ITU-T Recommendation H.320
Title: Narrow-band visual telephone systems and terminal equipment
Date of adoption : 07/1997
Summary
This Recommendation specifies technical requirements for narrow-band visual telephone systems and terminal equipment, typically for videoconferencing and videophone services. It describes a generic system configuration consisting of a number of elements which are specified by respective ITU-T Recommendations, definition of communication modes and terminal types, call control arrangements, terminal aspects and interworking requirements. This revision reflects the progress in relevant H-Series Recommendations such as G.723.1, G.729, H.262, H.263, H.310, H.322, H.323 and H.324.
TABLE OF CONTENTS
| Page | ||
| 1 | Scope | 1 |
| 2 | Definitions | 1 |
| 3 | System description | 2 |
| 3.1 | Block diagram and identification of elements | 2 |
| 3.2 | Signals | 3 |
| 3.3 | Bit rate options and infrastructure | 3 |
| 3.3.1 | Communication modes of visual telephone | 3 |
| 3.3.2 | Terminal types of visual telephone | 4 |
| 3.3.3 | Video codec | 5 |
| 3.3.4 | Audio codec | 5 |
| 3.3.5 | Frame structure | 5 |
| 3.3.6 | Control and Indication (C&I) | 5 |
| 3.3.7 | Communication procedure | 5 |
| 3.4 | Call control arrangements | 5 |
| 3.4.1 | Establishment of a visual telephone call – Normal procedure | 5 |
| 3.4.2 | Exceptional procedures for phases A and B | 8 |
| 3.4.3 | Exceptional procedures during phase C | 8 |
| 3.4.4 | Addition and dropping of channels during a visual telephone call | 8 |
| 3.4.5 | Transmission and presentation of audiovisual information at the start of a visual telephone call | 9 |
| 3.5 | Optional enhancements | 9 |
| 3.5.1 | Data ports | 9 |
| 3.5.2 | Encryption | 10 |
| 3.5.3 | Restricted networks | 10 |
| 4 | Terminal requirements | 10 |
| 4.1 | Environments | 10 |
| 4.2 | Audio and video arrangements | 10 |
| 4.2.1 | Audio arrangements | 10 |
| 4.2.2 | Video arrangements | 12 |
| 4.3 | Delay compensation in the audio path | 12 |
| 4.4 | Control and Indications (C&I) | 13 |
| 4.5 | Multipoint operation | 15 |
| 5 | Intercommunications | 15 |
| 5.1 | Intercommunication between different visual telephone terminal types | 15 |
| 5.2 | Intercommunication with telephony | 15 |
| 5.2.1 | Intercommunication with ISDN telephones | 15 |
| 5.2.2 | Intercommunication with PSTN telephones | 15 |
| 5.3 | Intercommunication with other audiovisual terminals | 15 |
| 5.3.1 | Intercommunication with H.324 terminals on GSTN | 15 |
| 5.3.2 | Intercommunication with H.322 terminals on Guaranteed QOS LANs | 16 |
| 5.3.3 | Intercommunication with H.323 terminals on Non-guaranteed QOS LANs | 16 |
| 5.3.4 | Intercommunication with H.310/H.321 terminals on ATM networks | 16 |
| 6 | Maintenance | 16 |
| 7 | Human factor aspects | 16 |
| 7.1 | Physical section | 16 |
| 7.2 | Logical section | 16 |
| Annex A | Optional enhanced video algorithms for H.320 systems | 17 |
| A.1 | Introduction to enhanced video algorithms | 17 |
| A.2 | Use of Recommendation H.262 in H.320 systems | 18 |
| A.2.1 | Image formats | 18 |
| A.2.2 | Forward error correction | 18 |
| A.2.3 | Syntax and semantics of video frame synchronous C&I | 18 |
| A.2.4 | Generic usage of ITU-T_extension() | 19 |
| A.3 | Use of Recommendation H.263 in H.320 systems | 20 |
| A.4 | Enhanced video algorithm hierarchy | 20 |