1     Scope 
 2     Normative references       
 3     Definitions  
 4     Symbols and abbreviations           
 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         
                  6.2.5     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     
        6.3     Gateway characteristics     
                  6.3.1     Gateway decomposition    
                  6.3.2     Gateway applications        
        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         
                  7.2.3     Endpoint location  
                  7.2.4     Admissions, bandwidth change, status and disengage         
                  7.2.5     Access tokens      
                  7.2.6     Alternate gatekeeper procedures   
                  7.2.7     Usage information reporting          
                  7.2.8     Call credit-related capabilities       
                  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      
                  7.8.2     Messages and information elements           
                  7.8.3     Actions at the originating endpoint 
                  7.8.4     Actions at the terminating endpoint
                  7.8.5     Actions at a gatekeeper    
        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  
                  7.9.4     Negotiation using the extensible framework – call signalling
 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    
                  8.1.8     Call setup via gateways     
                  8.1.9     Call setup with an MCU   
                  8.1.10     Call forwarding   
                  8.1.11     Broadcast call setup        
                  8.1.12     Overlapped sending        
                  8.1.13     Call setup to conference alias      
                  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 Q.931 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 
                  8.3.4     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       
                  8.4.4     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 (ITU-T Rec. H.320)      
        9.3     Visual telephone terminals over GSTN (ITU-T Rec. H.324)           
        9.4     Visual telephone terminals over mobile radio (ITU-T Rec. H.324/M - Annex C/H.324)    
        9.5     Visual telephone terminals over ATM (H.321 and H.310 RAST)    
        9.6     Visual telephone terminals over guaranteed quality of service LANs (ITU‑T Rec. H.322)    
        9.7     Simultaneous voice and data terminals over GSTN (ITU-T Rec. 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         
                  10.3.2     Invocation and operation 
                  10.3.3     Interaction with H.450 supplementary services    
       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.3.8     A/V streams on RTP on AAL5    
                  C.3.9     QOS considerations (Optional)    
        C.4     Protocol section    
                  C.4.1     ATM signalling information elements         
                  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 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.1.2     Signalling models  
                  E.1.3     Optional payload fields     
                  E.1.4     Wire-protocol      
        E.2     H.225.0 call signalling over Annex E          
                  E.2.1     Rationale  
                  E.2.2     H.323 Call-Setup using this annex 
                  E.2.3     Specifics  
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.7.4     Media Exchange   
                  F.7.5     Supplementary services (H.450.x)
                  F.7.6     Third-party initiated pause and re-routing  
                  F.7.7     Conference-mode Operation        
                  F.7.8     Support for loosely-coupled conferences (ITU‑T Rec. 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    
Annex G - Text conversation and Text SET    
        G.1     Introduction          
        G.2     Scope    
        G.3     References
        G.4     Definitions 
        G.5     Procedures for opening channels for T.140 text conversation         
        G.6     Framing and buffering of T.140 data          
                  G.6.1     Common considerations   
                  G.6.2     Usage of reliable channels
                  G.6.3    Usage of unreliable channels         
        G.7     Interaction with text conversation facilities in other devices 
        G.8     Multipoint considerations   
                  G.8.1     Situations for multipoint text conversation  
        G.9     Text SET: Text Conversation Simple Endpoint Type          
                  G.9.1     Introduction to Text SET  
                  G.9.2     Text SET System Functionality Overview (F.6/H.323)      
                  G.9.3     Procedures for Text SET devices (F.7/H.323)      
                  G.9.4     RAS Signalling (H.225.0 RAS - F.7.1/H.323)     
                  G.9.5     Call Signalling (H.225.0 Call Control - F.7.2/H.323)       
                  G.9.6     Data Capability (F.           
                  G.9.7     Additional rules for usage of capabilities (F.           
                  G.9.8     Logical Channel Signalling Messages (F.7.3.4/H.323)       
                  G.9.9     Media Exchange (F.7.4/H.323)    
                  G.9.10     Initiating side (F.7.6.1/H.323)    
                  G.9.11     Conference-unaware Text SET terminals (F.7.7.1/H.323)          
                  G.9.12     Support for loosely-coupled conferences (ITU‑T Rec. H.332) (F.7.8/H.323)     
Annex J      - Security for H.323 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 signaling protocols (ISUP) in H.323    
       M2.1     Scope  
       M2.2     Normative references      
       M2.3     Endpoint procedures       
       M2.4     Gatekeeper procedures   
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 H.245    
       IV.1     Introduction          
       IV.2     Signalling  
Appendix V - Use of 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