23856-A00 - Single Radio Voice Call Continuity (SRVCC) Enhancements; Stage 2

8/17/2019 23856-A00 - Single Radio Voice Call Continuity (SRVCC) Enhancements; Stage 2

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3GPP TR 23.856 V10.0.0 (2010-09)Technical Report

3rd Generation Partnership Project;Technical Specification Group Services and System Aspects;

Single Radio Voice Call Continuity SRVCC! enhancements;Stage "

Release #$!

The present document has been developed within the 3rd Generation Partnership Project (3GPP TM) and may be further elaborated for the purposes of 3GPP.

The present document has not been subject to any approval process by the 3GPP Orani!ational Partners and shall not be implemented.

This "pecification is provided for future development wor# within 3GPP only. The Orani!ational Partners accept no liability for any use of this

"pecification."pecifications and reports for implementation of the 3GPP TM system should be obtained via the 3GPP Orani!ational Partners$ Publications Offices.


2/823GPP

%eywordsIMS, SRVCC, Handover er!or"an#e

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Con%en%&

7oreword..........................................................................................................................................................

, "cope......................................................................................................................................................

* /eferences..............................................................................................................................................

3 8efinitions and abbreviations.................................................................................................................3., 8efinitions...........................................................................................................................................................3.* bbreviations.......................................................................................................................................................

9 /e:uirements..........................................................................................................................................9., General.................................................................................................................................................................9.* rchitectural /e:uirements.................................................................................................................................9.3 "/;11 Performance /e:uirements....................................................................................................................

< Performance nalysis of /el=> "/;11 solution....................................................................................

.,., rchitecture /eference Model..............................................................................................................

A.>.,.* 7unctional 2ntities..................................................................................................................................

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A.>.,.3 Messae flows........................................................................................................................................A.>.,.3., 1all oriination.................................................................................................................................A.>.,.3.* 1all termination................................................................................................................................A.>.,.3.3 "/;11 procedure............................................................................................................................

A.>.* "ub=alternative B*E "elective media anchorin controlled by a node other than the "11 "....................A.>.*., rchitecture /eference Model...............................................................................................................

A.>.*.* 7unctional 2ntities..................................................................................................................................A.>.*.3 Messae flows........................................................................................................................................A.>.*.3., 1all oriination.................................................................................................................................A.>.*.3.* 1all termination................................................................................................................................

A.>.*.3.3 "/;11 procedure............................................................................................................................A.F lternative F C "/=;11 2nhancement usin media detection.........................................................................A.F., &ntroduction..................................................................................................................................................A.F.* 1all flows.....................................................................................................................................................A.,+ lternatives ,+ = e"/;11 with P8' bi=castin...............................................................................................A.,+., rchitecture /eference Model.....................................................................................................................

A.,+.* 7unctional /e:uirements.............................................................................................................................A.,+.*a &M" voice codec retrieval from P11 flow...................................................................................................A.,+.3 Media plane handlin...................................................................................................................................

A.,+.9 "inallin Messae 7lows...........................................................................................................................A.,, lternative ,, = Media anchorin in the &M"=5G..........................................................................................

A.,,.+ General.........................................................................................................................................................A.,,., rchitecture /eference Model.....................................................................................................................A.,,.* 7unctional 2ntities.......................................................................................................................................A.,,.3 Messae 7lows.............................................................................................................................................A.,,.3., &M" /eistration....................................................................................................................................A.,,.3.* Oriinatin sessions in P"......................................................................................................................

A.,,.3.3 Terminatin sessions in P".....................................................................................................................A.,,.3.9 P" C 1" ccess Transfer........................................................................................................................A.,* lternative ,* = @O enhancement by local anchorin with &ndirect 7orwardin (Mered alternative of

alternatives A and D)...........................................................................................................................................A.,*., rchitecture /eference Model.....................................................................................................................

A.,*.* 7unctional 2ntities.......................................................................................................................................A.,*.*., M"1 "erver?MG enhanced for 2=T/'?T/' (@"P) and 3GPP T/'?G2/'

"/;11...................................................................................................................................................A.,*.*.* P11........................................................................................................................................................A.,*.*.3 MM2......................................................................................................................................................A.,*.*.9 "=G......................................................................................................................................................A.,*.3 Messae 7lows.............................................................................................................................................

A.,*.3., "/;11 @andover with P" @O support.................................................................................................A.,*.3.* "/;11 @andover without P" @O support............................................................................................A.,*.3.3 "/'" /elocation....................................................................................................................................A.,*.3.9 "8P related information pre=fetchin....................................................................................................A.,*.3.< "8P related information update.............................................................................................................A.,3 1onsolidated lternative C "&P based solution for e"/;11.............................................................................

A.,3., rchitecture /eference Model.....................................................................................................................A.,3.* 7unctional 2ntities.......................................................................................................................................A.,3.*., T17......................................................................................................................................................A.,3.*.,., General..............................................................................................................................................A.,3.*.,.* T17 anchorin...............................................................................................................................A.,3.*.* TG....................................................................................................................................................

A.,3.*.3 "11 "..................................................................................................................................................A.,3.*.9 @"".........................................................................................................................................................A.,3.3 Messae 7lows.............................................................................................................................................A.,3.3., "election of the T17............................................................................................................................A.,3.3.* Oriinatin sessions in P"......................................................................................................................A.,3.3.3 Terminatin sessions in P".....................................................................................................................

A.,3.3.9 P"=1" ccess Transfer...........................................................................................................................

A.,3.3.9., P"=1" ccess Transfer C TG anchored durin session setup and supportin M"1 "erverassisted mid=call feature...................................................................................................................

A.,3.3.9.* P"=1" ccess Transfer C TG anchored durin session setup and M"1 "erver assistedmid=call feature supported by "11 ".............................................................................................

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A.,3.3.9.3 P"=1" ccess Transfer C T17 not included durin reistration....................................................A.,3.3.9.9 P"=1" ccess Transfer C TG not anchored durin session setup...............................................A.,3.3.< 7ailure to complete P"=1" ccess Transfer...........................................................................................

D ssessment...........................................................................................................................................D., ssessment 1riteria...........................................................................................................................................D.* ssessment of alternatives.................................................................................................................................

> 1onclusion............................................................................................................................................

Annex A: Reducing the call drop probability.....................................................................................

., Pre=handover optimi!ation.....................................................................................................................,., rchitecture /eference Model............................................................................................................................,.* 7unctional 2ntities..............................................................................................................................................,.*., M"1 "erver..................................................................................................................................................

.,.*.* MM2.............................................................................................................................................................,.*.3 2=T/'.....................................................................................................................................................,.*.9 2.................................................................................................................................................................,.3 Messae 7lows..................................................................................................................................................

Annex B: Impacts on nodes of eSRVCC alternatives........................................................................

Annex C: xamples of A!C"#A!$% collocation & SI' based solution for eSRVCC......................

1., General.................................................................................................................................................

1.* &M" 5G?&M" G............................................................................................................................

1.3 &017?TrG..........................................................................................................................................

Annex (: Change history.....................................................................................................................

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oreord

This Technical "pecification has been produced by the 3rd Generation Partnership Project (3GPP).

The contents of the present document are subject to continuin wor# within the T"G and may chane followin formalT"G approval. "hould the T"G modify the contents of the present document- it will be re=released by the T"G with anidentifyin chane of release date and an increase in version number as followsE

;ersion .y.!

whereE

the first diitE

, presented to T"G for informationH

* presented to T"G for approvalH

3 or reater indicates T"G approved document under chane control.

y the second diit is incremented for all chanes of substance- i.e. technical enhancements- corrections-updates- etc.

! the third diit is incremented when editorial only chanes have been incorporated in the document.

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1 S#oe

"/=;11 has been standardi!ed in /elease > T" *3.*,A I3J to provide seamless continuity when 2 handovers from 2=T/' to T/'?G2/'.

This document contains the results of feasibility study of the re:uirements and the alternative solutions to improve thehandover performance of "/;11.

The objective of this study is as followsE

= 2valuatin the performance of current /el=> "/;11 solutionH

= 2nhancin the performance of the "/=;11 7low 0rea# with reard to the roamin and non=roamin caseH

= 2nhancin "/=;11 handover performance while minimi!in the impacts on the networ# architecture for the

directions

= from 2T/' to T/'?G2/'H and

= from T/' to T/'?G2/'.

2 Re!eren#e&

The followin documents contain provisions which- throuh reference in this tet- constitute provisions of the presentdocument.

• /eferences are either specific (identified by date of publication- edition number- version number- etc.) or

non=specific.

• 7or a specific reference- subse:uent revisions do not apply.

• 7or a non=specific reference- the latest version applies. &n the case of a reference to a 3GPP document (includin

a G"M document)- a non=specific reference implicitly refers to the latest version of that document in the same Release as the present document .

I,J 3GPP T/ *,.F+J 3GPP T" *3.**>E K&P Multimedia "ubsystem (&M")H "tae *K.

IFJ 3GPP T" 3A.9,3E K 2volved niversal Terrestrial /adio ccess (2=T/) H ", pplicationProtocol (",P)K.

I10J 3GPP T" *3.*D*E K1ircuit "witched 7allbac# in 2volved Pac#et "ystemH "tae *K.

I11J &2T7 /71 3*A9E Kn Offer?nswer Model with the "ession 8escription Protocol ("8P)K.

I,*J 3GPP T" *3.*+3E KPolicy and charin control architectureK.

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I,3J 3GPP T" *3.339E K&P Multimedia "ubsystem (&M") pplication 5evel Gateway (&M"=5G) = &M"ccess Gateway (&M"=G) interfaceE Procedures descriptionsK.

I,9J 3GPP T" *3.*+AE K;oice 1all 1ontinuity (;11) between 1ircuit "witched (1") and &PMultimedia "ubsystem (&M")H "tae *K.

3 e!n%on& and areva%on&

3.1 e!n%on&

7or the purposes of the present document- the terms and definitions iven in T/ *,.F+< I,J apply.

3.2 +reva%on&

7or the purposes of the present document- the abbreviations iven in T/ *,.F+< I,J apply.

Re$re"en%&

.1 Genera

= The impact to the eistin "/;11 architecture should be minimi!ed.

= 'O impact on 2.

= The impact to the 2P" should be minimi!ed.

= The impact to the eistin "/;11 procedure should be minimi!ed.

.2 +r#*%e#%$ra Re$re"en%&

2ditor$s 'oteEThis clause will contain the re:uirements for the enhanced "/;11 architecture.

= The solution shall #eep bac#ward compatibility to the 2 of previous releases.

= The solution shall support 5ocal 0rea#out scenarios accordin to T" *3.**> I>J- with the possibility of havinthe P=1"17 either in the visited networ# or in the home networ#.

= The "/;11 enhancement solution shall not neatively affect the "/;11 emerency call procedures.

.3 SRVCC Per!or"an#e Re$re"en%&

2ditor$s 'oteEThis clause will contain the re:uirements for the enhanced "/;11 handover performance.

= The interruption time of "/;11 is not hiher than 3++ms as re:uired in T" **.*D> I*J- from 2T/' to

T/'.

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5 Per!or"an#e +na:&& o! Re-8 SRVCC &o$%on

5.1 +na:&& o! SRVCC *andover er!or"an#e !ro" /;TR+ %o

;TR+G/R+&n T" **.*D> I*J- the re:uirement for voice interruption time of a /T chane is defined- which should also apply to"/;11E

) !he RA! change procedure executed to enable service continuity for an established voice call shall target

an interruption time not higher than *++ ms.

ccordin to T" *3.*,A I3J- the &M" "ession Transfer procedure is eecuted in parallel with the @andover from 2=T/' to T/'?G2/'. "uch as in clause A.*.*.,- it is described asE

'OT2 3E "teps ,, ("ession Transfer and pdate remote end procedure) and ,* ("ource &M" access le release) areindependent of step ,3(@andover from 2=T/' to G2/' procedure).

The procedure after /elocation Preparation procedure is shown in 7iure


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"o the interruption time is mainly determined by the maimum between the duration of the &M" "1 procedure(Ta,NNTa9) and the duration of the 2 handover procedure (Tb3).

'OT2E 7or the other cases not mentioned above (e.. the 2 and the remote and the networ# entities are in thesame P5M')- the duration of (Tb,NTb*) may not be much shorter than duration of (Ta,NTa*NTa3NTa9).&n this case- the voice interruption caused by the "/;11 procedures is not so lon as that in the roamin

case ("ession Transfer part).Tb3 is specified less than 3++ ms accordin to T" 3A.,33 I


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6 +%erna%ve&

6.1 +%erna%ve 1 - en*an#e"en% $&n7 dea: red#%on

6.1.1 S$-a%erna%ve


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-igure (%#%3%#. SRVCC enhancement alternative using synchroni4ation from )/TRA0 to GRA05ithout 6T72PS18 support

The "/;11 enhancement alternative usin synchroni!ation has a similar messae flow as the oriinal "/;11 eceptfor some steps.

The messae flow is described as followsE

Step , to step -: These steps are the same as step , to step F in fiure A.*.*.,=, of T" *3.*,A I3J.

Step ,+: M"1 "erver sends &';&T2 messae with the "T'="/ towards &M"?"11 " without the "8Pinformation of MG. &n addition- M"1 "erver stores the time (mar#ed as T9) when it sends the &';&T2re:uest.

Step ,+a: "11 " forwards a re=&';&T2 re:uest without "8P information to remote 2 based on the &';&T2re:uest at step ,+. The remote 2 responds a *++ O% messae with "8P information of the remote 2 to "11

" after processin the re=&';&T2 re:uest.

Step ,,: fter communicatin with the remote 2- the "11 " responds M"1 "erver by *++ O% messae with"8P information of the remote 2. The M"1 "erver stores the time (mar#ed as T


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&f P, is larer than P*- M"1 "erver set up a Timer whose value is P,=P*. M"1 "erver will eecute step ,* (send1% messae with "8P information of MG to "11 ") and step ,3 (start the Timer) simultaneously. Onlyafter the Timer epires- M"1 "erver will eecute step ,9 (send P" to 1" /esponse messae to MM2 to start 1"handover).

&f P* is larer than P,- the value of the Timer will be P*=P,. M"1 "erver will send P" to 1" /esponse messae

to MM2 to start 1" handover and start the Timer simultaneously. Only after the Timer epires- M"1 "erver willsend 1% messae with "8P information of MG to "11 ". &n other words- if P* is larer than P,- step ,9will be eecuted after step ,,- the Timer will be started after step ,9- and after the Timer epires- step ,* will be

eecuted.

&f P, is e:ual to P*- M"1 "erver will not set up the Timer and perform step ,* and step ,9 simultaneously.

Step ,/ to ,0: These steps are the same as step ,3 to step ,< in A.*.*.,=, of T" *3.*,A I3J.

Step ,1 to ,2: These steps are the similar to step ,, to step ,* in A.*.*.,=, of T" *3.*,A I3J. &t should be noticedthat only after "11 " receives 1% messae- step ,D will be eecuted. t "tep ,D- "11 " should forward1% messae to the remote 2 based on the 1% messae at step ,*.

Step ,- to 0: These steps are the same as step ,A to step *3 in A.*.*.,=, of T" *3.*,A I3J.

6.1.1. + a: $&n7 Pre-*andover o%">a%on %o red$#e %*e #a dro roa%:

Pre=handover optimi!ation in nne could be used to reduce the call drop probability. The timer in the 2 may notapply here for alternative ,.

6.1.2 S$-a%erna%ve


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for delay measurement- because the delay is sinificantly hiher than for re=&';&T2- due to pain- @"" :uery-etc.

2ditor$s 'oteE&t is 77" whether a round trip estimate based on one sample will be ade:uate for the alorithm. "incethe main part of the round trip time is contributed by the "&P node that processin "&P messaes and theestimate does not need to be very perfect- it shoud be further chec#ed if one round trip is enouh for this

alternative.*. "11 " returns the estimated delay to the M"1 "erver at the domain transfer procedure.

6.1.2.2.2 MSC Server

M"1 "erver should be enhanced with the followin capabilities besides the functions defined in T" *3.*,A I3JE

,. M"1 "erver shall be predefined with the averae time span for itself to send the messae related to 1" handover to the local 2.

*. M"1 "erver shall be able to measure the delay from M"1 "erver to "11 " in domain transfer.

3. M"1 "erver shall be able to receive the estimated delay from "11 " in the domain transfer procedure- and

initiate and manae a timer- which is used to synchroni!e the session transfer procedure and the 1" handover procedure to cause the flow brea#s caused by them to overlap- and so minimi!e the voice brea#.

6.1.2.3 Me&&a7e o&

2ditor$s 'oteEThis clause will contain the messae flows for the enhanced "/;11.

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-igure (%#%"%3%#. SRVCC enhancement alternative using synchroni4ation from )/TRA0 to GRA05ithout 6T72PS18 support

The "/;11 enhancement alternative usin synchroni!ation has a similar messae flow as the oriinal "/;11 eceptfor some steps.

The messae flow is described as followsE

Prior to "tep ,- the "11 " has measured the delay in "&P sinallin in the remote le.

Step , to step -: These steps are the same as step , to step F in fiure A.*.*.,=, of T" *3.*,A I3J.

Step ,+: M"1 "erver sends &';&T2 messae with the "T'="/ towards &M"?"11 ". &n addition- M"1 "erverstores the time (mar#ed as T9) when it sends the &';&T2 re:uest.

Step ,+a: "11 " returns the estimated delay for the remote le update to the M"1 "erver.

2ditor$s 'oteE&t is 77" how to ensure the messae ,+a is routed to the same M"1 server.

Step ,,: "11 " updates the remote le as with the current procedures in T" *3.*3D I9J.

Step ,: hen M"1 "erver receives the estimated delay- it will calculate the duration that it has ta#en to send a"&P messae from M"1 "erver to the "11 " to the reception of the response which carries the estimated delay.

@alf of this is the sinallin delay from M"1 "erver to "11 " (P,). "1" " has returned the delay from "11

" to the remote 2 (P*). On the other hand- it is assumed that the operator has predefined the averae timespan for M"1 "erver to send messae (related to 1" handover) to the local 2 (P3). s described in clause < inthis document- it is assumed P*NP3 is sinificantly loner than P,. &t is further assumed here that the P* isreater than P3NP,. The M"1 starts a timer for the duration of P*=P3=P,. That is- the remote le update (as

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measured by "11 ")- decreased by the predefined delay for local end transfer- decreased by the sinallindelay from M"1 "erver to "11 " (half of the measured round trip time). fter the Timer epires- M"1 "erverwill eecute step ,3 (send P" to 1" /esponse messae to MM2 to start 1" handover). &f P* is not reater thanP3NP,- the M"1 "erver does not start a timer but eecutes the "tep ,3 immediately.

Step ,* to ,3: These steps are the same as in T" *3.*,A I3J.

Step ,0: The remote 2 receives the remote le update and responds a *++ O% messae to "11 " after processin the re=&';&T2 re:uest.

Step ,1: fter communicatin with the remote 2- the "11 " responds M"1 "erver by *++ O% messae.

Step ,2: The "11 " releases the source access le as described in T" *3.*3D I9J.

Step ,- to 0: These steps are the same as step ,A to step *3 in A.*.*.,=, of T" *3.*,A I3J.

s a result of the procedure- the "teps ,A and ,F should occur very close to each other.

6.2 +%erna%ve 2 - Sera Handover

6.2.1 +r#*%e#%$re Re!eren#e Mode

The architecture model of /el=> "/;11 is not affected by this alternative.

6.2.2 $n#%ona /n%%e&

The remote end and M"1 server of /el=> "/;11 are affected by this alternative.

6.2.3 Me&&a7e o&

2ditor$s 'oteEThis clause will contain the messae flows for the enhanced "/;11.

"erial @andover means the /T handover is performed after the &M" "ervice 1ontinuity procedure completed. Theonly difference from /el=> "/;11 is that the M"1 "erver enhanced for "/;11 sends @andover response with 1"resource to MM2 when the &M" "ervice 1ontinuity Procedure is completed.

-igure (%"%3%#. SRVCC using Serial 1andover from /TRA0 1SPA! to /TRA02GRA0

7iure A.*.3.* shows the main steps for serial handover. &n this fiure- step b, follows step a9.

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-igure (%"%3%". Analysis of SRVCC using Serial 1andover

pon receivin an offer with MG "8P in step a*- the remote end switches the downlin# voice media stream towards

the MG (as specified in &2T7 /71 3*A9 clause >.3.,)- and then the downlin# media stream is interrupted until step b3is done. "o the interruption time of the downlin# media stream isE

= Td L Ta3NTa9NTb,NTb*NTb3

The remote end will not stop receivin the uplin# stream from the oriinal &M" 0earer until it receives the media data

from the new uplin# media stream arrives (as specified in &2T7 /71 3*A9 clause >.3.,).

2ditor$s 'oteE&t is 77" whether a typical terminal implementation on the remote end would #eep listenin on the oldaddress of the offerer once it has received a new offer.

'OT2 ,E The remote end may not support the capability. &n that case- for the interruption time- there$s no difference between the uplin# media stream and the downlin# media stream.nd after step b*- the uplin# media

steam is interrupted until step b3 is done. "o the interruption time of the uplin# media stream isE

= Tu L Tb3

'OT2 *E The assumption here is that the in=fliht uplin# media stream pac#ets transmitted from the old source (i.e.on the 2$s &M" access le) are not bloc#ed by the P127 of the remote party- once the P127 of theremote party has authorised the new "8P offer. &f this assumption is not valid- for the interruption time-there$s no difference between the uplin# media stream and the downlin# media stream.

Given that Tb, and Tb* are much shorter than Ta3 and Ta9- especially in the roamin case (either the 2 or the remoteor both) or in the case that the 2 and the remote end belon to different operators- the Td is simplified as followinE

= Td L Ta3NTa9N Tb3

= Tu LTb3

1omparin to the analysis in clause "/;11. Theuplin# interruption time depends on the interruption time of /T handover- and is much shorter than /el=> "/;11under the remote end assumption and the P127 assumption described previously (see 'OT2 , and 'OT2 * above).

6.3 Vod

6. +%erna%ve - Meda an#*or n %*e &ervn7 ne%or?

6..1 +r#*%e#%$re Re!eren#e Mode

'o chane to the current architecture is proposed.

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6..2 $n#%ona /n%%e&

'o additional functional entities are proposed.

@owever- a new functionality is proposed to be defined- i.e.- ;isited ccess Transfer 7unctionality (;T7)- that could be handled by the M"1 "erver or alternatively by the P=1"17 (co=located with &M" 5G). &n the followin- the

eample usae is mainly when the ;T7 is handled by the M"1 "erver. The ;T7 stays in the session path for theduration of the call and it supports the M"1 "erver assisted mid=call feature as specified in T" *3.*3D I9J for additionalheld sessions and conference calls with the difference that no additional information needs to be echaned between"11 " and M"1 "erver ? ;T7 durin the transfer as the session anchor is in the ;T7.

6..3 Me&&a7e o&

6..3.1a @r7na%n7 &e&&on& n PS

The ;T7 is included from the P=1"17 in the visited networ#. This scenario re:uires that the P=1"17 is in the visitednetwor#.

-igure (%+%3%#a)#. 8riginating session that uses only PS media

,. 2=, initiates an &M" multimedia session to 2=* and uses only P" media flow(s). The re:uest is forwarded to"=1"17 followin normal &M" session set up procedures.

*9. The P=1"17 detects the &M" multimedia session and based on the local policy it anchors the session in the;T7 prior forwardin the &';&T2 to the "=1"17. The P=1"17 finds the correct ;T7 to route to as specified

in clause A.9.


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6..3.1 Ter"na%on &e&&on& n PS

The ;T7 is included from the P=1"17 in the visited networ#. This scenario re:uires that the P=1"17 is in the visitednetwor#.

-igure (%+%3%#9)#. Terminating session that uses only PS media

,. 2=* initiates an &M" multimedia session to 2=, and uses only P" media flow(s). The re:uest is forwarded to

"=1"17 followin normal &M" session set up procedures.

*=9. The "=1"17 routes the &';&T2 to the "11 ". The "11 " performs T=8" and then session setupcontinues towards P=1"17.


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-igure (%+%3%")#. PS to CS access transfer

,. Procedures specified in T" *3.*,A I3J- clause A.*.*., result in that the MM2 will establish "v towards an M"1"erver enhanced for "/;11. The MM2 selects the same M"1 "erver for "v as for "Gs- which is the;T7?M"1 included durin session establishment. The M"1 "erver correlates the incomin P" to 1" @andover re:uest with the anchored session usin the 1=M"&"8' obtained when anchorin the session. The M"1 "erverupdates the media anchorin to forward the media towards the 1" access. t this point- no etra sinallin is

needed within the &M" networ#. The MG may insert codec towards the taret access le if needed. &n case thetaret cell is served by a different M"1 "erver- then the ;T7?M"1 will act as an anchor M"1 durin "/;11as specified in T" *3.*,A I3J.

'OT2E The MG can for a certain period of time send media both on the source access le and the new taretaccess le to minimi!e the interruption delay further.

*. The ;T7 informs the "11 " that the transfer has ta#en place. &f the Gm reference point is not retained uponP" handover procedure- the "ource ccess 5e is released.

6.. eo:"en% +%erna%ve&

8ifferent deployment alternatives for the ;T7 are possible- each of which re:uirin different type of support in thenode(s) and different type of functionalityE

) ;T7 included in M"1 "erver enhanced for "/;11 (as described in clause A.9.3)E

= The same M"1 "erver ? ;T7 has to be selected durin session setup and by the MM2 ? "G"' for "v.

0) ;T7 included in M"1 "erver and co=located with ? included in P=1"17

= The M"1 "erver ? ;T7 is automatically included into the oriinatin and terminatin session pathH

= MM2 ? "G"' needs to select the same ;T7 for "vH

= ;T7 ? M"1 "erver needs li#ely to play the role of an anchor M"1 (taret cell served by taret M"1different to ;T7).

1) ;T7 included in P=1"17 (no M"1 "erver included)

= /e:uires media anchorin functionality (control of MG) in the P=1"17- e.. by co=locatin with &M"

5GH

= ;T7 automatically included into the session pathH

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= "ession transfer re:uest from M"1 "erver enhanced for "/;11 needs to be routed to ;T7 ? P=1"17.

"ome of these deployment alternatives can also be combined with each otherE

= N 0E ;T7 in M"1 "erver and in P=1"17 (with M"1 "erver).

= N 1E ;T7 in M"1 "erver and in P=1"17 (without M"1 "erver.

&n these cases the M"1 "erver enhanced for "/;11 needs to determine whether it is havin the ;T7 role for thissession () and if not the session transfer re:uests needs to be send to the ;T7 (0 or 1).

6..5 See#%on o! V+T

"election of ;T7 for oriinated and terminated sessions

= 7or deployment alternatives 0E

= 0oth P=1"17 and servin node (MM2 ? "G"') use the same (standardi!ed) selection alorithm to find theM"1 "erver ? ;T7 in the ;P5M'. MM2 ? "G"' may include selected M"1 "erver for "v into the contetechane with other MM2 ? "G"'.

= 7or deployment alternative 1E included in P=1"17

"election of ;T7 durin "/;11E

= 7or deployment alternative 0- the MM2 selects the M"1 "erver ? ;T7 for "/;11.

= &n case of optimi!ed call setup- both P=1"17 and servin node (MM2 ? "G"') use the same (standardi!ed)

selection alorithm to select the ;T7 in the ;P5M'.

= 7or deployment alternative 1- the M"1 "erver routes the session transfer re:uest to the ;T7. This can beensured by one of the followin methodsE

= The M"1 "erver receives from the MM2 a visited "T'="/ (v"T'="/) that is suitable to route to the ;T7.

This can be achieved by one of the followin methodsE

= "ee e.. clause A.,, for a method to allocate the v"T'="/ durin session setup- if needed- and to push thev"T'="/ from the ;T7 to the @"" and from there to the MM2?"G"'.

= The ;T7 allocates the v"T'="/ when the user reisters in the &M". The v"T'="/ is provided to the&M" and via 3rd party reistration to the "11 ". The "11 " provides the v"T'="/ to the @""- whichin turn updates the MM2 ? "G"'.

= The M"1 "erver ? ;T7 can receive the address of the P=1"17?;T7 from the &M" (e.. durin &M"

reistration or usin an event pac#ae). This re:uires that the same M"1 "erver is selected for "Gs and for"v and that the M"1 "erver is enhanced for &1".

6..6 Man%ann7 IMS re7&%ra%ons a prere:uisite for "/;11- the 2 is &M" reistered over P". To avoid that the &M" reistration epires durin anonoin voice call over G2/' ? T/' after "/;11- the M"1 "erver ? ;T7 instructs the P=1"17 as followsE

= hile the voice call is onoin on the 1" access le (to?from the ;T7)- the P=1"17 shall update the local

reistration timer of the P" access le such that it does not epire durin the onoin call.

= &f needed- the P=1"17 will also further instruct the "=1"17 to update its reistration timer for the P" access lesuch that it does not epire durin the onoin call.

fter releasin the voice call(s)- and if needed- the 2 itself updates the &M" reistration- i.e.- in case the oriinal &M"reistration timer on the 2 has already epired- the 2 will immediately perform re=reistration.

'OT2E &f the 2$s &M" reistration timer epires locally durin the onoin call- the 2 inores this until thecall is completed and is able to perform a re=reistration.

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6.5 +%erna%ve 5 - Re"o%e $da%e o%">a%on


The architecture model of /el=> "/;11 is not affected by this alternative.

6.5.2 $n#%ona /n%%e&

2ditor$s 'oteEThis clause will define the functionalities of functional entities for the enhanced "/;11.

6.5.3 Me&&a7e o&

0ased on "erial @andover in lternative *- an optimi!ation to /emote pdate procedure is shown in 7iure A.


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b*. 2P" sends @andover 1ommand to 2.

b3. 2 tunes to the taret 1" access.

The voice downlin# media stream is interrupted once the remote end receives "8P answer in step a


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&t should be noted that the mechanism which allows the "11 " to anchor some or all of the media in an M/7P to hidechanes to the remote end and to allow for bi=castin could be useful- not only in the case of "/;11 but moreenerally in all session continuity and &nter=2 session cases.

'OT2E This solution has the limitation that it does not allow OM/ from the visited networ#.

6.8.1.1 +r#*%e#%$re Re!eren#e Mode

2ditor$s 'oteEThis clause will contain the architecture reference model for the enhanced "/;11.

-igure (%&%#)#. 8vervie5 of updated architecture

6.8.1.2 $n#%ona /n%%e&

2ditor$s 'ote This clause will define the functionalities of functional entities for the enhanced "/;11.

'o additional functional entities are introduced in addition to those already defined in T" *3.*F* IDJ and T" *3.**> I>J

6.8.1.3 Me&&a7e !o&

2ditor$s 'oteEThis clause will contain the messae flows for the enhanced "/;11

The followin call flows show how this can be implemented.

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6.8.1.3.1 Ca or7na%on

-igure (%&%#%3%#)#. Call origination

,. 2=, initiates a multimedia session to 2=* over P". The re:uest is forwarded to the "=1"17 of 2=, followin

normal &M" session set up procedures.

*3. The service loic with i71 causes the re:uest to be forwarded to the "11 " for anchorin the sessions toenable "ession Transfer.

9. The "11 " anchors the session and determines that part of the media needs to be anchored in an M/7P (the

voice component). &t therefore interacts with the M/71?M/7P to do so.


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6.8.1.3.2 Ca %er"na%on

-igure (%&%#%3%")#. Call termination

,. 2=* initiates a voice &M" session to 2=, over P". The re:uest is forwarded to the "=1"17 of 2=, followinnormal &M" session set up procedures.

*3. The service loic with i71 causes the re:uest to be forwarded to the "11 " for anchorin the sessions toenable "ession Transfer.

9. The "11 " anchors the session and determines that part of the media needs to be anchored in an M/7P (the

voice component). &t therefore interacts with the M/71?M/7P to do so.


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-igure (%&%#%3%3)#. nhanced SRVCC procedure

, Procedures specified in T" *3.*,A- clause A.*.*., result in an &';&T2 to be sent with an "T'="/ indicatin use

of "/;11 procedures for ccess Transfer to 1" access. The M"1 "erver enhanced for "/;11 includes the1=M"&"8' as callin party number.

* "tandard procedures are used at "=1"17 for routin of the &';&T2 to the "11 ".

3 The "11 " uses the "T'="/ to determine that ccess Transfer usin "/;11 is re:uested. The "11 " mayretrieve the 1=M"&"8' from the @"". The "11 " is able to identify the correct anchored session.

9 The "11 " interacts with the M/7 for the media anchored in the M/7 to be sent to the MG from now on-sends then an &';&T2 to the M/71- includin the call=reference=/&- as well as the "8P of the MG. The"11 " could either instruct the M/7 to send the media to the MG only- or to bi=cast to both the MG and

the source connection point (the &P address and port of the 2 on the source access). &n case it decides that bi=castin is to be performed- the "11 " starts a supervision timer for the bi=castin.


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6.8.2 S$-a%erna%ve


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6.8.2.3.1 Ca or7na%on

-igure (%&%"%3%#)#. Call origination

, 2=, initiates a multimedia session to 2=* over P". The re:uest is forwarded to the "=1"17 of 2=, followinnormal &M" session set up procedures.

*3 The service loic with i71 causes the re:uest to be forwarded to the "11 " for anchorin the sessions toenable "ession Transfer.

9 The "11 " anchors the session

< The "11 " issues an &';&T2 throuh the "=1"17 towards the remote end.

AD The service loic with i71 causes the re:uest to be forwarded to the "?M/71.

Alternative =,:

>a The T" decides (based on e.. operator policies- content of the /e:uest=/&R) that it needs to anchor thesession and the media usin an M/71?M/7P. &t then parses the "8P 2=, and determines that M/7P anchorinis re:uired for the voice component of the multimedia session.

>b "ession and media anchorin is performed by the T" in the M/7.

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>c>d The T" sends an &';&T2- of which the "8P is built on the "8P received from 2=, in step D- and oninformation received from the M/7 in step >b. That &';&T2 messae is forwarded to the remote party throuhthe "=1"17.

>e The session setup is completed- as per *3.**>- includin updatin the M/7 with the voice component connectioninformation and ports for the remote party.

Alternative =:

Fa The T" decides (based on e.. operator policies- content of the /e:uest=/& ...) 'OT to anchor the session andthe media usin an M/71?M/7P. &n the eample of this se:uence- the basis of that decision is that the call isdestined to a 2 belonin to another operator- and that the sinallin (resp the media) will therefore o throuhan &017 (resp. a TrG) which will be possible to use as an anchor in case of "/;11 handover.

FbFc The T" sends an &';&T2- of which the "8P is built on the "8P received from 2=, in step D. That&';&T2 messae is routed to &017 by the "=1"17.

Fd The &017 anchors the session and involves a TrG for anchorin the media.

Fe The &017 sends an &';&T2 towards the remote party. The "8P included in that &';&T2 contains the

information related to the TrG as confiured in step Fd.Ff The session setup is completed- as per *3.**>.

6.8.2.3.2 Ca %er"na%on

-igure (%&%"%3%")#. Call termination

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, 2=* initiates a voice &M" session to 2=, over P". The re:uest is forwarded to the "=1"17 of 2=, followinnormal &M" session set up procedures.

*3 The service loic with i71 causes the re:uest to be forwarded to the T" for providin call terminatinservices.

Alternative =,:

9a The T" decides (based on e.. operator policies- ;ia=header indicatin that the &';&T2 has not traversed any

node in 2=,$s home networ# before reachin the T"R) that it needs to anchor the session and the media usinan M/71?M/7P. &t then parses the "8P* and determines that M/7P anchorin is re:uired for the voicecomponent of the multimedia session.

9b "ession and media anchorin is performed by the T" in the M/7.

9c The T" sends an &';&T2- of which the "8P is built on the "8P* received in the &';&T2 of step 3- and oninformation received from the M/7 in step 9b. That &';&T2 messae is forwarded to the remote party throuhthe "=1"17.

Alternative =:

.

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6.8.2.3.3 SRVCC ro#ed$re

-igure (%&%"%3%3)#. nhanced SRVCC procedure

,. The MM2 sends a "/;11 P" to 1" /e:uest messae to the M"1 "erver for performin a "/;11 for 2=,

*. This causes the M"1 to send an &';&T2 with an "T'="/ indicatin use of "/;11 procedures for ccessTransfer to 1" access. The M"1 "erver enhanced for "/;11 includes the 1=M"&"8' as callin party number.

3. "tandard procedures are used at "=1"17 for routin of the &';&T2 to the "11 ".

9. The "11 " uses the "T'="/ to determine that ccess Transfer usin "/;11 is re:uested. The "11 " mayretrieve the 1=M"&"8' from the @"". The "11 " is able to identify the correct anchored session.

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6.9 +%erna%ve 9 = SR-VCC /n*an#e"en% $&n7 "eda de%e#%on

6.9.1 In%rod$#%on

This alternative proposes a modification of the MG and M"1 "erver to support detection of the arrival of the first 1"

downlin# media from 2=0- and trierin the 2= to handover based on that event. &n the flows included below theslope of the flows indicates the transit time of the sinallin and media. The duration of the voice brea#s eperienced by2= and 2=0 are shown separately as the downlin# voice brea# and the uplin# voice brea#.

2 followin /71 3*A9 I,,J will listen to the old source until media from the new source is available. @owever-dependin on 2 implementation and the usae of atin functions in the networ# (P11- TrGs etc)- the switch

between P" 5?85 and 1" 5?85 may start at the return of the *++ O%. "uch implementations in the 2 and networ#atin functions should be avoided- and chanes as necessary should be made to the eistin specifications to clarify theepected behaviour.

There has been some concern that allowin the reception of media before the *++O% could be at the ris# of eposin

entities to the reception of stray pac#ets- or even use of the &P address?port information by a fraudulent node. @owever-we note that completely closin such vulnerability isn$t in line with /71 3*A9 and in fact would have an impact on allfeatures (such as &nter=2 Transfer) where updates occur.

2= is triered to bein to handover by detection (by the networ#) of the arrival of the first downlin# 1" media pac#ets. The downlin# pac#ets are detected by the MG and an indication sent to the M"1 "erver to trier the @O

1M8.

The call flow with the new media detect functionality is shown in fiure A.F=,.

-igure (%*)#. 0on)roaming scenario 5ith ne5 media detect functionality

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&f no media is detected by the MG before the arrival of the *++O% then the networ# should initiate the handoverwhen the *++O% arrives.

&n this new procedure- it is the downlin# brea# that is determined by the time it ta#es for 2= to re=tune. @owever- because this re=tune time is typically shorter than the transit time of the *++O%- it will be the arrival of the *++O% thatdetermines when the first 1" uplin# data can be sent towards 2=0. &n the eample above- and typically- this means the

uplin# brea# is loner than in the baseline case. pproimately- it is the transit time of the *++O%- minus the mediatransit time- and so will certainly be at least ,++ms shorter than the downlin# voice brea# in the default procedures(since that is the *++O% transit time P5" the re=tune time.

&t is epected that the performance taret of 3++ms is only eceeded for the roamin scenarios when the networ# iseperiencin pea# load- and even then the brea# will not eceed 9++ms. ("ee below for the possible use of a fied delayto reduce the brea# further.) 1ompared with the baseline procedure- the interval between the Measurement /eport andhandover command will in eneral be increased by a time e:ual to the transit time of the &';&T2 plus the transit timefor the first 1" downlin# media. &n cases where there is no downlin# media before the *++O% arrives- the interval will

be increased by the transit time of the &';&T2 plus the transit time of the *++O%.

"uch additional delays to the handover would certainly be an issue for 5T2 =Q 5T2 scenarios- but in "/;11 we arediscussin inter=/T handover (different bands). The additional delays do not seem to be out of #eepin with the delaystypically eperienced in inter=/T (MT" =Q G"M) handovers. The main scenario we see as raisin potential issues is

in lare cities- with deep fadin- but in this case such areas can be epected to have a full 5T2 roll=out. &t is also possible to enineer the handover parameters?thresholds to cause an earlier handover- so that additional delays inhandover as a result of this alternative are cancelled out. &t is also possible- if seen as beneficial- for /elease ,+ 2$s to be updated to support pre=handover sinallin- as described in nne .

&n fact- the duration of the brea# eperienced by 2=0 can be further reduced by addin a delay between the detection

of 1" media by the MG and the M"1 "erver sendin the handover command. This has the effect of increasin thevoice brea# at 2=- but by selectin an appropriate delay value an appropriate balance between the two voice brea#scan be achieved.

n eample of this is shown in fiure A.F=*.

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-igure (%*)". 7edia detect function 5ith delay 9efore sending 18 C76

The additional delay etends the downlin# brea#- but shortens the uplin# brea#. 0y selectin an appropriate delayduration- a balance between uplin# and downlin# brea#s can be chosen. &t is epected that it is possible to brin theworst=case scenario voice brea# in under the taret of 3++ ms.

6.9.2 Ca !o&

0elow is an eample call flow for this solution- based on the call flow for "/;11 from 2=T/' to G2/' without

8TM support- as described in T" *3.*,A I3J- clause A.*.*.,. The only modification to the baseline "/;11 procedures isto add an event sinalled from the MG to the M"1 "erver when the first downlin# 1" media arrives at the MG.

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-igure (%*%")#. SRVCC from )/TRA0 to GRA0 5ithout 6T7 support: using media detect

"teps , C ,+ are as described in T" *3.*,A I3J- clause A.*.*.,.

,+a. rrival of the first downlin# 1" media from the remote end causes an event to be sent from the MG to theM"1 "erver. This event triers "tep ,3- as described in T" *3.*,A I3J.

"teps ,, C *9 are as described in T" *3.*,A I3J- clause A.*.*.,.

6.10 +%erna%ve& 10 - eSRVCC %* P -#a&%n7


This alternative does not chane the reference architecture of oriinal "/;11- i.e. the architecture reference model is

the same as T" *3.*,A I3J.

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6.10.2 $n#%ona Re$re"en%&

,. &M" voice codec info is retrieved via P11E

"elected codec could be delivered to MM2 from 7 on the path of Policy 1ontrol procedures. That is- 7 shallsend the selected codec to P1/7 and P1/7 sends not only Policy and 1harin control information over

G?G but delivers the selected codec as well. P8'=G and "=G sends the "8P info (e..- selected codectoether with source &P address?portB and destination &P address?portB- session state) information transparently toMM2- and MM2 stores that to the iven subscriber$s session?bearer. &f "8P info is updated durin the session-this updated "8P is also delivered to MM2 for updatin purpose. &f 2 has multiple sessions onoin- each of

this session$s "8P is stored separately in the MM2 for that 2.

To minimi!e the chanes due to roamin- this alternative assumes that the P=1"17 is allocated at the servinnetwor# (i.e. when roamin- P=1"17 is located at the servin networ#) via on local confiuration and roaminareement.

*.. "/;11 M"1 allocates the MG to interwor# between *G 1" with (1" speech) and &M" with (/TP speech)

3.. MM2 instructs the P8'=G to bi=cast the /TP streams to the desinated MG via "Gi interface.

9.. fter "ession 1ontinuity procedure is performed- MG and P8' G is returned to normal state.

6.10.2a IMS vo#e #ode# re%reva !ro" PCC !o

The followin fiure illustrates how &M" voice codec in used is relayed to MM2 from P=1"17 (7).

-igure (%#$%"a)#. 7S voice codec retrieval from PCC Procedure

,=*. 8urin &M" session setup or codec chanes durin the active session- P=1"17 which is actin as 7 in P11architecture updates the selected codec to P1/7 via / interface.

3. P=1"17 indicates the &M" codec in used to P127 via G interface.

9. 0ased on the procedure in T" *3.9+,- P8'=G uses either 1reate 0earer /e:uest if the &M" voice bearer hasnot yet be done- or pdate 0earer /e:uest if the voice bearer is already setup. The &M" codec info is sent viathese messaes transparently.

. P8'=G ac#nowledes step 3 with a /esponse.

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2ditor$s noteE The similar flow will be used for updatin MM2 for "8P re=neotiation. @ow the "8P info is to beformatted (i.e.- which entity does the formattin) for sendin to MM2 is T08.

6.10.3 Meda ane *andn7

&n order to allow seamless voice handlin for "/;11- the local end prepares a bridin mechanism such that the

switchin of the /TP voice in 5T2 to 1" voice over *?3G is not noticeable at the remote end. The followin fiureshows how this is done from the media perspectiveE

-igure (%#$)#. P60)G< =i)Casting 7edia Plane handling

2ditor$s noteE @ow 5 /TP traffic from MG is handled (e..- so the remote end is unaware) in step 3 is 77".

2ditor$s noteE &f 2 has multiple &M" voice sessions- it is 77" how to handle it.

"tep ,E This is prior to "/;11 where an &M" voice call over 5T2 is established with the remote end. The /TPstream is oin between 2=P8'=G and remote end.

"tep =*E 2=T/' triers an "/;11 operation by re:uestin the MM2 to perform an "/;11 to *?3G access.MM2 then invo#es the "/;11 M"1. 8urin this MM2="/;11 M"1 interaction- the P8' G is

instructed to replicate 5 and 85 /TP pac#et to a desinated MG address?portBs. This 85 /TP pac#etin the MG is converted to 1" voice in step 3 for connection to the *?3G access. The idea is that when2 switched over the access to *?3G then it can receive 1" voice immediately on the downlin# direction.The 85 /TP stream from the remote end is continuously sent to the P8' GH hence- no chane on theremote end. The MG also re:uires some conference bride function as first le is connected to *?3Gaccess- *nd le is from the P8' G- 3rd le is toward the &M" for session continuity. The MG also

re:uires usin the &P address of the "1 2 towards the remote end and not the &P address of the MG.

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"tep 3E 2 receives the @O command and connected to *?3G usin 1" voice. The 85 1" voice is alreadyconnected at this point due to step *. The 2 starts sendin 5 1" voice traffic to MG. MG thentranscodes this to an /TP stream and forwards it to remote end. The MG aware of the /TP streamcodec bein used based on the &M" codec information received from MM2. The 5 se:uence number

and timestamp of the 5 /TP stream is maintained toward the remote end by the MG. s the result of"/;11- the P8'=G receives re:uest from MM2 (that was trier by the taret "G"') to deactivate

G0/ bearer related to voice. P8' G responses to MM2?"G"' as defined in /el F T" *3.*,A I3J.@owever- P8' G starts a timer and continues to transmit the 85 /TP streams toward the MG untilthis timer epires- then complete the G0/ bearer deactivation.

"tep . "ession continuity procedure is successfully eecuted in the remote end. The remote end is sendin 1"voice directly to the MG. The 1" to /TP stream transcodin resource and the P8' G resources arereleased.

6.10. S7nan7 Me&&a7e o&

The followin fiure shows the sinallin aspectE

-igure (%#$)". P60)G< =i)Casting Signalling Plane 1andling

"tep * consists of procedure toE

= MM2 indicates to the "/;11 M"1 that 2P1 supports e"/;11 procedure- and the &M" codec information aswell as source &P address?portB and destination &P address?portB.

= M"1 allocates desinated MG resource to receive 5?85 /TP streams from P8' G

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= M"1 indicates to MM2 the MG address to which those 5?85 /TP streams to be sent

= MM2 to instruct P8' G to replicate 5?85 /TP to MG

= M"1 to instruct MG to transcode 85 /TP stream to 1" voice toward the *?3G access

"tep 3 consists of procedure to connect 5 1" traffic to /TP media stream. 85 /TP stream to 1" traffic can be thru

connected at step *. This allows the 2 to receive 85 1" traffic immediate after switch over to *?3G access. The 51" traffic to /TP stream cut over is done when @O complete indication is received from *?3G 0""?/'1.

"tep 9 consists of procedure to release the /TP to 1" transcodin resource and conferencin resources in MG. Thisstep is triered when *++ O% is received by the "/;11 M"1.

6.11 +%erna%ve 11 - Meda an#*orn7 n %*e IMS-+'G

6.11.0 Genera

The operator shall deploy &M"=5G(s) that can act as shown in the clause A.,,.3 for communications of roamin users-

and the operator shall deploy &M"=5G(s)?M/7 for inter=operator communications of home users. The &M"=5G shallallocate TrG(s) for the communications.

'OT2E &t is normal case that operator anchors the media in the visited networ# for the communication of roaminusers and inter=operator communication of home users- e.. usin "01 or &017?TrG.


'o chane to the current architecture is proposed.

6.11.2 $n#%ona /n%%e&

'o additional functional entities are proposed.

6.11.3 Me&&a7e o&

6.11.3.1 IMS Re7&%ra%on

2istin &M" /eistration procedures described in T" *3.**> I>J are used to reister the user in &M".

-igure (%##%3%#)#. 7S Registration

,. /oamin user 2=, sends a "&P (re)/eistration re:uest to home networ# via P=1"17.

*. The &M"=5G in the P=1"17 allocates a P"&=8' for e"/;11 for the 2=,- and includes the P"&=8' in there:uest forwarded to the "=1"17.

'OT2 ,E The &M"=5G can allocate the same P"&=8' for e"/;11 for all 2s.

3. The "=1"17 sends the "&P (re=)/eistration re:uest to the "11 " accordin to the three=party reistration procedure.

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On reception of the P"&=8' for e"/;11- if the "11 " has already received one before- it shall chec# whetherit is the same as the previous received one- otherwise- the "11 " shall chec# whether it is the same as the "T'="/ in the @"". &f the chec# fails- the "11 " shall modify the "T'="/ in the @"" usin the P"&=8' fore"/;11.

&f the "11 " receives an "&P (re=)/eistration re:uest without P"&=8' for e"/;11 and the "11 " has

modified the "T'="/ in the @"" usin a P"&=8' for e"/;11- the "11 " shall restore the "T'="/ in the@"".

'OT2 *E The visited networ# can chane the servin &M"=5G for an 2 durin &M" re=/eistration procedure.

6.11.3.2 @r7na%n7 &e&&on& n PS

2istin Mobile Oriination procedures described in T" *3.**> I>J are used to establish a session.

-igure (%##%3%")#. 8riginating session that uses only PS media

,,+. The "11 " determines that the 2=, is in a visited networ# supportin e"/;11 accordin to thereistration phase- and forwards the response to the 2=, with a dynamic?static "T& for e"/;11 and the 1=M"&"8'. The &M"=5G shall store the "T& for e"/;11 and the 1=M"&"8'.

'OT2 *E "11 " usin dynamic "T& to correlate the transferrin session is easier than static "T&.

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6.11.3. PS = CS +##e&& Tran&!er

This clause describes the main differences with eistin "/;11 procedures. "ome of the procedures that are notimpacted have been left out for clarity of the flow.

-igure (%##%3%+)#. PS to CS access transfer for roaming user

,. Procedures specified in T" *3.*,A I3J- the M"1 "erver initiates"ession transfer messae- e.. by sendin aninitial "&P &';&T2 re:uest to &M"=5G accordin to the P"&=8' for e"/;11 received from the source MM2.

The M"1 "erver shall provide all the supported codecs for voice in the "ession transfer messae. The sessiontransfer re:uest is transferred via ''& interface between M"1 "erver and the P=1"17

*. The &M"=5G receives the "ession transfer messae and updates the access le media sement of the session-

which is correlated with the 1=M"&"8'.

3 The &M"=5G sends response to the M"1 "erver.

'OT2E &n rare case that the M"1 "erver does not support the codec used for the oriinal communication- the&M"=5G must provide transcoder for the new access le.

9. fter receivin the "ession transfer messae- the &M"=5G forwards the "ession transfer messae- e.. bysendin an initial "&P &';&T2 re:uest- to the "11 " usin the stored "T& for e"/;11.


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-igure (%#"%#)#. SRVCC enhancement alternative using local anchoring

&n this alternative- the followin features are introduced in addition to the oriinal "/;11 as specified in T" *3.*,A I3J

== The "=G provides the anchorin function and switches the bearer path for media data forwardin- from the 2=

T/' to the MG. The path between the "=G and MG is the pac#et bearer as specified in T" *3.9+, IAJ.

= 7or P" bearers other than ones for ;o&P media- "=G performs normal P" handover procedure with "G"'.MM2 distinuishes bearers for ;o&P media- for which the "=G establishes the P" bearers with MG- based onS1& information- i.e. a bearer with S1&L, is switched to MG. MM2 commands the "=G to which entity. i.e."G"' or MG- it shall switch the bearers.

= M"1 "erver?MG obtains the 2,$s &P address from the "=G in the procedure to establish P" bearer between"=G and M"1 "erver?MG. The 2,$s &P address was allocated before the handover to receive?send themedia pac#ets with the 2*. The 2, &P address is used by the MG for the media.

= MM2 stores the media information via P11 that will be sinalled to M"1 "erver?MG enhanced for 2=T/'?T/' (@"P) i.e. from P=1"17 to M"1 "erver?MG via P=G (in case of GTP based "


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'OT2E &n this alternative- M"1 "erver?MG enhanced for 2=T/'?T/' (@"P) supports GTP= protocol in addition to the support of GTP=1 as specified in current "/;11.

6.12.2.2 PCC

"8P related information such as &M" voice codec info is retrieved via P11- which means the "8P related information

is delivered to MM2 from 7 via Policy 1ontrol procedures. That is- 7 shall send "8P related information to P1/7and P1/7 sends not only Policy and 1harin control information over G?G but delivers "8P related information aswell. P8'=G and "=G sends the information transparently to MM2- and MM2 stores that to the iven subscriber$s

session?bearer.

6.12.2.3 MM/

&n addition to the standard MM2 behaviour defined in T" *3.9+, IAJ- an MM2 which has been enhanced to optimi!e"/ ;11 handover by local anchorin provides the followin functionsE

- Providin the 2P1 bearer control function that enables to establish the 2P1 bearer between "G andMG toether with other normal 2P1 bearers.

'OT2E This can be reali!ed by the eistin /el>?F GTP capability without any impact. "tae3 wor# willinvestiate the protocol impact.

- "torin the "8P related information to the iven subscriber$s session?bearer- and that will be sinalled toM"1 "erver?MG enhanced for 2=T/'?T/' (@"P) in case of "/;11 occurrence.

6.12.2. S-GA

&n addition to the standard "=G behaviour defined in T" *3.9+, IAJ- an "=G which has been enhanced to optimi!e

"/ ;11 handover by local anchorin provides the followin functionsE

- Providin the 2P1 bearer control function that enables to establish the 2P1 bearer between "G andMG toether with other normal 2P1 bearers. 'oteE This can be reali!ed by the eistin /el>?F GTP

capability without any impact. "tae3 wor# will investiate the protocol impact.

'OT2E This can be reali!ed by the eistin /el>?F GTP capability without any impact. "tae3 wor# willinvestiate the protocol impact.

6.12.3 Me&&a7e o&

6.12.3.1 SRVCC Handover %* PS H@ &$or%

The difference from the release > "/;11 is denoted with the /28 font in fiure A.,*.3.*=,. This procedure can beapplied for the "G"' relocation procedure that miht happen after 2 handed over to the 3G. &n this case- "ource 2=T/' and "ource MM2 in the fiure A.,*.3.*=, can be replaced with the "ource /'" and "ource "G"'

respectively.

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-igure (%#"%3%#)#. call flo5 5ith PS 18 Support

2ditor$s 'oteEThe fiure will be update to clarify routin will be 2=MG="?P=G after step,> if step,< is performed.

2ditor$s 'oteEThe line of &ndirect 8ata 7orwardin will be clarified in this fiure.

dditional flow and modified nodal behaviour are eplained belowH


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Aa. MM2 sets the MG &P address- T2&8 and T2&8 for downlin# indirect data forwardin toether with the bearerinformation for 2P1 bearers in the forward relocation re:uest messae.

Ab- Ac. &f "=G relocation needs to be eecuted- taret "G"' sends 1reate session re:uest to the taret "G withthe "G"' &P address and T2&8 for control plane as specified in T" *3.9+,.

Af- A. Taret "G"' sends 1reate &ndirect 8ata 7orwardin Tunnel /e:uest for downlin# data to the taret "Gwith the MG &P address and T2&8 for downlin# indirect data forwardin toether with the 2P1 bearerinformation of the other P" services. The T2&8 for downlin# indirect data forwardin is used for data forwardin

from "=G to MG when inter /T @O is initiated in step,9 and e'ode0 starts indirect data forwardin.

Da. MM2 sends the P" to 1" c#nowlede messae to M"1 "erver?MG with the Taret "G &P address andT2&8.

,9. The source e'ode0 initiates downlin# data forwardin for bearers includin ;o&P media. 7rom now- ;o&P mediais forwarded to the MG via "=G.

,> &f MG supports the previously used codec of the 2- the M"1="erver does not send session transfer messaeto the "11 "- i.e. no remote end update procedure occurs. Otherwise- the M"1="erver initiates the remote endupdate procedure indicatin all codec available in the MG.

,Fc- ,Fd. hen taret "G"' receives the relocation complete messae from taret /'"?0""- taret "G"' sendsthe modify bearer re:uest messae to the taret "=G with the MG &P address and T2&8 toether with the2P1 bearer information of the other P" services. The taret "=G communicates with the M"1 server?MGonly for the ;o&P media traffic.

fter step ,Fc- ;o&P media is conveyed between 2 and peer end via the MG.

0ased on operator confiuration e.. operator policy- "ession Transfer to the "11 " can be initiated by theM"1 "erver?MG at any time after step,>d. &n this case followins are appliedE

/eardin the bearer in "=G side- upon the completion of the session transfer procedure- ;o&P bearer release procedure is to be triered by &M" via P11 i.e. PG?"G?the taret "G"' is to release the bearer at this pointin time.

/eardin the bearer in M"1 side- upon ac#nowledin the completion of the session transfer procedure (e..

receivin *++ O% from "11 ")- the M"1 server is to release the bearer towards "G.

'OT2E 0ased on implementation- MG should be able to decode the M/ without any re=synchroni!ation with peer end after @O by receivin a few M/ frames.


6.12.3.2 SRVCC Handover %*o$% PS H@ &$or%

The difference from the release > "/;11 is denoted with the /28 font in fiure A.,*.3. 3=,. &n this solution- the M"1"erver?MG behaves as the "G"' for 2P1 nodes in order to reduce @O disruption by adaptin indirect data

forwardin techni:ue.

3GPP

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-igure (%#"%3%")#. call flo5 5ithout PS 18 Support

2ditor$s 'oteEThe fiure will be update to clarify routin will be 2=MG="?P=G after step,


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F MG set up the codec based on the "8P information previously fetched via P11.

fter step ,,. The source e'ode0 initiates 8ata forwardin for bearers includin ;o&P media. fter this point-

;o&P media is forwarded to the MG via "=G.

fter step ,3- the suspendin related procedure is omitted in the flow since there is no chane from the /el=>"/;11.

,9. pon receivin step,9d- MM2 will not trier the release of voice bearer. The voice bearer will be deleted by

&M" session transfer triered in step,a- ;o&P media is conveyed between 2 and peer end via the MG.

/eardin the bearer in "=G side- upon the completion of the session transfer procedure- ;O&P bearer release procedure is to be triered by &M" via P11 i.e. PG?"G?the source MM2 is to release the bearer at this

point in time.

/eardin the bearer in M"1 side- upon ac#nowledin the completion of the session transfer procedure (e..receivin *++ O% from "11 ")- the M"1 server is to release the bearer towards "G.

'OT2E 0ased on implementation- MG should be able to decode the M/ without any re=synchroni!ation with

peer end after @O by receivin a few M/ frames.


6.12.3.3 SRS Reo#a%on

hen 2 moves to different /'1 area and "G"' relocation happens- followin procedure is triered. ith this procedure- M"1 "erver?MG always maintains the up=to=date information about the "G"' and "=G. This procedureis only applied if "/;11 @andover with P" @O support is performed but remote le update in step,>e of 7iureA.,*.3.*=, is not performed.

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-igure (%#"%3%3. SR0S Relocation

,=F. "/'" relocation procedure is initiated as specified in T"*3.+A+ clause A.F.*.*.,. 'o 1hane is made for

these steps ecept that the taret "G"' does not establish the /0 for voice bearer mar#ed with P"=to=1"indicator toward taret /'1.

'OT2E &f "=G relocation occurs- the new "G"' receives taret "G &P address?T2&8 for ;o&P bearer instep .

Fa. &f "=G chane occurs- the new "G"' notifies the M"1 "erver?MG with the taret "=G information bysendin P" to " pdate messae. P" to " pdate messae carries the taret "G &P address?T2&8 for ;o&P bearer. M"1 "erver?MG replies by sendin P" to " pdate c# messae.

,+=,


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6.12.3. SP rea%ed n!or"a%on re-!e%#*n7

hen ;oice media communication starts usin &M"- the P=1"17 informs "8P related information of the voice media-e.. used codec- to the MM2 usin the P11 architecture as specified in T" *3.*+A I,9J. The received information ismaintained in MM2 even inter MM2 @O happens.

-igure (%#"%3%+)#. S6P related information pre)fetching

+. 2 or peer end initiate a voice media communication by sendin "&P &';&T2 messae. This messae containsthe media information in its "8P.

,. Triered by P=1"17- &M" sends the service information to P1/7 accordin to the P11 architecture asspecified in the T" *3.*+3 I,*J. This messae contains "8P related information- e.. codec.

*. P1/7 sends ac# messae to &M".

3. Policy and 1harin /ules Provision is sent to PG as policy and charin provisionin. This messae alsocontains "8P related information.

9. PG sends the 1reate 0earer /e:uest messae to MM2 via "G in order to establish a dedicated bearer forvoice media. This messae also contains "8P related information. hen MM2 receives this messae- MM2

stores the voice media related information.


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-igure (%#"%3%')#. S6P related information update

+. 2 or peer end initiate a "8P update procedure any time durin the voice media communication by sendin "&PP8T2 messae. This messae contains the media information in its "8P- such as codec.

,. Triered by P=1"17- &M" sends the service information to P1/7 accordin to the P11 architecture as

specified in the T" *3.*+3 I,*J. This messae contains "8P related information.

*. P1/7 sends c# messae to &M".

3. Policy and 1harin /ules Provision is sent to PG as policy and charin provisionin. This messae also

contains "8P related information.

9. PG sends the Modify 0earer /e:uest messae to MM2 via "G in order to update "8P related information.hen MM2 receives this messae- MM2 updates "8P related information. "ince the Modify bearer re:uest issent in order to update "8P related information in MM2- there is no /adio bearer and /adio access bearerrelated procedure ta#es place.


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-igure (%#3%#)#. 7S Service Centrali4ation and Continuity Reference Architecture 5hen using ATC-enhancements%

'OT2 ,E &f neither the M"1 "erver assisted mid=call feature nor M"1 "erver enhanced for &1" is supported- theinterface between M"1 "erver and T17 is Mw.

'OT2 *E &f the M"1 "erver is enhanced for &1" or supports M"1 "erver assisted mid=call feature- the interface

between M"1 "erver and T17 is &*.

The followin fiures show the architecture view of control plane and user plane before and after transfer. &t is assumedthat PG and P=1"17 are in the servin networ# (supportin &M" ;oice roamin if not home). The T17 isfunctionality resident in the servin networ# (home if not roamin)- and the TG is depicted as a separate

functionality. The ccess 5e as defined in T" *3.*3D I9J is subdivided by the T17 into a "ervin 5e and a @ome5e.

-igure (%#3%#)". Architecture Vie5 of Control Plane

'OT2 3E Other &M" nodes in the servin networ# are not depicted in the architecture view of control plane.

The reference point between M"1 "erver and T17 is a networ#=internal reference point that is not eposed on the'&. "&P protocol is used for the reference point. "imilar to Mw- the &* reference point is only eposed to the operator$sinternal networ#. The same procedures for protection of the interface are epected to be in place for &* as for Mw.

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s specified in T" *3.*3D I9J- and in case the M"1 "erver is also enhanced for &1"- then the M"1 "erver may reisterthe user in the &M" after the transfer. The reistration from the M"1 "erver may not be routed via the T17.

-igure (%#3%#)3. Architecture Vie5 of /ser Plane ATG< controlled 9y ATC-!

6.13.2 $n#%ona /n%%e&

6.13.2.1 +TC

6.13.2.1.1 Genera

new functionality for control plane in the servin networ# (home if not roamin) is proposed to be defined- i.e.-ccess Transfer 1ontrol 7unctionality (T17). The T17 is included in the session control plane for the duration of thecall before and after ccess Transfer- based on the local policy of the servin networ# (if the servin networ# wishes to

provide "/;11 enhancement for this subscriber).

'OT2 ,E &t is recommended that the T17 be co=located with one of the eistin functional entities within theservin networ# (e..- P=1"17- &017- or M"1 "erver).

The T17 shallE

= 0ased on operator policy- decide to

= allocate a "T'="/H

= include itself for the "&P sessionsH and

= instruct the TG to anchor the media path for oriinatin and terminatin sessionsH

= #eep trac# of sessions (either in alertin state- active or held) to be able to perform ccess Transfer of theselected sessionH

= Perform the ccess Transfer and update the TG with the new media path for the (1") access le- withoutre:uirin updatin the remote leH

= fter ccess Transfer- update the "11 " that the ccess Transfer has ta#en place to ensure that T=8" has theupdate information on the currently used access.

= @andle failure cases durin the ccess Transfer.

fter ccess Transfer- and based on local policy- the T17 may remove the TG from the media path. This stepre:uires remote end update.

The T17 shall not modify the dynamic "T& that is echaned between the 2 and "11 ".

There are two options for providin M"1 "erver assisted mid=call featureE

= T17 handles mid=call support for the ccess Transfer usin M"1 "erver assisted mid=call featureH or

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'OT2 *E &f the T17 supports M"1 assisted mid=call feature- then the T17 needs to #eep trac# of sessions inalertin- active and held state to be able to support transferrin one session only (either in alertin state oractive- held- and ? or conference call)- a second already established session (which can be held and ? orconference call) and ? or a call in alertin state. "upport of M"1 "erver assisted mid=call feature in the

T17 ensures that alertin state- held state- - and ? or conference state can be transferred to the M"1"erver without delay caused by interactin with "11 " especially in roamin cases.

= "11 " and T17 handle mid=call support for the ccess Transfer usin M"1 "erver assisted mid=call feature.

'OT2 3E &f the T17 does not support the M"1 assisted mid=call feature- then the T17 needs to #eep trac# ofsessions in alertin- active and held state to be able to support transferrin the first session (either inalertin state- active or held). 'ote that oriinatin and terminatin sessions are anchored in theT17?TG already durin session setup. The "11 " provides then session state information onalertin- held and?or conference state of the first transferred session and on second established session.

6.13.2.1.2 +TC an#*orn7

The followin implementation methods could be used to determine if the T17 should be

Documents

23856-A00 - Single Radio Voice Call Continuity (SRVCC) Enhancements; Stage 2