1、 ETSI TR 126 916 V14.2.0 (2017-05) Universal Mobile Telecommunications System (UMTS); LTE; Media handling and Quality aspects of SRVCC (3GPP TR 26.916 version 14.2.0 Release 14) TECHNICAL REPORT ETSI ETSI TR 126 916 V14.2.0 (2017-05)13GPP TR 26.916 version 14.2.0 Release 14Reference DTR/TSGS-0426916
2、ve20 Keywords LTE,UMTS ETSI 650 Route des Lucioles F-06921 Sophia Antipolis Cedex - FRANCE Tel.: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16 Siret N 348 623 562 00017 - NAF 742 C Association but non lucratif enregistre la Sous-Prfecture de Grasse (06) N 7803/88 Important notice The present document can
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9、17-05)23GPP TR 26.916 version 14.2.0 Release 14Intellectual Property Rights IPRs essential or potentially essential to the present document may have been declared to ETSI. The information pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be f
10、ound in ETSI SR 000 314: “Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respect of ETSI standards“, which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web server (https:/ipr.etsi.org/). Pursuant to the ETSI IPR
11、Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become, essential to the present document. Foreword This
12、Technical Report (TR) has been produced by ETSI 3rd Generation Partnership Project (3GPP). The present document may refer to technical specifications or reports using their 3GPP identities, UMTS identities or GSM identities. These should be interpreted as being references to the corresponding ETSI d
13、eliverables. The cross reference between GSM, UMTS, 3GPP and ETSI identities can be found under http:/webapp.etsi.org/key/queryform.asp. Modal verbs terminology In the present document “should“, “should not“, “may“, “need not“, “will“, “will not“, “can“ and “cannot“ are to be interpreted as describe
14、d in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions). “must“ and “must not“ are NOT allowed in ETSI deliverables except when used in direct citation. ETSI ETSI TR 126 916 V14.2.0 (2017-05)33GPP TR 26.916 version 14.2.0 Release 14Contents Intellectual Property Ri
15、ghts 2g3Foreword . 2g3Modal verbs terminology 2g3Foreword . 6g3Introduction 6g31 Scope 7g32 References 8g33 Definitions, symbols and abbreviations . 8g33.1 Definitions 8g33.2 Symbols 9g33.3 Abbreviations . 10g34 eSRVCC Reference Architecture . 10g35 eSRVCC Reference Procedure . 12g35.1 General . 12g
16、35.2 Codec Selection during eSRVCC . 14g35.3 Voice Path Switching during eSRVCC 15g35.4 Possibilities to adjust codecs after eSRVCC without standards extensions . 16g35.4.1 IMS Selected Codec re-negotiation towards the remote end 16g35.4.2 Codec re-negotiation towards the SRVCC UE . 17g36 Selected e
17、xample scenarios for eSRVCC. 17g36.1 General . 17g36.2 eSRVCC AMR(.) to AMR(.) 18g36.3 eSRVCC AMR(.) to AMR-WB(.) 19g36.4 eSRVCC AMR(.) to UMTS_EVS(.) 19g36.5 eSRVCC AMR-WB(.) to AMR(.) 20g36.6 eSRVCC EVS (br=5.9-128; bw=nb-fb) to UMTS_EVS (Set1) . 20g36.7 eSRVCC EVS (br=16.4-128; bw=fb) to UMTS_EVS
18、 (Set1) 21g36.8 eSRVCC EVS (br=9.6-24.4; bw=swb) to UMTS_EVS (Set1) 23g36.9 eSRVCC EVS (.) to AMR-WB (.) . 23g36.10 eSRVCC EVS (.) to AMR (.) . 23g36.11 eSRVCC EVS (br=5.9-128; bw=nb-fb) to UMTS_EVS (Set 1) and subsequent Handover to AMR-WB(0,1,2) . 24g36.12 eSRVCC and Handover in speech pauses 24g3
19、7 Identified Problems with current eSRVCC 25g37.1 General . 25g37.2 IMS Selected Codec not known in Target RAN 25g37.2.0 General 25g37.2.1 Remote Access Network supports only lower quality codecs than Target RAN 25g37.2.2 Remote Access Network supports higher quality codecs than Target RAN . 26g37.2
20、.3 Assemble the remote IMS Preferred Codec List. 26g37.2.3.1 General 26g37.2.3.2 Call Setup Scenario 1: from remote to local . 26g37.2.3.3 Call Setup Scenario 2: from local to remote . 27g37.3 Late Information about the Target RAN Codec . 27g37.4 Access Transfer and Handover Command . 28g37.5 Target
21、 MGW is blocked in Uplink . 29g37.6 The remote UE does not follow CMR commands 29g38 Speech Quality and Media Handling Aspects 30g38.1 General . 30g38.2 Blind Selection of the Target RAN Codec . 30g38.3 Unnecessary speech break by missing Rate Control 30g3ETSI ETSI TR 126 916 V14.2.0 (2017-05)43GPP
22、TR 26.916 version 14.2.0 Release 148.4 Unsynchronized, early Handover switching by ATGW . 30g38.5 Synchronized hard Handover . 32g38.6 Ideal eSRVCC Handover . 32g39 Codec Mode Control before, during and after SRVCC . 34g39.1 General . 34g39.2 g68g381g282g286g3g18g381g374g410g396g381g367g3g272g381g37
23、3g373g258g374g282g400g3g349g374g3g410g346g286g3g104g400g286g396g3g87g367g258g374g286 36g39.3 Mode Control Rules for AMR and AMR-WB . 36g39.4 Mode Control Rules for EVS . 36g39.5 Call Setup and Initial Codec Mode. 37g39.6 Mode Control before eSRVCC 39g39.7 Mode Control during eSRVCC 39g39.8 Mode Cont
24、rol after eSRVCC . 41g310 SDP Offer-Answer between MSC and ATCF 41g310.1 General . 41g310.2 Message and Information from MSC to ATCF 42g310.3 Information in ATCF and ATGW and actions . 42g310.4 Message from ATCF to MSC, MGW actions 42g310.5 Message from MSC to MME and LTE UE 43g311 Codec Compatibili
25、ty. 43g311.1 Digital Mobile Communication 43g311.2 Transcoding 44g311.3 EVS configurations 44g311.3.1 General 44g311.3.2 The EVS Bottom-up Configurations 45g311.3.3 The EVS Punctured Configurations 46g311.3.3.1 General 46g311.3.3.2 EVS Configurations with single audio bandwidth 47g311.4 Transcoding
26、Less Operation . 48g311.4.1 General 48g311.4.2 GSM_EFR and AMR (mode-set=7) . 49g311.4.2.1 General 49g311.4.2.2 Additional Conditions for TLCI-Compatibility for GSM_EFR 49g311.4.3 AMR . 49g311.4.3.1 General 49g311.4.3.2 Additional Conditions for TLCI-Compatibility for AMR . 49g311.4.4 AMR-WB and EVS
27、-IO . 51g311.4.4.1 General 51g311.4.4.2 Additional Conditions for TLCI-Compatibility for AMR-WB and EVS-IO 52g311.4.5 EVS . 52g311.4.5.1 General 52g311.4.5.2 Additional Conditions for TLCI-Compatibility for EVS 52g311.5 Transcoding Less Operation at call setup . 53g311.6 Transcoding Less Operation a
28、fter Handover 53g312 Enhancements for media and quality aspects . 53g312.1 General . 53g312.2 Early Information exchange between MSC and ATCF 53g312.2.1 Proposed Requirement 53g312.2.2 Proposed Solution 1: CS/IMS Bi-directional Codec List Exchange . 54g312.2.2.1 Overview . 54g312.2.2.2 Information i
29、n Handover Preparation Response . 55g312.2.2.3 Information in Handover Preparation Request 55g312.2.3 Proposed Solution 2: MSS initiated codec inquiry . 56g312.2.3.1 Overview . 56g312.2.3.2 Procedures. 57g312.2.3.3 Impact on Existing Entities and Interfaces 58g312.3 Access Transfer and Handover Comm
30、and . 58g312.4 Unblock the Target MGW in Uplink 59g312.5 Clarify that it is indispensable to follow CMR commands . 59g312.6 Updated Message flow according to proposed solution 1 60g3ETSI ETSI TR 126 916 V14.2.0 (2017-05)53GPP TR 26.916 version 14.2.0 Release 1413 Proposals for Stage 2 and Stage 3 61
31、g3Annex A: Change history 62g3History 63g3ETSI ETSI TR 126 916 V14.2.0 (2017-05)63GPP TR 26.916 version 14.2.0 Release 14Foreword This Technical Report has been produced by the 3rdGeneration Partnership Project (3GPP). The contents of the present document are subject to continuing work within the TS
32、G and may change following formal TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an identifying change of release date and an increase in version number as follows: Version x.y.z where: x the first digit: 1 presented to TSG for inform
33、ation; 2 presented to TSG for approval; 3 or greater indicates TSG approved document under change control. y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, updates, etc. z the third digit is incremented when editorial only changes have been in
34、corporated in the document. Introduction Single Radio - Voice Call Continuity (SRVCC) is an existing standard (3, 4), specifying the handover of a Voice or Video call from LTE access to CS radio access, either to GERAN (2G) or to UTRAN (3G) or other CS networks. The present document considers only e
35、SRVCC for voice calls between 3GPP accesses. In the IMS Core Network, the voice call is typically anchored in the ATCF/ATGW (Access Transfer Control Function / Access Transfer Gate Way). The eSRVCC procedure, as specified, may cause additional transcoding between the target radio leg and the ATGW, e
36、ven though in theory it would be possible to avoid it. As a result, the eSRVCC procedures may add one or more unnecessary transcoding point(s) for the call and thereby degrade the quality of the ongoing call unnecessarily. Transcoding-Less Codec Interworking (TLCI) is always desirable to achieve goo
37、d voice quality. Furthermore TLCI preserves network resources, i.e. by avoiding transcoding. TLCI is especially important for HD Voice. The Mobility Management Entity (MME) of the LTE-RAN, which sends the PS-to-CS Handover Request to the Target Network, does not know the IMS Selected Codec, which is
38、 in use before the eSRVCC in the ongoing call towards the remote end. Thus the MME cannot support the Target Network for selecting the optimal Target RAN Codec. The Target Network thus selects this Target RAN Codec on own criteria; often the Target RAN Codec is then not compatible to the IMS Selecte
39、d Codec. Transcoding is then the immediate reaction. While it is possible for the ATCF, based on the current procedure, to renegotiate the IMS Selected Codec with the remote end to fit any selected Target RAN Codec at call transfer, this may extend the perceived time it will take to conclude the cal
40、l transfer and this might extend the speech interruption time that might result due to the time the additional negotiation with the remote end will take. The ATCF was introduced for exactly that reason: avoid renegotiation with the remote end - accelerate eSRVCC. But even worse: in a substantial num
41、ber of call scenarios the remote end may not be able to support the arbitrarily chosen Target RAN Codec and the transcoding cannot even be avoided by that renegotiation. The first attempt will optimize the Target RAN Codec to fit the IMS Selected Codec. If that is impossible or not optimal, then the
42、 renegotiation with the remote end might be attempted. The last resort has to be transcoding; sometimes it is unavoidable. ETSI ETSI TR 126 916 V14.2.0 (2017-05)73GPP TR 26.916 version 14.2.0 Release 141 Scope Enhanced Single Radio - Voice Call Continuity (eSRVCC) is an existing standard (3, 4) spec
43、ifying the handover of a Voice or Video call from LTE access to CS-radio access, either to GERAN (2G) or to UTRAN (3G) or other CS networks. The present document considers only enhanced SRVCC for voice calls between 3GPP accesses. This study assumes that the Codecs defined in TS 26.114 are used on t
44、he LTE access and the Codecs defined in 3GPP TS 26.103 7 on the CS accesses. Since Rel-13, the specifications for CS networks include the Codec Type UMTS_EVS with several Configurations, called UMTS_EVS (Set 0) to UMTS_EVS (Set 3). In the IMS Core Network, the voice call is typically anchored in the
45、 ATCF/ATGW (Access Transfer Control Function/ Access Transfer Gate Way). The eSRVCC procedure, as specified, may cause additional transcoding between the target radio leg and the ATGW, even though in theory it would be possible to avoid it. As a result, the eSRVCC procedures may add one or more unne
46、cessary transcoding point(s) for the call and thereby degrade the quality of the ongoing call unnecessarily. The main objectives of this study are to analyse example call scenarios and find potential solutions to minimize the number of transcoding cases. Another objective is to optimize the interwor
47、king and the transition between EVS and AMR-WB during eSRVCC. The study should also show the reasons and potential solutions for too long speech path interruptions during eSRVCC. The present Technical Report has the following detailed objectives: - Identify relevant eSRVCC scenarios, especially with
48、 Codec Mode Control; from AMR-WB and/or EVS in VoLTE to AMR-WB and/or EVS in CS; but include also other important Codecs, such as AMR and G.722. - Analyse Speech Quality Aspects and Media Handling Aspects, based on these scenarios. - Analyse Codec Mode Control before, during and after eSRVCC; recent
49、ly SA4 has clarified some essential details on Rate Control for AMR and AMR-WB; Rate Control and Audio Bandwidth Control for EVS are still under discussion to some extent. - Analyse the existing SDP Offer - Answer protocol between Target MSC and Anchor-ATCF during eSRVCC, as specified in 3GPP TS 23.216 3, Stage 2; This analysis will include the whole eSRVCC procedure for at least one essential scenario (e.g. eSRVCC to GERAN) and will identify the potential reasons for transcoding and too long speech path interruptions. - Clarify the existing Codec Compatibility as
