Recommendation ITU-T H.323 (03/2022) Packet-based multimedia communications systems
Summary
History
FOREWORD
Table of Contents
1 Scope
2 References
3 Definitions
4 Abbreviations and acronyms
5 Conventions
6 System description
     6.1 Information streams
     6.2 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 Packet-based network interface
          6.2.4 Video codec
               6.2.4.1 Terminal-based continuous presence
          6.2.5 Audio codec
               6.2.5.1 Audio mixing
               6.2.5.2 Maximum audio-video transmit skew
               6.2.5.3 Low bit rate operation
          6.2.6 Receive path delay
          6.2.7 Data channel
               6.2.7.1 T.120 data channels
               6.2.7.2 Remote device control
          6.2.8 H.245 control function
               6.2.8.1 Capabilities exchange
               6.2.8.2 Logical channel signalling
               6.2.8.3 Mode preferences
               6.2.8.4 Master-slave determination
               6.2.8.5 Timer and counter values
               6.2.8.6 Multiplexed stream transmission over a single logical channel
                    6.2.8.6.1 Capability exchange related to multiplexed stream
                    6.2.8.6.2 Logical channel signalling to transport multiplexed stream
                    6.2.8.6.3 Logical channel signalling to transport media stream over multiplexed stream
                    6.2.8.6.4 Logical channel signalling to close multiplexed stream
          6.2.9 RAS signalling function
          6.2.10 Call signalling function
          6.2.11 H.225.0 layer
               6.2.11.1  Logical channel numbers
               6.2.11.2  Logical channel bit rate limits
     6.3 Gateway characteristics
          6.3.1 Gateway decomposition
               6.3.1.1 Physical decompositions
                    6.3.1.1.1 Separate SS7 gateways
                    6.3.1.1.2 FAS gateway decomposition
                    6.3.1.1.3 SS7 gateway with H.323 signalling in the MG
                    6.3.1.1.4 FAS and H.323 signalling in the media gateway
                    6.3.1.1.5 SS7 in the media gateway
          6.3.2 Gateway applications
               6.3.2.1 Overview of trunking and access gateways
                    6.3.2.1.1 SCN terminology
                    6.3.2.1.2 H.323 terminology
                    6.3.2.1.3 H.248 terminology
               6.3.2.2  Service provider trunking gateways
               6.3.2.3 Service provider access gateways
               6.3.2.4 Enterprise trunking gateways
               6.3.2.5 Enterprise to service provider access gateways
     6.4 Gatekeeper characteristics
     6.5 Multipoint controller characteristics
     6.6 Multipoint processor characteristics
     6.7 Multipoint control unit characteristics
     6.8 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
     6.9 Models for supplementary services
7 Call signalling
     7.1 Addresses
          7.1.1 Network address
          7.1.2 TSAP identifier
          7.1.3 Alias address
          7.1.4 H.323 URL scheme
     7.2 Registration, Admission and Status (RAS) channel
          7.2.1 Gatekeeper discovery
          7.2.2 Endpoint registration
               7.2.2.1 Use of lightweight RRQ
               7.2.2.2 Use of additive registrations
          7.2.3 Endpoint location
          7.2.4 Admissions, bandwidth change, status and disengage
          7.2.5 Access tokens
          7.2.6 Alternate gatekeeper procedures
               7.2.6.1 Assigned gatekeeper procedures
          7.2.7 Usage information reporting
               7.2.7.1 Advertising usage information reporting capabilities
               7.2.7.2 Requesting usage information reports
               7.2.7.3 Sending usage information reports
          7.2.8 Call credit-related capabilities
               7.2.8.1 Endpoint advertisement of credit-related capabilities
               7.2.8.2 Balance information sent by the gatekeeper to the endpoint
          7.2.9 Alternate transport addresses
     7.3 Call signalling channel
          7.3.1 Call signalling channel routing
          7.3.2 Control channel routing
          7.3.3 Call signalling and control protocol revisions
     7.4 Call reference value
     7.5 Call ID
     7.6 Conference ID and conference goal
     7.7 Endpoint call capacity
     7.8 Caller identification services
          7.8.1 Description of services
               7.8.1.1 Calling party address presentation
               7.8.1.2 Calling party address restriction
               7.8.1.3 Connected party address presentation
               7.8.1.4 Connected party address restriction
               7.8.1.5 Called (alerting) party address presentation
               7.8.1.6 Called (alerting) party address restriction
               7.8.1.7 Busy party address presentation
               7.8.1.8 Busy party address restriction
          7.8.2 Messages and information elements
               7.8.2.1 Calling party address information
               7.8.2.2 Connected party address information
               7.8.2.3 Called (alerting) party address information
               7.8.2.4 Busy party address information
          7.8.3 Actions at the originating endpoint
               7.8.3.1 Gateway as originating endpoint
               7.8.3.2 Terminal or MCU as originating endpoint
          7.8.4 Actions at the terminating endpoint
               7.8.4.1 Gateway as terminating endpoint
               7.8.4.2 Terminal or MCU as terminating endpoint
          7.8.5 Actions at a gatekeeper
               7.8.5.1 Gateway as originating endpoint
               7.8.5.2 Terminal or MCU as originating endpoint
               7.8.5.3 Gateway as terminating endpoint
               7.8.5.4 Terminal or MCU as terminating endpoint
     7.9 Generic extensible framework
          7.9.1 Format of a GenericData structure
          7.9.2 Negotiation using the extensible framework – General
          7.9.3 Negotiation using the extensible framework – RAS
               7.9.3.1 Processing by the requesting entity
               7.9.3.2 Processing by the responding entity
          7.9.4 Negotiation using the extensible framework – Call signalling
               7.9.4.1 Processing by the initiating endpoint
               7.9.4.2 Processing by intermediate entities
               7.9.4.3 Processing by the called endpoint
8 Call signalling procedures
     8.1 Phase A – Call setup
          8.1.1 Basic call setup – 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 Optional called endpoint signalling
          8.1.7 Fast connect procedure
               8.1.7.1 Proposal, selection and opening of media channels
               8.1.7.2 Switching to H.245 procedures
               8.1.7.3 Terminating a call
               8.1.7.4 In-band and out-of-band tones and announcements
          8.1.8 Call setup via gateways
               8.1.8.1 Gateway in-bound call setup
               8.1.8.2 Gateway out-bound call setup
          8.1.9 Call setup with an MCU
          8.1.10 Call forwarding and call transfer
          8.1.11 Broadcast call setup
          8.1.12 Overlapped sending
          8.1.13 Call setup to conference alias
               8.1.13.1 Joining to a conference alias, with no gatekeeper
               8.1.13.2 Joining to a conference alias, with gatekeeper
               8.1.13.3 Create or invite with a conference alias
               8.1.13.4 Consideration for version 1 endpoints
          8.1.14 Gatekeeper modification of destination addresses
          8.1.15 Indicating desired protocols
          8.1.16 Gatekeeper requested tones and announcements
     8.2 Phase B – Initial communication and capability exchange
          8.2.1 Encapsulation of H.245 messages within H.225.0 Call Signalling messages
          8.2.2 Tunnelling through intermediate signalling entities
          8.2.3 Switching to a separate H.245 connection
          8.2.4 Initiating H.245 tunnelling in parallel with fast connect
     8.3 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
               8.3.3.1 Generic Control Capability: SingleTransmitterMulticast
          8.3.4 Correlation of media streams in multipoint conferences
          8.3.5 Communication mode command procedures
     8.4 Phase D – Call services
          8.4.1 Bandwidth changes
          8.4.2 Status
          8.4.3 Ad hoc conference expansion
               8.4.3.1 Direct endpoint call signalling – conference create
               8.4.3.2 Direct endpoint call signalling – conference invite
               8.4.3.3 Direct endpoint call signalling – conference join
               8.4.3.4 Gatekeeper routed call signalling – conference create
               8.4.3.5 Gatekeeper-routed call signalling – conference invite
               8.4.3.6 Gatekeeper-routed call model – conference join
               8.4.3.7 Handling of the facility message
               8.4.3.8 Conference out of consultation
                    8.4.3.8.1 Scenario 1: Conference provided by endpoint
                    8.4.3.8.2 Scenario 2: Conference provided by MCU
               8.4.3.9 Conference out of conference list
          8.4.4 Supplementary services
          8.4.5 Multipoint cascading
          8.4.6 Third party initiated pause and re-routing
     8.5 Phase E – Call termination
          8.5.1 Call clearing without a gatekeeper
          8.5.2 Call clearing with a gatekeeper
          8.5.3 Call clearing by gatekeeper
     8.6 Protocol failure handling
9 Interoperation with other terminal types
     9.1 Speech-only terminals
     9.2 Visual telephone terminals over the ISDN (Rec. ITU-T H.320)
     9.3 Visual telephone terminals over GSTN (Rec. ITU-T H.324)
     9.4 Visual telephone terminals over mobile radio (Annex C/H.324, a.k.a. "H.324/M")
     9.5 Visual telephone terminals over ATM (H.321 and H.310 RAST)
     9.6 Visual telephone terminals over guaranteed quality of service LANs (Rec. ITU-T H.322)
     9.7 Simultaneous voice and data terminals over GSTN (Rec. ITU-T V.70)
     9.8 T.120 terminals on the packet-based network
     9.9 Gateway for H.323 media transport over ATM
10 Optional enhancements
     10.1 Encryption
     10.2 Multipoint operation
          10.2.1 H.243 control and indication
     10.3 Call Linkage in H.323
          10.3.1 Description
               10.3.1.1 General description
               10.3.1.2 Service definitions
                    10.3.1.2.1  Thread identification, thread ID, TID
                    10.3.1.2.2  Global call identification, global call ID, GID
          10.3.2 Invocation and operation
          10.3.3 Interaction with H.450 supplementary services
               10.3.3.1 Call transfer
                    10.3.3.1.1  Transfer without consultation
                    10.3.3.1.2  Transfer with consultation
               10.3.3.2 Call diversion
               10.3.3.3 Call hold and consultation
               10.3.3.4 Call park/call pickup
               10.3.3.5 Call waiting
               10.3.3.6 Message waiting indication
               10.3.3.7 Name identification service
     10.4 Tunnelling of non-H.323 signalling messages
          10.4.1 Indicating support of tunnelled protocols
          10.4.2 Requesting a specific protocol tunnel to a gatekeeper
          10.4.3 Tunnelling a signalling protocol in H.225.0 call signalling messages
          10.4.4 Gatekeeper considerations
     10.5 Use of RTP payload for DTMF digits, telephony tones and telephony signals
11 Maintenance
     11.1 Loopbacks for maintenance purposes
     11.2 Monitoring methods
Annex A  H.245 messages used by H.323 endpoints
Annex B  Procedures for layered video codecs
     B.1 Scope
     B.2 Introduction
     B.3 Scalability methods
     B.4 Call establishment
     B.5 Use of RTP sessions and codec layers
          B.5.1 Associate base to audio for lip synchronization
          B.5.2 Enhancement layer dependency
     B.6 Possible layering models
          B.6.1 Multiple logical channels and RTP sessions for a layered stream
          B.6.2 Impact of one layer per logical channel and per RTP session
     B.7 Impact on multipoint conferences
          B.7.1 MC Impartial model
          B.7.2 MC Decision model
          B.7.3 Multipoint conference containing endpoints on different bandwidths
     B.8 Use of network QoS for layered video streams
Annex C  H.323 on ATM
     C.1 Introduction
     C.2 Scope
          C.2.1 Point-to-point conferencing
          C.2.2 MCU-based multipoint
          C.2.3 H.323 interoperability with endpoints using IP
     C.3 Architecture
          C.3.1 Overview of system
          C.3.2 Interoperation with other ITU-T H-series Recommendations endpoints
          C.3.3 H.225.0 on IP over ATM
          C.3.4 H.245 on TCP/IP over ATM
          C.3.5 Addressing for A/V streams
          C.3.6 Transport Capabilities added to TransportCapability Set
          C.3.7 Elements of ATM signalling
               C.3.7.1 ATM address
               C.3.7.2 Port Number
          C.3.8 A/V streams on RTP on AAL 5
               C.3.8.1 Unidirectional logical channels
               C.3.8.2 Bidirectional logical channels
               C.3.8.3 Maximum transmission unit size
               C.3.8.4 RTCP on IP over ATM
          C.3.9 QoS considerations (Optional)
               C.3.9.1 QoS classes defined in Rec. ITU-T I.356
               C.3.9.2 ATM transfer capability defined in Rec. ITU-T I.371
               C.3.9.3 Broadband transfer capability defined in Rec. ITU-T Q.2961.2
               C.3.9.4 Opening of Virtual Channels
               C.3.9.5 Use of DBR
               C.3.9.6 Setting the proper cell rate
     C.4 Protocol section
          C.4.1 ATM signalling information elements
               C.4.1.1 Generic information transport
               C.4.1.2 Broadband High Layer Information
               C.4.1.3 ATM Adaptation Layer parameters
               C.4.1.4 ATM Broadband bearer capability Information Element
          C.4.2 H.245 usage
          C.4.3 RTP usage
          C.4.4 Interoperation with H.323 on IP
Annex D  Real-time facsimile over H.323 systems
     D.1 Introduction
     D.2 Scope
     D.3 Procedures for opening channels to send T.38 packets
          D.3.1 Opening the voice channel
          D.3.2 Opening the facsimile channels
          D.3.3 DTMF transmission
     D.4 Non-fast connect procedures
     D.5 Replacing an existing audio stream with a T.38 fax stream
     D.6 Usage of the maxBitRate/bandWidth in messages
     D.7 Interactions with gateways and T.38/Annex B devices
Annex E  Framework and wire-protocol for multiplexed call signalling transport
     E.1 Scope
          E.1.1 Introduction
               E.1.1.1 Multiplexed transport
               E.1.1.2 Multiple payloads in a single PDU
               E.1.1.3 Flexible header options
               E.1.1.4 Ack message
               E.1.1.5 Nack message
               E.1.1.6 Sender sequence number policy
               E.1.1.7 Receiver sequence number policy
               E.1.1.8 Retransmissions
               E.1.1.9 Connection keep-alive
               E.1.1.10 Forward error correction
               E.1.1.11 Reply hints
               E.1.1.12 Well-known port and port spawning
          E.1.2 Signalling models
               E.1.2.1 Real-time model
               E.1.2.2 Serial model
               E.1.2.3 Mixed model
               E.1.2.4 Annex E over TCP
          E.1.3 Optional payload fields
               E.1.3.1 Session identifier
               E.1.3.2 Source/Destination address identifier
          E.1.4 Wire-protocol
               E.1.4.1 Header structure
               E.1.4.2 Payload structure
                    E.1.4.2.1 Payload header flags
                    E.1.4.2.2 Annex E transport messages
                         E.1.4.2.2.1 I-Am-Alive message
                         E.1.4.2.2.2 Ack message
                         E.1.4.2.2.3 Nack message
                         E.1.4.2.2.4 Restart message
               E.1.4.3 Static-typed messages
                    E.1.4.3.1 Basic static-typed message (S-bit and A-bit cleared)
                    E.1.4.3.2 Extended-1 static-typed message (S-bit set and A-bit cleared)
                    E.1.4.3.3 Extended-2 static-typed message (S-bit and A-bit set)
                    E.1.4.3.4 Extended-3 static-typed message (S-bit cleared, A-bit set)
               E.1.4.4 OBJECT IDENTIFIER typed messages
                    E.1.4.4.1 Basic OBJECT IDENTIFIER typed message (S-bit and A-bit cleared)
                    E.1.4.4.2 Extended-1 OBJECT IDENTIFIER typed message (S-bit set and A-bit cleared)
                    E.1.4.4.3 Extended-2 OBJECT IDENTIFIER typed message (S-bit and A-bit set)
                    E.1.4.4.4 Extended-3 OBJECT IDENTIFIER typed message (S-bit cleared, A-bit set)
     E.2 H.225.0 call signalling over UDP
          E.2.1 Rationale
          E.2.2 Advantage of using UDP
               E.2.2.1 UDP-based procedure
               E.2.2.2 Mixed TCP and UDP procedure
          E.2.3 Specifics
               E.2.3.1 Message identification
               E.2.3.2 Well-known port
               E.2.3.3 Signalling model
               E.2.3.4 Timers
               E.2.3.5 Session field
               E.2.3.6 Source/destination address field
               E.2.3.7 MTU
               E.2.3.8 H.245
               E.2.3.9 Receiver sequence number policy for H.225.0 over Annex E
Annex F  Simple endpoint types
     F.1 Introduction
     F.2 Specification conventions
     F.3 Scope
     F.4 Normative references
     F.5 Abbreviations
     F.6 Simple (Audio) Endpoint Type – System functionality overview
     F.7 Procedures for Simple Endpoint Types
          F.7.1 RAS Signalling (H.225.0 RAS)
          F.7.2 Call signalling (H.225.0 Call Control)
          F.7.3 Multimedia system control signalling (H.245)
               F.7.3.1 H.245 control channel
               F.7.3.2 Master-Slave Determination
               F.7.3.3 Terminal capability exchange
                    F.7.3.3.1 Audio capability
                    F.7.3.3.2 Video Capability
                    F.7.3.3.3 Data Capability
                    F.7.3.3.4 Conference Capability
                    F.7.3.3.5 User Input Capability
                    F.7.3.3.6 Security Capability
                    F.7.3.3.7 maxPendingReplacementFor
                    F.7.3.3.8 nonStandardCapability
                    F.7.3.3.9 Additional rules for the use of capabilities
               F.7.3.4 Logical Channel Signalling Messages
          F.7.4 Media exchange
          F.7.5 Supplementary services (H.450.x)
          F.7.6 Third-party initiated pause and re-routing
               F.7.6.1 Initiating side
               F.7.6.2 Receiving side (SET device)
          F.7.7 Conference-mode operation
               F.7.7.1 Conference-unaware SET devices
               F.7.7.2 Conference-aware SET Devices
          F.7.8 Support for loosely-coupled conferences (Rec. ITU-T H.332)
          F.7.9 Management Information Bases (MIBs)
     F.8 Security extensions
     F.9 Interoperability considerations
     F.10 Implementation notes (Informative)
          F.10.1 Open Logical Channel
               F.10.1.1 Forward Logical Channel parameters
                    F.10.1.1.1  Recs ITU-T G.711 and G.729
                    F.10.1.1.2  G.723.1 codec
                    F.10.1.1.3  GSM
               F.10.1.2 Reverse Logical Channel Parameters
                    F.10.1.2.1  Recs ITU-T G.711 and G.729
                    F.10.1.2.2  Rec. ITU-T G.723.1
                    F.10.1.2.3  GSM
Annex G  Text conversation and Text SET
     G.1 Introduction
     G.2 Scope
     G.3 References
     G.4 Definitions
     G.5 Capability Advertisement for Text in H.323
          G.5.1 Data Channel Text Capabilities
          G.5.2 Audio Channel Text Capability
          G.5.3 Characters per Second Generic Parameter
     G.6 Procedures for opening channels for T.140 text conversation
     G.7 Framing and buffering of T.140 data
          G.7.1 Common considerations
          G.7.2 Usage of reliable channels
          G.7.3 Usage of unreliable channels
     G.8 Interaction with text conversation facilities in other devices
     G.9 Multipoint considerations
          G.9.1 Situations for multipoint text conversation
               G.9.1.1 One-to-one
               G.9.1.2 Many-to-many
               G.9.1.3 One-to-many with managed right to type
               G.9.1.4 One-to-many with fixed right to type
     G.10 Text SET: Text Conversation Simple Endpoint Type
          G.10.1 Introduction to Text SET
          G.10.2 Text SET System Functionality Overview (see clause F.6)
          G.10.3 Procedures for Text SET devices (see clause F.7)
          G.10.4 RAS Signalling (H.225.0 RAS ( see clause F.7.1)
          G.10.5 Call Signalling (H.225.0 Call Control ( see clause F.7.2)
          G.10.6 Data Capability (See clause F.7.3.3.3)
          G.10.7 Additional rules for usage of capabilities (see clause F.7.3.3.9)
          G.10.8 Logical channel signalling messages (see F.7.3.4)
          G.10.9 Media exchange (see clause F.7.4)
          G.10.10  Initiating side (see clause F.7.6.1)
          G.10.11  Conference-unaware Text SET terminals (see clause F.7.7.1)
          G.10.12  Support for loosely-coupled conferences (Rec. ITU-T H.332) (see clause F.7.8)
Annex J  Security for Annex F
     J.1 Introduction
     J.2 Specification conventions
     J.3 Scope
     J.4 Abbreviations
     J.5 Normative references
     J.6 Secure Audio Simple Endpoint Type (SASET)
          J.6.1 Assumptions
          J.6.2 Overview
Annex K  HTTP-based service control transport channel
     K.1 Introduction
          K.1.1 Notation
     K.2 Service control in H.323
          K.2.1 Service control session
          K.2.2 Non-call-related service control
          K.2.3 Call-related service control
     K.3 Usage of HTTP
          K.3.1 Non-call-related services control channel
          K.3.2 Call-related services control channel
     K.4 Example scenarios
     K.5 References
          K.5.1 Normative references
          K.5.2 Informative references
Annex L  Stimulus control protocol
     L.1 Scope
          L.1.1 Terminology
          L.1.2 Relationship of H.323 stimulus to H.248
          L.1.3 Relationship of H.323 stimulus to HTTP
          L.1.4 Relationship to H.450 supplementary services
     L.2 Introduction
     L.3 Stimulus framework
          L.3.1 Overview
          L.3.2 Protocol signalling
          L.3.3 Use of H.248
          L.3.4 H.225.0 encapsulation
     L.4 References
Annex M1  Tunnelling of signalling protocols (QSIG) in H.323
     M1.1 Scope
     M1.2 Normative references
     M1.3 Endpoint procedures
     M1.4 Tunnelling of QSIG connection-oriented call-independent signalling
     M1.5 Gatekeeper procedures
Annex M2  Tunnelling of signalling protocols (ISUP) in H.323
     M2.1 Scope
     M2.2 Normative references
     M2.3 Endpoint procedures
     M2.4 Gatekeeper procedures
Annex M3  Tunnelling of DSS1 through H.323
     M3.1 Scope
     M3.2 Normative references
     M3.3 Endpoint procedures
     M3.4 Tunnelling of bearer-independent DSS1 signalling
          M3.4.1  DSS1 connectionless transport
          M3.4.2  DSS1 bearer-independent connection-oriented transport
     M3.5 Gatekeeper procedures
Annex M4  Tunnelling of narrow-band signalling syntax (NSS) for H.323
     M4.1 Scope
     M4.2 References
     M4.3 H.225.0 Endpoint procedures
     M4.4 Gatekeeper procedures
     M4.5 RAS procedures for direct-routed calls
          M4.5.1 RAS Protocol Tunnel feature
          M4.5.2 RAS Protocol Tunnel parameter
          M4.5.3 Protocol Tunnel ASN.1 definition
          M4.5.4 Description of ASN.1 types and fields
Annex M5  Tunnelling of common alerting protocol (CAP) messages in H.323
     M5.1 Scope
     M5.2 Normative references
     M5.3 Identifying CAP messages
     M5.4 Signalling support for CAP
     M5.5 Transporting CAP within H.225.0 messages
     M5.6 Transmitting and processing CAP messages
     M5.7 Requesting CAP support when initiating calls
     M5.8 Gatekeeper procedures
Annex O  Usage of URLs and DNS
     O.1 Scope
     O.2 Normative references
     O.3 Informative references
     O.4 H.323 URL
     O.5 Encoding of H.323 URL in H.323 messages
     O.6 Non-H.323 URLs and URIs within the context of H.323
     O.7 H.323 URL parameters
          O.7.1 ABNF syntax
          O.7.2 User parameter
          O.7.3 Service parameter
          O.7.4 Transport Parameter
     O.8 Usage of the H.323 URL
          O.8.1 Locating H.323 destination
          O.8.2 Locating a Gatekeeper
     O.9 Resolving an H.323 URL to IP Address using DNS
     O.10 Using DNS SRV Resource Records
          O.10.1 Applicability
          O.10.2 IANA registration
          O.10.3 SRV RR population
          O.10.4 SRV RR retrieval and processing
          O.10.5 Example 1
          O.10.6 Example 2
Annex P  Transfer of modem signals over H.323
     P.1 Scope
     P.2 References
     P.3 Definitions
     P.4 Abbreviations
     P.5 Introduction
     P.6 Capability advertisement
     P.7 Call establishment
     P.8 Logical channel signalling
          P.8.1 Extended fast connect
          P.8.2 H.245 signalling
Annex Q  Far-end camera control and H.281/H.224
     Q.1 Scope
     Q.2 References
     Q.3 Introduction
     Q.4 Far-end camera control protocol
          Q.4.1 General
          Q.4.2 H.320 to H.323 gateways
          Q.4.3 H.324 to H.323 gateways
          Q.4.4 H.245 signalling
     Q.5 RTP header information
Annex R   Robustness methods for H.323 entities
     R.1 Introduction and scope
     R.2 Normative references
     R.3 Definitions
     R.4 Abbreviations
     R.5 Overview of the two methods
          R.5.1 Method A: State recovery from neighbours
               R.5.1.1 Partial method A
          R.5.2 Method B: State recovery from a shared repository
          R.5.3 Comparison
     R.6 Common mechanisms
          R.6.1 Detection of TCP-based connection lost
          R.6.2 Protocol failure handling
          R.6.3 Detecting failure – KeepAlive
          R.6.4 Transport address and re-established connections
               R.6.4.1 Establishment of a new TCP connection
               R.6.4.2 Association between the call and the new TCP connection
               R.6.4.3 An old TCP connection closure
          R.6.5 Support for extended Status
     R.7 Method A: State recovery from neighbours
          R.7.1 Introduction
          R.7.2 Scope
          R.7.3 The robustness procedure
          R.7.4 SDL for Method A state machine
     R.8 Method B: State recovery from a shared repository
          R.8.1 Fault-tolerant platform
          R.8.2 Fault-tolerant cluster
          R.8.3 Call signalling connection re-establishment
          R.8.4 H.245 connection re-establishment
          R.8.5 Data items shared through shared repository
          R.8.6 Checkpoints
     R.9 Interworking between robustness methods
     R.10 Procedures for recovery
          R.10.1 Recovery procedures with conflicting CRV values
     R.11 GenericData usage
          R.11.1 GenericData usage in H.225.0 messages
Appendix I  Sample MC to terminal communication mode command
     I.1 Sample conference Scenario A
     I.2 CommunicationModeTable sent to all endpoints
     I.3 Sample conference Scenario B
     I.4 CommunicationModeTable sent to all endpoints
Appendix II  Transport level resource reservation procedures
     II.1 Introduction
     II.2 QoS support for H.323
     II.3 RSVP background
     II.4 The H.245 capability exchange phase
     II.5 Open logical channel and setting up reservations
     II.6 Close logical channel and tearing down reservations
     II.7 Resource reservation for multicast H.323 logical channels
     II.8 Synchronized RSVP
          II.8.1 Synchronizing RSVP when not using Fast Connect
          II.8.2 Synchronizing RSVP with fast connect
Appendix III  Gatekeeper-based user location
     III.1 Introduction
     III.2 Signalling
Appendix IV  Signalling prioritized alternative logical channels in ITU-T H.245
     IV.1 Introduction
     IV.2 Signalling
Appendix V  Use of ITU-T E.164 and ISO/IEC 11571 numbering plans
     V.1 E.164 numbering plan
     V.2 Private network number
     V.3 H.323 versions 1, 2 and 3 usage
Appendix VI  Description of a typical ITU-T H.323 system over IP
Appendix VII  Informative notes on robustness methods for ITU-T H.323 entities
     VII.1 Informative Note 1: Background on robustness methods
          VII.1.1 Types of robustness methods
          VII.1.2 Robust entities
          VII.1.3 Robust system scope
          VII.1.4 System termination and failures
               VII.1.4.1 Types of failures
               VII.1.4.2 Failure detection
               VII.1.4.3 Failure handling
               VII.1.4.4 Failure scenarios
     VII.2 Informative Note 2: Call state sharing between an entity and its backup peer
          VII.2.1 Shared memory
          VII.2.2 Shared disk
          VII.2.3 Message passing
               VII.2.3.1 SCTP/ASAP
                    VII.2.3.1.1  References
                    VII.2.3.1.2  Protocol stacks
                    VII.2.3.1.3  An architectural view of an H.323 system
                    VII.2.3.1.4  An example H.323 call
                         VII.2.3.1.4.1 General description
                         VII.2.3.1.4.2 Failure scenarios
                         VII.2.3.1.4.3 State saving issues
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