1、 International Telecommunication Union ITU-T T.128TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2008) SERIES T: TERMINALS FOR TELEMATIC SERVICES Data protocols for multimedia conferencing Multipoint application sharing Recommendation ITU-T T.128 ITU-T T-SERIES RECOMMENDATIONS TERMINALS FOR TEL
2、EMATIC SERVICES Facsimile Framework T.0T.19 Still-image compression Test charts T.20T.29 Facsimile Group 3 protocols T.30T.39 Colour representation T.40T.49 Character coding T.50T.59 Facsimile Group 4 protocols T.60T.69 Telematic services Framework T.70T.79 Still-image compression JPEG-1, Bi-level a
3、nd JBIG T.80T.89 Telematic services ISDN Terminals and protocols T.90T.99 Videotext Framework T.100T.109 Data protocols for multimedia conferencing T.120T.149 Telewriting T.150T.159 Multimedia and hypermedia framework T.170T.189 Cooperative document handling T.190T.199 Telematic services Interworkin
4、g T.300T.399 Open document architecture T.400T.429Document transfer and manipulation T.430T.449 Document application profile T.500T.509 Communication application profile T.510T.559 Telematic services Equipment characteristics T.560T.649 Still-image compression JPEG 2000 T.800T.849 Still-image compre
5、ssion JPEG-1 extensions T.850T.899 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T T.128 (06/2008) i Recommendation ITU-T T.128 Multipoint application sharing Summary Recommendation ITU-T T.128 defines a protocol that supports multipoint application sharing. The T.
6、128 protocol supports multipoint computer application sharing by allowing a view onto a computer application executing at one site to be advertised within a session to other sites. Each site can, under specified conditions, take control of the shared computer application by sending remote keyboard a
7、nd pointing device information. This style of application sharing does not require and does not make provision for synchronizing multiple instances of the same computer application running at multiple sites. Instead, it enables remote viewing and control of a single application instance to provide t
8、he illusion that the application is running locally. This Recommendation uses services provided by Recommendations ITU-T T.122 (MCS) and T.124 (GCC). This revised version of Recommendation ITU-T T.128 introduces a number of modifications to legacy mode ASN.1 definition of the application sharing pro
9、tocol. Source Recommendation ITU-T T.128 was approved on 13 June 2008 by ITU-T Study Group 16 (2005-2008) under Recommendation ITU-T A.8 procedure. ii Rec. ITU-T T.128 (06/2008) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecomm
10、unications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommun
11、ications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the proced
12、ure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a teleco
13、mmunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of thes
14、e mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU
15、draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU member
16、s or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not repr
17、esent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2009 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T T.128 (06/20
18、08) iii CONTENTS Page 1 Scope 1 2 References. 2 3 Definitions 3 4 Abbreviations and acronyms 4 5 Overview 4 5.1 Legacy and base modes 4 5.2 AS concepts 5 6 Use of MCS 10 6.1 MCS channel usage 11 6.2 Use of MCS data services. 11 7 Use of GCC 13 8 Protocol specification . 14 8.1 AS sessions. 14 8.2 Ca
19、pabilities. 14 8.3 ASPDU formats 36 8.4 ASCE activation . 40 8.5 Flow control 47 8.6 Synchronization 52 8.7 Remote sharing. 56 8.8 Fonts . 57 8.9 Application management 69 8.10 Window list management. 70 8.11 Window activation 76 8.12 Control 80 8.13 Mediated control. 83 8.14 Pointers. 87 8.15 Palet
20、te updates 91 8.16 Order updates 92 8.17 Bitmap updates . 133 8.18 Input 139 8.19 Conducted mode operation. 147 9 ASPDU definitions . 148 9.1 Legacy mode ASN.1 definition 148 9.2 Base mode ASN.1 definition 168 9.3 Legacy mode encoding rules 190 9.4 Base mode non-collapsing capabilities encoding rule
21、s 190 Annex A Static channel ID assignments. 192 iv Rec. ITU-T T.128 (06/2008) Page Annex B Legacy application protocol key 193 Annex C Object identifier assignments 194 Appendix I Informative values . 195 I.1 Flow control 195 I.2 Bitmap caching. 196 I.3 ColorTable caching 196 I.4 Pointer caching .
22、196 I.5 Desktop save cache. 196 I.6 General compression 196 Rec. ITU-T T.128 (06/2008) 1 Recommendation ITU-T T.128 Multipoint application sharing 1 Scope This Recommendation defines a protocol that supports multipoint application sharing. It uses services provided by ITU-T T.122 (MCS) and ITU-T T.1
23、24 (GCC). The details of communication with the input and output devices and the user interfaces on the host terminal are considered out of the scope of this Recommendation and are left to the discretion of the implementer. Therefore, this Recommendation makes no assumption that these input and outp
24、ut devices and user interfaces are of any specific architecture. Figure 1 presents an overview of the scope of this Recommendation and its relationship to the other elements of the T.120 framework within a single node. T1602310-97.User application(s)(Using both standard and non-standard application
25、protocols) NodecontrollerUser application(s)(Using std. appl. protocols)User application(s)(Using non-std. protocols)Rec. T.127 (MBFT)Rec. T.126 (SI)Rec. T.128 (AS)Application protocol entityITU-T T.120Application protocolRecommendationsNon-standard applicationprotocol entityGeneric Conference Contr
26、ol (GCC)Rec. T.124Multipoint Communications Service (MCS)Rec. T.122/T.125Network specific transport protocolsRec. T.123ITU-T T.120 Infrastructure RecommendationsFigure 1 Scope of this Recommendation 2 Rec. ITU-T T.128 (06/2008) 2 References The following ITU-T Recommendations and other references co
27、ntain 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; users of this Recommendation are therefore encouraged to investigate
28、the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of
29、a Recommendation. ITU-T F.710 Recommendation ITU-T F.710 (1991), General principles for audiographic conference service. ITU-T H.221 Recommendation ITU-T H.221 (1997), Frame structure for a 64 to 1920 kbit/s channel in audiovisual teleservices. ITU-T T.35 Recommendation ITU-T T.35 (1991), Procedure
30、for the allocation of CCITT defined codes for non-standard facilities. ITU-T T.50 Recommendation ITU-T T.50 (1992), International Reference Alphabet (IRA) (Formerly International Alphabet No. 5 or IA5) Information technology 7-bit coded character set for information interchange. ITU-T T.120 Recommen
31、dation ITU-T T.120 (2007), Data protocols for multimedia conferencing. ITU-T T.121 Recommendation ITU-T T.121 (1996), Generic application template. ITU-T T.122 Recommendation ITU-T T.122 (1993), Multipoint communication service for audiographics and audiovisual conferencing service definition. ITU-T
32、 T.123 Recommendation ITU-T T.123 (1996), Network-specific data protocol stacks for multimedia conferencing. ITU-T T.124 Recommendation ITU-T T.124 (1995), Generic Conference Control. ITU-T T.125 Recommendation ITU-T T.125 (1994), Multipoint communication service protocol specification. ITU-T V.42 b
33、is Recommendation ITU-T V.42 bis (1990), Data compression procedures for data circuit-terminating equipment (DCE) using error correcting procedures. ITU-T X.509 Recommendation ITU-T X.509 (1997) | ISO/IEC 9594-8:1998, Information technology Open Systems Interconnection The Directory: Authentication
34、framework. ITU-T X.680 Recommendation ITU-T X.680 (1994) | ISO/IEC 8824-1:1995, Information technology Abstract Syntax Notation One (ASN.1) Specification of basic notation. ITU-T X.691 Recommendation ITU-T X.691 (1997) | ISO/IEC 8825-2:1998, Information technology ASN.1 encoding rules Specification
35、of Packed Encoding Rules (PER). ISO/IEC 8859-1 ISO/IEC 8859-1:1998, Information technology 8-bit single-byte coded graphic character sets Part 1: Latin alphabet No. 1. ISO/IEC 10646 ISO/IEC 10646:2003, Information technology Universal Multiple-Octet Coded Character Set (UCS). Rec. ITU-T T.128 (06/20
36、08) 3 3 Definitions This Recommendation defines the following terms: 3.1 application sharing (AS): A process whereby two or more terminals cooperate to share the output of applications running on one or more terminals to the other terminals and to provide input to the applications. 3.2 application s
37、haring conference entity (ASCE): An application protocol entity that interacts with a user application above and with the local multipoint communication service (MCS) and local generic conference control (GCC) providers below to implement application sharing. Data are exchanged between peer ASCEs us
38、ing application sharing protocol data units (ASPDUs). 3.3 bitmap: A rectangular area described by a two-dimensional array of pixels. These pixels can be coded using a variety of encoding methods. 3.4 ColorTable: A finite set of colours defined by at least three linearly-independent colour primaries.
39、 This is a synonym for palette (see definition below), but is used in this Recommendation to reference the particular cached palette associated with cached bitmap data. 3.5 desktop: The logical or physical display area for a particular terminal or window manager advertised by the application sharing
40、 conference entity (ASCE) in the application sharing (AS) capabilities. An ASCE may choose to advertise a size corresponding to the actual terminal display area or some other logical display area. 3.6 handle: An application sharing (AS) session-wide unique number used to identify an addressable item
41、. 3.7 non-standard capability: The capability is outside the scope of this Recommendation but it has been determined through negotiation that it is recognized among all session participants. 3.8 palette: A finite set of colours defined by at least three linearly-independent colour primaries. 3.9 pal
42、ettized: A term used to describe protocol elements (such as bitmap data) comprised of palettized pixels. The colour of a palettized pixel is specified by the colour value at the location in a palette referenced by the pixel value. 3.10 pointer: A bitmap that is moveable over the virtual desktop that
43、 is used as an indicator of position. 3.11 standard capability: The capability is defined within the scope of this Recommendation but is not required for all application sharing conference entity (ASCE) implementations. Note that all standard capabilities must be negotiated before use. 3.12 unicode:
44、 Multilingual text string format as defined in ISO/IEC 10646. 3.13 virtual desktop: A logical desktop that is the largest size of all desktops of hosting application sharing conference entities (ASCEs). 3.14 window: A rectangular area on the desktop corresponding to a user interface display area man
45、aged by the terminal window manager. 3.15 window manager: A program executing on the terminal, which is responsible for managing a collection of user interface windows on the terminal desktop. 4 Rec. ITU-T T.128 (06/2008) 4 Abbreviations and acronyms This Recommendation uses the following abbreviati
46、ons and acronyms: APE Application Protocol Entity AS Application Sharing ASCE Application Sharing Conference Entity ASPDU Application Sharing Protocol Data Unit GCC Generic Conference Control ID Identifier MCS Multipoint Communication Service SAP Service Access Point 5 Overview The AS protocol enabl
47、es multipoint computer application sharing by allowing a view onto a computer application executing at one site to be advertised within a session to other sites. Each site can, under specified conditions, take control of the shared computer application by sending remote keyboard and pointing device
48、information. This style of application sharing does not require and does not make provision for synchronizing multiple instances of the same computer application running at multiple sites. Instead, it enables remote viewing and control of a single application instance to provide the illusion that th
49、e application is running locally. An AS session consists of one or more ASCEs which cooperate via the AS protocol to share one or more applications within the session. The AS protocol defines interactions between ASCEs. It does not define interactions between an ASCE and the operating system or input and output devices on the local terminal. 5.1 Legacy and base modes The AS protocol supports two modes of operation. Legacy mode is provided for interoperability with an existin
