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6 Best Practices for Launching Vowifi, Volte and EVS

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6 Best Practices for Launching Vowifi, Volte and EVS White Paper 6 Best Practices for Launching VoWiFi, VoLTE and EVS Launching Next-Gen Voice Services Powered by new wireless and IP technology, we live in an The latest development in the next generation of voice increasingly connected world. Now we expect to be able to services is the introduction of the EVS codec. EVS encodes access services anytime and anywhere and seamlessly move input audio signals with a bandwidth of up to 20kHz, the full between locations. Oh, and the quality needs to be great— bandwidth of audio perceptible to the human ear. EVS- everywhere! With the advent of Voice over Wi-Fi (VoWiFi) encoded speech is more faithfully reproduced than previous and Voice over LTE (VoLTE) and a range of supporting generation codecs such as AMR-WB and AMR–NB. In short, technologies including the Enhanced Voice Services (EVS) audio over EVS sounds more like the real thing. On the codec, Internet Multimedia Subsystem (IMS) and new “carrier- technical side the EVS codec also holds a lot of promise—it grade” Wi-Fi standards, providers are now able to deliver has been touted to perform better than previous generation next-generation voice services with unprecedented quality codecs when signal levels are poor and to improve call and accessibility. quality for connections to lower bandwidth codecs. 6 Best Practices for Launching VoWiFi, VoLTE and EVS Up to 20 kHz Up to 7 kHz Up to 3.4 kHz VoLTE EVS 3G AMR-WB 3G AMR-NB Figure 1: The EVS codec encodes audio inputs up 20kHz whereas previous generation codecs supported narrower bandwidths of 3.4 to 7kHz. Over the past few years, Spirent has worked closely with industry’s first round of providers rolling out next-generation voice services. Based on that experience, Spirent has developed best practices for assuring the successful launch of next-generation voice services with a focus on VoLTE, VoWiFi and EVS-enabled voice services. This white paper details the key challenges providers face as they launch these services and shares Spirent’s recommended best practices and lessons learned. The whitepaper also illustrates key principles with test results of next-gen voice services from actual operational networks. Assurance Challenges for Launching Next-Gen Voice Services Evaluating Inter-service, Inter-codec Calling (VoLTE & VoWiFi) The first challenge we will examine is how to assess the To illustrate the importance of testing these various performance of EVS voice services within a VoLTE network. combinations, we’ll share results from some mobile-to- To do this comprehensively it’s important to test how well mobile tests we performed on a live operational network the service works only when placing calls between EVS enabled with EVS and AMR-WB codecs. Our tests focused capable devices, but also when placing calls to the previous on comparing EVS and AMR-WB speech quality in a variety generation of devices that use narrow and wideband codecs of typical user locations. The chart on the left of Figure 2 including phones outside the mobile network via the PSTN shows that EVS to EVS calling was superior in terms of speech (public switched telephone network). quality when compared to AMR-WB to AMR-WB calling. The chart on the right side of Figure 2 shows cross-codec test In each of these scenarios different parts of the mobile results for AMR-WB to EVS codec calling (and vice versa). network are exercised and different transcoding is required. During this particular test, we observed a problem with It’s possible (and common) that the voice service may be transcoding which led to degraded speech quality for cross- working well in one scenario but exhibit an issue in another codec connectivity only. After this problem was identified, scenario. That means it’s critical to test VoLTE to VoLTE calls, the carrier was able to isolate the root cause to an IMS VoLTE to 3G calls and VoLTE to Landline calls as well as firmware issue which was quickly fixed. making sure all the combinations of narrow and wideband codecs are exercised. An identical challenge exists for evaluating EVS services over VoWiFi: it’s critical to test VoWiFi to VoWiFi calls, Wi-Fi to 3G, VoWiFi to 3G, VoWiFi to Landline calls and again to make sure all combinations of codecs are exercised. www.spirent.com Speech quality (POLQA MOS) Speech quality (EVS to AMR) AMR-WB EVS AMR-WB party EVS party Good 4.4 4.1 speech 4.1 Lower quality than 3.8 quality AMR-AMR 3.8 3.4 3.4 3.0 3.0 Mean Max Mean Max Figure 2: Test results for EVS, AMR-WB and cross-codec EVS / AMR-WB calling in an operational network. Troubleshooting Mobile-to-Mobile Issues (VoLTE & VoWiFi) The next challenge we’ll look at is how to troubleshoot The nature of Wi-Fi means congestion, interference and mobile-to-mobile voice service issues in a VoLTE network. latency are additional possible causes of the problem and Tests based on mobile to mobile calling are often the only often outside the direct control of the mobile operator. way to “exercise” a new service or technology due to the Following is a practical example of a set of mobile-to-mobile fact that the service only works on a subset of devices or for calling issues which could have multiple root causes and certain network infrastructure. If the test results reveal a voice are therefore extremely challenging to troubleshoot. We services problem exists it can be challenging to pinpoint and performed over 1,500 mobile-to-mobile calls in multiple troubleshoot exactly what could be causing it: locations served by operational Wi-Fi and 3G (UMTS) • Is it a device issue? networks. We used two pairs of mobile phones, where one pair was making Wi-Fi to Wi-Fi calls and the other was making • Is it an LTE Access network issue? Wi-Fi to 3G calls. In Figure 3, which shows the test results, we • Is it a core/IMS network issue? can see Wi-Fi to Wi-Fi performance is superior compared to • Is the problem is occurring in the uplink of one device or Wi-Fi to 3G in terms of call completion, call setup and speech the downlink of the other? quality. Because the Wi-Fi to 3G calls in this test campaign include an uplink and downlink on each technology, it is These challenges also apply to VoWiFi networks—is it a extremely challenging to isolate the root causes of the device issue, a network issue or perhaps a problem with the performance differences observed. venue Wi-Fi network or its backhaul to the core network? Wi-Fi to Wi -Fi was more Wi-Fi to Wi -Fi had faster call Wi-Fi to Wi -Fi had better speech reliable vs. Wi-Fi to Mobile setup vs. Wi-Fi to Mobile quality vs. Wi-Fi to Mobile 95% 4 More 10 Slower Better 92% Reliable 8.6 Quality s 3.3 s e ) 8 c 90% s 3 c ( ) y u t 2.5 S i e l S 87% ) O a m i n u % 6 5.1 M ( T o i Q t e A 85% p 2 t e h l u Q a c t p L R e e 4 e m O S l p o P l ( S C a 80% 1 l l C 2 a C Less Worse Reliable Faster 75% 0 0 Quality WiFi-WiFi WiFi-Mobile WiFi-WiFi WiFi-Mobile WiFi-WiFi WiFi-Mobile Call Completion Success = Successful Initiation + Successful Retention (No Drop) Figure 3: Over 1,500 VoWiFi calls made in multiple locations in an operational network. Two scenarios: Wi-Fi to Wi-Fi and Wi-Fi to 3G Mobile. 3 6 Best Practices for Launching VoWiFi, VoLTE and EVS Evaluating VoLTE-VoWiFi Handoff The next challenge we’ll examine is evaluating the impact of handoff between VoLTE and VoWiFi on user experience. More and more mobile network operators are using VoWiFi as a way of easing the load on their LTE / 3G networks and expanding their coverage. An important aspect of this policy is to ensure seamless handover of calls from the VoLTE network to the VoWiFi network (and vice versa) without the user perceiving discontinuity in the call or degradation in audio quality. As the call hands over from one access technology to the other the routing through the backhaul and core IMS network often changes and there are number of places where things can go wrong. Figure 4 and 5 depict measurements of speech quality for VoLTE to VoWiFi handoffs in an operational network. For these measurements, we evaluated speech quality before, during and after a handoff. The test scenario included the following steps: establish a call on VoLTE, emulate a user walking into Wi-Fi coverage (by adjusting the attenuation of the Wi-Fi signal transmitted by the access point), waiting for the handoff to Wi-Fi, staying on Wi-Fi and collecting multiple speech samples and then emulating walking out of Wi-Fi coverage (again by varying Wi-Fi signal levels) until the call transitions back to VoLTE. In the chart at the top of Figure 4, MOS values before the handoffs were very strong, averaging a score around 4. However, during the handoff we see scores that fluctuate between 1.5 and 2 with one example just below 3, reflecting a substantial degradation in user experience. The bottom graph in Figure 4 shows the WAV file for the speech during the handoff. During the handoff period from 5.7 seconds to 7.2 seconds, speech was almost non-existent.
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