VOLTE Solution

diversifEye

PDN GWSGW

Fully load S1 - S1u interfaces

Millions of GTP tunnelswith real application requests

Large Scale Tunnel Requests Use real phone Credentials Stateful Application Requests

MME

S5S1u

S11

SGieNodeB

Emulated server Side responses

The ChallengeVoice over LTE will play a key part in determining a subscriber’s Quality of Experience (QoE) on a 4G network. However, a QoS test plan cannot be solely focused on voice and must include other services, which include video and data. The VoLTE application will compete 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 voice element is accurate, but to also ensure that there is no negative performance impact on other revenue generating sources which include IMS enablers of presence and location.

With the proliferation of smartphones and tablet computing devices, more applications are appearing which are enabled by the Session Initiation Protocol (SIP). The increasing capacity requirement on the management layer, plus the addition of appli-cations means QoS optimization for VoLTE is a two dimensional challenge in which both layers need attention.

Performance Test VoLTE

Figure 1: VoLTE call quality is dependant on the LTE network handling thousands of concurrent SIP sessions per second. Dedicated QoS for Voice in LTE will impact Data applications running on the same limited band-width resources.

Delivering 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 optimized correctly 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 successful delivery of any application on a 4G network is dependent on the smooth transition of packets between distinct elements on the 4G bearer path. With the focus on VoLTE, a number of test requirements immediately appear when considering QoS.

At a basic level, performance testing will include call establishment, call billing and call termination procedures. However, to understand the impact that variances in LTE network QoS settings have, carriers need to look to the actual subscriber or Quality of Experience (QoE) performance measurement. An example subscriber QoE measurement which is impacted by QoS settings is the individual call quality rating, which must be measured in real-time. This is achieved using subjective call analysis, 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 IP packet level, there are many performance tests required with varying degrees of complexity. These complex test challenges are overcome by using per flow emulation with stateful application flows.

Figure 2: 4G/LTE radio access networks are smarter, with more functionality based on the reach of IP to the tower. QoS for VoLTE is more than analyzing power of the radio network, analysis must be performed at a packet level. Testing is not limited to the call itself but must also include security attack mitigation type tests, assessing known vulnerabilities associated with IP.

The advantages of per flow stateful application traffic emulation and performance testing are highlighted when it comes to testing VoLTE QoS performance on mobility or in call handover scenarios. To identify some basic LTE QoS performance test requirements an example approach is to step through each element on the 4G network bearer path:

Radio Access NetworkenodeBs manage a number of complex processes which include bandwidth management of the subscriber applications, manage-ment of the User Equipment (UE) measurement reports, communi-cation with the Mobility Management Entity (MME) and Serving Gateway (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 to implement call handovers. A basic LTE QoS test ensures connectiv-ity between enodeBs, alongside packet latency measurements between enodeBs. Tight control over QoS settings covering the delivery of packets passing between enodeBs is critical, further testing will include scaling to include multiple device handovers or increased traffic on the enodeB interconnect path (X2).

LTE subscribers will have multiple bearer paths assigned to them, so QoE performance tests should include as many different applica-tions as possible. Per flow performance testing enables carriers measure actual voice quality and to also show how the focused QoS settings on the dedicated voice bearer, enforced by the enodeB, impacts bandwidth management on the other application types. The aim is to find a reliable QoS bearer path setting for VoLTE, whilst maintaining connectivity for all other applications running.

VOLTE

Performance TESTING

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, it’s 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 Shenick’s 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 requests accessing unique applications connecting to global web services. Large scale activity testing emphasizes the need for emulation testing in the EPC.

Scale is not the only limiting factor to VoLTE; performance testing needs to examine the Session Initiation Protocol (SIP), in all instances there will be a large volume of concurrent SIP sessions. Detailed testing should outline the overhead associ-ated with maintaining each of those sessions.

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.

UE IPv4/6UE IPv4/6

Stateful Applications(Video, Voice, Web, Email, etc)

GTP TEID GTP TEID

eNodeB

INTERNET

Performance test eNodeB, SGW, PDN GW & mobile DPI devices :Test per application flow QoE for voice, video and data.

Packet Data NetworkGateway + DPI devices

diversifEye : Emulate multiple applications per emulated UE

diversifEye : Emulate application server responses or connect to external 3rd party servers

Serving Gateway

UE

UE

diversifEye

UE emulator

VoLTE Performance TESTING

Table 1 : Dependant on the SIP configuration (typically 9 to 16 SIP messages per session) the signalling plane will require tight management. To identify how configuration optimization impacts quality a unique set of metrics is required detailing each step in the VoLTE call process. Highlighted above are a sample set of metrics.

UE SIP Metrics Description UE In RTP Bits/sec The number of RTP bits/second received in by this UE. UE Out RTP Bits/sec The number of RTP bits/second sent out by this UE. UE In RTP Packets/sec The number of RTP packets/second received in by this UE. UE Out RTP Packets/sec The number of RTP packets/second sent out by this UE. UE RTP Out of Sequence Packets The number of packets out of sequence sent out by this UE.

UE RTP Dropped Packets The number of packets dropped by this UE. UE Duplicate RTP Packets The number of duplicate packets received in by this UE. UE Out Calls Attempted The number of calls out attempted by this UE. UE Out Calls Established The number of calls established by this UE. UE Out Calls Rejected The number of calls rejected by this UE.

UE In Calls Attempted The number of incoming calls that this UE attempted to receive.

UE In Calls Established The number of incoming calls established by this UE. UE In Calls Rejected The number of incoming calls rejected by this UE. UE Calls Errored The number of calls with errors logged by this UE. UE SIP Out Messages The number of SIP messages sent out by this UE. UE SIP Messages Resent The number of SIP messages resent out by this UE. UE SIP In Messages The number of SIP messages received by this UE. UE In RTCP Packets The number of RTCP packets received in by this UE. UE Out RTCP Packets The number of RTCP packets sent out by this UE UE Registrations Attempted The number of registrations attempted by this UE. UE Registrations Successful The number of successful registrations by this UE. UE Registrations Rejected The number of registrations rejected by this UE. UE Registrations Errored The number of registrations with errors logged by this UE. UE Calls Received Ringing The number of ringing calls received in by this UE. UE Mean Time to Ringing (ms) The average time for incoming calls to this UE to ring. UE Min Time to Ringing (ms) The minimum time for incoming calls to this UE to ring. UE Max Time to Ringing (ms) The maximum time for incoming calls to this UE to ring.

UE Calls Received RTP Packet The number of messages with RTP packets received in by this UE.

UE Mean Time to RTP Packet (ms) The Mean time for this UE to receive the first RTP packet. UE Min Time to RTP Packet (ms) The Minimum time for this UE to receive the first RTP packet. UE Max Time to RTP Packet (ms) The Maximum time for this UE to receive the first RTP packet UE RTP Jitter (RFC 3350) ms The Jitter per ms. UE RTP Max Jitter (RFC 3350) The maximum Jitter per ms.

UE SIP Metrics Description UE In RTP Bits/sec The number of RTP bits/second received in by this UE. UE Out RTP Bits/sec The number of RTP bits/second sent out by this UE. UE In RTP Packets/sec The number of RTP packets/second received in by this UE. UE Out RTP Packets/sec The number of RTP packets/second sent out by this UE. UE RTP Out of Sequence Packets The number of packets out of sequence sent out by this UE.

UE RTP Dropped Packets The number of packets dropped by this UE. UE Duplicate RTP Packets The number of duplicate packets received in by this UE. UE Out Calls Attempted The number of calls out attempted by this UE. UE Out Calls Established The number of calls established by this UE. UE Out Calls Rejected The number of calls rejected by this UE.

UE In Calls Attempted The number of incoming calls that this UE attempted to receive.

UE In Calls Established The number of incoming calls established by this UE. UE In Calls Rejected The number of incoming calls rejected by this UE. UE Calls Errored The number of calls with errors logged by this UE. UE SIP Out Messages The number of SIP messages sent out by this UE. UE SIP Messages Resent The number of SIP messages resent out by this UE. UE SIP In Messages The number of SIP messages received by this UE. UE In RTCP Packets The number of RTCP packets received in by this UE. UE Out RTCP Packets The number of RTCP packets sent out by this UE UE Registrations Attempted The number of registrations attempted by this UE. UE Registrations Successful The number of successful registrations by this UE. UE Registrations Rejected The number of registrations rejected by this UE. UE Registrations Errored The number of registrations with errors logged by this UE. UE Calls Received Ringing The number of ringing calls received in by this UE. UE Mean Time to Ringing (ms) The average time for incoming calls to this UE to ring. UE Min Time to Ringing (ms) The minimum time for incoming calls to this UE to ring. UE Max Time to Ringing (ms) The maximum time for incoming calls to this UE to ring.

UE Calls Received RTP Packet The number of messages with RTP packets received in by this UE.

UE Mean Time to RTP Packet (ms) The Mean time for this UE to receive the first RTP packet. UE Min Time to RTP Packet (ms) The Minimum time for this UE to receive the first RTP packet. UE Max Time to RTP Packet (ms) The Maximum time for this UE to receive the first RTP packet UE RTP Jitter (RFC 3350) ms The Jitter per ms. UE RTP Max Jitter (RFC 3350) The maximum Jitter per ms.

As in the RAN, roaming UEs place additional resource requirements on the EPC. Once the enodeBs and the UE have finalized handover, it is up to the target enodeB to communicate this message with the MME. It’s critical that the latency and the avail-able memory buffers on interlinking paths (S1-MME) are set correctly. With packet latency performance, it’s often the case that buffer sizes are set too aggressively which has a negative impact on QoS performance especially during a period of low traffic requests. It only requires tens of milliseconds of latency to perceive a VoLTE call as poor quality.

Testing the management paths with varied traffic load scenarios will result in an optimized QoS setting, preserving VoLTE call continuity.

The EPC MME manages both the interconnected enodeBs and a varying number of gateways in which the bearer traffic passes through. Returning to the roaming subscriber’s call; call continuity is further dependent on the speed in which the MME updates the SGW, with a message indicating the change to the user plane path for the UE. Latency measurements again are an important parameter to maintaining the VoLTE call quality.

Another important QoS feature in the LTE EPC concerns the speed in which the address redirection request is carried out, it must be managed by the SGW so as to minimize the volume of traffic heading back to the source enodeB. A sample QoS performance optimization test will cover bandwidth utilization, an example test is to force an excessive number of redirec-tion updates for the MME to handle.

As each request increases the CPU cycles required in the MME, this has an effect of slowing the MME’s ability to manage the SGWs. To determine what impact these loads have on performance, analysis is done covering the number of packets still arriving to the UE address after the UE handover request has been initiated by the source enodeB.


Figure 4 : Optimization is a key requirement for LTE as each SIP session enabled on the carrier costs revenue. IMS enablers such as Presence and Location are one way in which carriers can counteract revenue loss to OTT content providers and benefit from an all IP network. For these services to a success carriers must performance test in the application layer.


IMS Core

The IMS core contains a number of elements, for the purpose of VoLTE QoS performance testing, it’s crucial to examine the core in terms of the SIP functionality and handling.

Focusing on the Call Session Control Function (CSCF), the dual purpose of this element is to handle SIP messaging and manage the IP address assignment requests from the UE (DHCP). The CSCF may also use encryption (IPSec or TLS) for secu-rity purposes on its ports.

QoS performance testing aimed at VoLTE in the IMS core should cover all the protocols in use. As a minimum, VoLTE QoE tests in the IMS core must cover: - UE IP address assignment timing performance - SIP registration performance - Actual voice quality analysis in real-time - Call release and teardown performance

An example performance test is to see how quickly an IP address is assigned to the UE or how quickly that device can send the first SIP “Invite” message. This scaled to several thousand users will give an accurate representation on how well the IMS core is primed.

The IMS Core will pass millions of SIP messages a second. This puts the rates of concurrent SIP sessions in the order of tens of thousands. Clearly it’s not feasible to try to actively test these numbers with a group of friendly users. To create large volumes of concurrent SIP sessions requires high performance, scalable emulation tools that can analyze each and every session in real-time.

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About Shenick Network Systems

Shenick is an award winning provider of per-flow IP communications test systems, enabling converged IP network service providers and communications equipment vendors to test the complete service delivery life cycle from lab to live deployment. Established in 2000, Shenick has deployed its diversifEye™ integrated network, application and security attack emulation and performance monitoring systems to converged IP-oriented network service providers, communications equipment manufacturers, large enterprise and govern-ments globally. diversifEye is a registered trademark of Shenick Network Systems.

For more information contact: [email protected]

diversifEyediversifEye™ is a test and performance measurement solution for next generation networks such as 4G-LTE and Cloud Com-puting. diversifEye provides emulation, test and performance measurements of individual application flows such as Video, Voice and Data applications running in the LTE network. diversifEye’s per flow architecture with real time analysis provides the granularity necessary to determine any Quality of Experience performance issues on a per application basis relating to poorly configured QoS settings on the 4G network.

As an emulation tool diversifEye saves considerable time when testing 4G network performance with its pre-configured applications and emulated UE end-points. Testing includes performance analysis of SIP, SIP over IPSec, SIP over GTP, etc. Furthermore diversifEye provides IMS type applications such as SIP enabled RTSP or SIP enabled HTTP flows.

diversifEye provides large scale emulation of stateful application flows, by accurately representing UEs and parameters such as IMSI and user authentication details. diversifEye’s emulated traffic flows are used to load various interfaces on the 4G path.

diversifEye is not limited to solely loading the LTE network paths but also enables the delivery of real user activity on a per UE basis. diversifEye’s per flow architecture means multiple application flow requests per registered UE, representing a real subscriber’s smartphone activity. diversifEye enables testing utilization performance of the LTE EPC.

diversifEye’s per flow architecture provides performance measurements on each and every emulated application flow asso-ciated with each and every emulated UE, enabling users to quantify how LTE QoS feature changes impact a subscriber’s VoLTE service.

Summary Optimizing 4G networks to save costs has been greatly simplified by Shenick’s per-flow emulation and test approach. With per-flow emulation and real time analysis it’s possible to limit the impact to customer QoS. Using Shenick’s solutions, service providers and network equipment manufacturers are given the necessary granular view of end-user quality in real time. Any subtle changes in quality are picked up by Shenick’s thresholding facility, enabling service providers to quickly judge, in real time, if a decision to change or optimize a device setting is the correct one. This win-win situation ensures service providers continue to deliver services at the right price!


Figure 5 : Dedicated VoLTE performance windows provide real-time views on QoE. Capture live performance issues when changing core LTE QoS settings.

VOLTE Solution

Technology

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