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Making the Shift to Mobile HD Voice
End-to-end voice management for a better mobile end user experience
Abstract 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. Unfortunately, although each stage of the call is important, mobile service providers cannot
control the quality of every end user’s handset. Fortunately, they can control the radio portion of
their network, which requires its own approach to quality assurance and which service providers
have addressed with RF planning. Service providers can also control the quality of the signal
through the mobile network core, which offers significant opportunity for enhancement. With
Adaptive Multi-Rate Wideband (AMR-WB), a new speech coding standard commonly referred to as
high definition (HD) voice, service providers can provide better fidelity voice signals from handsets
and 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 way
that optimizes the network to ensure continuing profitability.
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Making the Shift to Mobile HD Voice Alcatel-Lucent 2
VOICE IS THE MAINSTAY OF MOBILE SERVICE .................................................................................. 3
THE NEED FOR BETTER QUALITY VOICE............................................................................................. 5
Demand for HD Voice expected to grow....................................................................................................................... 6
BUILDING BETTER VOICE QUALITY ...................................................................................................... 7
New codec supports higher quality voice ..................................................................................................................... 7
Codec management requirements................................................................................................................................ 8
ALCATEL-LUCENT AND HD VOICE........................................................................................................11
Alcatel-Lucent Mobile HDV Core................................................................................................................................. 12
CONCLUSION................................................................................................................................................14
ACRONYMS ...................................................................................................................................................16
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Voice Is the Mainstay of Mobile Service
Multimedia. 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 mobile
service providers. Industry insiders, media, and analysts have devoted reams of printed and digital
text 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 respect
to mobile services and voice quality will probably be at or near the top of the list. The fact is that
after all the texting and Internet surfing are done, mobile end users turn to their mobile phone to
send and receive voice calls. And they expect the quality of each call with friends, family and
colleagues 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 of
2009, which reported that an end user’s perception of poor voice quality usually manifests itself as
dissatisfaction with the service provider.1 The study revealed that while 64 percent of those surveyed
would contact their service provider if they experienced poor voice service, 41 percent would switch
service providers (Figure 1).
Figure 1. Effect of poor sound quality on end user action and service provider loyalty
Sixty-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 service
1 “Market Perceptions of Voice Quality in Mobile Networks: Understanding how mobile voice quality affects service provider business”, Alcatel-
Lucent, January 2010.
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provider. While 44 percent of business users and 36 percent of high end consumers said it would
only have to occur seldom or occasionally (Figure 2).
Figure 2. Frequency of poor sound quality in order to switch service providers
Mobile service providers have always understood this simple fact and have, over the years, gone to
great lengths to maintain and improve voice quality. In the early days of mobile service the
emphasis was on providing more coverage to enable calls in more areas and satisfy end user
demand for true “voice” mobility. As mobile networks became more ubiquitous and coverage issues
were no longer a major concern, the emphasis shifted to maintaining the connection so users would
not experience dropped calls. Now, with more users on the network, coverage available virtually
everywhere and anywhere, and networks robust enough to ensure calls don’t get dropped, service
providers 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 the
importance of voice as the mainstay of their business, hope to improve the quality of the customer
experience. 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 is
delivered from the handset, through the access portion of the network, and then through the mobile
core. Unfortunately, although each stage of the call is important, mobile service providers cannot
control the quality of every end user’s handset. Fortunately, they can control the radio portion of
their network, which requires its own approach to quality assurance. Service providers have
addressed quality requirements in the access with RF planning, but this is not the subject of this
paper. This paper addresses how service providers can control the quality of the signal through the
mobile network core, which offers significant opportunity for enhancement.
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Making the Shift to Mobile HD Voice Alcatel-Lucent 5
New technologies are now available that allow mobile service providers to manage the quality of
voice signals as they travel through the network core. Adaptive Multi-Rate Wideband (AMR-WB) is
a new speech coding standard that can be used to enhance voice signals in mobile networks and
deliver CD quality voice to end users. Commonly referred to as high definition (HD) voice, this new
approach to voice delivery provides excellent speech quality because it samples the signal over a
wider speech bandwidth of 50–7000Hz compared to narrowband speech coders, which are based
on 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 voice
calls where the handsets support the codec, and in a way that optimizes the use of network
resources to ensure continuing profitability. By enabling effective digital conversion of the voice
signal, establishing Transcoder Free Operation (TRFO) and Tandem-Free Operation (TFO) where
possible or necessary to avoid transcoding in an integrated, end-to-end intelligent codec negotiation
framework, 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 mobile
service providers the ability to take their mobile voice service to the next level and maintain a
competitive edge.
The Need for Better Quality Voice
Market studies show that voice continues to account for the majority of a mobile service provider’s
revenues. At the end of 2009 Gartner projected that even though voice revenues are declining, they
will still account for close to 60 percent of revenues in most markets by 2013.2 But despite the
continuing importance of voice to a mobile service provider’s business, the quality of the mobile
voice 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 show
that mobile voice quality continues to be a major concern for end users. A 2009 study by JD Power
and Associates revealed that mobile call quality decreased from 11 PP100 to 13 PP100 between June
2009 and January 2010.3
Yet, end user expectations of voice service continue to be high. The results of the market study noted
in the introduction revealed that mobile voice quality is important. End users are not only able to
perceive and characterize it, but they also recognize good voice quality when they hear it. In
addition, voice quality is a major contributor to the overall quality of experience (QoE) associated
with mobile voice service. Three-quarters of end users surveyed agreed completely that they hate
missing what someone is saying because they may miss something important. The majority of end
users also agreed they get frustrated if they can’t hear people they are calling. In fact, the results
2 “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/.
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showed that half of the end users surveyed feel anxious when they can’t hear someone clearly on
their cell phone.4
It’s safe to say that as service providers roll out 4G Long Term Evolution technology end users will
expect that the quality of their mobile voice service will move out of the 20th century and into the
21st century. Recent trials of HD Voice by a number of service providers confirm end users not only
expect 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 nine
countries.5
For example, France Telecom/Orange tested the market for HD Voice in Moldova at the end of
2009 with the world’s first commercial mobile HD Voice service. The company reported that the
service 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 to
purchase an HD Voice phone the next time they upgraded their handset.6 Since then, Orange has
rolled out HD Voice service in France, Switzerland, Spain, the U.K., and Armenia, and the company
has announced that all its handsets will support HD Voice by the end of 2011.
Demand for HD Voice expected to grow
The seeds of end user expectations and demand for HD Voice have been sown by a variety of
services 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 to
social networks, or interactive online gaming. The majority of these VoIP calls are connected from
one wideband voice processor to another. However, more calls are increasingly being connected
from a wideband processor to traditional PSTN or mobile endpoints. When these types of
connections are made the call processing reverts to the lowest common denominator, the
narrowband used in the PSTN network or the mobile network. As a result, end users notice the
difference 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 to
expect a certain QoE from their VoIP connection and are unhappy when it is not available. This
expectation will fuel demand for better quality voice on mobile, especially as VoIP services gain
traction on mobile networks and service providers adopt the new AMR-WB codec. As noted by ABI
Research in a 2009 report, these factors will result in a substantial increase in HD Voice traffic on
mobile 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.
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Figure 3. Mobile HD Voice traffic by region, world market forecast, 2009 to 20157
Building Better Voice Quality
For end users, a high quality voice call is one where the conversation occurs without difficulty and
without any annoying or distracting effects. It is characterized by clear, audible speech without any
degradation (clicks, buzz noises, or static), periods of interruptions, or echo. Creating higher quality
voice is becoming a lot easier as a result of advancements in wideband codec standards.
New codec supports higher quality voice
Traditional 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 low
end 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 for
Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS)
networks. It provides audio data compression optimized for speech, and it was adopted as a
standard by the 3rd Generation Partnership Project (3GPP) in October 1998. This codec is a little
more complex. Based on link conditions, it uses link adaptation to select the best codec mode from
one 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 adopted
7 “Mobile HD Voice”, ABI Research, Q1, 2010.
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by most mobile phone manufacturers as the future basis of mobile voice encoding. It provides
excellent speech quality because it doubles the sampling rate and more than doubles the width of
the sound spectrum reproduced, from 50Hz to 7 KHz. This adds significant depth and nuance to the
transmitted sound, and it reduces the bandwidth requirement to 32Kbps, half that of a typical PSTN
transmission.
Because it delivers the highest quality voice experience available, AMR-WB is commonly referred to
as HD Voice. The GSA notes that HD-voice “provides significantly higher voice quality for calls
between 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 allows
people to better share feelings, do business and communicate information.”8
But having the right codec is only part of the solution mobile service providers need to create a
higher 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 requirements
Today’s mobile networks are engineered to deal with the typical network impairments to voice
quality. All mobile networks have integrated processes specifically designed to reduce or eliminate
echo, delay, jitter, and packet loss. In addition, to optimize network resources and deliver voice
between 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. It
takes place in the network as the signal is delivered from one element to another and it can
adversely 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 greater
the amount of information that is stripped. Transcoding from one codec format to another, further
compounds this problem because the compressed signal must be decompressed into a base format
and then recompressed into a second codec format, so more information is stripped away. In
addition, multiple transcoding stages degrade voice quality, add delay and amplify speech
degradation anomalies, such as noise and distortion, introduced by the codecs used for
compression.
In legacy circuit switched networks, transcoding does not adversely affect voice quality because
these networks have one or at a maximum two transcoding stages. However, packet voice networks
can easily have three or even four transcoding stages with two or more transcoders working in
tandem. As a result, the quality of the voice signal can be significantly reduced by the time it reaches
an end user’s mobile device. To properly manage the quality of a HD Voice signal, the original
encoding 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.
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transcoding must be eliminated (Figure 4).
Figure 4. Transcoder Free Operation (TrFO) improves sound quality
But the compressed voice must still be managed as it travels through the network to and from end
user devices. By intelligently managing codec usage, a wireless call server (WCS) can maintain
compressed 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 transcoding
TrFO Improvements
0
12
34
5
AMR Rate
MOS
TrFO On
TrFO Off
Improvement
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
12.2
K
10.2
K
7.95
K
7.40
K
6.70
K
5.90
K
5.15
K
4.75
K
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Likewise, intelligent codec negotiation ensures the signal travels through the network using the
highest quality codec. So, if both ends of a call do not support the AMR-WB codec then the WCS
should be capable of finding a common codec for both. In this way, the WCS can eliminate the need
to 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 users
always experience smooth, undistorted voice calls (Figure 6).
Figure 6. TrFO can interwork with TFO to preserve end-to-end voice quality
For 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 this
transcoding cannot be avoided, it should be completed at the edge of the network — at the last
gateway 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 interworking
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Efficient codec management also requires intelligent routing to ensure the HD Voice signals get to
their intended endpoint by following the shortest possible route. To do this, the network must limit
the number of gateways the call must travel through as it makes its way through the mobile core. In
addition, there must be a mechanism in place to intelligently detect the optimal path through the IP
network.
Finally, intelligent codec management requires support for a variety of coding and signaling
between call servers, as well as support for two types of bearer traffic, Internet Engineering Task
Force (IETF) framing and 3GPP.
Alcatel-Lucent and HD Voice
The 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 of
the network, and the environment on the quality of voice calls (Table 1). Key features include
electrical echo cancellation, automatic noise reduction (ANR), automatic level control (ALC),
adaptive jitter buffers, and packet loss concealment.9 In addition, these network components are
engineered to eliminate the effects of speech coding and compression, and transcoding on voice
signals. This is accomplished with the Alcatel-Lucent Mobile HDV Core, a new system
embedded in the solution’s WCS. This system intelligently determines what the voice call quality
should be and sends the information to the gateway to enable optimal routing of the signal through
a 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.
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Table 1. Alcatel-Lucent Mobile NGN solution voice quality features vs. voice quality impairment factors
Alcatel-Lucent Mobile HDV Core
The Alcatel-Lucent Mobile HDV Core brings support for the AMR-WB codec to the Alcatel-Lucent
5060 Wireless Call Server (WCS) and Alcatel-Lucent 7549 Media Gateway (MGW). With this
software, 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 gateway
needs to properly deliver the signal. Based on this information, the 7549 MGW establishes the
appropriate 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, with
packet or TDM interconnect trunks. The AMR-WB codec is selected whenever its usage is possible
end-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 to
transparently transmit the compressed speech frames from mobile station to mobile station and
bypass 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 the
communication path. This reduces the port-to-port delay for mobile-to-mobile calls, which is
particularly dramatic given that without TrFO or TFO, a typical GSM mobile-to-mobile call could be
transcoded up to four times on a compressed packet backbone. More importantly, by eliminating
transcoding, the potential for voice impairment caused by transcoding is also eliminated, fewer
digital 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-
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efficient transmission is achieved by reducing the use of transcoding equipment in the transmission
path (Figure 8). And, because wireless codecs are bandwidth efficient, these savings can be carried
end-to-end without any “processing”.
Figure 8. Alcatel-Lucent Mobile NGN solution TrFO
To take advantage of the benefits of both TFO and TrFO, the Alcatel-Lucent Mobile HDV core
supports TFO and TrFO interworking. This results in a communication path that is optimized with
the concatenation of both TrFO and TFO links (Figure 9).
Figure 9. Alcatel-Lucent Mobile NGN Solution TFO and TrFO interworking
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Finally, the Mobile HDV Core software has a dynamic codec selection feature, which provides codec
negotiation and selection that enables TrFO whenever possible. This minimizes the number of
required transcoding steps and compressed links present on a call path. With this feature, the
mobile service provider configures the use of codecs within the core network based on codec
configuration used in the network and the level of TFO/TrFO support present. The software then
uses this information to negotiate and select the best codec for the call path based on requirements
for voice quality and bandwidth optimization.
The Mobile HDV Core software supports standards based out-of-band codec negotiation as well as
TFO. It offers a rich set of configuration options to allow service providers to make intelligent
tradeoffs between selection and de-selection/prioritization of all relevant codecs in a core network
and mobile access trunk group for various call scenarios. Likewise it enables intelligent bandwidth
vs voice quality tradefoffs. And it provides seamless intelligent codec negotiation across any
combination of different access types (2G over IP, and TDM, 3G over IP and ATM) and core
network types (Session Initiation Protocol (SIP), SIP-I, Bearer Independent Call Control (BICC),
and ISDN User Part (ISUP)).
Conclusion
Voice quality is a major contributor to the overall QoE associated with mobile voice service. Because
better voice quality keeps end users happy mobile service providers need a new approach to the
management 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 new
benchmark for a high quality voice experience on mobile. It provides excellent speech quality
because it doubles the sampling rate and more than doubles the width of the sound spectrum
reproduced. In addition, it is more efficient because it reduces the bandwidth required for high
quality voice delivery.
But the difficulty with analog to digital conversion is maintaining digital coding through the
network so that the quality of the voice is consistent end-to-end. Therefore, to truly capitalize on the
benefits HD Voice offers, mobile service providers must ensure the AMR-WB codec is managed
properly. By enabling TFO and TrFO management of the voice signal, mobile service providers can
avoid the problems associated with decompression and recompression of the signal as it travels
through the network. As a result, service providers can deliver a higher voice service QoE for end
users based on this new coding standard. This was confirmed through the France/Telecom Orange
AMR-WB trials in Moldova. Orange chose the Moldovan network for the trials because it was built
on 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 brings
support for the AMR-WB codec to the Alcatel-Lucent 5060 Wireless Call Server (WCS) and Alcatel-
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Lucent 7549 Media Gateway (MGW). With this software, 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 gateway needs to properly deliver the signal. Based on this
information, the 7549 MGW establishes the appropriate HD quality connection and acts as
transport for the call between two end users. Most importantly, it supports TrFO and TFO operation
to ensure optimal HD Voice for all calls whenever usage is possible end-to-end.
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Acronyms
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 server