Friday, 16 October 2015

Voice Over LTE

 Incident Description (Incident Phenomena)
How the solution for voice over LTE


 Problem Cause Analysis
Voice over LTE – a step towards future telephony
Which voice over LTE solution offers the most advantages for operators and satisfies user expectations? And what steps need to be taken to deploy such a solution?
Today, GSMA VoLTE is the preferred industry choice for mass-market voice services over LTE. It leverages traditional telecom characteristics, such as high quality and global reach, and at the same time offers an optimal evolution path towards full multimedia services. GSMA VoLTE is based on existing 3GPP MMTel standards.
 Solution
1、 Mobile broadband is driving LTE
Driven by the success of mobile broadband, LTE is now rapidly gaining momentum in the market. Mobile broadband gives operators new revenue and many business opportunities. However, it also
challenges the operators’s current SMS and voice revenues, which today represent more than 70 percent of their global business. So a key question is how to take advantage of the mobile broadband opportunities while maintaining and growing current revenue from traditional communication services (with more attractive service packages).
LTE is set to play a key role in these efforts, since this new technology brings higher capacities and lower latencies, resulting in an improved user experience for all kinds of services. This, in turn, puts pressure on telecom operators to come up with a global voice and messaging solution for LTE, providing a communication service package that can be evolved to support the rich multimedia experience that consumers demand.
What is the solution for voice over LTE that is both advantageous for operators and satisfies user expectations? And what steps need to be taken to deploy such a solution?

2、 The voice overLTE solution
In the new LTE Radio and Evolved Packet Core (EPC) architecture, there is no circuit-switched domain to handle voice calls in the traditional 2G/3G way. A solution for voice over LTE will, therefore, be needed as LTE access becomes more widespread. Over the past two years, the industry has identified four main tracks:
• Circuit Switched Fallback (CSFB) to 2G/3G CS – for example, 3rd Generation Partnership
Project (3GPP) CSFB
• IMS-based, such as 3GPP IP Multimedia Subsystem (IMS) Multimedia Telephony (MMTel) over LTE
• Over-the-top (OTT) – for example, Skype
• Circuit Switched over Packet Switched (CS over PS) – for example, voice over LTE via Generic
Access (VoLGA)
The first and last tracks, CSFB and CS over PS, are interim solutions for early LTE deployment stages. The OTT-based and MMTEL-based tracks can be viewed as more permanent solutions for mature LTE networks.
1)、CirCuit SwitChed FallbaCk
CSFB is the 3GPP standard solution for early LTE deployment stages, where no IMS voice service is available. Through CSFB, the terminal is directed to WCDMA/GSM to initiate or take a voice call, and the call remains in the CS domain until it is completed. This solution is currently recommended by the Next Generation Mobile Networks (NGMN) Alliance as a minimum roaming requirement for LTE terminal vendors and LTE operators that provide a CS voice service over WCDMA/GSM. As CSFB only provides support for voice and SMS, it is considered an intermediate step in the evolution towards fully fledged multimedia communication services.

2)、MMtel-baSed
The 3GPP MMTel solution gives operators the possibility to evolve their telephony service by incorporating the multimedia feature-richness needed to compete with OTTs. Additionally, MMTel can leverage the world’s biggest mobile user community – Mobile Subscriber Integrated Services Digital Network number (MSISDN) – as well as classical telecommunication values, such as:
• High-quality, guaranteed end-to-end QoS
• Regulatory services support (such as emergency calls)
• Global reach.

3)、Ott
OTT solutions, such as Skype and Google Talk, are being pre-installed in high-end phones. As mobile barriers for OTT players are gradually disappearing and smartphone penetration is expected to flourish over the next few years, OTT solutions will probably drive competition in the mobile domain as we saw in the fixed domain.
However, because OTT solutions cannot provide a satisfactory user experience in non-continuous LTE coverage (due to the lack of a handover mechanism to the CS network), the adoption of OTT clients will depend on mobile broadband coverage. Therefore, if operators react soon, it should be possible to consolidate a global voice over LTE solution even before the LTE coverage is fully deployed.
4)、CS Over PS
VoLGA, specified by the VoLGA Forum, is perhaps the best-known alternative in the CS over PS family. The main idea is to adapt Universal Mobile Access / Generic Access Network (UMA/GAN) for LTE, and reuse the 3GPP Single Radio Voice Call Continuity (SRVCC) mechanism for handover from LTE to 2G/3G CS. It has very low impact on the existing CS core, but does not offer the possibility of evolving toward a full multimedia service experience. Therefore, VoLGA has been positioned as an interim alternative that addresses pre-IMS LTE deployments. However, the VoLGA solution is not standardized by 3GPP, and after GSMA adopted the One Voice initiative for GSMA VoLTE, VoLGA has been constantly loosing traction in the industry.
From the above possibilities, the MMTel-based alternative has been chosen by GSMA as the unified solution for voice – and SMS – over LTE, termed GSMA VoLTE, and has wide backing in the industry with more than 40 key players declaring their support at the 2010 GSMA Mobile World Congress.
GSMA VoLTE will not only bring unified profiling for the deployment of an interoperable, high- quality voice and SMS service over LTE, but will also facilitate the development of interconnect and international roaming agreements among LTE operators. Furthermore, the global GSMA collaboration widens industry support and brings economy of scale for both terminals and network infrastruture, as required for mass-market uptake.
With GSMA VoLTE, a solution based on well established standards and supported by the entire industry, operators can easily evolve their voice services toward a rich multimedia offering to both protect and grow their communication business. At the same time, users will benefit from richer multimedia services, available anywhere on any device, combining mobility with service continuity to provide users with the high-quality experience they expect.
 Summary and Notes
The road to Voice over LTE
-With GSMA in the driver’s seat and industry players aligned around GSMA VoLTE, the 3GPP standard track has become the industry’s preferred solution for voice and SMS over LTE. But what are the necessary steps to introduce GSMA VoLTE in LTE networks? Can it be introduced immediately after LTE deployment or is an interim solution needed?
There are no simple answers; the solution depends on initial LTE coverage and chosen deployment strategy. Operators starting with spotty LTE coverage – LTE islands – will probably deploy CSFB as a first step to avoid too frequent call handovers between the CS and the VoIP domain. On the other hand, operators with aggressive LTE deployment plans are likely to introduce GSMAVoLTE immediately, making it easier to evolve to richer multimedia services and support fixed mobile convergence scenarios earlier. For the sake of simplicity, let us look at an operator in the first group, where three different scenarios
reflect three successive expansion phases of the operator’s LTE network:
• In the first expansion phase, for mobile broadband purposes, the chosen operator introduces
spotty LTE coverage.
• In the second phase, the operator expands LTE coverage and builds areas of continuous LTE
coverage for all types of services.
• In the third and final phase the operator bridges the remaining gaps in the LTE coverage – or complements it with other PS access technologies – building a complete packet based network for all types of services.

PhaSe 1 – SPOtty lte COverage
The operator starts by introducing LTE dongles in laptops that need SMS support for configuration purposes and roaming cost alerts Since the LTE coverage is not continuous, the selected solution is the 3GPP SMS over SGs mechanism (see Fact Box 1 in the appendix), which allows for the transfer of SMS to/from terminals that are attached to LTE via the SGs interface (without performing fallback to WCDMA/GSM). When LTE smartphones are launched, operators can introduce CSFB to simplify the LTE introduction by reusing the existing WCDMA/GSM CS voice service (see Fact Box 2).
By using CSFB, operators avoid the problem of frequent handovers between the CS and the VoIP domain, which may arise in an initial LTE deployment scenario with IMS voice over spotty LTE coverage. Through CSFB, the terminal always shifts to WCDMA/GSM to initiate or take a voice call, and the call remains in the CS domain until it is completed. The use of CSFB also allows the operator to retain existing CS roaming agreements. However, since CSFB provides only voice and SMS, while packet In summary, MMTel-based voice is introduced in this phase as an evolutionary step toward multimedia services, following a standard solution that provides full service coverage and continuity even if the LTE network is not yet perfected.
The deployed CSFB solution will also be required in this phase to support inbound LTE roamers that do not have an IMS voice service. Similarly, for outbound roamers CSFB support, in combination with ICS, will be required when they visit non-IMS LTE networks, allowing the reuse of existing CS roaming agreements.

PhaSe 3 – Full lte COverage
In the final phase, operators complete LTE coverage, or complement remaining areas with another
3GPP/3GPP2 PS access technology capable of VoIP, such as High Speed Packet Access (HSPA) or
Evolution-Data Optimized (1xEVDO).
Post deployment, GSMA VoLTE is supported in the whole network through Inter-Radio Access Technology (IRAT) PS handover between different PS access domains (see Fact Box 6). As before, CSFB will be retained to support inbound LTE roamers without an IMS voice service.
For outbound roaming (own subscribers), it is expected that many other operators will already have IMS support, so IMS roaming agreements would be in place. In visited networks that do not yet have full LTE coverage, IMS Centralized Services (ICS) and enhanced SRVCC mechanisms will be needed to support call handovers to CS.
With the few exceptions stated above, seamless MMTel voice together with presence and messaging services will now be supported across different operators in all roaming scenarios. As MMTel services evolve, users will enjoy ever richer communication experiences across all devices.


Conclusion
Mobile broadband is exploding and LTE deployment is gaining momentum with mass-market reach expected by 2011. Operators will benefit from evaluating their voice over LTE strategy to take advantage of their strengths before LTE coverage is fully deployed, and link the resulting LTE strategy to communication services evolution and fixed mobile convergence plans.
With GSMA VoLTE, a solution based on well established standards with full industry support, operators can easily evolve their services toward fully fledged multimedia to protect and grow their communication business.
Users will benefit from richer multimedia services, available from any device, any place and any operator, combining mobility with service continuity. Together with the mobile broadband expansion, GSMA VoLTE will fully support the evolution of communication services as desired by operators and users, today and in the future.



sessions (such as web-browsing), would be interrupted, it is an intermediate step in the evolution toward fully fledged multimedia communication services. Once CSFB is introduced, it will probably be retained in later phases (after IMS voice is introduced), because CSFB is the industry choice for supporting inbound LTE roamers without IMS services or without IMS roaming capabilities.

PhaSe 2 – areaS with COntinuOuS lte COverage
The second phase involves LTE network expansion, creating wider coverage areas for big cities and densely populated areas.
Thanks to wider LTE coverage, operators can introduce GSMA VoLTE for LTE subscribers, providing them with an IMS/MMTel-based service that can quickly be evolved to support full multimedia offerings and fixed mobile convergence scenarios (see Fact Box 3).
However, as full LTE coverage has not been achieved, a complement for LTE access with existing WCDMA/GSM CS coverage is needed. Firstly, operators must provide an MMTel voice service to LTE subscribers outside LTE coverage areas. Secondly, handover of MMTel calls from LTE to WCDMA/ GSM – when subscribers move out of LTE coverage – must be supported. Complementary mechanisms for these two scenarios, based on the 3GPP IMS MMTel standard, already exist in the GSMA VoLTE profile, namely IMS Centralized Services (see Fact Box 4) and Single Radio Voice Call Continuity
(SRVCC) (see Fact Box 5).

Budi Prasetyo

About Budi Prasetyo

All About LTE

Subscribe to this Blog via Email :