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     
        6.4     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  
 7     Call signalling    
        7.1     Addresses 
                  7.1.1     Network address  
                  7.1.2     TSAP identifier     
                  7.1.3     Alias address        
        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      
        7.3     Call signalling channel         
                  7.3.1     Call signalling channel routing        
                  7.3.2     Control channel routing     
        7.4     Call reference value           
        7.5     Call ID   
        7.6     Conference ID and Conference Goal         
 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      
        8.2     Phase B – Initial communication and capability exchange    
                  8.2.1     Encapsulation of H.245 messages within Q.931 messages 
                  8.2.2     Tunneling through intermediate signalling entities     
                  8.2.3     Switching to a separate H.245 connection 
        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 (H.320) 
        9.3     Visual telephone terminals over GSTN (H.324)      
        9.4     Visual telephone terminals over mobile radio (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 (H.322)           
        9.7     Simultaneous voice and data terminals over GSTN (V.70)  
        9.8     T.120 terminals on the packet based network         
10     Optional enhancements   
       10.1     Encryption
       10.2     Multipoint operation          
                  10.2.1     H.243 Control and Indication      
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 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 Terminal Capability 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   
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    
Appendix III – Gatekeeper based user location    
      III.1     Introduction           
      III.2     Signalling