single radio voice call continuity application-note

8/10/2019 Single Radio Voice Call Continuity Application-Note

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Single Radio Voice Call Continuity (SRVCC)Testing Using Spirent CS8 Interactive TesterSeptember 2013

Rev. A 09/13

Application Note


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Single Radio Voice Call Continuity (SRVCC) Testing

Using Spirent CS8 Interactive Tester

TABLE OF CONTENTS

Executive Summary 4

SRVCC Technology Overview 5

Spirent Solutions Overview For SRVCC Testing 7

CS8 Mobile Device Tester 7

CS8 Interactive Tester 7

System Architecture 8

SRVCC Mobility Using CS8 Interactive Tester 9

Step 1: Select Appropriate Test Configuration & Network View 9

Step 2: Configure Appropriate Downlink Configuration & PDN-GW Settings 10

Step 3: Enable SRVCC In MME Test Configuration Setting 11

Step 4: Connect To Instruments/Load IMS Message Flow/Enable Call Processing 11

Step 5: Initiate Mobile Originated VoLTE Call 14

Step 6: Initiate SRVCC Procedure 16

Conclusion 19

Acronyms 20

References 21

Table of Figures 22


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Single Radio Voice Call Continuity (SRVCC) Testing Using Spirent CS8 Interactive Tester

4 SPIRENT APPLICATION NOTE

1. EXECUTIVE SUMMARY

Voice continues to be a viable source of revenue for Network Operators. Consumers have

been accustomed to assured Quality of Service (QoS) standards while using voice services on

their mobile devices. According to Infonetics Research, an international market research andconsulting firm, voice will continue to comprise 60 percent of the mobile services market by

2014, signifying $522 billion in global mobile revenues (Figure 1).

Figure 1: Mobile Services Market Forecast For 2014

Source: Infonetics Research

As LTE networks are continuing to be deployed alongside legacy networks such as GERAN/

UTRAN/1xRTT, the ability for multimode 3G/LTE mobile devices to connect to different network

technologies will be an important part of providing the best possible mobile voice and dataexperience to customers. However, adoption of LTE and its all-Internet Protocol (IP) Radio Access

Network (RAN) has produced one of the key challenges of LTE deployment: delivery of voice

services in an all-IP network.

Three approaches were decided by the wireless industry to overcome these challenges:

VoLTE (Voice Over LTE)

CSFB (Circuit Switched Fallback)

SVLTE (Simultaneous Voice and LTE)

Unlike CSFB, VoLTE allows call continuity. With cost, size, and battery efficiency advantages

over dual radio solutions such as SVLTE, the industry is standardizing on VoLTE for the future.

VoLTE is based on the IP Multimedia Subsystem (IMS) network, with voice services being

delivered as data flows within the LTE data bearer. As a result, Single Radio Voice Call Continuity

(SRVCC) is required in order to execute a seamless handover of a voice call from an LTE network

to a 3G network and provide continuity for traditional circuit-switched networks.

This application note provides an overview of the SRVCC technology and outlines SRVCC

mobility testing using Spirent solutions. Since SRVCC implementation introduces a number of

challenges to development and test teams its testing is as important as ever.


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SPIRENT APPLICATION NOTE

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2. SRVCC TECHNOLOGY OVERVIEW

SRVCC is a method for ensuring fast and reliable handover of an LTE user to a legacy network

coverage area while it is in an active IMS based voice session. One challenge with SRVCC is

to handover while the UE is connected to only a single radio at a given time. Two variations ofSRVCC have been identified UTRAN to 3GPP2 1xCS and E-UTRAN to 3GPP UTRAN/GERAN.

The UE, LTE Network, and Target Legacy Networks should all support SRVCC. In addition, a

special interface known as Sv is formed between MME and MSC Server. The Sv interface is

an interface between the Mobility Management Entity (MME) or Serving GPRS Support Node

(SGSN) and 3GPP MSC server enhanced for SRVCC. The Sv interface is used to support Inter-RAT

handover from VoIP/IMS over EPS to CS domain over 3GPP UTRAN/GERAN access. To support

SRVCC the IMS network should also include application server called SCC-AS. The SCC (Service

Centralization and Continuity) AS is responsible for handling the signalling required for the

process (Figure 2).

Figure 2: High Level Concept for SRVCC from E-UTRAN to UTRAN/GERAN

As the UE moves away from the LTE coverage area, LTE Reference Signal Transmit Power (RSTP)

starts diminishing. The UE then notifies eNodeB about the change in the signal strength and

SRVCC handover is initiated. The LTE network determines that the active voice call needs to

be moved from the packet to the circuit domain. MME then receives the handover request

from E-UTRAN with the indication that it is for SRVCC handling, and it then triggers the SRVCC

procedure with the MSC Server via the Sv reference point.

A new voice call request is sent to the IMS using a special number known as STN-SR. STN-SR

is a unique number that is generated for each UE and is stored in the HSS. This number is sent

to the MME by the HSS when the UE first contacts with the network. Receiving STN-SR number

indicates to the SCC-AS that the corresponding call needs to be routed to a different network,

and it starts the redirection process to the legacy endpoint.


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3. SPIRENT SOLUTIONS OVERVIEW FOR SRVCC TESTING

3.1. CS8 Mobile Device Tester

CS8 Mobile Device Tester is a single network emulator designed to address all stages of

the mobile device design and testing cycles (Figure 4). CS8 can be used in radio protocol

development, platform validation, system testing and as the network emulator in automated

test systems, bringing value to every stage of the mobile device lifecycle. Available CS8

configurations can immediately address needs ranging from realistic LTE network emulation to

advanced multi-RAT mobility testing.

Figure 4: Spirent CS8 Mobile Device Tester

3.2. CS8 Interactive Tester

CS8 Interactive Tester is a GUI that controls the network emulator and offers intuitive control

over multi-cell multi-RAT network emulation (Figure 6). It integrates multiple radio access

technologies with a fully developed real-time IPv4 and IPv6 Evolved Packet Core (EPC), providing

a multi-RAT system with complete end-to-end emulation. The CS8 Interactive Tester real-time

state machine emulates an entire cellular environment including LTE, WCDMA, GSM, HSPA,

CDMA, EV-DO and Evolved High-Rate-Packet Data (eHRPD) services, with multiple cells available

per technology.

CS8 Interactive Tester Software window is divided into four panels:

1. Network View

2. Test Configuration

3. Test Results

4. Message Analyzer

Network Viewand Test Configurationpanels are used to configure network topologies. These

panels are used to configure both the Evolved Packet Core (EPC) and the Evolved UMTS

Terrestrial Radio Access Network (eUTRAN). For instance, PDN-GW, HSS, MME/SGW, and eNodeB

are all configured from within these panels.


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The Test Resultspanel provides diagnostic interpretation of test progress and outputs real-

time interactive message exchange between network and DUT. It also logs the NAS/AS state

transitions, EPC status, and system control information.

The Message Analyzerpanel displays a real-time log of all RRC/NAS messaging between

the network and the Device Under Test (DUT). The left side of the panel lists the message

sequences, while the right side shows the ASN.1-based contents for each message.

Figure 5: CS8 Interactive Tester User Interface Overview

3.3. System Architecture

Figure 6: CS8 Mobile Device Tester UMTS-LTE Hardware Setup

Spirent CS8 Mobile Device Tester coupled with the CS8 Interactive Tester provides emulation of

all network components and is able to handle testing requirements for SRVCC capable devices

including mobility scenarios.


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4. SRVCC MOBILITY USING CS8 INTERACTIVE TESTER

4.1. Step 1: Select Appropriate Test Configuration & Network View

Open CS8 Interactive Tester (Figure 7) and ensure the Application Password and Annual Support

Agreement is up-to-date (Figure 8).

Figure 7: CS8 Interactive Tester Icon

Figure 8: Application Password and Annual Support Agreement

Click on the Network Viewdropdown list from the CS8 Interactive Tester User Interface to

select from combinations of different technologies. Selecting a network topology brings

up the network components as well as configuration options for those components. Each

icon represents a network entity. Select appropriate Test Configuration based on the testing

requirement by choosing the applicable network from the Network Viewpane. In this example,

SRVCC from E-UTRAN to UTRAN is intended to be tested, therefore LTE, one UTRANnetwork

topology needs to be selected (Figure 9).

Figure 9: Test Configuration In Network View

The network components for both E-UTRAN and UTRAN networks are emulated and controlled

by CS8 Interactive Tester User Interface. The Evolved Packet Core, including PDN-GW, HSS, MME,

and SGW, are all emulated by Spirents SR3620. Both EPC and E-UTRAN are controlled by a

single user interface, providing unified control and a complete emulation of the LTE network.


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4.2. Step 2: Configure Appropriate Downlink Configuration & PDN-GW Settings

To attach to the LTE network successfully, correct Downlink Configurations such as Frequency

Band, Downlink EARFCN, and Transmission Mode need to be inputted in eNodeB entity based

on the DUTs capability (Figure 10). In addition, appropriate PDN values need to be assigned in

PDN-GW for a successful SIP Registration (Figure 11).

Figure 10: Downlink Configuration Settings

Figure 11: PDN Configuration Settings


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4.3. Step 3: Enable SRVCC In MME Test Configuration Setting

As SRVCC is Core Network related its setting is under the MME entity. In the SRVCC

Configurationsection, set Support SRVCCfield to Trueand select the appropriate SRVCC Type.

In this example CS + PSwas selected (Figure 12). CS8 Interactive Tester will manage and handle

the entire network configurations required to enable signalling messages.

Figure 12: SRVCC Configuration Settings

4.4. Step 4: Connect To Instruments/Load IMS Message Flow/Enable Call Processing

Click on the Connectbutton to connect the CS8 Interactive Tester to the instruments (Figure 12).

This connects the LTE eNodeB emulator and enables EPC emulation.

Figure 13: Connect To Instruments

At this stage IMS Message Flow script (DMF file) needs to be loaded. IMS Message Flow scriptis targeted for testing of IMS Applications. To load the file from CS8 Interactive Tester software

navigate to (Figure 14):


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NetworkIMS ServiceLoad an IMS Msg Flow File

Figure 14: Load IMS Message Flow File

This will open the LoadIMSMsgFlowwindow. In this window, ensure P-CSCF #1is selected and

click on Open File(Figure 15) to browse to the IMS Message Flow script (DMF file) located in:

C:\Program Files\Spirent Communications\CS8\CS8 Interactive Tester\DMF Scripts

Figure 15: DMF File Browse Window

This folder contains pre-defined IMS Message Flow scripts. Select one of already configured

SRVCC IMS Message Flow files. In this example, a VoLTE Mobile Originated (MO) call will be

initiated. Therefore SRVCC_verified_MO_mainscript is selected (Figure 16):

Figure 16: Load IMS Message Flow File


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The eNodeB is now ready to transmit signals and the EPC is waiting for the DUT to attach. To

enable call processing, click the Enable Call Processingbutton (Figure 16).

Figure 17: Enable Call Processing

Check to see if the connection to instruments succeeded, IMS Message Flow script is loaded,

and call processing is enabled (Figure 18).

Figure 18: Instrument Connection Successful


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4.5. Step 5: Initiate Mobile Originated VoLTE Call

CS8 Interactive Tester controls the network emulator and runs a real-time state machine to

handle RRC/NAS procedures. After the DUT detects the broadcasting information and starts

RACH to camp on the cell, the Attach Procedure initiates the state transitions on the RRC, ECM

and EMM. The Test Resultspanel logs the state transition and system status during the attach

procedure and PDN establishment. At this point, powering up the DUT will start the cell selection

process.

Ensure UE successfully attaches to the LTE network and IMS Registration is successful by

monitoring following messages in Test Resultspanel (Figure 19):

EPS Authentication Succeeded

EPS Attach Succeeded

UE Attached to PDN Successfully

SIP Message is ReceivedREGISTER

SIP Message is Sent200 OK

Figure 19: EPS Attach & IMS Registration Messages


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Use the VoLTE Application on the DUT to initiate a VoLTE MO call. Monitor the Test Resultspanel

for real-time SIP messages sent and received to confirm the call is active and MO VoLTE Call is

established (Figure 20):

SIP Message is Received180 Ring

SIP Message is SentPRACK SIP Message is Received200 OK

Figure 20: VoLTE Call Established


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4.6. Step 6: Initiate SRVCC Procedure

To initiate the SRVCC handover in CS8 Interactive Tester navigate to (Figure 21):

CallInitiate Handover Command

Figure 21: Initiate Handover Command

In the Handover Commandwindow, ensure Handover to UTRANbox is checked and correct Cell

IDis selected from the drop down menu (Figure 22).

Figure 22: Handover Command Window


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The CS8 Interactive Tester then determines that the active voice call needs to be moved from

the packet to the circuit domain. Inter-RAT handover from LTE to UTRAN is initiated. As CS + PS

SRVCC type was selected prior to the test in MME, CS + PS type is observed in the handover

message (Figure 23).

Figure 23: Inter-RAT Handover from LTE to UTRAN Initiated


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Monitor real-time messages in Test Resultspanel to determine if the Inter-RAT handover from

LTE to UTRAN is successful and both CS and PS calls are established on UTRAN. Content of

handover success message indicates the SRVCC type and its status. If the SRVCC procedure fails

due to call drop or handover failure, theTest Resultpanel will highlight it through its real-time

logging. By analyzing the logs, it can be concluded that SRVCC procedure was successful andboth CS and PS calls were established on UTRAN (Figure 24).

Figure 24: SRVCC Procedure Success


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Message Analyzerpanel can also be examined for further investigation to measure the SRVCC

Key Performance Indicators (KPI). The left side of the panel lists the message sequences, while

the right side shows the ASN.1-based contents for each message. In this specific scenario

mobilityFromEUTRACommandmessage is viewed (Figure 25). It can be confirmed that the

Access Stratum Release 9 mobility from E-UTRAN to UTRAN was completed (Figure 26).

Figure 25: Message Analyzer Message Sequence

Figure 26: Message Analyzer ASN.1-Based Content

5. CONCLUSION

SRVCC is an extremely complicated technology. For an SRVCC call to function properly, keyfactors such as MobilityForEUTRAN IEs, SRVCC Type, Carrier Frequency, and SIP Negotiation

need to be configured appropriately by the network elements. Spirents proven leadership

in Mobility and Channel Emulation in addition to expertise in VoLTE has made SRVCC testing

comprehensive and intuitive. As a result, testing cycles can be drastically decreased for the

users. As highlighted in this Application Note, SRVCC testing using CS8 Interactive Tester is

simply faster.

Message Analyzer


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6. ACRONYMS

1xRTT 1x (Single-Carrier) Radio Transmission Technology2G 2nd-Generation Wireless Telephone Technology3G 3rd-Generation Wireless Telephone Technolog y

ASN.1 Abstract Syntax Notation OneCDMA Code Division Multiple AccessCS Circuit-SwitchedCSFB Circuit-Switched FallbackDMF Data Message FlowDUT Device Under TestE-HRPD Evolved High-Rate-Packet DataE-UTRAN Evolved UMTS Terrestrial Radio Access NetworkEARFCN EUTRA Absolute Radio Frequency Channel NumberECM EPS Connection ManagementEMM EPS Mobility ManagementEPC Evolved Packet Core

EPS Evolved Packet SystemEV-DO Evolution Data OptimizedFDD Frequency Division Multiplexing GERAN GSM EDGE Radio Access NetworkGSM Global System for Mobile CommunicationsHSPA High Speed Packet AccessHSS Home Subscriber Server IMS IP Multimedia SubsystemIP Internet ProtocolIRAT Inter-Radio Access TechnologyLTE Long Term EvolutionMME Mobility Management EntityMO Mobile Originated

MSC Mobile Switching Center NAS Non-Access-StratumP-CSCF Proxy Call Session Control FunctionPDN Packet Data NetworkPDN-GW Packet Data Network GatewayPS Packet-SwitchedQoS Quality of ServiceRACH Random Access ChannelRAN Radio-Access NetworkRAT Radio-Access TechnologyRRC Radio Resource ControlRSTP Reference Signal Transmit Power

SCC-AS Service Centralization and Continuity ApplicationSGSN Serving GPRS Support NodeSGW Serving GatewaySIP Session Initiation ProtocolSRVCC Single Radio Voice Call ContinuitySTN-SR Session Transfer Number for SRVCCUE User EquipmentUTRAN UMTS Terrestrial Radio Access NetworkVoIP Voice over IPVoLTE Voice over LTEWCDMA Wideband Code Division Multiple Access


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7. REFERENCES

1. 3GPP TS.23.216 V11.9.0 (2013-06): Single Radio Voice Call Continuity (SRVCC)

2. 3GPP TS 129 280 V8.3.0 (2010-01): Sv interface (MME to MSC, and SGSN to MSC) for SRVCC

3. 3GPP TS 22.278 V11.6.0 (2012-09): Service Requirements for the Evolved Packet System

4. 3GPP TS 23.401 V10.7.0 (2012-03): GPRS enhancements for E-UTRAN access (Release 10)

5. GSMA, 2010, IR.92 IMS Profile for Voice and SMS V3.0

6. GSMA, 2011, IR.94 IMS Profile for Conversational Video Service V1.0

7. GSMA, 2011, IR.64 IMS Service Centralization and Continuity Guidelines V2.0

8. Vittal, Shwetha. Single Radio Voice Call Continuity (SRVCC) with LTE. Radisys Corporation.

September 2011

9. QUALCOMM. (October 2012) VoLTE with SRVCC: The second phase of voice evolution for

mobile LTE devices [White Paper]. Retrieved from www.qualcomm.com/media/documents/files/

srvcc-white-paper.pdf

10. QUALCOMM. Qualcomm Chipset Powers First Successful VoIP-over-LTE Call with

Single Radio Voice Call Continuity. Retrieved from http://www.qualcomm.com/media/

releases/2012/02/02/qualcomm-chipset-powers-first-successful-voip-over-lte-call-single-radio

11. CISCO. Voice over Long Term Evolution Migration Strategies [White Paper]. Retrieved from

http://www.cisco.com/en/US/solutions/collateral/ns341/ns973/white_paper_c11-711982.html


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8. TABLE OF FIGURES

Figure 1: Mobile Services Market Forecast For 2014 ...................................................... 4

Figure 2: High Level Concept for SRVCC from E-UTRAN to UTR AN/GERAN ....................... 5

Figure 3: SRVCC from E-UTRAN to UTRAN/GERAN Message Flow .................................... 6

Figure 4: Spirent CS8 Mobile Device Tester .................................................................... 7

Figure 5: CS8 Interactive Tester User Interface Overview................................................ 8

Figure 6: CS8 Mobile Device Tester UMTS-LTE Hardware Setup ...................................... 8

Figure 7: CS8 Interactive Tester Icon .............................................................................. 9

Figure 8: Application Password and Annual Support Agreement .................................... 9

Figure 9: Test Configuration In Network View ................................................................. 9

Figure 10: Downlink Configuration Settings ..................................................................10

Figure 11: PDN Configuration Settings ..........................................................................10

Figure 12: SRVCC Configuration Settings ......................................................................11

Figure 13: Connect To Instruments ................................................................................11

Figure 14: Load IMS Message Flow File .........................................................................12

Figure 15: DMF File Browse Window..............................................................................12

Figure 16: Load IMS Message Flow File .........................................................................12

Figure 17: Enable Call Processing..................................................................................13

Figure 18: Instrument Connection Successful ...............................................................13

Figure 19: EPS Attach & IMS Registration Messages .....................................................14

Figure 20: VoLTE Call Established .................................................................................15

Figure 21: Initiate Handover Command .........................................................................16

Figure 22: Handover Command Window .......................................................................16

Figure 23: Inter-RAT Handover from LTE to UTRAN Initiated ...........................................17

Figure 24: SRVCC Procedure Success ............................................................................18

Figure 25: Message Analyzer Message Sequence ........................................................ 19

Figure 26: Message Analyzer ASN.1-Based Content ..................................................... 19


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