IMS is the center of future communication

IP Multimedia Subsystem (IMS) is becoming a pressing need for operators wanting to take advantage of the high quality voice communications capabilities of LTE

With voice services continuing to account for around 50% of a typical mobile operator’s revenue, Smartphone use in LTE networks requires a voice solution for LTE networks. This solution is Voice over LTE (VoLTE), set to be the mainstream technology for voice. LTE and VoLTE offer a number of advantages for operators, the chief ones being better spectral efficiency, simplified service delivery and the ability to offer higher voice quality and richer communication services.

A range of VoLTE-capable smartphones are expected to come to market in 2013, leading to a fast increase in VoLTE subscriptions and services that could see as many as 74 million VoLTE enabled subscribers by the end of 2016. VoLTE and LTE are principal technologies to help operators maintain voice revenues and address new business opportunities.

The question is not really if operators should introduce VoLTE, but how and when?

VoLTE tackles the OTT threat

With a network-based VoLTE service, mobile operators have new ways to compete with over-the-top (OTT) players. The first is that an operator voice service has a single identity, offering anywhere to anywhere service at any time, around the globe. This contrasts with OTT VoIP services, which require both users to be in the particular service ‘world’ offered by the OTT provider.

Another benefit for operators is the use of an IMS centralized service (ICS), which allows the same voice services such as call forwarding and voicemail, in both CS and LTE. This also allows operators to continue using CS voice for as long as possible, safeguarding previous investments.

If operators can offer lower long distance and roaming call fees, users will probably abandon alternative VoIP offerings and return to the more convenient operator-based services.

VoLTE will be implemented in several steps, with most operators initially offering a combination of CS voice and LTE data on LTE devices using Circuit Switched FallBack (CSFB). Eventually, however, the revenue-generating opportunities from enriched voice services for LTE smartphones are likely to be so compelling that most, if not all, operators will adopt full IP Multimedia Subsystem (IMS) based VoLTE.

IMS-based VoLTE

The GSMA Voice over LTE initiative defines that the VoLTE core is based on the IP-multimedia subsystem (IMS). The IMS is a 3GPP standardized service core system that controls all-IP voice and multimedia services over 3G, LTE and convergent networks.

All IMS functions and interfaces are well standardized by 3GPP, allowing operators to build networks using equipment and systems from multiple vendors and enabling interoperability between networks owned by different operators.

Essential for Rich Voice

Rich Communication Suite (RCS) services, based on the same IMS that supports VoLTE, provides operators with a simple and interoperable service extension to voice and text.

Spearheaded by the G5 operator community (France Telecom Orange, Vodafone, Deutsche Telekom, TIM and Telefónica), RCS-e is being rolled out in several European countries. This “joyn” service offering provides end users with an initial set of services enhancing the voice service experience with for example, Rich Call, Instant Messaging and File Transfer.

Combined with joyn’s built-in capability discovery mechanism, joyn enabled phones empower end-users to see their peers’ communication capabilities. They can share images and video in real time with friends or colleagues around the globe as simply as using voice and SMS.

RCS and joyn services, as well as VoLTE, are built on top of the IP Multimedia Subsystem (IMS) as a common IP service core, which also allows the creation of a unified voice core solution that provides a service to all access domains.

Committed to IMS

Nokia Siemens Networks is committed to supporting operators’ evolution to IMS-based VoLTE. The company has the most advanced and comprehensive solution, allowing operators to smoothly introduce VoLTE on top of the existing network and at the same time allow for unmatched scalability for new LTE based services.

Solutions include Circuit-switched Fall Back (CSFB), which allows LTE devices to receive and set-up voice calls from and to the legacy Mobile Network - CSFB can be rolled out in live networks in just 30 days.

Seamless handover of voice calls between LTE and legacy Voice can be based on the Single Radio Voice Call Continuity (SRVCC) functionality, while a Voice Application Server allows seamless Service and Backoffice interworking between legacy and new VoLTE services

The company’s position in IMS is underlined by a report from Infonetics Research, which shows that due to its commitment to the technology, Nokia Siemens Networks is in the lead with some 39.3 % share in CSCF shipments.(1)  In addition the company has based its subscriber data management system on its market leading One-NDS platform, which carries 3.4 billion (Dec 2012) subscribers around the world.

“We have the most comprehensive and robust IMS and VoLTE platform and our clear goal is to smoothly migrate six billion voice users of today to the new LTE world. This will provide unmatched customer experience for Voice and other mobile broadband services,” says Michael Clever, Head of the Voice and IP transformation, Nokia Siemens Networks. “With our Liquid Core and Virtualization strategy we can further help our customers to always stay on top of new services demands, increasing traffic and the need for network efficiency and cost optimization.”


  1. Source: Infonetics Research Service Provider VoIP and IMS Equipment and Subscribers Quarterly Worldwide and Regional Market Share, Size, and Forecasts: 3Q12