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- 1. Performance Test VoLTE diversifEye Large Scale Tunnel Requests Use real phone Credentials Stateful Application Requests Millions of GTP tunnels with real application requests MME Emulated server S11 Side responses eNodeB S1u S5 SGi SGW PDN GW Fully load S1 - S1u interfacesDelivering high quality Voice over LTE networks (VoLTE)IntroductionOne of the major challenges associated with Voice over LTE (VoLTE) for carriers is defining the Quality of Service (QoS)features for the LTE network.VoLTE is positioned as a high quality voice service enabling call quality equivalent to or better than a 2.5G/3G cellular call,except the network is now all IP. The challenge for the carrier is to ensure each element of the network from the User Equip-ment (UE), Radio Access Network (RAN), Evolved Packet Core (EPC) and IP Multimedia Subsystem (IMS) core are optimizedcorrectly to deliver voice with an uncompromising level of quality. In addition it will most likely be the first time all compo-nents are tested with a mission critical application.The ChallengeVoice over LTE will play a key part in determining a subscribersQuality of Experience (QoE) on a 4G network. However, a QoS testplan cannot be solely focused on voice and must include otherservices, which include video and data. The VoLTE application willcompete with other applications for bearer paths and bandwidth.A common reason for 4G carriers to test performance at an appli-cation layer level is to ensure the QoS prioritization of the voiceelement is accurate, but to also ensure that there is no negativeperformance impact on other revenue generating sources whichinclude IMS enablers of presence and location.With the proliferation of smartphones and tablet computingdevices, more applications are appearing which are enabled by Figure 1: VoLTE call quality is dependant on the LTEthe Session Initiation Protocol (SIP). The increasing capacity network handling thousands of concurrent SIP sessionsrequirement on the management layer, plus the addition of appli- per second. Dedicated QoS for Voice in LTE will impact Data applications running on the same limited band-cations means QoS optimization for VoLTE is a two dimensional width resources.challenge in which both layers need attention.
- 2. VOLTEThe successful delivery of any application on a 4G network is dependent on the smooth transition of packets betweendistinct elements on the 4G bearer path. With the focus on VoLTE, a number of test requirements immediately appear whenconsidering QoS.At a basic level, performance testing will include call establishment, call billing and call termination procedures. However, tounderstand the impact that variances in LTE network QoS settings have, carriers need to look to the actual subscriber orQuality of Experience (QoE) performance measurement. An example subscriber QoE measurement which is impacted byQoS settings is the individual call quality rating, which must be measured in real-time. This is achieved using subjective callanalysis, giving an insight into the actual audio quality over the duration of the call.Defining a test strategy for VoLTE4G network performance testing requires multiple approaches. This application note focuses in on the IP aspect. At an IPpacket level, there are many performance tests required with varying degrees of complexity. These complex test challengesare overcome by using per flow emulation with stateful application flows.The advantages of per flow stateful application traffic emulationand performance testing are highlighted when it comes to testingVoLTE QoS performance on mobility or in call handover scenarios.To identify some basic LTE QoS performance test requirements anexample approach is to step through each element on the 4Gnetwork bearer path:Radio Access NetworkenodeBs manage a number of complex processes which includebandwidth management of the subscriber applications, manage-ment of the User Equipment (UE) measurement reports, communi-cation with the Mobility Management Entity (MME) and ServingGateway (SGW).A critical factor in any cellular network is call continuity when roam-ing. Call continuity success is based on the ability of the enodeBs toimplement call handovers. A basic LTE QoS test ensures connectiv-ity between enodeBs, alongside packet latency measurementsbetween enodeBs. Tight control over QoS settings covering thedelivery of packets passing between enodeBs is critical, furthertesting will include scaling to include multiple device handovers orincreased traffic on the enodeB interconnect path (X2). Figure 2: 4G/LTE radio access networks areLTE subscribers will have multiple bearer paths assigned to them, so smarter, with more functionality based on theQoE performance tests should include as many different applica- reach of IP to the tower. QoS for VoLTE is more thantions as possible. Per flow performance testing enables carriers analyzing power of the radio network, analysismeasure actual voice quality and to also show how the focused QoS must be performed at a packet level. Testing is notsettings on the dedicated voice bearer, enforced by the enodeB, limited to the call itself but must also includeimpacts bandwidth management on the other application types. security attack mitigation type tests, assessingThe aim is to find a reliable QoS bearer path setting for VoLTE, whilst known vulnerabilities associated with IP.maintaining connectivity for all other applications running. Performance TESTING
- 3. UE Performance test eNodeB, SGW, PDN GWUE eNodeB & mobile DPI devices :Test per application flow QoE for voice, video and data. UE emulator Serving diversifEye : Emulate multiple Gateway applications per emulated UE Packet Data Network Gateway + DPI devices Stateful Applications (Video, Voice, Web, Email, etc) INTERNET UE IPv4/6 UE IPv4/6 GTP TEID GTP TEID diversifEye : Emulate application diversifEye server responses or connect to external 3rd party servers Figure 3 : diversifEye provides large scale emulation of stateful application flows, by accurately representing UEs (IPv4/IPv6) and parameters such as IMSI and user authentication details. diversifEye per flow architecture and large scale test capabilities are not only used to test the scalability of the LTE EPC, but provide vital details on a per subscriber Quality of Experience basis. Evolved Packet Core (EPC) A function of the LTE EPC is to scale to meet the increasing demands made by subscribers and their applications. In most instances each subscriber device will have multiple bearer paths assigned, dependant on the application, each bearer path will be assigned a QoS priority level. Initial VoLTE application testing will assess that the application QoS quality level is correct and the network core is prioritiz- ing VoLTE flows. Following on from that, its possible to examine performance on other applications. Examination of QoS is not limited to a single user entity. The level of scalability that is achievable in the EPC is dependent on the number of sessions the MME will establish, closely linked with the volume of traffic flows the SGW can cope with. QoS performance testing has a knock on effect in terms of utilization on the control/signalling plane in LTE. See Shenicks companion note for more details http://www.shenick.com/media_lib/files/Shenick_Optimizing_4G_networks.pdf. Essen- tially, QoS is put in place to handle the millions of session request