VoLTE Book

2

VoLTE: Better Voice, More Profitable Data

The writing is on the wall for the traditional mobile service business model. Revenues from voice services, the industry’s “bread and butter” for decades, comprise a smaller percentage of the total each year. Data traffic continues to explode, taxing networks without fully offsetting losses on the voice side.

Also, the ability of mobile operators to capitalize on the rising popularity of smartphones, tablets, video, and Rich Communications Services (RCS) is compromised by “over the top” providers. OTT players piggy-back VoIP, messaging, chat, and location services on top of operators’ networks, often for free.

ARCChart predicts that by 2016 the installed base of OTT mobile VoIP subscribers alone will exceed 500 million.1 _{Skype and GoogleTalk have nearly a billion registered users worldwide.} By offering increased functionality at little to no cost, these services raise user tolerance for lower-grade performance while serving to relegate multi-million-dollar networks to providing the “pipes.”

Needless to say, mobile operators worldwide have gone on the offensive. Many have embarked on aggressive, innovative strategies to:

• Protect their share of diminishing voice revenues

• Improve the economics of service delivery and average revenue per user (ARPU) • Profit from the growth of data by fast-tracking their own compelling new services VoLTE stands to protect existing revenues while reducing opex and staunching the flow of revenues to OTT players—if providers can guarantee quality. Needless to say, the road is long, with many more decisions and challenges looming large.

Validating VoLTE: A “Lab to Live” Challenge

As they roll out VoLTE services, mobile operators need new ways of ensuring maximum quality and high ROI. Both can be accomplished by validating designs and performance in the lab, before and after deployment. From early on in the planning and prototype stages through the day-to-day monitoring of live production networks, life-cycle strategies are now needed to achieve predictable service delivery and optimize visibility.

Why Read This Book?

To extract the needed benefits from investments in VoLTE, and LTE in general, operators need to get deployments right the first time. To that end, this book presents a step-by-step guide for validating VoLTE implementations cost-effectively in the lab prior to deployment. This includes evaluating:

• Device and network performance • Interoperability

• Quality of Service and Quality of Experience • Network visibility and monitoring

Before embarking on the 40+ detailed test procedures contained in the Test Case section, let’s begin by taking a closer look at the current state of VoLTE, operator deployment plans, and the elements needed to optimize deployments.

About Ixia

The most trusted names in networking trust Ixia solutions to optimize equipment, networks, services, and applications. We help deliver innovative, differentiated offerings, improve management and visibility, and ensure a high-quality, always-on user experience.

Leading mobile operators worldwide use Ixia’s award-winning LTE solutions to accelerate and optimize 4G deployments and speed new services to market. A comprehensive suite of products and services are used to test, assess, and optimize key technology initiatives:

• Network performance, compliance, and security • Visibility into applications and services that

accelerates troubleshooting and enhances monitoring performance

• Securing mission-critical networks and services against attack • Cloud /virtualization and data center initiatives

For more information about Ixia, visit www.ixiacom.com. Also check out our groundbreaking new book, Small Cells, Big Challenge: A Definitive Guide to Designing and Deploying HetNets.

4

CHAPTER 1

VoLTE Market Drivers and Benefits ... 9

Protecting Voice Revenues... 9

Monetizing Quality ... 10

Improving the Economics of Service Delivery ... 11

Increased Spectrum Efficiency ... 11

Improved Battery Life ... 11

Fast-Tracking Profitable New Services ... 12

More than Just Voice ... 12

Faster Call Setup ...13

The Appeal of Convenience ...13

Improving Existing Voice Quality ...13

Operator Deployment Plans: How Much, How Soon? ...13

CHAPTER 2

Importance of QoS and Policy Control to Enable VoLTE ... 16

CHAPTER 3

Validating New Devices and Configurations ...19

Interoperability in Increasingly Multi-vendor Environments ...20

Signaling ...20

Fallback ... 21

Ensuring Quality of Experience (QoE) ... 21

Impact on value-added services ... 21

Stress / Scalability ...22

CHAPTER 4

Critical Test Capabilities ... 26

Realism / Traffic Generation ... 26

Subscriber Modeling ... 27

Load Testing ... 28

QoS / Service Validation ... 28

Live Network Monitoring ... 28

CHAPTER 5

VoLTE Test Configurations ...31

Test Configuration: VoLTE Client End to End Across the Network ...32

Test Configuration: UE/eNodeB Emulation Across the VoLTE Network ...33

Test Configuration: IMS Isolation ...34

Test Configuration: eNodeB Isolation ... 35

Test Configuration: EPC Isolation ...36

CHAPTER 6

Test Case Format ...40

CHAPTER 7

LTE Attach Call Flow ...43

IMS Registration Call Flow ...44

Test Case 1: IMS Registration ...45

Test Case 2: IMS Registration with IMS AKA ... 47

Test Case 3: SIP Subscribe Procedure ... 49

Test Case 4: SIP De-Registration on UE Power Down ...51

Test Case 5: SIP De-Registration on Network Release ... 52

CHAPTER 8

Measuring Quality of Voice ... 55

Test Case 6: VoLTE Voice-Only Call with Wideband AMR ... 59

Test Case 7: VoLTE Call Release Initiated by the Calling Party ...62

Test Case 8: VoLTE Call Release Initiated by the Called Party ... 63

Test Case 9: Redirect VoLTE Call to Voice Mail after Called Party is Busy ... 64

Test Case 10: Redirect VoLTE Call Not Answered to Voice Mail ...66

Test Case 11: Originator Cancels the Call Before Ringing ... 68

Test Case 12: Originator Cancels Call after Ringing ... 70

Test Case 13: Loss of PDN Connectivity ... 72

Test Case 14: Loss of SIP Signaling ... 74

Test Case 15: Loss of Media Bearer ... 76

Test Case 16: Voice Call Waiting, Second-Party Hold ... 78

Test Case 17: Voice Call Switch Hold ...81

Test Case 18: Voice Third Call Redirect to Voice Mail ... 84

Test Case 19: Handover During VoLTE Voice-Only Call ...86

6

CHAPTER 9

Section 3: VoLTE SMS ... 95

Test Case 23: VoLTE Send SMS ... 96

CHAPTER 10

Test Case 24: VoLTE IR.94 Registration with IMS AKA Authentication ... 102

Test Case 25: VoLTE 2-Way Video Call with 2-Way Audio ... 103

Test Case 26: VoLTE Video Call Originator Terminates ... 105

Test Case 27: VoLTE Video Call, Called Party Terminates ... 107

Test Case 28: Change of Video Parameters ... 109

Test Case 29: Video Call – a User Stops Video ... 111

Test Case 30: Video Third Call Redirect to Voice Mail on Ignore ...113

Test Case 31: Video Call Accepted as Voice Only ...115

Test Case 32: Voice Call Transition to Video Call Accepted ... 117

Test Case 33: Voice Call Transition to Video Call Ignored/ Time-out ...119

Test Case 34: Voice Call Transition to Video Call Rejected ...121

Test Case 35: Handover During VoLTE Video Call ... 123

Test Case 36: Video Call Put on Hold ... 125

Test Case 37: Video Call Switch Hold ... 128

Test Case 38: Video Third Call Redirect to Voice Mail ...131

CHAPTER 11

Test Case 39: Voice Ad-Hoc Multi-Party Conference ... 136

Test Case 40: Video Ad-Hoc Multi-Party Conference ... 140

Test Case 41: Multitasking + Video Call ... 144

Test Case 42: VoLTE Video Load Scenario ... 146

CHAPTER 12

Test Case 43: Airbus A380 Landing ... 150

Test Case 44: Power Outage Restored ...151

Test Case 45: High-Density Financial District ... 152

Test Case 46: Rush Hour Commuter Traffic ...153

CHAPTER 13

Monitoring Challenges, Solutions, and Best Practices ...157

CHAPTER 14

Key Performance Indicators for Monitoring VoLTE ... 165

CHAPTER 15

IxLoad Access ...170

IxLoad ... 171

Key Features ... 171

Wireless Triple-Play Bundle ...173

Xcellon-Ultra NP Load Module ...174

Key Features ...174

XAir Module ...175

Key Features ...175

r10 Wideband Radio Head ...176

Key Features ...176

High-Performance Chassis ...177

Key Features ...178

Ixia Hardware Configuration for VoLTE Testing ...179

One-Sector Configuration ...179

Three-Sector Configuration ...179

Six-Sector Configuration ... 180

CHAPTER 1

VoLTE Market Drivers and Benefits

• Protect critical voice revenues from attrition

• Improve the economics and efficiency of service delivery (including leveraging LTE’s improved spectral efficiency to re-farm 2G/3G resources)

• Fast-track compelling new services

• Maximize quality while simultaneously delivering HD voice alongside data Let’s take a closer look.

Protecting Voice Revenues

According to Informa Research & Telecoms, voice accounted for $634 billion in mobile service revenues in 2013, more than 60% of the worldwide total. As data traffic continues to surge, voice revenues will continue to suffer attrition—Informa estimates a drop of roughly 9% by 2018—but they’ll still represent a massive global market of $579B.

1,400

1,200

1,000

800

600

400

200

0

2013

2018

634

Voice

Data

385

579

675

10 Chapter 1: VoLTE Market Drivers and Benefits operators to guarantee quality in order to prevent losses to OTT services.

Monetizing Quality

VoLTE becomes one of first services to fully leverage the end-to-end quality of service (QoS) capabilities built into IMS-based LTE networks. Operators can market—and monetize—this advantage by making deals with OTT providers seeking to differentiate on quality, and by rolling out their own premium services to generate new revenues.

By fully leveraging IMS and the QoS mechanisms inherent in LTE, VoLTE supports HD voice as well as services based on guaranteed quality. The question is: how much will customers pay for it?

Services like Skype, Facebook, WhatsApp, and Fring have proven wildly popular, introducing functionality and novelty at virtually no cost. But history has shown that users will pay for real-time services like GoToMeeting and Microsoft Lync to ensure higher quality and security. Business customers in particular still shy away from any free or low-cost service that delivers a less than satisfactory experience, and may be inclined to pay a premium to bolster their own customer service.

To offset revenue loss to OTT services, operators have two viable options for monetizing quality: 1) they

can partner with or sell to OTT provider seeking differentiation, or 2) launch compelling paid services that let customers do something more, better, or cheaper. OTT providers that can’t guarantee service quality on their own may do well to pay to leverage it.

Either way, VoLTE figures to leave mobile operators at a clear advantage—if they can deliver a superior QoE.

“HD voice could bring

landline call quality to

cell phones and could be

offered as a premium

service to those tired

of repeating what they

think they heard on the

other end of the line.”

— Lars Johnsson, senior director of product marketing for mobile LTE platforms at Broadcom

Improving the Economics of Service Delivery

By basically allowing voice and data services to be delivered over a single network via a single radio interface, LTE offers unique advantages for improving the economics of service infrastructures.

Increased Spectrum Efficiency

Voice calls also consume less bandwidth on LTE than they do on legacy networks so that the same spectrum can be used to deliver nearly twice as many calls with VoLTE than using 3G services. And obviously, migrating a fair percentage of voice load off of 2G/3G networks onto LTE frees up existing bandwidth. The migration to VoLTE in turn allows 2G/3G spectrum to be reused for LTE.

LTE may also pave the way for operators to avail themselves of a wider range of spectral frequencies. Typically handled in the 1850-2150MHz, bands, voice might be able to migrate to 850MHz or use higher bands above 2150MHz.

Ultimately, better use of spectrum makes for better quality, which in turn leads to higher subscriber satisfaction and retention.

Improved Battery Life

LTE promises to improve device battery life, some say as much as 40%. According to

Broadcom, “the biggest benefit of VoLTE calls may be that they put far less drain on a phone’s battery than 3G voice calls.” The positive net impact of LTE on battery life performance is becoming widely acknowledged since devices don’t have to maintain contact with two distinct networks to run voice and data applications.

“There is a technical case

to be made for a mass

movement to VoLTE. The

technology would make

roaming easier, alleviate

concerns with spectrum,

and leverage backhaul.

VoLTE is easier on the

battery life of phones

compared to 3G.”

12 Chapter 1: VoLTE Market Drivers and Benefits VoLTE unlocks the future of profitable voice. Mobile operators can leverage LTE and RCS to develop innovative new services and offer attractive service bundles and rate plans. To date, nearly 200 LTE deployments have gone live, supporting some 160 million

subscriptions. Early deployments have been predominately data-only, and some providers have deployed without using IMS.

The exclusion of voice is likely to change, however, as LTE rapidly gains traction in North America, Asia Pacific, and other regions throughout the world. Operators migrating voice to 4G networks can increasingly benefit from the technological and economic advantages of LTE and IMS to improve quality and profitability.

45%

40%

35%

30%

25%

20%

15%

10%

5%

0%

Kor

ea

Japan

US

A

Singapor

e

Austr

alia

Canada Sw

eden

Saudi Ar

abia

UK

Germany

Rus

sia

Source: Informa Telecoms & Media

LTE to mobile subscribers penetration, Jun-13

More than Just Voice

By leveraging the superior QoS capabilities inherent in IMS and LTE, operators are free to roll out a wide variety of innovative and compelling new services. Coupling VoLTE with Rich Communications Services (RCS) supports real-time video chat and messaging.

While the availability of convenient, feature-rich applications and services from their trusted service provider may appeal to customers in and of itself, the real selling point once again is likely to be the higher quality network operators can provide.

Faster Call Setup

VoLTE delivers sub-second call setup times, a major improvement upon 3G call setups taking approximately 3 seconds. True VoLTE also significantly improves upon interim LTE solutions using CSFB where the latency resulting from handoffs to circuit-switched networks result in setup times exceeding 4 seconds.

The Appeal of Convenience

VoLTE-based services also have the advantage of not requiring either or both parties to download specific clients or applications. Nor are customers limited to calling other subscribers on one provider’s network.

Improving Existing Voice Quality

For a time, the evolution of voice traffic to LTE may even improve the quality of voice calls over 3G. With more bandwidth available, operators have more flexibility to prioritize services to enhance the quality of voice calls without significantly compromising the performance of data applications.

While the benefits of rolling out VoLTE are clear and compelling, the challenges are many and formidable.

Operator Deployment Plans: How Much, How Soon?

Informa Telecoms & Media predicts that 2014 will be the “breakthrough year” for voice over LTE (VoLTE). Other estimates expect steadily accelerating deployments through 2018.

North America VoLTE Subcribers, VoLTE Revenue and VoLTE POP

Revenues US ($M) Subscribers and POP in Thousands, 2013-2018

2013 2014 2015 2016 2017 2018 CAGR 2014-2018 VoLTE Subscribers 13 300 4,250 13,250 38,300 71,250 293% VoLTE Revenues (US $M) $2 $29 $467 $2,199 $7,140 $15,595 383% VoLTE POP 300 30,000 120,000 210,000 300,00 350,000 85% Source: MindCommerce

CHAPTER 2

What is VoLTE?

Voice-over-LTE, VoLTE, leverages the multimedia telephony (MMTel) service, the standardized IMS-based (IP Multimedia System) VoIP service designed to replace existing circuit-switched voice. By implementing the GSMA VoLTE IR.92 specification based on global 3GPP standards, mobile operators can deliver a new conversation experience of enriched voice, enlivened video, and intuitive messaging.

While migrating voice to an all-IP packetized infrastructure, VoLTE unlocks richer conversation services and lays a foundation for operators to offer toll-grade quality using well-defined quality of service (QoS) mechanisms. Rich Communications Services (RCS), marketed under joyn™ by GSMA, complement VoLTE by defining:

• Enhanced phonebook service capabilities and contact information such as presence and service discovery

• Enhanced messaging enabling a variety of options including chat, emoticons, location share, and file sharing

• Enriched calls featuring multimedia content-sharing during voice calls, video calls, and video sharing

After years of debate over alternative technology proposals, VoLTE has emerged as the hands-on favorite for supporting new rich-media services with broad industry support from both the vendor and operator communities. Initial launches and trials began in 2012 and will ramp aggressively during the next five years.

Circuit Switched Fallback (CSFB)

Until we get to VoLTE, initial LTE deployments are focused on data applications with circuit-switched fallback used to deliver interim voice services for LTE subscribers. With CSFB, an incoming or outgoing voice call forces a radio fallback from LTE to the legacy 2G or 3G service. Any 4G data is stopped at this point, limiting voice and texting to slower legacy 3G mobile services.

CSFB will primarily use narrowband codecs, and not the AMR-WB (Adaptive Multi-Rate Wideband) used for HD audio. Additionally, it will not enable all-IP services such as video calls.

16 Chapter 2: What is VoLTE? By nature, cellular systems are constrained by finite radio spectrum and transport resources. Voice, video, and other rich media applications each have unique traffic-handling and QoE requirements such that resource issues cannot economically be solved “the old way,” by simply over-provisioning the network.

For VoLTE rollouts to succeed in delivering superior QoE, efficient partitioning of wireless network resources is needed. End-to-end QoS is essential. LTE networks must be able to identify and treat service flows with well-known QoS characteristics for latency, jitter, packet loss, and error rates. The network must deliver guaranteed QoS end-to-end from the user equipment (phone or tablet) all the way to external TDM-based networks.

Advanced policy and charging control (PCC) is a major advancement in LTE networks compared to previous wireless generations. PCC allows operators to adopt fair-use policies limiting subscriber service abuse – for example, bandwidth hogs such as file sharing—and helping to maintain network performance during peak traffic times.

Policy management, the process of applying operator-defined rules for resource allocation and network usage, plays a fundamental role in implementing QoS in mobile broadband by enabling efficient allocation of network resources. Policy enforcement, in turn, involves service data flow detection and applies QoS rules to individual service data flows.

Since different services have varying QoS requirements in terms of packet delay tolerance, acceptable packet loss rates, and required minimum bit rates, granular control of service quality is critical. As such, QoS and policy management are essential to differentiated services and related challenges.

CHAPTER 3

Challenges To Deploying VoLTE

The “flipside” of being able to deliver voice and data over one network is that those networks must now be optimized for both voice and data. Delivering high-quality voice is more challenging, and doing so in the form of data packets even more so.

Aside from the sheer novelty of this undertaking, VoLTE involves lots of new moving pieces, unproven technologies, and interdependencies. Major challenges to ensuring successful deployments out of the gate include:

Validating New Devices and Configurations

By 2016, ARCChart expects the installed base of VoLTE-enabled handsets to top 74 million. Such devices are already available in Korea and other countries leading adoption. Informa expects to see many more devices available in many more countries by the end of 2014, and all of these new devices need to be evaluated for performance, interoperability, and reliability. At the network level, some operators have counted as many as sixty distinct network

components that come into play for a VoLTE call to be completed. Some of these are LTE-specific devices, others are “non-3GPP” components like application servers, DNS, and firewalls.

Along with the obvious interoperability challenges, subsystems like firewalls and DNS can become bottlenecks. Devices, subsystems and end-to-end service infrastructures must be validated thoroughly to keep costly issues from occurring upon deployment.

20 Chapter 3: Challenges To Deploying VoLTE With so many more components in play, many more vendors are in play as well. Many of the interfaces involved in VoLTE are also prone to customization by vendors, including critical Diameter protocols used in the EPC core, and Session Initiation Protocol (SIP) implementations within IMS.

The traditional model of relying upon one or even a handful of trusted vendors to validate performance becomes unwieldy and impractical. Mobile network operators must directly take control of ensuring interoperability, scalability, and the ultimate end-user experience.

Nor is each provider evaluating their own networks sufficient. Interoperability validation must further extend to effecting seamless roaming, and billing, between multiple operators.

Signaling

Spikes in hard-to-predict signaling traffic are already occurring due to smartphones generating up to 20x the signaling traffic of traditional phones. Signaling volumes may actually overwhelm infrastructures, leading to costly and embarrassing outages.

VoLTE is expected to significantly increase the amount of signaling traffic in the network. To help handle the load, Diameter routing agents (DRA) are deployed in the EPC core to provide intelligent switching and mediation between different devices and networks. DRAs handle load balancing, and play a vital role in scalability.

This approach changes the traditional topology, adding, essentially, a single point of failure. Though redundant DRAs are usually deployed, the function itself represents a highly centralized processing point. If, for example, policy server queries could not be completed, voice calls would be stopped in their tracks.

Operators must be assured that DRAs will perform as expected. Devices and configurations must be evaluated for interoperability, failovers, and performance under realistic stress and overload conditions.

Fallback

VoLTE is not a forklift upgrade; it’s a whole new deal. Until every mobile phone in use supports it, operators will need to support legacy air-links and provide seamless fallback to 2G/3G networks where LTE is unavailable.

For the foreseeable future, VoLTE calls will leverage CSFB and Single Radio Voice Call Continuity (SRVCC) to move from packetized networks to circuit-switched infrastructures. These techniques may involve extra signaling to the core network and SRVCC servers via IMS. The impact of the extra steps on performance, capacity, scalability, security, and QoE must be measured.

Aside from the actual handovers, operators need to coordinate and integrate billing systems, monitoring, and backhaul between both infrastructures and across all protocols. They must also maintain the continuity of mandated services such as CALEA and Lawful intercept.

Ensuring Quality of Experience (QoE)

For VoLTE to be worth the formidable investment, it not only has to deliver better quality than what OTT players provide, but exceed what 2G/3G networks deliver as well. Early indicators point to lower latencies and faster connection speeds, but operators may need to back these claims with hard data in order to satisfy businesses and savvy consumers.

Impact on value-added services

What impact will increased complexity have on features like Call Waiting, forwarding, voicemail, and conferencing? In migrating voice to LTE, operators need to be sure subscribers’ satisfaction with the features they’ve come to rely on won’t be compromised.

22 Chapter 3: Challenges To Deploying VoLTE Does voice get prioritized effectively as the network become stressed? Where are the new bottlenecks and congestion points? What happens when failovers occur?

QoS and reliability must be assessed under realistic load and high-stress conditions to ensure satisfaction and bring high-risk surprises to light before they do damage.

CHAPTER 4

Validating VoLTE “Lab to Live”

To date, service providers worldwide have relied heavily upon equipment manufacturers to validate the performance both of their own devices and overall network designs. Today, in the face of steadily rising traffic volumes and expectations for quality, this approach is far too risky.

Most operators’ networks increasingly consist of equipment from multiple vendors. And obviously, each network is unique such that operators need to test their specific

configurations, services, and traffic mixes to find potential issues and bottlenecks. Having the flexibility to quickly roll out new services or charging plans without going back to the vendor every time the network changes proves a valuable advantage over time.

With so many new and moving pieces involved, ensuring a high-quality VoLTE rollout requires end-to-end validation that begins in the lab and continues into the live network. Life-cycle validation strategies are needed, and should include:

• Design, planning and device selection. Throughout design, operators need an efficient means of evaluating prospective devices and proposed network designs. • Prototyping services. Before going

live, new services should be modeled and tested against realistic scenarios, including high-stress conditions, at scale.

• Visibility monitoring. Once things get up and running, operators need to maintain visibility into the network, making sure that the tools and solutions used to monitor and optimize performance and security are functioning optimally. This includes making sure each tool receives the data it needs automatically and efficiently. Ultimately, operators want to have easy access to a network’s KPIs.

• Problem resolution. Whether issues arise in the field or in the data center, operators must be able to take actionable data back to the test lab to devise ideal solutions. Visibility solutions gather data on KPIs and traffic patterns that can be used to inform testing in the lab that quickly replicates and resolves issues.

Throughout the process, the ultimate quality of voice, video, and other applications and services must be assessed, not with a focus on protocol testing, but on measuring the quality of the end-user experience with voice, video, messaging, and the other services.

A botched VoLTE would not

only compromise customers’

satisfaction and loyalty, but have

larger implications as well since

first responders— the healthcare

industry, local, state and

federal government, as well as

businesses— all rely upon cellular

voice.

26 Chapter 4: Validating VoLTE “Lab to Live” VoLTE testing should focus on end-to-end service validation versus individual device (node) testing. Network operators do not need to duplicate their vendors’ development testing, but rather measure the expected user experience.

To do this effectively, testing must be performed with all the components that will be used in the live network. Since maintaining a lab-based replica of the entire live network is not practical or effective, purpose-built test systems can be used much more cost-effectively.

These systems must be able to subject devices and configurations to stress, high-scale conditions. In general, a VoLTE test system must support functional, performance, and stability testing of SIP-based VoIP network components as well as a wide mix of voice, video, and data applications.

Using an automated, repeatable, and proven approach enables operators to assess the impact of each decision they make on device and network performance, as well as the ultimate quality of experience delivered. Validation strategies and test methodologies should include several critical components and capabilities:

Realism / Traffic Generation

It’s common for equipment manufacturers to state performance metrics in terms of specific or “best case” configurations and use models. Operators rolling out VoLTE need more realistic assessments based on actual or intended network configurations.

Test systems must be able to provide high-rate emulation of video, voice over IP (VoIP), VoLTE, data, and peer-to-peer protocols and application traffic. Performance, scalability, and capacity should all be benchmarked under realistic traffic conditions. Operators must be able to assess the subscriber experience in the face of mobility, system overload, and even device failure on a large-city scale. This includes simulating peak conditions, power outages, security threats, and other unforeseeable events.

For VoLTE, end-to-end test coverage encompasses everything from the wireless base stations to the Internet core. Operators need to be able to evaluate the entire LTE/VoLTE network as a whole, and also isolate individual subsystems such as the RAN, EPC, and the IMS core. Test tools must support SIP, SDP, H.323, MGCP, H.248, SKINNY, and RTP/RTCP protocols with voice codecs, in addition to video and data/web protocols.

Test solutions must also be capable of testing a variety of network components in LTE and IMS topologies, including:

• SIP proxies and registrar servers • Media gateways

• Call agents

• Session border controllers (SBCs) and application-layer gateways • Application servers

• EUTRAN components (eNodeB)

• EPC components (S-GW, P-GW, MME, HSS, PCRF) • IMS components (x-CSCF)

Important traffic emulation and SIP test functionalities include the ability to: • Simulate SIP endpoints behind one or many SIP proxies

• Simulate SIP proxy and SIP registrar server

• Maintain full control over SIP state machines, messages, and contents • Create any test case, including negative testing

Subscriber Modeling

An extension of the realism needed to validate new services is the ability for operators to define subscriber types (residential, corporate, SMB, etc.) complete with the correlating application profiles. By modeling the use and mobility patterns of actual subscribers, testers gain accurate insight into network capacity and the QoE achieved for each rich media or differentiated service.

28 Chapter 4: Validating VoLTE “Lab to Live” Since most issues occur at high scale, operators can’t qualify performance, scalability, and resiliency just by using a handful of actual client devices as has been done in the past. Realistic traffic must be generated at realistic scale to simulate high-load or stress conditions where network and application performance might suffer.

This means modeling peak usage and varying times throughout the day, simultaneously generating data, voice, and video protocols to emulate the respective multimedia traffic loads.

QoS / Service Validation

As noted earlier, policy management will play an increasingly integral role in enabling new services such as VoLTE as well as new business models to emerge. Operators must be able to assess and implement policies on multiple devices simultaneously, measuring the QoS capabilities of each along with the end-to-end performance achievable across the overall network.

Live Network Monitoring

LTE/VoLTE solutions require large, complex networks with many moving parts. Even with extensive planning and lab testing, the final network may bog down under load, or as a result of a failure.

For example, a software upgrade to one component in a chain might result in an incompatibility with neighboring components. Network monitoring allows issues to be identified before they become serious problems, and to troubleshoot any problems that might occur.

General Requirements on Network-based VoLTE Measurements

Requirement Explanation

Complete Monitoring of Network VoLTE traffic

24/7 Monitoring of every data flow with regard to SIP signaling and Voice Media

Network Visibility Ability to filter KPI results with regard to mobile network elements (APNs, gateways, eNodeBs, Cells, P-CSCFs) Device Visibility Ability to filter KPI results with regard to the Individual

Device and Device Models

Subscriber Visibility Ability to filter KPI results with regard to the Individual subscriber

Near Real Time Availability of results 10 minutes after capturing from network traffic

Scope of Testing

The comprehensive benchmarking needed to optimize VoLTE deployments includes: • Functional / feature testing

• Interoperability testing • Capacity planning

• QoS and policy control assessment • QoE measurement

• Ongoing validation to maximize value throughout the service life-cycle.

So let’s take a look at some real-world test cases, then at the challenges and best practices for ongoing network monitoring and visibility.

CHAPTER 5

VoLTE Test Configurations

To ensure a reliable VoLTE service, testing must occur under a variety of VoLTE test configurations. Operators will test end-to-end from the UE to the external networks; they will also need to isolate a sub-system, such as the EPC, to understand its scalability or to isolate a network problem. Generally, product development teams are more concerned with testing individual components like an eNodeB, whereas system test groups need to look at the network more holistically.

Common test configurations include:

1. End-to-end system test. In this scenario the test tool must emulate UEs with SIP agents over the Uu interface (RF), generating voice and SMS traffic into the LTE eNodeB. On the other side of the network under test, the tool emulates land-based SIP user agents or the PSTN.

2. Isolation of the evolved packet core (EPC). In this configuration the test tool supports the emulation of millions of mobile subscribers and hundreds of eNodeBs generating voice and SMS traffic directly into the EPC. On the other side of the network, the entire core network is emulated by replicating the behavior of the Proxy Call Session Control Function P-CSCF and all other devices behind it.

3. Isolation of the combined EPC and IMS core. In this scenario mobile subscribers and eNodeBs are emulated on one side and land-based SIP user agents are emulated on the other.

The following VoLTE test cases can be run from a number of points within the LTE network. To ensure full functionality, it is important that full end-to-end tests (VoLTE client to VoLTE client) are performed. This will validate that all network elements are operating correctly across the VoLTE network. It is possible and preferable in certain cases to test under different configurations. These are considered below.

32 Chapter 5: VoLTE Test Configurations This configuration represents the deployed network, with UEs connecting end to end across the network. Testing under this scenario involves Ixia emulation (indicated in diagrams using yellow highlights) of the LTE UEs and possibly SIP/PSTN clients or additional core servers e.g., web/video servers available through the Internet Access Point Name APN, all other elements are real.

Test Configuration: UE/eNodeB Emulation Across the

VoLTE Network

This configuration brings in the emulation of the eNodeB (eNodeB) with the UE. The eNodeB, with its air interface operation and scheduling challenges, can often be the key element of impairment. This test configuration allows direct validation that the rest of the wired network is operating correctly.

This configuration is also useful for testing VoLTE load in the network, by allowing much greater loading of the EPC and IMS than is possible solely through UE emulation. Each eNodeB is limited to less than a Gbps of traffic, whereas the LTE EPC can handle tens to hundreds of gigabits per second (Gbps) of traffic, along with the IMS and MME servers that can handle thousands of signaling transactions per second.

34 Chapter 5: VoLTE Test Configurations This configuration involves emulation of the PCRF directly to the IMS core. This will validate the signaling functionality and also can validate the expect IMS load capacity.

Test Configuration: eNodeB Isolation

While the eNodeB does not directly process the IMS (SIP) signaling used for VoLTE, it is the element most likely to introduce impairment of VoLTE operation from achieving high signal quality. Ensuring fast and effective eNodeB operation is essential to VoLTE operation. The eNodeB has strong challenges in scheduling the UEs for their Uplink (UL) and Downlink (DL) transmissions. By its nature, a VoLTE stream has small voice packets with small inter-arrival times. eNodeB functionality like Semi-Persistent Scheduling, TTI Bundling, and Robust Header Compression RoHC are all designed to assist VoLTE operation, but add complexity that must be examined. By testing an eNodeB in isolation, additional focus can be applied to validating this functionality.

36 Chapter 5: VoLTE Test Configurations

Isolating the EPC with emulation of the UE/eNodeBs and IMS network allows focused investigation of issues that may be affecting VoLTE operation from within the EPC.

CHAPTER 6

VoLTE Test Cases: Overview

The following sections propose a set of VoLTE test cases that ensure correct operation across a VoLTE network. These test cases are approached from the perspective of a full end-to-end VoLTE test across the network from UE to UE. This is the first test configuration illustrated in the Test Configuration section. All other Test Configurations can be used to run these scenarios.

The test cases can be divided into the following sections:

• Section 1: Setup/Registration • Section 2: Voice

• Section 3: SMS • Section 4: Video • Section 5: Advanced

40 Chapter 6: VoLTE Test Cases: Overview Each of the test cases presented will follow the following format.

Test Case Number: Title

Title describes the key scenario of the test (e.g. VoLTE voice-only call)

Description

• Scenario overview

• Diagram that shows the critical network elements and positive results for the test case

• UE1 is the default for result pass criteria if another UE is not identified

Initial State

• Numbered pretest configuration details

• May include earlier test scenarios denoted by number

Test Steps

• Numbered bullets of each test step in the call flow

• Messages can be shown in a different font with key parameters identified: SIP REGISTER … FROM:<PhoneNumber>@ims… P:ASSERTED_ID Cell_ID

Results

CHAPTER 7

Section 1: VoLTE Setup

LTE Attach Call Flow

Before a VoLTE test scenario can be run, it is assumed that the UE has gone through the Attach process. This handles the underlying LTE-based signaling and configuration before the VoLTE (IMS) signaling is started.

The following diagram shows the call flow.

2.AttachRequest 3.AttachRequest 4.UpdateLocationRequest 6.UpdateLocationAck(IMSAPN,QCI5) 7.CreateSessionRequest(IMSAPN,QCI5) 8.CCR(Initial,IMSAPN,QCI5) 9.CCA(PCCRulesfordefaultbearer) 10.CreateSessionResponse(IMSAPN,QCI5,UEIPaddress,PͲCSCFaddress 11.InitialContextSetupRequest/Attachaccept(IMSAPN,QCI5,UEIPaddress,PͲCSCFaddress 12.RRCConnectionReconfiguration/AttachAccept(IMSAPN,QCI5,UEIPaddress,PͲCSCFaddress 13.RRCConnectionReconfigurationComplete 14.InitialContextSetupResponse 15.DirectTransfer(AttachComplete) 16.ULNASTransport(AttachComplete) 17.ModifyBearerRequest 18.ModifyBearerResponse Uplinkdata Downlinkdata eNodeB MME S/PͲGW 1.RRCSetup SPRquery CSFBregistration 4.Authentication HSS PCRF SPR

44 Chapter 7: Section 1: VoLTE Setup The UE must register with the IMS network. This allows its presence to be updated.

This call flow looks like this:

IͲCSCF HSS (SM1)Register (SM2)Register (SM3)Register (CM1)AVͲReq (CM2)AVͲReqͲResp (SM4)4xxAuth_Challenge (SM5)4xxAuth_Challenge (SM6)4xxAuth_Challenge (SM7)Register CxͲSelectionͲInfo CxͲPut CxͲPut CxͲPull CxͲQuery (SM8)Register (SM9)Register (SM10)2xxAuth_Ok (SM11)2xxAuth_Ok (SM12)2xxAuth_Ok UE PͲCSCF SͲCSCF

Test Case 1: IMS Registration

Description

A UE will register with the IMS to allow VoLTE services using MD5 Digest Authentication.

Initial State

1. UE is EPS attached and has the default bearer activated for VoLTE APN

Test Steps

1. UE sends a REGISTER message to home network (to S-CSCF via P-CSCF and I-CSCF) to perform SIP registration with a public user identity:

REGISTER FROM:<PhoneNumber>@ims… P:ASSERTED_ID Cell_ID

2. UE receives SIP “401 Unauthorized” response from the IMS core (P-CSCF): 401 Challenge Random challenge (RAND)

3. UE sends a second REGISTER with calculated response (RES) based on a shared secret and previously received RAND

46 Chapter 7: Section 1: VoLTE Setup 1. UE successfully receives 401 with Random Challenge (RAND)

Test Case 2: IMS Registration with IMS AKA

Description

A UE will register with the IMS to allow VoLTE services using IMS AKA authentication.

Initial State

1. UE is EPS attached and has the default bearer activated for VoLTE APN

Test Steps

1. UE sends a REGISTER message to home network (to S-CSCF via P-CSCF and I-CSCF) to perform SIP registration with a public user identity:

REGISTER FROM:<PhoneNumber>@ims… P:ASSERTED_ID Cell_ID

2. UE receives SIP “401 Unauthorized” response from the IMS core (P-CSCF):

401 Challenge

Random challenge (RAND) Network authentication token (AUTN) Authentication scheme (IMS authentication and key agreement AKA)

3. UE sends a 2nd REGISTER with calculated response (RES) based on a shared secret and previously received RAND

48 Chapter 7: Section 1: VoLTE Setup 1. UE successfully receives 401 with Random Challenge (RAND) and AKA fields

Test Case 3: SIP Subscribe Procedure

Description

A UE subscribes for an Event of Notification from the IMS network. Event notifications are used in services including automatic callback services (based on terminal state events), buddy lists (based on user presence events), message waiting indications (based on mailbox state change events), and PSTN and Internet Interworking status (based on call state events).

Initial State

1. UE is EPS attached and has the default bearer activated for VoLTE APN 2. UE has successfully Registered to the IMS network

Test Steps

1. UE initiates Subscribe indicating Event subscription:

SIP SUBSCRIBE (REG-EVENT) (Event: reg), new Dialog

2. UE receives 200 OK indicating subscription has been accepted and containing Expires header field to indicate the actual duration for which the subscription will remain active (unless refreshed)

50 Chapter 7: Section 1: VoLTE Setup 1. UE receives 200 OK in response to SUBSCRIBE

Test Case 4: SIP De-Registration on UE Power Down

Description

A Registered UE powers down and causes de-registration from the IMS network.

Initial State

1. UE is EPS attached and has the default bearer activated for VoLTE APN 2. UE is Registered with the IMS network and is in Idle or Connected state

Test Steps

1. UE is powered down causing a de-registration, by sending a REGISTER request to the S-CSCF with expiry time set to 0:

REGISTER Expiry Time:0

2. The S-CSCF clears all temporary information it has for UE and updates the HSS 3. UE receives a “200 OK” response from the S-CSCF

Results

52 Chapter 7: Section 1: VoLTE Setup

Description

A Registered UE is released from the Network. This can happen for various reasons (reported stolen, unpaid bills, administrative reasons).

Initial State

1. UE is EPS attached and has the default bearer activated for VoLTE APN 2. UE is Registered with the IMS network and is in Idle or Connected state

Test Steps

1. S-CSCF sends a NOTIFY message with registration-state information to UE:

NOTIFY Deactivated Event

2. UE sends a “200 OK” back to S-CSCF to acknowledge de-registration

Results

CHAPTER 8

Section 2: VoLTE Voice-Only Call

This section provides test cases that focus on IR.92 Voice calls only. VoLTE through dedicated bearers provides the quality difference to VoIP over the top traffic.

PͲCSCF SͲCSCF AS IͲCSCF SͲCSCF AS PͲCSCF Kristina’shomenetwork Jennifer’shomenetwork Dedicatedbearer (QC11)established Ringing User Answers Dedicatedbearer (QC11)established HSS UPDATE INVITE 100Trying PRACK 200(OK) 200(OK) 180(Ringing) 200(OK) ACK 183 INVITE 100Trying 183 PRACK 200(OK) UPDATE 200(OK) 180(Ringing) 200(OK) ACK INVITE INVITE 183 PRACK PRACK 200(OK) UPDATE UPDATE 200(OK) 180(Ringing) 200(OK) ACK ACK 100Trying 183 200(OK) 180(Ringing) INVITE 100Trying 183 200(OK) 200(OK) 180(Ringing) 200(OK) INVITE INVITE 183 LIR LIA PRACK PRACK 200(OK) UPDATE UPDATE 200(OK) 200(OK) 180(Ringing) ACK ACK 100Trying 183 200(OK) 200(OK) 180(Ringing) 200(OK) ACK INVITE 183 200(OK) UPDATE 200(OK) 180(Ringing) 200(OK) PRACK

Measuring Quality of Voice

Speech quality in a telephony system is a subjective judgment that depends on technical attributes of the system and the participants’ speaking and listening preferences. A mean opinion score (MOS) provides a numerical indication of the quality of transmission, in the range of 1 to 5 (see table).

56 Chapter 8: Section 2: VoLTE Voice-Only Call MOS Quality 5 Excellent 4 Good 3 Fair 2 Poor 1 Bad

There are 2 types of MOS algorithms:

1. Perceptual/Subjective (POLQA and PESQ)

• Perceptual Objective Listening Quality Analysis

Perceptual Objective Listening Quality Analysis (POLQA®) is the voice quality testing standard for fixed, mobile, and IP-based networks that was adopted as ITU-T Recommendation P.863 and successor to P.862/PESQ. POLQA provides strong support for testing of new wideband 4G/LTE networks delivering HD-quality voice services. POLQA is particularly important for measuring QoE of wideband HD voice mobile calls in the 7 kHz and 14 kHz frequency range. The POLQA perceptual measurement algorithm is the joint development of OPTICOM, SwissQual, and TNO.

• Perceptual Evaluation of Speech Quality

Perceptual evaluation of speech quality (PESQ) is a mechanism that measures the quality of speech in the automated way as defined by ITU-T standard P.862. PESQ is an objective measurement method that predicts the results of subjective listening tests. The PESQ algorithm produces results analogs with the subjective MOS standard. A mapping between PESQ results and MOS was defined after the release of the P.862 recommendation. PESQ-LQ (PESQ- listening quality) is defined in ITU-T Rec. P.862.1, and improves the correlation with subjective test results at the high and low ends of the scale. It is important to measure both values: PESQ-LQ and PESQ-LE (listening effort).

PESQ is a full-reference method designed for end-to-end quality of voice assessment using a psycho-acoustic and cognitive model. PESQ analyzes the degraded audio signal (the signal after passing through the communication system) versus the reference (the signal injected in the system). The method requires access to actual audio information in both reference and degraded signals, performs level and time alignment to accommodate attenuations and delays, process the disturbances and finally applies the cognitive model. This is done using signal processing algorithms requiring considerable processing power.

The ITU-T P.800 specification defines methods for subjective determination of transmission quality. These methods use a large number of human subjects who listen to sentences read aloud by professional male and female speakers and transmitted over the telephony system. The listeners rate the quality of the individual audio signals, which are averaged into a MOS score.

2. Network Packet Transmission Based (E-Model and R-Factor)

In packet networks, quality of voice measurements can be performed by assessing the packets transmission using the E-Model and then generating the metric R-Factor. As defined by ITU-T G.107, R-Factor combines a number of values measuring the effect of various impairments; some of these are:

• The effect of coding/decoding – defined as constants for every codec

• Jitter, packet loss, and delay

• The effect of audio signal capture (mouth to microphone) and reproduction (speaker to ear), defined as a constant

The E-Model does not require reference signal information as it does not look at the actual audio content of the degraded signal. This method requires far less processing power than PESQ.

The R-Factor method predicts a user satisfaction on a scale from 0 to 100, where 100 is the highest satisfaction. A formula is defined for conversions between R-Factor and MOS. For example, a perfect transmission with the codec G.711 has an R-Factor of 94 and a MOS of 4.4.

R-Factor

R-Factor User Satisfaction

91-100 Very satisfied

81-90 Satisfied

71-80 Some users dissatisfied

61-70 many users dissatisfied

51-60 Nearly all users dissatisfied

58 Chapter 8: Section 2: VoLTE Voice-Only Call expected signal. Beside the effect of the impairments of the transmission network, PESQ also captures the effects of trans-coding, voice activity detector, echo cancelation, and any other type of audio signal alteration.

Because the PESQ algorithm is computationally intensive, it is not practical to use it for testing the speech quality on high-scale devices or systems. However, if E-Model is used exclusively, some issues may remain hidden if the system performs audio signal processing. The best practice is to combine the two methods by performing E-Model measurement on all calls and PESQ on a smaller percentage of them.

Test Case 6: VoLTE Voice-Only Call with Wideband AMR

Description

This test case details the fundamental VoLTE scenario of a user-to-user call using Wideband AMR.

Initial State

1. UE₁ and UE₂ are EPS attached and have the default bearer activated on VoLTE APN 2. UE₁ and UE₂ are subscribed with the IMS network and are available

Test Steps

1. UE₁ initiates the call by sending INVITE message to UE₂: INVITE SDP

a=rtpmap 99 AMR-WB/16000

2. UE₂ responds with 183 Session Progress

3. UE₁ sends PRACK for reliability of the provisional response 4. UE₂ sends 180 Ringing

5. UE₂ responds with 200 OK and receives ACK; 200 OK contains a SDP answer that selects AMR-WB as the voice codec to be used

60 Chapter 8: Section 2: VoLTE Voice-Only Call 7. PCRF receives the 183 response and forwards it to UE₁, but in addition sends a

Diameter AA Request (AAR) with session information from SDP (IPs, ports, media and codecs, bandwidth)

8. PCRF creates policy rules based on the session information from AAR and sends the Rx AA Answer (AAA) with a success value towards P-CSCF

9. PCRF also sends the created policy rule to P-GW using a diameter re-auth request (RAR); P-GW uses this information to enforce QoS and to apply traffic policy for voice media (PCEF)

10. P-GW also recognizes that is no bearer established for the provided QCI and ARP pair so it initiates a new dedicated bearer creation using this QoS information; for this P-GW sends Create Bearer Request to MME

11. MME allocates EPS bearer identity for this dedicated bearer and sends it together with EPS bearer QoS and TFT info to the UE in a Session Management Request inside the Bearer Setup Request to the eNodeB

12. eNodeB maps the EPS bearer QoS to the radio bearer QoS and sends a RRC Connection Reconfiguration message to the UE; this RRC Reconfig contains also a session management request sent by MME

13. UE stores the new bearer QoS settings and EPS bearer identity and uses the TFT to identify voice traffic flow coming from the application layer and matches uplink traffic to right radio bearer

14. After configuration, the UE returns the RRC Connection Reconfiguration Complete message to the eNodeB

15. eNodeB acknowledges the bearer activation to the MME with a Bearer Setup Response

16. MME acknowledges the bearer activation to the S/P-GW by sending a Create Bearer Response with Success outcome

17. Moving from the default bearer to dedicated if QCI matched and MBR received in Create Bearer Request is higher than configured value

18. Call is maintained for 3 minutes 19. UE₁ on hangup initiates a BYE 20. UE₂ responds with 200 OK

Results

1. Successful SIP Signaling execution to complete the INVITE process; ACK is received by UE₂

2. Successful initiation of the Voice stream, with correct properties, on a dedicated bearer (QCI=1)

3. QoE assessment of MOS and PESQ for voice quality

62 Chapter 8: Section 2: VoLTE Voice-Only Call

Description

In this scenario the VoLTE call release is initiated by the Calling party.

Initial State

1. UE₁ and UE₂ are EPS attached and have the default bearer activated on VoLTE APN 2. UE₁ and UE₂ are subscribed with the IMS network and are involved in a bidirectional

voice call for the last 3 minutes, with UE1 being the call initiator

Test Steps

1. UE₁ sends a BYE that is propagated through IMS proxies to UE₂

2. UE₂ responds with 200 OK, which is propagated through the network to UE₁

Results

1. UE₂ receives BYE from his P-CSCF 2. UE₁ receives 200 OK from his P-CSCF

Test Case 8: VoLTE Call Release Initiated by the Called Party

Description

In this scenario the VoLTE call release is initiated by the Called party.

v

Initial State

1. UE₁ and UE₂ are EPS attached and have the default bearer activated on VoLTE APN 2. UE₁ and UE₂ are subscribed with the IMS network and are involved in a bidirectional

voice call for the last 3 minutes, with UE1 being the call initiator

Test Steps

1. UE₂ sends a BYE that is propagated through IMS proxies to UE₁

2. UE₁ responds with 200 OK, which is propagated through the network to UE₁

Results

1. UE₁ receives BYE from P-CSCF 2. UE₂ receives 200 OK from P-CSCF

64 Chapter 8: Section 2: VoLTE Voice-Only Call

is Busy

Description

This test explores a case where the called party rejects incoming call (BUSY scenario) and the voice mail forwarding is triggered.

Initial State

1. UE₁ and UE₂ are VoLTE Registered and available

Test Steps

1. UE₁ initiates the call by sending INVITE message containing SDP with 2-way audio/ video info towards UE₂ via IMS network (P,I,S-CSCF proxies)

2. UE₂ responds with 180 Ringing without SDP, which is propagated back to UE₁ 3. UE₂ sends 486 Busy Here response

4. Upon receiving 486 Busy Here message S-CSCF proxy on UE₂ side will forward it to TAS (Telephony Application Services) module

5. TAS will trigger the Call Forwarding Procedure for UE₂ 6. UE₁ receives UPDATE (with SDP offer) from S-CSCF

8. A voice prompt is played (RTP stream is sent from Voice Mail Server to UE₁); after the prompt, UE₁ can deposit his voice message to be delivered to UE₂ voice mail box (RTP stream is sent from UE1 to Voice Mail Server)

9. After RTP streams for voice mail stop, UE₁ receives BYE from S-CSCF

Results

1. UE₂ sends 486 Busy Here

2. UE₁ receives UPDATE with SDP offer 3. UE₁ sends 200 OK UPDATE

66 Chapter 8: Section 2: VoLTE Voice-Only Call

Description

This test explores a case where the called party doesn’t answer incoming call and forwarding to voice mail is triggered.

Initial State

1. UE₁ and UE₂ are VoLTE Registered and available

Test Steps

1. UE₁ initiates the call by sending INVITE message containing SDP with 2-way audio (a=sendrecv) info towards UE₂ via IMS network (P,I,S-CSCF proxies)

2. UE₂ responds with 180 Ringing with SDP, which is propagated back to UE₁ 3. UE₂ does not answer the incoming call, as a result Call Forward No Answer timer

expires at TAS for UE₂

4. TAS sends CANCEL for the call to UE₂ through S-CSCF

5. UE₂ sends 200 OK to S-CSCF as response to CANCEL; S-CSCF forwards the 200 OK to TAS module

6. UE₂ sends 487 Request Terminated to S-CSCF; which forwards 487 to TAS module 7. TAS responds with an ACK, which is propagated through S-CSCF to UE₂

8. TAS triggers Call Forward procedure for Voice Mail 9. UE₁ receives 181 Call is Being Forwarded from S-CSCF 10. Voice Mail receives INVITE with SDP offer

11. Voice Mail responds with 180 Ringing and 200 OK (with SDP answer) to UE₁ via S-CSCF

12. UE₁ sends ACK

13. A voice prompt is played (RTP stream is sent from Voice Mail Server to UE₁); after the prompt, UE₁ can deposit his voice message to be delivered to UE₂ Voice Mail (RTP stream is sent from UE₁ to Voice Mail Server)

14. After RTP streams for voice mail are stopped, UE₁ receives BYE from S-CSCF

Results

1. UE₂ receives CANCEL

2. UE₂ sends 487 Request Terminated 3. UE₁ receives 181 Call is Being Forwarded 4. UE₁ receives 200 OK

68 Chapter 8: Section 2: VoLTE Voice-Only Call

Description

This test case explores a VoLTE scenario where the originator changes his mind and cancels the call before receiving “180 Ringing.”

Initial State

1. UE₁ and UE₂ are EPS attached and have the default bearer activated on VoLTE APN 2. UE₁ and UE₂ are subscribed with the IMS network and are available

Test Steps

1. UE₁ initiates the call by sending INVITE message to UE₂ 2. UE₂ responds with 100 Trying

3. UE₁ sends CANCEL

4. UE₂ responds with 200 OK 5. UE₂ sends 487 Request Terminated 6. UE₁ sends ACK

Results

1. UE₂ receives CANCEL 2. UE₁ receives 200 OK

70 Chapter 8: Section 2: VoLTE Voice-Only Call

Description

This test case explores a VoLTE scenario where the originator changes his mind and cancels the call after receiving “180 Ringing.”

Initial State

1. UE₁ and UE₂ are EPS attached and have the default bearer activated on VoLTE APN 2. UE₁ and UE₂ are subscribed with the IMS network and are available

Test Steps

1. UE₁ initiates the call by sending INVITE message to UE₂ 2. UE₂ responds with 100 Trying

3. UE₂ sends 180 Ringing 4. UE₁ sends CANCEL C_seq=1 5. UE₂ responds with 200 OK 6. UE₂ sends 487 Request Terminated 7. UE₁ sends ACK

Test Case 12: Originator Cancels Call after Ringing

Description

This test case explores a VoLTE scenario where the originator changes his mind and cancels the call after receiving “180 Ringing.”

Initial State

1. UE₁ and UE₂ are EPS attached and have the default bearer activated on VoLTE APN 2. UE₁ and UE₂ are subscribed with the IMS network and are available

Test Steps

1. UE₁ initiates the call by sending INVITE message to UE₂ 2. UE₂ responds with 100 Trying

3. UE₂ sends 180 Ringing 4. UE₁ sends CANCEL C_seq=1 5. UE₂ responds with 200 OK 6. UE₂ sends 487 Request Terminated 7. UE₁ sends ACK

Results

1. UE₁ receives 180 Ringing 2. UE₂ receives CANCEL 3. UE₁ receives 200 OK

72 Chapter 8: Section 2: VoLTE Voice-Only Call

Description

In this Negative Test scenario, a call is re-established after PDN connectivity loss. This is an implicit detach by the network.

Initial State

1. UE₁ and UE₂ are VoLTE Registered

2. UE₁ has initiated an ongoing voice call with UE₂

3. RTP voice media packets are using dedicated bearer (QCI=1 and GBR)

Test Steps

1. UE₁ loses PDN connectivity

2. UE₂ receives BYE request with 503 “Service Unavailable” response code: BYE: Reason header

503 Service Unavailable

3. UE₁ re-establishes PDN connection by sending NAS Attach request + PDN Connectivity request

4. After bearer configuration the UE returns the RRC Connection Reconfiguration Complete message to the eNodeB