LTE Voice Services Agenda • Voice Options in LTE • Comparison of Voice Options • Voice Deployment Strategies • MultiService Forum • VoLTE Recent Announcements • Voice Enhancements – Rel 8 & 9 • Conclusion Voice Options with LTE • Data Only • Circuit Switched Fallback (CSFB) to 2G/3G CS • VoLGA • VoLTE (IMS-based) – On LTE Only – On LTE & 2G/3G via SR-VCC – On LTE & 3G via UMTS PS • Over-the-top (OTT) – à la Skype Data Only • PROS – Simple – Device availability – Easy and gradual deployment of LTE • CONS – Not useful for smartphones – Single radio limitation – May encourage OTT competition The initial LTE offering for many carriers is based on devices with no native voice support - eg PC Dongles CS Fallback Procedures - 1 • Registration: – a combined UE registration procedure on both LTE and GSM/UMTS – from the MME to the MSC via the SG interface – GSM/UMTS Location Area ID (LAI) calculated from the LTE Tracking Area ID (TAI) • Call Origination – UE requests the MME to perform a CSFB – MME requests the eNodeB to redirect UE to the target 2G/3G cell (determined via UE measurements or preconfigured) – The eNodeB redirects the UE to the target cell – The UE performs an RRC on the target cell (and possibly a location update as well) CS Fallback Procedures - 2 • Call Termination: – The MSC sends the page request to the MME over the SG interface – The MME pages the UE with the CSFB indicator – UE responds with a service request with the CSFB indicator – MME instructs the eNodeB to redirect UE to the target 2G/3G cell (determined via UE measurements or preconfigured) – The eNodeB redirects the UE to the target cell – The UE performs an RRC on the target cell (and possibly a location update as well) • Active Data Sessions: – Must be handed-over to the 2G/3G or dropped – Via a Packet Switch HandOver (PSHO) on 3G – Requires Dual Transfer Mode (on both 2G and UE) if fallback on 2G CS Fallback Procedures - 3 • SMS: – No fallback for SMS origination/termination – UE sends/receives SMSs to/from the MME – MME sends/receives SMSs to/from the MSC over the SG interface CS Fallback Architecture GERAN MSC/VLR UTRAN Um SGs HSS S6a Ch, Sx Uu S1-MME MME PCRF S10 S7 RX+ S11 UE eNodeB S-GW P-GW IMS LTE Uu S1-U S5 SGi X2 CS Fallback Call Flow UE UE eNodeB BSS MME MSC SGSN S-S-GW P-GW 1a. Extended Service Request UE to MME: I want to move to UTRAN 1b. S1-AP Request message with CS Fallback indicator 1c. S1-AP Response message MME to ENB: UE wants to move to UTRAN 2. Optional Measurement Report Solicitation ENB to UE: where are you? 3a. PS HO as specified in 23.401 [2] (preparation phase and start of execution phase) if PS HO fails -» CSFB fails 3b. Suspend ONLY FOR GERAN SGSN deactivates GBR Bearers (SGW+PDN) 3c. Update Bearer(s) 4a. Location Area Update or Combined RA/LA Update LA in UE is nok? Then LAU 4b. CM Service Request 4b. A/Iu-cs message (with CM Service Request) UE to MSC: Context Modification 5. CM Service Reject 5. CM Service Reject If the MSC is changed Location Area Update or Combined RA/LA Update 6. CS call establishment procedure The call is established on 3G 7. PS HO as specified in 23.401 [2] (continuation of execution phase) Once the call is ended, PS HO to LTE CS Fallback – UE and Network Requirements • UE: – Support for both LTE and GSM/UMTS – Support for combined EPS/IMSI attach, detach, and location update procedures – Support for CS fallback and SMS procedures • Network – 2G/3G MSCs: – Support of SGs interface to the MME – Support of simultaneous paging on the A, Iu, and SGs interfaces – Support of sending and receiving SMS over the SGs interface • Network – LTE MME: – SGs interface support – MSC procedures such as IMSI attach/detach, location update, and paging – CS fallback SMS procedures • Network – LTE E-UTRAN: – Redirect UE to a GSM/UMTS cell – Forwar • Network Engineering – Additional LTE traffic over the GSM/UMTS network (RAN and MSC) – iTrack ng/location and coverage areas shall be consistent between LTE and GSM/UMTS CSFB issue due to TA/LA misalignment Source : GSMA IR.88 LTE Roaming Guidelines In the case of TA/LA misalignment, the Roaming Retry procedure allows transferring the incoming call from MSC1 to MSC2, which increases both the call setup time and the call success ratio. CS Fallback – PROs & CONs • PROS – Reuse of all GSM/UMTS voice infrastructure including existing OSS/BSS systems – lFastout rol of voice services – Voi ce service transparency between LTE and 2G/3G – Minor upgrades on legacy network (SG interface similar to the MSC- SGSN G interface) • CSON – Call set-up delay i.e. 500+ msec – Concurrent data session may be dropped VoLGA • Based on 3GPP TS 23.879 option 2, with further development by the VoLGA Forum • Uses a new dedicated Interworking Function (IWF), also known as VoLGA Access Network Controller (VANC), to interwork the LTE and GSM/UMTS networks. Inserted between the EPS and MSC • All voice traffic goes through the LTE but using the 2G/3G voice Source: 3GPP VoLGA Stage 2 V2.0.0 (2010-06-14) infrastructure in a transparent manner VoLGA • PROS – Reu se of all GSM/UMTS voice infrastructure including existing OSS/BSS systems – Fast rollout of voice services – rVoice se vice transparency between LTE and 2G/3G – No changes on legacy network – Fast LTE-to-GSM/UMTS handovers – Supports concurrent voice and data sessions • CSON – Voice traffic hits both the LTE and the 2G/3G networks – tIn roduces three new network elements: VANC, security GW, AAA server – Does not support advanced IMS services – Notd accepte by 3GPP IMS – Historical Overview • Ra tionale & Purpose – IMS is an SIP-based (Session Initiation Protocol) session and service control platform that enables delivery of multimedia applications across a broadband wireline or wireless network – IMS was first introduced in the 3GPP Release 5 standards and predates the development of LTE by nearly seven years – Builds on IETF SIP technology (perceived Internet scaling and low cost) – Split the access network from the service network permitting common service network across fixed, mobile and internet – Mul timedia in addition to voice; No need to standardised services only enablers • The Reality – IMS was intended to be access agnostic, but interaction with existing technologies requires access specific functionality be added to the IMS network. – Complex standard with many options to SIP – Large legacy service load; Service parity with CS is complicated – Commel rcia systems available, but take up has been very slow – 3G PP extensions in 3GPP TS 24.229 for management, security and billing reasons • Initial Deployment Issues – Co st – IMS requires a complete new core network – Ri sk – Scaling up to support 10’s of millions to subscribers is still an unknown. – P erformance is also seen as a risk – Int egration – Existing services have to be integrated with IMS based service – Operator business models – Services run as separate P&L centres IMS – Key Components The Call Session Control Functions (CSCF) are the core components of the IMS. There are three CSCF: • Proxy-CSCF (P-CSCF): The P-CSCF is the first point of contact for a user. The PCSCF behaves like a proxy, i.e. it accepts requests and forwards them on. • Interrogating-CSCF (I-CSCF): The I-CSCF is the entry contact within an operator’s network for all connections destined to a subscriber. • Serving-CSCF (S-CSCF): The S-CSCF is responsible for handling the registration process, making routing decisions, maintaining sessions, and downloading user information and service profiles from the HSS. VoLTE with LTE Access Only • Based on 3GPP TS 23.228 IMS supporting both legacy voice services and advanced multi- media services • GSMA IR.92 defines the profile HSS for Voice and SMS based on One MME PCRF Voice Initiative IMS eNode • Can be extended to support voice UE S-GW P-GW P-CSCF AF B service service continuity to 2G I-CSCF S-CSCF GSM network (i.e. handovers) • Can be extended to support voice service service continuity to 3G UMTS/HSPA network (i.e. VoLTE with SRVCC-based voice delivery • SIP signaling between the UE and the IMS core • Ov er the existing transport capabilities of the GSM/UMTS network • fUs e o ICS (CS-to-IMS call control) and SRVCC (handovers) • Support simultaneous PS and CS services, the IP connection is provided by the legacy packet core as per the Gm reference point. 3GPP TS 23.216 V9.6.0 (2010-12): "Single radio voice call continuity (SRVCC); Stage 2 (Release 9)". VoLTE with UMTS-PS voice delivery Um/Uu Iu-CS/A UTRAN UE GERAN MSC I2 • UM TS PS access, allowing voice, Iu-PS/Gb data and multimedia services to SV be carried simultaneously over SGSN the same PS-domain IP S3 3GPP connection (no need for ICS and IMS SRVCC) S6a MME HSS • Concurrent voice and data S1-MME SGis multimedia services S11 • Seamless mobility between the Uu S1-U UE E- P-GW LTE and UMTS networks with the UTRAN use of PS handovers and handbacks VoLTE Procedures - 1 • Registration: – The UE always registers on the IMS network (for both LTE and GSM/UMTS) – Registration includes the ICS and SRCVCC indicators (if supported) • Call Origination – Session is set-up as standard IMS procedures according to 3GPP TS 23.228 – Ine th GSM/UMTS, the ICS-enabled UE sets-up 2 signaling paths (one over legacy packet to the IMS SCC AS, one CS-bearer via legacy procedures to the MSC) – CCThe AS S combines the 2 procedures on the CS-access leg and establishes the IMS-leg of the call VoLTE Procedures - 2 • Call Termination: – IMS terminating session is initiated toward the UE’s selected contact address – Upon receiving the invite message, the ICS-enabled UE originates a CS call to the SCC AS using its associated directory number – Similar procedure as for call origination • LTE to UMTS PS Handover: – Ind itiate by the eNode B via a request to the MME to establish resources in the target RNC, SGSN and SGW – The MME only needs to coordinate and perform a PS handover.