voice in 4g: csfb, voip & volte › training › advanced0001.pdfcircuit switched fallback (csfb)...

Voice in 4G: CSFB, VoIP & VoLTE

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Did you hear this joke about 4G?

Now lets get back to the serious discussions

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IMT-Advanced and 4G Technologies

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Different paths to 4G

4G LTE / LTE-A

(FDD – TDD)

3GPP 3GPP2

1xEV-DO: Enhanced Voice-Data Optimized CDMA ONE: Code Division Multiple Access One EDGE: Enhanced Data rates for GSM Evolution eHRPD: Enhanced High Rate Packet Data GPRS: General Packet Radio Service GSM: Global System for Mobile Communications HSPA: High Speed Packet Access HSPA+: High Speed Packet Access Plus OFDMA: Orthogonal Frequency Division Multiple Access SCDMA: Synchronous CDMA TD: Time Division TD-SOFDMA TD Scalable OFDMA UMTS: Universal Mobile Telecommunication System

The ‘4G’ LTE Network Architecture

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BSC

BTS

MSC

Voice (PSTN) Network

SGSN

Data (IP) Network

RNC

Node B eNodeB

MME

GGSN

Access Network

Core Network

Air Interface

MS UE UE

BSS RNS

S-GW

P-GW

2G 2.5G

3G 4G

EPC

Circuit Switched Fallback (CSFB)

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LTE

2G/3G UE

CSFB

• CSFB has been designed as an interim solution until the LTE networks are rolled out completely.

• In case of CSFB, the UE falls back to 2G/3G network when a voice call / SMS needs to be initiated / sent or received.

• Since the UE has just one receiver, the data rates after CSFB would be the data rates offered by the 2G/3G network.

CSFB Approaches

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• Redirection: When UE starts a call in Idle (RRC_IDLE) state

• Handover: When the UE already has an active data connection (in

RRC_Connected state). The active data connection is handed over to 2G/3G network

SVLTE (Simultaneous Voice and LTE)

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• Also known as Dual Radio Concept

• Separate registration takes place for the CDMA/EV-DO and LTE networks

• Each network need not be aware of what the UE is doing with the other one.

• Since Voice and Data are independent one of them does not impact the other one.

LTE

CDMA/EV-DO

• CDMA/EV-DO registration • Paging for Voice call • MO/MT Voice call

• LTE registration • Paging for Data call • Data call

UE

SGLTE (Simultaneous GSM and LTE)

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• Same as SVLTE but for GSM Network

LTE

2G – GSM

• 2G registration • Paging for Voice call • MO/MT Voice call


UE

SRLTE (Single Radio LTE)

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• Similar to SVLTE but Single Radio • Only Apple implemented it in

iPhone • Separate registration takes place

for the 2G/3G and LTE networks • Each network is not aware of

what the UE is doing with the other one.

• Only Voice or Data can be done at any time, not both.

• UE scans paging channel regularly making it inefficient

LTE

CDMA/EV-DO

• CDMA/EV-DO registration • Paging for Voice call • MO/MT Voice call


UE

SxLTE was strongly discouraged

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• Devices were more expensive because of dual radios

• Higher Power Consumption

• Does not allow legacy networks to be switched off

• Can have competitive disadvantage

2G

WiMAX

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UE

eNB

S-GW

P-GW

Peer Entity

Radio S1 S5 / S8 Gi

E-UTRAN EPC Internet

End-to-End Service

EPS Bearer External Bearer

E-RAB S5/S8 Bearer

S1 Bearer Radio Bearer

Type Error Rate Delay Priority QCI Examples

1

GBR

10-2 100 ms 2 Conversational voice

2 10-3 150 ms 4 Conversational video

3 10-3 50 ms 3 Real-time games

4 10-6 300 ms 5 Streaming video

5

Non – GBR

10-6 100 ms 1 IMS Signalling

6 10-6 300 ms 6 Steaming video, web, email

7 10-3 100 ms 7 Voice, video, games

8 – 9 10-6 300 ms 8 – 9 Streaming video, web, email

Voice over IP (VoIP)

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• Voice goes as data, the same way as any other IP data.

Default Bearer

eNB

Internet

UE

APN1

Over The Top (OTT) Apps

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Why have 4G Voice?

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• Better for MNO’s with no legacy Infrastructure

• Re-farm Spectrum

• Better Voice Quality

• Faster Data Rates while voice calling – other services are not impacted

• Simpler operation

• Better Battery Life

Voice over LTE (VoLTE)

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• Voice is independent of Data and is carried by different bearer • An additional signalling and data bearer is used for VoLTE

VoLTE bearer

Default Bearer eNB

Internet

UE

APN1

APN2

VoLTE to VoHSPA Handover

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• HSPA call is controlled by IMS Core

E-UTRAN

UTRAN

IMS Call

IMS Call

Telephony server

Rich Communication

Suites

SMS server

MGW

IMS CORE

VoHSPA Handover

Single Radio Voice Call Continuity (SRVCC)

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• The Voice call continues on CS Core

E-UTRAN

UTRAN GERAN

IMS Client

UE

Telephony server

Rich Communication

Suites

SMS server

MGW

IMS CORE

SRVCC – PS to CS

Voice path before and after SRVCC

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UE

E-UTRAN

UTRAN GERAN

HSS

S-GW P-GW

MSC

MME

SGSN

SV

S3

UE

E-UTRAN

UTRAN GERAN

HSS

MSC

SV

MME

SGSN

S3

SRV

CC

P

S to

CS

S-GW P-GW

Thank You

To learn more, visit:

3G4G Website – http://www.3g4g.co.uk/

3G4G Blog – http://blog.3g4g.co.uk/

3G4G Small Cells Blog – http://smallcells.3g4g.co.uk/

Follow us on Twitter: https://twitter.com/3g4gUK

Follow us on Linkedin: https://www.linkedin.com/company/3g4g

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voice in 4g: csfb, voip & volte › training › advanced0001.pdfcircuit switched fallback (csfb)...

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