1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T H.460.11TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (03/2004) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Supplementary services for multimedia Delayed call establishment within H.323 systems ITU-T Recommendation
2、 H.460.11 ITU-T H-SERIES RECOMMENDATIONS AUDIOVISUAL AND MULTIMEDIA SYSTEMS CHARACTERISTICS OF VISUAL TELEPHONE SYSTEMS H.100H.199 INFRASTRUCTURE OF AUDIOVISUAL SERVICES General H.200H.219 Transmission multiplexing and synchronization H.220H.229 Systems aspects H.230H.239 Communication procedures H.
3、240H.259 Coding of moving video H.260H.279 Related systems aspects H.280H.299 Systems and terminal equipment for audiovisual services H.300H.349 Directory services architecture for audiovisual and multimedia services H.350H.359 Quality of service architecture for audiovisual and multimedia services
4、H.360H.369 Supplementary services for multimedia H.450H.499 MOBILITY AND COLLABORATION PROCEDURES Overview of Mobility and Collaboration, definitions, protocols and procedures H.500H.509 Mobility for H-Series multimedia systems and services H.510H.519 Mobile multimedia collaboration applications and
5、 services H.520H.529 Security for mobile multimedia systems and services H.530H.539 Security for mobile multimedia collaboration applications and services H.540H.549 Mobility interworking procedures H.550H.559 Mobile multimedia collaboration inter-working procedures H.560H.569 BROADBAND AND TRIPLE-P
6、LAY MULTIMEDIA SERVICES Broadband multimedia services over VDSL H.610H.619 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. H.460.11 (03/2004) i ITU-T Recommendation H.460.11 Delayed call establishment within H.323 systems Summary This Recommendation defines procedu
7、res to provide for delayed call establishment (delayed ringing) functionality within the context of ITU-T Rec. H.323. Delayed call establishment may be used to place a call, query capabilities, perform testing, or perform other functions without alerting the called user. Additionally, it may be used
8、 to place a call and guarantee that some condition is satisfied, such as the establishment of bidirectional media, before alterting the called party. Source ITU-T Recommendation H.460.11 was approved on 15 March 2004 by ITU-T Study Group 16 (2001-2004) under the ITU-T Recommendation A.8 procedure. i
9、i ITU-T Rec. H.460.11 (03/2004) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, ope
10、rating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications 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,
11、produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure 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
12、 this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g.
13、interoperability or applicability) and compliance with the Recommendation is achieved when all of these 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 sugge
14、st that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU 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 evide
15、nce, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which ma
16、y be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2004 All rights reserved. No part of this publication may be reproduced, by any means whatso
17、ever, without the prior written permission of ITU. ITU-T Rec. H.460.11 (03/2004) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Terms and definitions . 1 4 Abbreviations 1 5 Feature description 2 6 Capability advertisement 2 7 Requesting delayed call establishment . 3 8 Responding to a Delayed Call E
18、stablishment Request. 4 9 Delayed Call Establishment Release 5 Appendix I Sample call flows. 7 ITU-T Rec. H.460.11 (03/2004) 1 ITU-T Recommendation H.460.11 Delayed call establishment within H.323 systems 1 Scope This Recommendation defines the capability and procedures for delayed call establishmen
19、t (DCE). Delaying the establishment of a call allows an H.323 entity to perform maintenance loops, provide network-based services (e.g., call completion on busy without the use of ITU-T Rec. H.450.9), or other functions without alerting the called user until so desired or when appropriate. 2 Referen
20、ces The following ITU-T Recommendations and other references contain 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
21、of this Recommendation are therefore encouraged to investigate 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 Recommendat
22、ion does not give it, as a stand-alone document, the status of a Recommendation. 1 ITU-T Recommendation H.323 (2003), Packet-based multimedia communications systems. 2 ITU-T Recommendation H.225.0 (2003), Call signalling protocols and media stream packetization for packet-based multimedia communicat
23、ion systems. 3 ITU-T Recommendation H.460.1 (2002), Guidelines for the use of the generic extensible framework. 4 ITU-T Recommendation H.245 (2003), Control protocol for multimedia communication. 3 Terms and definitions This Recommendation defines the following terms: 3.1 delayed call establishment
24、(DCE): Allows a call to be initiated, but not progressed to the point where the user is alerted or the call is connected. 3.2 delay point (DP): The point in the call establishment procedures that must be reached before the call may proceed to the Alerting or Connected state. 3.3 delay point indicato
25、r (DPI): A specific point of interest to the calling entity in the call establishment process. 3.4 DP reached (DPR): The message transmitted by the called endpoint to the calling entity to indicate that the DP has been reached. 3.5 DCE release: The message transmitted by the calling entity to the ca
26、lled endpoint releasing the endpoint from the DCE procedures and allowing the call to proceed as normal. 4 Abbreviations This Recommendation uses the following abbreviations: DCE Delayed Call Establishment DP Delay Point DPI Delay Point Indicator 2 ITU-T Rec. H.460.11 (03/2004) DPR Delay Point Reach
27、ed RAS Registration, Admission and Status 5 Feature description This Recommendation defines a procedure wherein a calling entity may request that an initiated call be progressed to a specified point, but then progress delayed, without alerting the user to the presence of the call or connecting the c
28、all. This allows, for example, for media channels to be established or for other conditions to be met before the user is alerted to the presence of the call. In some cases, it is expected that the call may actually never progress to the point of alerting the user or fully connecting, such as when th
29、e called device is being probed for supported capabilities or when the called device is called for the purpose of establishing media channels to be used for testing purposes (e.g., maintenance loop functions of H.245). Network-based devices that offer services such as Call Completion on No Answer an
30、d Call Completion on Busy may also use this feature. While supplementary services specified in the H.450-series Recommendations may be used for the aforementioned services, these services and other services may be implemented using this generic construct. When a called endpoint receives a Setup mess
31、age from a calling entity and when that called endpoint supports the DCE feature, the called endpoint shall not alert the user to the fact that the call has been received and shall not transmit an Alerting message or Connect message. Instead, the called endpoint shall first notify the calling endpoi
32、nt when the Delay Point has been reached and proceed with call establishment only if either Implicit DCE Release parameter is signalled in the initial setup or after an explicit DCE Release message is received. This delay may make it necessary for the calling endpoint to cancel or prolong H.225.0 ca
33、ll control timers (e.g., T310). The DCE procedures do not preclude the endpoint from carrying out any initial call signalling up to, but not including, alerting the user or connecting the call. That is, terminal capabilities may be exchanged, media channels may be opened, media packets may be sent a
34、nd received, etc., without violating any part of this Recommendation. Special consideration must be given to Gateway devices that perform signalling interworking between H.323 and other networks. Other networks may or may not have the ability to delay call establishment in accordance with this Recom
35、mendation. If the other network served by the Gateway supports comparable functionality, the Gateway may advertise support for this capability. Otherwise, the Gateway may elect to not advertise support or may elect to withhold presenting the call to the other network until the Delay Point is reached
36、. Such design choices are considered an implementation matter and are outside the scope of this Recommendation. Consideration must also be given to possible security concerns, e.g., to guard against denial-of-service attacks by tying up resources at the called endpoint. Further restrictions may resu
37、lt from the environment in which this service is employed, for instance charging requirements may restrict the usage of media channels before the call is in active state. 6 Capability advertisement Endpoints capable of supporting DCE shall advertise this capability via the Generic Extensibility Fram
38、ework defined in ITU-T Recs H.323 and H.460.1. Endpoints may advertise this capability through RAS or through H.225.0 Call Signalling messages as a supported, desired, or needed feature. Calling entities shall advertise this capability as a needed or desired feature in Call Signalling messages when
39、needing or desiring DCE feature activation at the called party, respectively. Called endpoints that are capable of supporting DCE shall advertise this capability in the list of supported features when responding to the incoming call. The identifier for the delayed call establishment capability is sh
40、own in Table 1. ITU-T Rec. H.460.11 (03/2004) 3 Table 1/H.460.11 Indication of the delayed call establishment feature Feature name: Delayed call establishment Feature description: This feature allows an originating endpoint to request a terminating endpoint to delay establishment of a call based on
41、some specified event Feature identifier type: Standard Feature identifier value: 11 Parameters associated with the advertisement of this capability are specified in the following clauses. In consideration of backward compatibility with further revisions to this Recommendation, the recipient shall si
42、mply ignore any parameters received other than those specified in this Recommendation. 7 Requesting delayed call establishment An endpoint may initiate a call and request delayed call establishment by including the capability shown in clause 5 in the outgoing Setup message. Along with the capability
43、, the calling entity shall include a parameter or list of parameters called Delay Point Indicators (DPIs), which indicates points of interest to the calling entity in the call establishment process. The DPI parameter definition is shown in Table 2. Table 2/H.460.11 Delay Point Indicator (DPI) parame
44、ter Parameter name: Delay Point Indicator (DPI) Parameter description: Indicates the point of interest to which the call must progress before being delayed Parameter identifier type: Standard Parameter identifier value: 1 Parameter type: number8 Parameter cardinality: One or more in the initial DCE
45、request, zero or more in the DPR message, and zero in the DCE Release message The possible values of the Delay Point Indicator (DPI) are shown in Table 3: Table 3/H.460.11 Delay Point Indicator (DPI) values Value Meaning 0 NULL 1 Terminal Capabilities are received by the called endpoint. 2 Master/Sl
46、ave determination has completed. 3 Media channels are opened from the called endpoint. 4 Media channels are opened to the called endpoint. 5 Media channels are established bidirectionally. NOTE Additional delay point values may be added in future versions of this Recommendation and are hereby reserv
47、ed. The DPI parameters are independent and suggest no ordering of events. For example, it is possible that the calling and called endpoints may utilize Fast Connect to establish bidirectional media before Master/Slave Determination completes. As such, the calling entity shall not assume that, simply
48、 because media is established bidirectionally that Master/Slave procedures have completed. 4 ITU-T Rec. H.460.11 (03/2004) The calling endpoint shall not include the same DPI more than once and the called device shall ignore any duplicate DPIs received. The “Delay Point“ (DP) in the call establishme
49、nt procedure is the point at which all of the DPI events have been satisfied. For example, if the calling entity provides a DPI 2 and DPI 5, the called endpoint shall perform both Master/Slave negotiation and opening bidirectional media flows before notifying the calling party that it has successfully reached the DP. The “NULL“ DPI (Indicator 0) is used to simply indicate that there are no specific conditions that must be satisfied before reaching the DP, meaning that the DP is reached immediately following the reception of the initial Setup message. T
