1、 I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n ITU-T Y.2255 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (01/2018) SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS, NEXT-GENERATION NETWORKS, INTERNET OF THINGS AND SMART CITIES Next Generation Networks
2、 Service aspects: Interoperability of services and networks in NGN Voice and video call continuity over LTE, Wi-Fi and 2G/3G Recommendation ITU-T Y.2255 ITU-T Y-SERIES RECOMMENDATIONS GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS, NEXT-GENERATION NETWORKS, INTERNET OF THINGS AND SMART
3、 CITIES GLOBAL INFORMATION INFRASTRUCTURE General Y.100Y.199 Services, applications and middleware Y.200Y.299 Network aspects Y.300Y.399 Interfaces and protocols Y.400Y.499 Numbering, addressing and naming Y.500Y.599 Operation, administration and maintenance Y.600Y.699 Security Y.700Y.799 Performanc
4、es Y.800Y.899 INTERNET PROTOCOL ASPECTS General Y.1000Y.1099 Services and applications Y.1100Y.1199 Architecture, access, network capabilities and resource management Y.1200Y.1299 Transport Y.1300Y.1399 Interworking Y.1400Y.1499 Quality of service and network performance Y.1500Y.1599 Signalling Y.16
5、00Y.1699 Operation, administration and maintenance Y.1700Y.1799 Charging Y.1800Y.1899 IPTV over NGN Y.1900Y.1999 NEXT GENERATION NETWORKS Frameworks and functional architecture models Y.2000Y.2099 Quality of Service and performance Y.2100Y.2199 Service aspects: Service capabilities and service archi
6、tecture Y.2200Y.2249 Service aspects: Interoperability of services and networks in NGN Y.2250Y.2299 Enhancements to NGN Y.2300Y.2399 Network management Y.2400Y.2499 Network control architectures and protocols Y.2500Y.2599 Packet-based Networks Y.2600Y.2699 Security Y.2700Y.2799 Generalized mobility
7、Y.2800Y.2899 Carrier grade open environment Y.2900Y.2999 FUTURE NETWORKS Y.3000Y.3499 CLOUD COMPUTING Y.3500Y.3999 INTERNET OF THINGS AND SMART CITIES AND COMMUNITIES General Y.4000Y.4049 Definitions and terminologies Y.4050Y.4099 Requirements and use cases Y.4100Y.4249 Infrastructure, connectivity
8、and networks Y.4250Y.4399 Frameworks, architectures and protocols Y.4400Y.4549 Services, applications, computation and data processing Y.4550Y.4699 Management, control and performance Y.4700Y.4799 Identification and security Y.4800Y.4899 Evaluation and assessment Y.4900Y.4999 For further details, pl
9、ease refer to the list of ITU-T Recommendations. Rec. ITU-T Y.2255 (01/2018) i Recommendation ITU-T Y.2255 Voice and video call continuity over LTE, Wi-Fi and 2G/3G Summary Recommendation ITU-T Y.2255 specifies the voice and video call continuity (VCC) over long term evolution (LTE), Wi-Fi and 2G/3G
10、. The scenarios and relevant requirements are specified, as well as the solutions for access transfer between each of the access types, handover policy, terminating access domain selection (T-ADS), evolved packet data gateway (ePDG) selection and other call continuity related solutions. History Edit
11、ion Recommendation Approval Study Group Unique ID* 1.0 ITU-T Y.2255 2018-01-13 13 11.1002/1000/13462 Keywords Multi-connection, voice and video call continuity. * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendation
12、s unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T Y.2255 (01/2018) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Teleco
13、mmunication 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 telecommunications on a worldwide basis. The World Telecommunication Standardization As
14、sembly (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 procedure laid down in WTSA Resolution 1. In some areas of information technology w
15、hich 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 telecommunication administration and a recognized operating agency. Compliance with
16、 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 these mandatory provisions are met. The words “shall“ or some other obligatory l
17、anguage 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 RIGHTSITU draws attention to the possibility that the practice or implementation of thi
18、s 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 members or others outside of the Recommendation development process. As of the date
19、 of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult
20、the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2018 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 Y.2255 (01/2018) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definition
21、s 1 3.1 Terms defined elsewhere 1 3.2 Terms defined in this Recommendation . 1 4 Abbreviations and acronyms 2 5 Conventions 3 6 Scenarios and requirements 3 6.1 Scenarios . 3 6.2 Requirements 4 7 Solutions . 5 7.1 Overview 5 7.2 Description of solutions 6 8 Security considerations . 15 Bibliography.
22、 16 Rec. ITU-T Y.2255 (01/2018) 1 Recommendation ITU-T Y.2255 Voice and video call continuity over LTE, Wi-Fi and 2G/3G 1 Scope This Recommendation specifies the requirements and solutions for voice and video call continuity (VCC). These requirements and solutions are applied for the scenarios where
23、 the multi-connection user equipment (MUE) is attached to the network with multi-connection via long term evolution LTE, Wi-Fi and 2G/3G accesses. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of
24、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 the possibility of applying the most recent edition of the Recommendations and ot
25、her 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 a Recommendation. ITU-T Y.2027 Recommendation ITU-T Y.2027 (2012), Functional arc
26、hitecture of multi-connection. ITU-T Y.2251 Recommendation ITU-T Y.2251 (2011), Multi-connection requirements. 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the following terms defined elsewhere: 3.1.1 connection b-ITU-T X.200: A connection is an association established for the
27、transfer of data between two or more peer-(N)-entities. This association binds the peer-(N)-entities together with the (N1)-entities in the next lower layer. 3.1.2 multi-connection ITU-T Y.2251: The functionality which provides capability to the user equipment (UE) and network to maintain more than
28、one access network connection simultaneously. NOTE 1 All connections are coordinated to provide service to higher layer entities. NOTE 2 In a multi-connection communications at least one UE is required to be a multi-connection UE. 3.1.3 multi-connection user equipment (MUE) ITU-T Y.2027: A user equi
29、pment which can support two or more network connections simultaneously under the control of a network enhanced for multi-connection capability. 3.2 Terms defined in this Recommendation This Recommendation defines the following term: 3.2.1 voice and video call continuity (VCC): When the MUE moves bet
30、ween different access types, the ongoing voice and video call is not impacted and continues to serve the user. The user is not aware of the access transfer. 2 Rec. ITU-T Y.2255 (01/2018) 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: AAA Authenticatio
31、n, Authorization and Accounting APN Access Point Name CS Circuit Switched Domain CSCF Call Session Control Function EDGE Enhanced Data for GSM Evolution EPC Evolved Packet Core ePDG Evolved Packet Data Gateway E-UTRAN Evolved Universal Terrestrial Radio Access Network FQDN Fully Qualified Domain Nam
32、e GERAN GSM EDGE Radio Access Network GSM Global System for Mobile communication HLR Home Location Register HPLMN Home Public Land Mobile Network HSPA High Speed Packet Access HSS Home Subscriber Server I-CSCF Interrogating Call Session Control Function IMS IP Multimedia Subsystem IUT-AS Inter UE Tr
33、ansfer Application Server LTE Long Term Evolution MME Mobility Management Entity MSC Mobile Switching Centre MUE Multi-connection User Equipment PCRF Policy and Charging Rules Function P-CSCF Proxy Call Session Control Function PDN Packet Data Network PLMN Public Land Mobile Network PGW Packet data
34、network Gateway PS Packet Switch RAT Radio Access Technologies S-CSCF Serving Call Session Control Function SDP Session Description Protocol SRVCC Single Radio Voice Call Continuity SSID Service Set Identifier T-ADS Terminating Access Domain Selection URI Uniform Resource Identifier Rec. ITU-T Y.225
35、5 (01/2018) 3 UTRAN Universal Terrestrial Radio Access Network VCC Voice and video Call Continuity VoLTE Voice over Long Term Evolution VPLMN Visited Public Land Mobile Network Wi-Fi Wireless Fidelity 5 Conventions In this Recommendation: The keywords “is required to“ indicate a requirement which mu
36、st be strictly followed and from which no deviation is permitted if conformance to this Recommendation is to be claimed. 6 Scenarios and requirements 6.1 Scenarios In a multi-connection environment (LTE, Wi-Fi, 2G/3G, etc.), the voice or video call session can move among multiple connections accordi
37、ng to the wireless environment and policy seamlessly. Voice or video call continuity over LTE, Wi-Fi and 2G/3G can enhance user experience of voice and video calling, especially in the switching scenarios. The switching scenarios are described as follows: Scenario I (LTE Wi-Fi) Multi-connection user
38、 equipment (MUE) establishes a voice or video call session over LTE. While the session is going on, MUE moves to an environment with weak LTE coverage but strong Wi-Fi coverage. In this scenario, the voice or video call session can handover from the LTE connection to a Wi-Fi connection seamlessly to
39、 keep call continuity. Scenario II (Wi-Fi LTE) MUE establishes a voice or video call session over Wi-Fi. While the session is going on, MUE moves to an environment with weak Wi-Fi coverage but strong LTE coverage. In this scenario, the voice or video call session can handover from the Wi-Fi connecti
40、on to an LTE connection seamlessly to keep call continuity. Scenario III (LTE 2G/3G) MUE establishes a voice or video call session over LTE. While the session is going on, MUE moves to an environment with weak LTE coverage but strong 2G/3G coverage. In this scenario, the voice or video call session
41、can handover from the LTE connection to a 2G/3G connection seamlessly to keep call continuity. Scenario IV (2G/3G LTE) MUE establishes a voice or video call session over 2G/3G. While the session is going on, MUE moves to an environment with weak 2G/3G coverage but strong LTE coverage. In this scenar
42、io, the voice or video call session can handover from the 2G/3G connection to an LTE connection seamlessly to keep call continuity. Scenario V (LTE Wi-Fi, 2G/3G) MUE establishes a voice or video call session over LTE. While the session is going on, MUE moves to an environment with weak LTE coverage
43、but strong Wi-Fi and 2G/3G coverage. In this 4 Rec. ITU-T Y.2255 (01/2018) scenario, the voice or video call session can handover from the LTE connection to a Wi-Fi or 2G/3G connection according to the policy seamlessly to keep call continuity. Scenario VI (inter MUE transfer) The subscriber signed
44、for multi-device service. MUE establishes a voice or video call session over Wi-Fi/LTE. While the session is going on, the subscriber can transfer the call session to other Wi-Fi/LTE devices such as a PAD or watch to keep call continuity. 6.2 Requirements The requirements of voice and video call con
45、tinuity over LTE, Wi-Fi and 2G/3G are based on the requirements described in ITU-T Y.2251, in addition to those described in clauses 6.2.1, 6.2.2 and 6.2.3. 6.2.1 Voice and video call continuity When the MUE moves out of the coverage of an access type under which the ongoing session was initiated an
46、d into the coverage of another access type (see scenarios described in clause 6.1), the ongoing session must be maintained. 6.2.2 Handover policy The handover between different access types can be triggered by the following means: The network instructs the MUE to perform handover; The MUE automatica
47、lly decides to perform handover; The user instructs the MUE to perform handover. When a handover conflict happens, i.e., when more than one target accesses are available, the MUE shall select only one of the target accesses to perform handover in accordance with the handover policy. It shall be poss
48、ible for the network to control the handover policy. The handover policy can take into account factors such as: Whether the coverage strength exceeds a specific threshold; The type of ongoing session, e.g., voice call, video call; Whether the MUE is in a roaming case. 6.2.3 Terminating access domain
49、 selection The network which serves an MUE must support terminating access domain selection (T-ADS) functionality. T-ADS directs an incoming call to an MUE via circuit switched (CS) domain or via IP multimedia subsystem (IMS). T-ADS must be able to take into account the following factors: The radio access type the MUE is currently using, i.e., 2G/3G, LTE or Wi-Fi; The network capability, e.g., whether voice service over the current radio access type is supported by the network; The MU
