Making the shift_to_mobile_hd_voice

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To deliver a better quality voice signal, mobile service providers must consider how the signal is …

To deliver a better quality voice signal, mobile service providers must consider how the signal is
delivered from the handset, through the access portion of the network, and then through the mobile
core

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  • 1. TECHNOLOGY WHITE PAPERMaking the Shift to Mobile HD VoiceEnd-to-end voice management for a better mobile end user experienceAbstractTo deliver a better quality voice signal, mobile service providers must consider how the signal isdelivered from the handset, through the access portion of the network, and then through the mobilecore. Unfortunately, although each stage of the call is important, mobile service providers cannotcontrol the quality of every end user’s handset. Fortunately, they can control the radio portion oftheir network, which requires its own approach to quality assurance and which service providershave addressed with RF planning. Service providers can also control the quality of the signalthrough the mobile network core, which offers significant opportunity for enhancement. WithAdaptive Multi-Rate Wideband (AMR-WB), a new speech coding standard commonly referred to ashigh definition (HD) voice, service providers can provide better fidelity voice signals from handsetsand deliver CD quality voice to end users through mobile networks. But even with this new codec,the challenge is to deliver HD Voice end-to-end for all voice calls on an ongoing basis, and in a waythat optimizes the network to ensure continuing profitability.
  • 2. TECHNOLOGY WHITE PAPERVOICE IS THE MAINSTAY OF MOBILE SERVICE .................................................................................. 3THE NEED FOR BETTER QUALITY VOICE............................................................................................. 5Demand for HD Voice expected to grow....................................................................................................................... 6BUILDING BETTER VOICE QUALITY ...................................................................................................... 7New codec supports higher quality voice ..................................................................................................................... 7Codec management requirements................................................................................................................................ 8ALCATEL-LUCENT AND HD VOICE ........................................................................................................11Alcatel-Lucent Mobile HDV Core................................................................................................................................. 12CONCLUSION................................................................................................................................................14ACRONYMS ...................................................................................................................................................16Making the Shift to Mobile HD Voice Alcatel-Lucent 2
  • 3. TECHNOLOGY WHITE PAPERVoice Is the Mainstay of Mobile ServiceMultimedia. Data. Long Term Evolution (LTE).It seems you can’t turn to a telecommunications outlet these days without one more article, analysis,or dissertation about the effects these three issues will have on mobile networks and on mobileservice providers. Industry insiders, media, and analysts have devoted reams of printed and digitaltext to explaining their importance to the long term viability of the mobile service provider business.But ask any business or consumer end user to explain what is most important to them with respectto mobile services and voice quality will probably be at or near the top of the list. The fact is thatafter all the texting and Internet surfing are done, mobile end users turn to their mobile phone tosend and receive voice calls. And they expect the quality of each call with friends, family andcolleagues to be comparable to the quality of calls on their landline, from anywhere and at any time.End user expectations of voice quality were confirmed by a market study conducted at the end of2009, which reported that an end user’s perception of poor voice quality usually manifests itself asdissatisfaction with the service provider.1 The study revealed that while 64 percent of those surveyedwould contact their service provider if they experienced poor voice service, 41 percent would switchservice providers (Figure 1).Figure 1. Effect of poor sound quality on end user action and service provider loyaltySixty-six percent of those surveyed said they would have to experience poor sound quality usually(25 percent), occasionally (27 percent), or seldom (14 percent) for them to switch their service1 “Market Perceptions of Voice Quality in Mobile Networks: Understanding how mobile voice quality affects service provider business”, Alcatel-Lucent, January 2010.Making the Shift to Mobile HD Voice Alcatel-Lucent 3
  • 4. TECHNOLOGY WHITE PAPERprovider. While 44 percent of business users and 36 percent of high end consumers said it wouldonly have to occur seldom or occasionally (Figure 2).Figure 2. Frequency of poor sound quality in order to switch service providersMobile service providers have always understood this simple fact and have, over the years, gone togreat lengths to maintain and improve voice quality. In the early days of mobile service theemphasis was on providing more coverage to enable calls in more areas and satisfy end userdemand for true “voice” mobility. As mobile networks became more ubiquitous and coverage issueswere no longer a major concern, the emphasis shifted to maintaining the connection so users wouldnot experience dropped calls. Now, with more users on the network, coverage available virtuallyeverywhere and anywhere, and networks robust enough to ensure calls don’t get dropped, serviceproviders are turning to the last piece of the puzzle: clearer, more perceptible audio quality.By enhancing the audio quality of voice calls, mobile service providers who understand theimportance of voice as the mainstay of their business, hope to improve the quality of the customerexperience. In this way they hope to establish a competitive edge and ensure end user loyalty,increase average revenue per user (ARPU), and reduce churn.To deliver a better quality voice signal, mobile service providers must consider how the signal isdelivered from the handset, through the access portion of the network, and then through the mobilecore. Unfortunately, although each stage of the call is important, mobile service providers cannotcontrol the quality of every end user’s handset. Fortunately, they can control the radio portion oftheir network, which requires its own approach to quality assurance. Service providers haveaddressed quality requirements in the access with RF planning, but this is not the subject of thispaper. This paper addresses how service providers can control the quality of the signal through themobile network core, which offers significant opportunity for enhancement.Making the Shift to Mobile HD Voice Alcatel-Lucent 4
  • 5. TECHNOLOGY WHITE PAPERNew technologies are now available that allow mobile service providers to manage the quality ofvoice signals as they travel through the network core. Adaptive Multi-Rate Wideband (AMR-WB) isa new speech coding standard that can be used to enhance voice signals in mobile networks anddeliver CD quality voice to end users. Commonly referred to as high definition (HD) voice, this newapproach to voice delivery provides excellent speech quality because it samples the signal over awider speech bandwidth of 50–7000Hz compared to narrowband speech coders, which are basedon Plain Old Telephone Service (POTS) wireline quality of 300–3400Hz.But even with this new coding standard, the challenge is to deliver HD Voice end-to-end for all voicecalls where the handsets support the codec, and in a way that optimizes the use of networkresources to ensure continuing profitability. By enabling effective digital conversion of the voicesignal, establishing Transcoder Free Operation (TRFO) and Tandem-Free Operation (TFO) wherepossible or necessary to avoid transcoding in an integrated, end-to-end intelligent codec negotiationframework, mobile service providers can establish true HD Voice quality for their end users.Integrated properly as part of a complete HD Voice solution, these capabilities will give mobileservice providers the ability to take their mobile voice service to the next level and maintain acompetitive edge.The Need for Better Quality VoiceMarket studies show that voice continues to account for the majority of a mobile service provider’srevenues. At the end of 2009 Gartner projected that even though voice revenues are declining, theywill still account for close to 60 percent of revenues in most markets by 2013.2 But despite thecontinuing importance of voice to a mobile service provider’s business, the quality of the mobilevoice experience has not made much improvement over the past 15 years, except for price bundling,discounts on volume and/or “in-circle” plans and fewer dropped calls. In fact, yearly studies showthat mobile voice quality continues to be a major concern for end users. A 2009 study by JD Powerand Associates revealed that mobile call quality decreased from 11 PP100 to 13 PP100 between June2009 and January 2010.3Yet, end user expectations of voice service continue to be high. The results of the market study notedin the introduction revealed that mobile voice quality is important. End users are not only able toperceive and characterize it, but they also recognize good voice quality when they hear it. Inaddition, voice quality is a major contributor to the overall quality of experience (QoE) associatedwith mobile voice service. Three-quarters of end users surveyed agreed completely that they hatemissing what someone is saying because they may miss something important. The majority of endusers also agreed they get frustrated if they can’t hear people they are calling. In fact, the results2 “Forecast: Mobile Services, 2004-2013,” Gartner, June to September 2009.3 “2010 Wireless Call Quality Performance Study—Volume 1”, J.D. Power and Associates, January 2010,http://www.jdpower.com/telecom/articles/2010-Wireless-Call-Quality-Performance-Study-Volume-1/page-2/.Making the Shift to Mobile HD Voice Alcatel-Lucent 5
  • 6. TECHNOLOGY WHITE PAPERshowed that half of the end users surveyed feel anxious when they can’t hear someone clearly ontheir cell phone.4It’s safe to say that as service providers roll out 4G Long Term Evolution technology end users willexpect that the quality of their mobile voice service will move out of the 20th century and into the21st century. Recent trials of HD Voice by a number of service providers confirm end users not onlyexpect this, but they are willing to pay for it. As a result, the Global mobile Suppliers Association(GSA) reports that there are already 10 commercial HD Voice networks up and running in ninecountries.5For example, France Telecom/Orange tested the market for HD Voice in Moldova at the end of2009 with the world’s first commercial mobile HD Voice service. The company reported that theservice resulted in longer phone usage by some subscribers when they were calling HD handsets.More importantly, a survey of end users revealed that 72 percent of users on HD calls intended topurchase an HD Voice phone the next time they upgraded their handset.6 Since then, Orange hasrolled out HD Voice service in France, Switzerland, Spain, the U.K., and Armenia, and the companyhas announced that all its handsets will support HD Voice by the end of 2011.Demand for HD Voice expected to growThe seeds of end user expectations and demand for HD Voice have been sown by a variety ofservices already available. Notably, end users worldwide have adopted some form of voice over IP(VoIP) application, either as a supplement to their existing voice services, or as an enhancement tosocial networks, or interactive online gaming. The majority of these VoIP calls are connected fromone wideband voice processor to another. However, more calls are increasingly being connectedfrom a wideband processor to traditional PSTN or mobile endpoints. When these types ofconnections are made the call processing reverts to the lowest common denominator, thenarrowband used in the PSTN network or the mobile network. As a result, end users notice thedifference in quality compared to calls managed on both ends by a wideband voice processor.For end users who have experienced these types of calls, quality is an issue. They have come toexpect a certain QoE from their VoIP connection and are unhappy when it is not available. Thisexpectation will fuel demand for better quality voice on mobile, especially as VoIP services gaintraction on mobile networks and service providers adopt the new AMR-WB codec. As noted by ABIResearch in a 2009 report, these factors will result in a substantial increase in HD Voice traffic onmobile networks over the next five years (Figure 3).4 “Market Perceptions of Voice Quality in Mobile Networks: Understanding how mobile voice quality affects service provider business”, Alcatel-Lucent, January 2010.5 “HD Voice: Global Update Report”, Global mobile Suppliers Association, November 16, 2010.6 “Mobile HD Voice”, ABI Research, Q1, 2010.Making the Shift to Mobile HD Voice Alcatel-Lucent 6
  • 7. TECHNOLOGY WHITE PAPERFigure 3. Mobile HD Voice traffic by region, world market forecast, 2009 to 20157Building Better Voice QualityFor end users, a high quality voice call is one where the conversation occurs without difficulty andwithout any annoying or distracting effects. It is characterized by clear, audible speech without anydegradation (clicks, buzz noises, or static), periods of interruptions, or echo. Creating higher qualityvoice is becoming a lot easier as a result of advancements in wideband codec standards.New codec supports higher quality voiceTraditional narrowband telephony is based on sampling the sound stream 8,000 times a second,and constraining the reproduction of the sound spectrum to the range between 200Hz on the lowend to 3.3 KHz on the high end. The sampled voice is then fit into a 64K bandwidth.The Adaptive Multi-Rate (AMR) audio codec is the current standard used in Global System forMobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS)networks. It provides audio data compression optimized for speech, and it was adopted as astandard by the 3rd Generation Partnership Project (3GPP) in October 1998. This codec is a littlemore complex. Based on link conditions, it uses link adaptation to select the best codec mode fromone of eight available bit rates.The new benchmark for a high quality voice experience on mobile is based on the Adaptive Multi-Rate Wideband (AMR-WB) codec. This codec was standardized by the ITU-T in 2007 and adopted7 “Mobile HD Voice”, ABI Research, Q1, 2010.Making the Shift to Mobile HD Voice Alcatel-Lucent 7
  • 8. TECHNOLOGY WHITE PAPERby most mobile phone manufacturers as the future basis of mobile voice encoding. It providesexcellent speech quality because it doubles the sampling rate and more than doubles the width ofthe sound spectrum reproduced, from 50Hz to 7 KHz. This adds significant depth and nuance to thetransmitted sound, and it reduces the bandwidth requirement to 32Kbps, half that of a typical PSTNtransmission.Because it delivers the highest quality voice experience available, AMR-WB is commonly referred toas HD Voice. The GSA notes that HD-voice “provides significantly higher voice quality for callsbetween mobile phones supporting the feature, and can be implemented in GSM and WCDMA(UMTS) networks. The higher voice quality of HD Voice improves the call experience and allowspeople to better share feelings, do business and communicate information.”8But having the right codec is only part of the solution mobile service providers need to create ahigher quality voice experience for end users. To truly capitalize on the benefits HD Voice offers,mobile service providers must also consider how the codec is managed end-to-end.Codec management requirementsToday’s mobile networks are engineered to deal with the typical network impairments to voicequality. All mobile networks have integrated processes specifically designed to reduce or eliminateecho, delay, jitter, and packet loss. In addition, to optimize network resources and deliver voicebetween different types of devices, all networks include transcoding functions.Transcoding is the direct digital conversion of a voice signal from one codec format to another. Ittakes place in the network as the signal is delivered from one element to another and it canadversely affect sound quality. That’s because when voice is initially compressed and encoded,details of the voice transmission are stripped away. The lower the compression bit rate, the greaterthe amount of information that is stripped. Transcoding from one codec format to another, furthercompounds this problem because the compressed signal must be decompressed into a base formatand then recompressed into a second codec format, so more information is stripped away. Inaddition, multiple transcoding stages degrade voice quality, add delay and amplify speechdegradation anomalies, such as noise and distortion, introduced by the codecs used forcompression.In legacy circuit switched networks, transcoding does not adversely affect voice quality becausethese networks have one or at a maximum two transcoding stages. However, packet voice networkscan easily have three or even four transcoding stages with two or more transcoders working intandem. As a result, the quality of the voice signal can be significantly reduced by the time it reachesan end user’s mobile device. To properly manage the quality of a HD Voice signal, the originalencoding must be maintained as the signal travels from the sender to the recipient. Therefore,8 “HD Voice: Global Update Report”, Global mobile Suppliers Association, November 16, 2010.Making the Shift to Mobile HD Voice Alcatel-Lucent 8
  • 9. TECHNOLOGY WHITE PAPERtranscoding must be eliminated (Figure 4).Figure 4. Transcoder Free Operation (TrFO) improves sound quality TrFO Improvements 5 4 TrFO On MOS 3 TrFO Off 2 1 Improvement 0 12.2 10.2 7.95 7.40 6.70 5.90 5.15 4.75 K K K K K K K K TrFO On 4.18 4.07 3.91 3.89 3.83 3.77 3.57 3.48 TrFO Off 3.87 3.69 3.38 3.34 3.33 3.12 2.93 2.8 Improvement 0.31 0.38 0.53 0.55 0.5 0.65 0.64 0.68 AMR RateBut the compressed voice must still be managed as it travels through the network to and from enduser devices. By intelligently managing codec usage, a wireless call server (WCS) can maintaincompressed speech in its original state as it travels between a pair of call servers on a network(Figure 5).Figure 5. Intelligent codec negotiation allows calls to be established without unnecessary transcodingMaking the Shift to Mobile HD Voice Alcatel-Lucent 9
  • 10. TECHNOLOGY WHITE PAPERLikewise, intelligent codec negotiation ensures the signal travels through the network using thehighest quality codec. So, if both ends of a call do not support the AMR-WB codec then the WCSshould be capable of finding a common codec for both. In this way, the WCS can eliminate the needto transcode from AMR-WB to a lesser codec in the middle of a call and the same codec is used end-to-end. This ensures the highest quality voice signal is sent and received and guarantees end usersalways experience smooth, undistorted voice calls (Figure 6).Figure 6. TrFO can interwork with TFO to preserve end-to-end voice qualityFor voice calls made between a mobile handset capable of HD Voice and a wireline HD VoIP phone,the network must also be able to efficiently support HD wireline interworking. Since thistranscoding cannot be avoided, it should be completed at the edge of the network — at the lastgateway before the call leaves the mobile core and enters a wireline network (Figure 7).Figure 7. Transcoding at the edge of the network for HD wireline interworkingMaking the Shift to Mobile HD Voice Alcatel-Lucent 10
  • 11. TECHNOLOGY WHITE PAPEREfficient codec management also requires intelligent routing to ensure the HD Voice signals get totheir intended endpoint by following the shortest possible route. To do this, the network must limitthe number of gateways the call must travel through as it makes its way through the mobile core. Inaddition, there must be a mechanism in place to intelligently detect the optimal path through the IPnetwork.Finally, intelligent codec management requires support for a variety of coding and signalingbetween call servers, as well as support for two types of bearer traffic, Internet Engineering TaskForce (IETF) framing and 3GPP.Alcatel-Lucent and HD VoiceThe Alcatel-Lucent Mobile NGN solution has been designed to ensure optimal voice quality in next-generation mobile networks. This solution is built on two key components: • The Alcatel-Lucent 5060 Wireless Call Server (WCS), which provides the call control and signaling functions. It is designed specifically for 3GPP, R4/R5/R6-compliant architectures and it significantly improves network simplicity, capacity and operational efficiency. • The Alcatel-Lucent 7549 Media Gateway (MGW), which is a high-density, multi- service gateway designed with voice and data-bearer interfaces, including Time Division Multiplexing (TDM), IP and Asynchronous Transfer Mode (ATM). It performs any-to-any switching, including native TDM-to-TDM, native packet-to-packet and TDM-to-packet, and delivers a dramatically simplified architecture that supports seamless evolution to an IP Multimedia Subsystem (IMS).Together, the WCS and the MGW include a variety of features designed to counteract the effects ofthe network, and the environment on the quality of voice calls (Table 1). Key features includeelectrical echo cancellation, automatic noise reduction (ANR), automatic level control (ALC),adaptive jitter buffers, and packet loss concealment.9 In addition, these network components areengineered to eliminate the effects of speech coding and compression, and transcoding on voicesignals. This is accomplished with the Alcatel-Lucent Mobile HDV Core, a new systemembedded in the solution’s WCS. This system intelligently determines what the voice call qualityshould be and sends the information to the gateway to enable optimal routing of the signal througha mobile core.9 For more information about the Alcatel-Lucent Mobile NGN solution, see the “Mobile NGN Core-Voice Quality White Paper, Edition 1.4”, Alcatel-Lucent, 2010.Making the Shift to Mobile HD Voice Alcatel-Lucent 11
  • 12. TECHNOLOGY WHITE PAPERTable 1. Alcatel-Lucent Mobile NGN solution voice quality features vs. voice quality impairment factorsAlcatel-Lucent Mobile HDV CoreThe Alcatel-Lucent Mobile HDV Core brings support for the AMR-WB codec to the Alcatel-Lucent5060 Wireless Call Server (WCS) and Alcatel-Lucent 7549 Media Gateway (MGW). With thissoftware, the 5060 WCS is able to recognize when a call should be delivered as an HD Voice call,determine when to use coding techniques, how to use coding, and what information the gatewayneeds to properly deliver the signal. Based on this information, the 7549 MGW establishes theappropriate HD quality connection and acts as transport for the call between two end users.The software allows usage of AMR-WB codec in intra-MSC 3G mobile to 3G mobile calls, withpacket or TDM interconnect trunks. The AMR-WB codec is selected whenever its usage is possibleend-to-end, thereby enabling true “wideband” sound quality, assuming all elements on the call path,including end user devices, support the AMR-WB codec.The Mobile HDV Core also supports TrFO and TFO operation. With TFO, it is possible totransparently transmit the compressed speech frames from mobile station to mobile station andbypass the transcoding function, when both end terminals are using the same speech coding.For TrFO, the Mobile HDV Core eliminates transcoding on the media gateways in thecommunication path. This reduces the port-to-port delay for mobile-to-mobile calls, which isparticularly dramatic given that without TrFO or TFO, a typical GSM mobile-to-mobile call could betranscoded up to four times on a compressed packet backbone. More importantly, by eliminatingtranscoding, the potential for voice impairment caused by transcoding is also eliminated, fewerdigital signal processing resources are needed in the network, and bandwidth is optimized.As a result, core and access transport bandwidth savings are realized with TrFO because cost-Making the Shift to Mobile HD Voice Alcatel-Lucent 12
  • 13. TECHNOLOGY WHITE PAPERefficient transmission is achieved by reducing the use of transcoding equipment in the transmissionpath (Figure 8). And, because wireless codecs are bandwidth efficient, these savings can be carriedend-to-end without any “processing”.Figure 8. Alcatel-Lucent Mobile NGN solution TrFOTo take advantage of the benefits of both TFO and TrFO, the Alcatel-Lucent Mobile HDV coresupports TFO and TrFO interworking. This results in a communication path that is optimized withthe concatenation of both TrFO and TFO links (Figure 9).Figure 9. Alcatel-Lucent Mobile NGN Solution TFO and TrFO interworkingMaking the Shift to Mobile HD Voice Alcatel-Lucent 13
  • 14. TECHNOLOGY WHITE PAPERFinally, the Mobile HDV Core software has a dynamic codec selection feature, which provides codecnegotiation and selection that enables TrFO whenever possible. This minimizes the number ofrequired transcoding steps and compressed links present on a call path. With this feature, themobile service provider configures the use of codecs within the core network based on codecconfiguration used in the network and the level of TFO/TrFO support present. The software thenuses this information to negotiate and select the best codec for the call path based on requirementsfor voice quality and bandwidth optimization.The Mobile HDV Core software supports standards based out-of-band codec negotiation as well asTFO. It offers a rich set of configuration options to allow service providers to make intelligenttradeoffs between selection and de-selection/prioritization of all relevant codecs in a core networkand mobile access trunk group for various call scenarios. Likewise it enables intelligent bandwidthvs voice quality tradefoffs. And it provides seamless intelligent codec negotiation across anycombination of different access types (2G over IP, and TDM, 3G over IP and ATM) and corenetwork types (Session Initiation Protocol (SIP), SIP-I, Bearer Independent Call Control (BICC),and ISDN User Part (ISUP)).ConclusionVoice quality is a major contributor to the overall QoE associated with mobile voice service. Becausebetter voice quality keeps end users happy mobile service providers need a new approach to themanagement and delivery of every encoded digital bit as it travels the network end-to-end.Because it delivers the highest quality voice experience available, AMR-WB, or HD Voice, is the newbenchmark for a high quality voice experience on mobile. It provides excellent speech qualitybecause it doubles the sampling rate and more than doubles the width of the sound spectrumreproduced. In addition, it is more efficient because it reduces the bandwidth required for highquality voice delivery.But the difficulty with analog to digital conversion is maintaining digital coding through thenetwork so that the quality of the voice is consistent end-to-end. Therefore, to truly capitalize on thebenefits HD Voice offers, mobile service providers must ensure the AMR-WB codec is managedproperly. By enabling TFO and TrFO management of the voice signal, mobile service providers canavoid the problems associated with decompression and recompression of the signal as it travelsthrough the network. As a result, service providers can deliver a higher voice service QoE for endusers based on this new coding standard. This was confirmed through the France/Telecom OrangeAMR-WB trials in Moldova. Orange chose the Moldovan network for the trials because it was builton a next-generation 3G infrastructure that supported TrFO operation upon initial deployment.As part of the Alcatel-Lucent Mobile NGN solution, the Alcatel-Lucent Mobile HDV Core bringssupport for the AMR-WB codec to the Alcatel-Lucent 5060 Wireless Call Server (WCS) and Alcatel-Making the Shift to Mobile HD Voice Alcatel-Lucent 14
  • 15. TECHNOLOGY WHITE PAPERLucent 7549 Media Gateway (MGW). With this software, the 5060 WCS is able to recognize when acall should be delivered as an HD Voice call, determine when to use coding techniques, how to usecoding, and what information the gateway needs to properly deliver the signal. Based on thisinformation, the 7549 MGW establishes the appropriate HD quality connection and acts astransport for the call between two end users. Most importantly, it supports TrFO and TFO operationto ensure optimal HD Voice for all calls whenever usage is possible end-to-end.Making the Shift to Mobile HD Voice Alcatel-Lucent 15
  • 16. TECHNOLOGY WHITE PAPERAcronyms Term Definition 3GPP 3rd Generation Partnership Project ALC automatic level control AMR Adaptive Multi-Rate AMR-WB Adaptive Multi-Rate Wideband ARPU average revenue per user ATM Asynchronous Transfer Mode ANR automatic noise reduction BICC Bearer Independent Call Control GSA Global mobile Suppliers Association GSM Global System for Mobile Communications HD high definition IETF Internet Engineering Task Force IMS IP Multimedia Subsystem ISDN Integrated Services Digital Network ISUP ISDN User Part ITU International Telecommunication Union ITU-T International Telecommunication Union-Telecommunication Standardization Sector LTE Long Term Evolution MGW media gateway POTS Plain Old Telephone Service SIP Session Initiation Protocol TDM Time Division Multiplexing TFO Tandem Free Operation TrFO Transcoder Free Operation QoE quality of experience UMTS Universal Mobile Telecommunications System VoIP voice over IP wcs wireless call serverMaking the Shift to Mobile HD Voice Alcatel-Lucent 16