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SRVCC Call Flow Guide

The document describes the call flow for a SRVCC (Single Radio Voice Call Continuity) handover from an LTE network to a circuit switched network. It involves 3 phases: 1) Phase 0 establishes the UE's registration in the IMS network and sets up a VoLTE call between two UEs. 2) Phase 1 describes the ongoing VoLTE call between the UEs. 3) Phase 2 covers the handover decision, preparation, and execution where bearer information is passed to the target MSC server to complete the handover to the circuit switched network.

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Anderson Medina
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106 views10 pages

SRVCC Call Flow Guide

The document describes the call flow for a SRVCC (Single Radio Voice Call Continuity) handover from an LTE network to a circuit switched network. It involves 3 phases: 1) Phase 0 establishes the UE's registration in the IMS network and sets up a VoLTE call between two UEs. 2) Phase 1 describes the ongoing VoLTE call between the UEs. 3) Phase 2 covers the handover decision, preparation, and execution where bearer information is passed to the target MSC server to complete the handover to the circuit switched network.

Uploaded by

Anderson Medina
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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2e

SRVCC Call Flow


(Circuit Switched Domain)

General Introduction (Day 4) 1 Thomas Hammann


SRVCC Call Flow (Circuit Switched Domain)
Overview 2e

Phase 0: LTE Attach and SIP Register

Phase 1: VoLTE Call

Phase 2: Handover (Handover Decision, Handover Preparation, Handover Execution, Handover Completion)

General Introduction (Day 4) 2 Thomas Hammann


SRVCC Call Flow (Circuit Switched Domain)
Phase 0: LTE Attach and SIP Register

UE-A UE-B Target NodeB Target RNC MME HLR P/I/S-CSCF MSS DNS NVS MGW

SGsAP.Location-Update-Request (IMSI, EPS location update type=IMSI attach,


LAI (MNC, MCC, LAC))
SGsAP-Location-Update-Accept (TMSI)
PS-Core
SGsAP-TMSI-REALLOCATION-COMPLETE

SIP REGISTER (To=sip:+491725670014@tb11.mchm.nsn-rdnet.com,


NVS included From=sip:scscf1.tb11.mchm.nsn-rdnet.com)
because of
Trigger SIP 200 OK
IMS

Subscriber is SIP
registered
in NVS (Contact-Info,
SIP-URI, IMSI, GroupID,
MSISDN in SPD) and
data from HLR is
restored to VLR

General Introduction (Day 4) 3 Thomas Hammann


SRVCC Call Flow (Circuit Switched Domain)
Phase 0: VoLTE Call

UE-A UE-B Target NodeB Target RNC MME HLR P/I/S-CSCF MSS DNS NVS MGW

SIP INVITE (From=sip:+491725670014@tb11.mchm.nsn-rdnet.com,


NVS included To=sip:+49172128004090@tb11.mchm.nsn-rdnet.com,
because of Record-Route=sip:isc@scscf1. tb11.mchm.nsn-rdnet.com,
Trigger Call-ID: 147…252
P-Asserted-Identity=sip:+491725670014@tb11.mchm.nsn-rdnet.com

DNS query (Queries=scscf1.tb11.mchm.nsn-rdnet.com)

DNS response (<IP address of S-CSCF>)

SIP INVITE (From=sip:+491725670014@tb11.mchm.nsn-rdnet.com,


To=sip:+49172128004090@tb11.mchm.nsn-rdnet.com,
Record-Route=sip:isc@scscf1. tb11.mchm.nsn-rdnet.com,
Call-ID: 490…0DE
P-Asserted-Identity=sip:+491725670014@tb11.mchm.nsn-rdnet.com,
ENUM-DNS:
tel:+491725670014)
Subscriber B does not
exist in IMS Domain
-> Breakout
SIP INVITE (From=sip:+491725670014@tb11.mchm.nsn-rdnet.com,
with Numbered based
To=sip:+49172128004090@tb11.mchm.nsn-rdnet.com,
Routing to MGCF Record-Route=sip:isc@scscf1. tb11.mchm.nsn-rdnet.com,
Call-ID: 490…0DE
P-Asserted-Identity=sip:+491725670014@tb11.mchm.nsn-rdnet.com,
tel:+491725670014)

General Introduction (Day 4) 4 Thomas Hammann


SRVCC Call Flow (Circuit Switched Domain)
Phase 0: VoLTE Call

UE-A UE-B Target NodeB Target RNC MME HLR P/I/S-CSCF MSS DNS NVS MGW
SIP 183 Session Progress (From=sip:+491725670014@tb11.mchm.nsn-rdnet.com,
To=sip:+49172128004090@tb11.mchm.nsn-rdnet.com,
Call-ID: 490…0DE
SDB (Connection Information=10.200.136.98) )

SIP 183 Session Progress (From=sip:+491725670014@tb11.mchm.nsn-rdnet.com,


To=sip:+49172128004090@tb11.mchm.nsn-rdnet.com,
Call-ID: 490…0DE
SDB (Connection Information=10.200.136.98) )

SIP 183 Session Progress (From=sip:+491725670014@tb11.mchm.nsn-rdnet.com,


To=sip:+49172128004090@tb11.mchm.nsn-rdnet.com,
IMS Call-ID: 147…252
SDB (Connection Information=10.200.136.98) )

Request: PRACK (Call-ID: 147…252)

Request: PRACK (Call-ID: 490…0DE)


Request: PRACK (Call-ID: 490…0DE)

STATUS: 200 OK (Method: PRACK, Call-ID: 490…0DE)

STATUS: 200 OK (Method: INVITE, Call-ID: 490…0DE)

STATUS: 200 OK (Method: PRACK, Call-ID: 490…0DE)

STATUS: 200 OK (Method: PRACK, Call-ID: 147…252)


STATUS: 200 OK (Method: INVITE, Call-ID: 490…0DE)

STATUS: 200 OK (Method: INVITE, Call-ID: 147…252)

General Introduction (Day 4) 5 Thomas Hammann


SRVCC Call Flow (Circuit Switched Domain)
Phase 2: Handover (Handover Decision, Handover Preparation, Handover Execution, Handover Completion)

UE-A UE-B Target NodeB Target RNC MME HLR P/I/S-CSCF MSS DNS NVS MGW

Handover Decision

Handover Preparation
Here comes
The GBR Bearer SRVCC PS to CS Request (Sv Flags (Emergency Indicator=False), STN-SR=499040110, MSISDN,
IMSI, MM Context for E-UTRAN SRVCC, Source-ToTarget-TransparentContainer,
with QCI 1 ☺
Target RNC ID (RAI (MCC, MNC, LAC), RNC-ID))

CR

CC

RelocationResourceAllocation (Relocation Request (Cause=time-critical-relocation, CN-DomainIndicator=cs-domain,


Source-ToTarget-TransparentContainer (numberofIuInstances=2, relocationType=ue-involved, targetCellId,
UE-History-Information (E-UTRAN)), RAB-Setup-RelocReq (Item 0 (rAB-ID=01, rAB-Parameter (trafficClass=conversational,
mbr,gbr, sDU, allocationOrRententionPriority,userPlaneInformation,transportLayerAddress, iuTransportAssociation)))

NBAP Radio Link Setup

NBAP Radio Link Setup Response

RelocationResourceAllocation (Relocation Request Acknowledge (RAB-SetupList-RelocReqAck (


Item 0 (rAB-ID=01, transportLayerAddress, iuTransportAssociation)))

SRVCC PS to CS Response (Cause=Request accepted, TEID-C, Target to source


PS-Core Transparent Container)

General Introduction (Day 4) 6


Thomas Hammann
SRVCC Call Flow (Circuit Switched Domain)
Phase 2: Handover (Handover Decision, Handover Preparation, Handover Execution, Handover Completion)

UE-A UE-B Target NodeB Target RNC MME HLR P/I/S-CSCF MSS DNS NVS MGW

LocationReportingControl (RequestType (event=change-of-servicearea))

SRVCC PS to CS Response (Cause=Request accepted, TEID-C, Target to source


Transparent Container)
PS-Core
Handover Preparation

Handover Execution
DNS query (Queries=icscf1.tb11.mchm.nsn-rdnet.com)
DNS response (<IP address of I-CSCF>)

Break in SIP INVITE ( Request-Line: INVITE +99499040110, From=+491725670014,


To=+49499040110, P-Asserted-Identity=sip:+491725670014@tb11.mchm.nsn-rdnet.com,
tel:+491725670014 ,Call-ID: 5A8…9C6
SDP (Connection Information=10.200.136.106, Media Description))
IMS removes prefix SIP INVITE ( Request-Line: INVITE +499040110, From=+491725670014,
and sends STN-SR on To=+49499040110, P-Asserted-Identity=sip:+491725670014@tb11.mchm.nsn-rdnet.com,
originating leg tel:+491725670014 ,Call-ID: 5A8…9C6
SDP (Connection Information=10.200.136.106, Media Description)) 74974ESPE03
SIP INVITE ( Request-Line: INVITE sip:+10.200.136.34, From=sip:+491725670014@tb11.mchm.nsn-rdnet.com,
reINVITE on terminating
To=sip:+49172128004090@tb11.mchm.nsn-rdnet.com,
leg, since CMN mode Call-ID: 490…0DE
SDP (Connection Information=10.200.136.106, Media Description))

SIP INVITE ( Request-Line: INVITE sip:+10.200.136.34, From=sip:+491725670014@tb11.mchm.nsn-rdnet.com,


To=sip:+49172128004090@tb11.mchm.nsn-rdnet.com,
Call-ID: 490…0DE
SDP (Connection Information=10.200.136.106, Media Description))

General Introduction (Day 4) 7


Thomas Hammann
SRVCC Call Flow (Circuit Switched Domain)
Phase 2: Handover (Handover Decision, Handover Preparation, Handover Execution, Handover Completion)

UE-A UE-B Target NodeB Target RNC MME HLR P/I/S-CSCF MSS DNS NVS MGW

SIP 200 OK (From=sip:+491725670014@tb11.mchm.nsn-rdnet.com,


To=sip:+49172128004090@tb11.mchm.nsn-rdnet.com,
Call-ID: 490…0DE
SDP (Connection Information=10.200.136.98, Media Description (<For Subscriber B>))

SIP 200 OK (From=sip:+491725670014@tb11.mchm.nsn-rdnet.com,


To=sip:+49172128004090@tb11.mchm.nsn-rdnet.com,
Call-ID: 490…0DE
SDP (Connection Information=10.200.136.98, Media Description (<For Subscriber B>))

SIP 200 OK (From=+491725670014,To=+ +99499040110,


Call-ID: 5A8…9C6
SDP (Connection Information=10.200.136.98, Media Description (<For Subscriber B>))

SIP 200 OK (From=+491725670014,To=+ +99499040110,


Call-ID: 5A8…9C6
SDP (Connection Information=10.200.136.98, Media Description (<For Subscriber B>))

Relocation Detect
Handover is detected by Target RNC
Handover Execution

Relocation Complete on CS Domain Handover Completion


Handover to UTRAN Complete
Realocation Complete , LocationReport (AreaIdendity (SAI (pLMNIdentity (MNC,MCC), lAC,sAC),
RequestType=change-of-service-area)

General Introduction (Day 4) 8


Thomas Hammann
SRVCC Call Flow (Circuit Switched Domain)
Phase 2: Handover (Handover Decision, Handover Preparation, Handover Execution, Handover Completion)

UE-A UE-B Target NodeB Target RNC MME HLR P/I/S-CSCF MSS DNS NVS MGW

SRVCC PS to CS Complete Notification (IMSI)


PS-Core
SRVCC PS to CS Complete Acknowledge (Cause:Request Accepted)

TMSI Reallocation Command(LAI (MNC, MCC, LAC), TMSI)

TMSI Reallocation Complete

SIP BYE (Call-ID: 147…252 )


Release old orig. leg IMS
after handover is
completed SIP Status 481 Transaction Does not exist
(Call-ID: 147…252 )

CC Disconnect
Call release
CC Release
SIP BYE (Call-ID: 5A8…9C6)

SIP BYE (Call-ID: 5A8…9C6)


STATUS : 200 OK (Call-ID: 5A8…9C6)

STATUS : 200 OK (Call-ID: 5A8…9C6)


SIP BYE (Call-ID: 490…0DE)
SIP BYE (Call-ID: 490…0DE)

General Introduction (Day 4) 9


Thomas Hammann
SRVCC Call Flow (Circuit Switched Domain)
Phase 2: Handover (Handover Decision, Handover Preparation, Handover Execution, Handover Completion)

UE-A UE-B Target NodeB Target RNC MME HLR P/I/S-CSCF MSS DNS NVS MGW

STATUS : 200 OK (Call-ID: 490…0DE)

STATUS : 200 OK (Call-ID: 490…0DE)

CC Release Complete

Location Update Request

General Introduction (Day 4) 10


Thomas Hammann

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