Multipoint Controllers, Multipoint Processors and Multipoint Control Units.
`Control messages and procedures within this Recommendation define how these components
`communicate. Detailed descriptions of these components are contained in clause 6.
`The components described in this Recommendation consist of H.323 endpoints and H.323 entities.
`The endpoints can call and are callable according to the call set-up procedures of clause 8. The
`entities are not callable however, they can be addressed in order to perform their specific functions.
`For example, a terminal cannot place a call to a Gatekeeper however, the Gatekeeper is addressed as
`part of the call establishment procedures.
`
`2ECOMMENDATION ((cid:14)(cid:19)(cid:18)(cid:19)
`
`(cid:8)(cid:17)(cid:17)(cid:15)(cid:25)(cid:22)
`
`3UPERSEDED BY A MORE RECENT VERSION
`
`1
`
`

`
`Superseded by a more recent version
`-------------------~---~-----------------
`
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`H.323
`Tenninal
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`(Note)
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`
`Figure l/H.323 - Interoperability of H.323 terminals
`
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`operating in
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`
`Normative references
`2
`The following ITU-T 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 cunently
`valid ITU-T Recommendations is regularly published.
`
`[1]
`
`[2]
`[3]
`
`[4]
`[5]
`
`[ 6]
`
`ITU-T Recommendation H.225.0 (1996), Media stream packetization and synchronization
`for visual telephone systems on non-guaranteed quality of service LANs.
`
`ITU-T Recommendation H.245 (1996), Control protocol for multimedia communications.
`CCITT Recommendation G.711
`(1988), Pulse Code Modulation (PCM) of voice
`frequencies .
`CCITT Recommendation G.722 (1988), 7 kHz audio-coding within 64 kbit/s.
`ITU-T Recommendation G.723.1 (1996), Speech coders: Dual rate speech coder for
`multimedia communications transmitting at 5.3 and 6.3 kbit/s.
`CCITT Recommendation G. 728 (1992), Coding of speech at 16 kbit/s using low-delay code
`excited linear prediction.
`
`2
`
`Recommendation H.323
`
`(11196)
`
`Superseded by a more recent version
`
`

`
`3UPERSEDED BY A MORE RECENT VERSION
`
`ITU-T Recommendation G.729 (1996), #ODING OF SPEECH AT (cid:24) KBIT(cid:15)S USING CONJUGATE
`STRUCTURE ALGEBRAIC CODE EXCITED LINEAR PREDICTION (cid:8)#3 !#%,0 .
`ITU-T Recommendation H.261 (1993 (cid:12) 6IDEO CODEC FOR AUDIOVISUAL SERVICES AT P ·
`(cid:22)(cid:20) KBIT(cid:15)S.
`ITU-T Recommendation H.263 (1996), 6IDEO CODING FOR LOW BIT RATE COMMUNICATION.
`ITU-T Recommendation T.120 (1996), 4RANSMISSION PROTOCOLS FOR MULTIMEDIA DATA.
`ITU-T Recommendation H.320 (1996), .ARROW BAND VISUAL TELEPHONE SYSTEMS AND TERMINAL
`EQUIPMENT.
`ITU-T Recommendation H.321 (1996), !DAPTATION OF ((cid:14)(cid:19)(cid:18)(cid:16) VISUAL TELEPHONE TERMINALS TO
`" )3$. ENVIRONMENTS.
`ITU-T Recommendation H.322 (1996), 6ISUAL TELEPHONE SYSTEMS AND TERMINAL EQUIPMENT
`FOR LOCAL AREA NETWORKS WHICH PROVIDE A GUARANTEED QUALITY OF SERVICE.
`FOR
`LOW BIT
`(1996), 4ERMINAL
`ITU-T Recommendation H.324
`COMMUNICATION.
`ITU-T Recommendation H.310 (1996), "ROADBAND AND AUDIOVISUAL COMMUNICATION SYSTEMS
`AND TERMINALS.
`ITU-T Recommendation Q.931 (1993), )3$. USER NETWORK INTERFACE LAYER (cid:19) SPECIFICATION
`FOR BASIC CALL CONTROL.
`ITU-T Recommendation Q.932 (1993), ’ENERIC PROCEDURES FOR THE CONTROL OF )3$.
`SUPPLEMENTARY SERVICES.
`ITU-T Recommendation Q.950 (1993), 3UPPLEMENTARY SERVICES PROTOCOLS(cid:12) STRUCTURE AND
`GENERAL PRINCIPLES.
`5NIVERSAL -ULTIPLE /CTET #ODED
`ISO/IEC 10646-1:1993, )NFORMATION TECHNOLOGY
`#HARACTER 3ET (cid:8)53# 0ART )(cid:26) !RCHITECTURE AND "ASIC -ULTILINGUAL 0LANE.
`CCITT Recommendation E.164 (1991), .UMBERING PLAN FOR THE )3$. ERA.
`
`RATE MULTIMEDIA
`
`[7]
`
`[8]
`
`[9]
`[10]
`[11]
`
`[12]
`
`[13]
`
`[14]
`
`[15]
`
`[16]
`
`[17]
`
`[18]
`
`[19]
`
`[20]
`
`(cid:19)
`
`$EFINITIONS
`
`For the purposes of this Recommendation the definitions given in clause 3/H.225.0 [1] and
`clause 3/H.245 [2] apply along with those in this clause. These definitions apply to the LAN side
`only. Other terms may be appropriate when referring to the Switched Circuit Network (SCN) side.
`(cid:19)(cid:14)(cid:17)
`ACTIVE -#: An MC that has won the master-slave determination procedure and is currently
`providing the multipoint control function for the conference.
`(cid:19)(cid:14)(cid:18)
`AD HOC MULTIPOINT CONFERENCE: An Ad Hoc Multipoint conference was a point-to-point
`conference that had been expanded into a multipoint conference at some time during the call. This
`can be done if one or more of the terminals in the initial point-to-point conference contains an MC, if
`the call is made using a Gatekeeper that includes MC functionality, or if the initial call is made
`through an MCU as a multipoint call between only two terminals.
`(cid:19)(cid:14)(cid:19)
`ADDRESSABLE: An H.323 entity on the LAN having a Transport Address. Not the same as
`being callable. A terminal or MCU is addressable and callable. A Gatekeeper is addressable but not
`callable. An MC or MP is neither callable nor addressable but is contained within an endpoint or
`Gatekeeper that is.
`(cid:19)(cid:14)(cid:20)
`AUDIO MUTE: Suppressing of the audio signal of a single or all source(s). Send muting means
`that the originator of an audio stream mutes its microphone and/or does not transmit any audio signal
`
`2ECOMMENDATION ((cid:14)(cid:19)(cid:18)(cid:19)
`
`(cid:8)(cid:17)(cid:17)(cid:15)(cid:25)(cid:22)
`
`3UPERSEDED BY A MORE RECENT VERSION
`
`3
`
`

`
`3UPERSEDED BY A MORE RECENT VERSION
`
`at all. Receive mute means that the receiving terminal ignores a particular incoming audio stream or
`mutes its loudspeaker.
`(cid:19)(cid:14)(cid:21)
`BROADCAST CONFERENCE: A Broadcast conference is one in which there is one transmitter of
`media streams and many receivers. There is no bidirectional transmission of control or media
`streams. Such conferences should be implemented using LAN transport multicast facilities, if
`available. This conference type is for further study.
`(cid:19)(cid:14)(cid:22)
`BROADCAST PANEL CONFERENCE: A Broadcast Panel conference is a combination of a
`Multipoint conference and a Broadcast conference. In this conference, several terminals are engaged
`in a multipoint conference, while many other terminals are only receiving the media streams. There
`is bidirectional transmission between the terminals in the multipoint portion of the conference and
`no bidirectional transmission between them and the listening terminals. This conference type is for
`further study.
`(cid:19)(cid:14)(cid:23)
`CALL: Point-to-point multimedia communication between two H.323 endpoints. The call
`begins with the call set-up procedure and ends with the call termination procedure. The call consists
`of the collection of reliable and unreliable channels between the endpoints. In case of interworking
`with some SCN endpoints via a gateway, all the channels terminate at the Gateway where they are
`converted to the appropriate representation for the SCN end system.
`(cid:19)(cid:14)(cid:24)
`CALL SIGNALLING CHANNEL: Reliable channel used to convey the call set-up and teardown
`messages (following Recommendation H.225.0) between two H.323 entities.
`(cid:19)(cid:14)(cid:25)
`CALLABLE: Capable of being called as described in clause 8. Terminals, MCUs and Gateways
`are callable, but Gatekeepers and MCs are not.
`(cid:19)(cid:14)(cid:17)(cid:16)
`CENTRALIZED MULTIPOINT CONFERENCE: A Centralized Multipoint conference is one in which
`all participating terminals communicate in a point-to-point fashion with an MCU. The terminals
`transmit their control, audio, video, and/or data streams to the MCU. The MC within the MCU
`centrally manages the conference. The MP within the MCU processes the audio, video, and/or data
`streams, and returns the processed streams to each terminal.
`(cid:19)(cid:14)(cid:17)(cid:17)
`CONTROL AND INDICATION (cid:8)#(cid:6)) : End-to-end signalling between terminals, consisting of
`Control, which causes a state change in the receiver, and Indication which provides for information
`as to the state or functioning of the system (see also Recommendation H.245 [2] for additional
`information and abbreviations).
`(cid:19)(cid:14)(cid:17)(cid:18)
`DATA: Information stream other than audio, video, and control, carried in the logical data
`channel (see Recommendation H.225.0 [1]).
`(cid:19)(cid:14)(cid:17)(cid:19)
`DECENTRALIZED MULTIPOINT CONFERENCE: A Decentralized Multipoint conference is one in
`which the participating terminals multicast their audio and video to all other participating terminals
`without using an MCU. The terminals are responsible for:
`a)
`summing the received audio streams; and
`b)
`selecting one or more of the received video streams for display.
`No audio or video MP is required in this case. The terminals communicate on their H.245 Control
`Channels with an MC which manages the conference. The data stream is still centrally processed by
`the MCS-MCU which may be within an MP.
`(cid:19)(cid:14)(cid:17)(cid:20)
`ENDPOINT: An H.323 terminal, Gateway, or MCU. An endpoint can call and be called. It
`generates and/or terminates information streams.
`(cid:19)(cid:14)(cid:17)(cid:21)
`GATEKEEPER: The Gatekeeper (GK) is an H.323 entity on the LAN that provides address
`translation and controls access to the local area network for H.323 terminals, Gateways and MCUs.
`
`4
`
`2ECOMMENDATION ((cid:14)(cid:19)(cid:18)(cid:19)
`
`(cid:8)(cid:17)(cid:17)(cid:15)(cid:25)(cid:22)
`
`3UPERSEDED BY A MORE RECENT VERSION
`
`

`
`3UPERSEDED BY A MORE RECENT VERSION
`
`The Gatekeeper may also provide other services to the terminals, Gateways and MCUs such as
`bandwidth management and locating Gateways.
`(cid:19)(cid:14)(cid:17)(cid:22)
`GATEWAY: An H.323 Gateway (GW) is an endpoint on the local area network which provides
`for real-time, two-way communications between H.323 Terminals on the LAN and other ITU
`Terminals on a wide area network, or to another H.323 Gateway. Other ITU Terminals include those
`complying with Recommendations H.310 (H.320 on B-ISDN), H.320 (ISDN), H.321 (ATM), H.322
`(GQOS-LAN), H.324 (GSTN), H.324M (Mobile), and V.70 (DSVD).
`(cid:19)(cid:14)(cid:17)(cid:23)
`((cid:14)(cid:19)(cid:18)(cid:19) %NTITY: Any H.323 component, including terminals, Gateways, Gatekeepers, MCs,
`MPs, and MCUs.
`(cid:19)(cid:14)(cid:17)(cid:24)
`((cid:14)(cid:18)(cid:20)(cid:21) CONTROL CHANNEL: Reliable Channel used to carry the H.245 control information
`messages (following H.245) between two H.323 endpoints.
`(cid:19)(cid:14)(cid:17)(cid:25)
`((cid:14)(cid:18)(cid:20)(cid:21) LOGICAL CHANNEL: Channel used to carry the information streams between two H.323
`endpoints. These channels are established following the H.245 OpenLogicalChannel procedures. An
`unreliable channel is used for audio, audio control, video, and video control information streams. A
`reliable channel is used for data and H.245 control information streams. There is no relationship
`between a logical channel and a physical channel.
`(cid:19)(cid:14)(cid:18)(cid:16)
`((cid:14)(cid:18)(cid:20)(cid:21) SESSION: The part of the call that begins with the establishment of an H.245 Control
`Channel, and ends with the receipt of the H.245 %ND3ESSION#OMMAND or termination due to
`failure. Not to be confused with a ca