VoLTE or VoIP over LTE – Who is the ultimate winner?

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The IEEE Santa Clara Valley Consumer Electronics Society is an exciting forum for San Francisco Bay Area industry experts, engineers, press and analysts interested in all aspects of consumer electronics. It was a pleasure to recently be in a room buzzing with enthusiasm about my presentation discussing carrier grade VoLTE vs. VoIP over LTE OTT apps.

This is an important question, as consumers increasingly expect to be able to communicate with each other using affordable, high quality voice and video connections.

There are multiple options available today for mobile applications. This includes Over-The-Top (OTT) applications, services that are generally offered by third party (non-operator) developers that can be downloaded from popular app stores, often for free. Second, we have Web-based applications. These applications run directly from a Web browser, or are included as part of Cloud-based services that run thin client applications on a device platform. Third are pre-loaded applications which are bundled with a platform and cannot be deleted or disabled. This includes applications such as camera, maps, mail and calendar. Finally, there are embedded applications, which are deeply integrated applications that are part of the native dialer; VoLTE falls in this category.

Today we are seeing explosive growth in OTT applications for VoIP/Video/Messaging apps. By quickly browsing through Google Play and Apple Store, we see a couple hundred (or more) VoIP/Video/Messaging apps available for free! Most of these apps use their own proprietary protocols/infrastructure/network and use the operator’s best-effort data network. Most consumers today have one or more of these apps installed on their mobile device.

VoLTE or VoIP over LTE apps

But, at what cost? Do these apps meet all of the requirements of real-time voice and video over Internet protocol (V.VoIP)? Let’s look at some of the requirements of V.VoIP, and how each is addressed by VoIP over LTE versus embedded VoLTE.

The requirements of VoLTE and V.VoIP applications

One of the most important requirements for V.VoIP applications is that they must have guaranteed Quality of Service (QoS). Since all OTT apps use VoIP over LTE (on the operators’ data networks) do not offer QoS because the same pipe is used for real-time voice/video communication as is used for web browsing and audio/video streaming. This leads to competition for bandwidth – meaning there can be no guaranteed QoS. Conversely, carrier-grade VoLTE utilizes dedicated bearer/bandwidth thus guaranteeing superior voice and video quality.

VoLTE or VoIP over LTE guaranteed QoS

Low latency is also a key requirement for V.VoIP. With OTT apps, latency suffers as tasks queue up in the pipeline as they compete for bandwidth. OTT apps are integrated at high-level user space interfaces, whereas the embedded VoLTE integrates with low-level audio drivers for audio capture/rendering and network interfaces, thus reducing the TX/RX processing delays considerably. OTT end-to-end latency is approximately 3x higher than with embedded VoLTE.

Interoperability must also be considered. Almost all OTT apps use proprietary methods, and hence do not interoperate with each other. To overcome this, and make calling a hassle-free experience for consumers, embedded VoLTE has the opportunity to thrive through ecosystem collaboration between chipset, OEM and infrastructure vendors and mobile operators.

Embedded vs OTT aproaches

Standards can obviously help in this collaboration. Embedded carrier grade VoLTE/Video over LTE and RCS (Rich Communication Suite) applications are compliant to GSMA PRD IR.92 (IMS Profile for Voice, and SMS), GSMA PRD IR.94  (IMS Profile for Conversational Video Service) and Rich Communication Suite 5.1 (Advanced Communications Services and Client Specification) respectively.

Because these apps are running on mobile devices, it is clear that optimizing for low-power consumption and optimal bandwidth is key. Some of the techniques that embedded VoLTE/Video over LTE/RCS uses to reduce power consumption and increase bandwidth include:

  • Integration with hardware accelerators (such as video) thus reducing the overall CPU MHz requirements and enabling higher-resolution/fps video
  • Hand-coding assembly for CPU-intensive algorithms (media engine), since the power consumption increases for every MHz used
  • Discontinuous Reception (DRX) in connected mode – stopping the transmission during silence packets and aggregation of packets
  • Semi-Persistent Scheduling (SPS) – assignment of a predefined chunk of radio resources for VoIP users with an interval of 20ms so that devices aren’t required to request resources at each TTI (Transmission Time Interval)
  • RoHC (Robust Header Compression) – For VoIP packets, the size of headers (IP/UDP/RTP) is usually larger than the data itself—for IPv4, UDP and RTP, the amount of overhead due to headers is 40 bytes, and RoHC can compress this to 2 or 3 bytes

Network integration is also critical. All OTT apps drop the real-time voice/video calls when migrating from one network to the other, which is an obvious problem. Embedded VoLTE supports Single Radio Voice Call Continuity (SRVCC) which enables a seamless handover to legacy 2G/3G cellular networks when there is no LTE coverage, as well as handover to WiFi with IP2IP and ANDSF (Access Network Discovery and Selection Function).

For a smooth user experience, it’s also important to have a single user interface for both circuit switched and packet switched calls. As an integrated native application, embedded VoLTE uses one interface for both circuit switched and packet switched VoLTE calls. On the other hand, OTT applications have their own dialer/user interface for VoIP over LTE/WiFi calling, but a native dialer must be used for circuit-switched calls.

VoLTE or VoIP over LTE integrated native applications

To further increase customer satisfaction, operators’ embedded VoLTE provides the same user experience across the platforms. It supports all circuit-switched features (voice calling, and supplementary call features – call waiting, transfer, forwarding, emergency calling, and SMS). It also supports some of the enhanced features such as HD Voice (AMR-WB) and HD Video, with reduced call setup times and improved voice quality that is 40 percent better than 3G due to using a wider bandwidth (50–7000 Hz instead of 300–2400 Hz).

Operator’s VoIP super-app

The Rich Communication Suite (RCS) is the operators’ response to real-time VoIP/Video/Messaging OTT apps. It not only supports VoIP/Video/Messaging, but also integrates an enhanced phonebook which includes capability discovery exchange and social presence information. It also supports enhanced messaging (1-1 chat, group chat, emoticons, location share and file sharing and enriched calls) and enables multimedia content sharing during a voice call, video call and video sharing. It also addresses a much larger subscriber base (more than 5 billion) compared to a fragmented OTT user base. With the Joyn consumer-facing RCS brand.

Embedded VoLTE was launched in August 2012 by MetroPCS, LGU+, SK Telecom. The world’s first country-wide interoperable RCS network was launched in Spain by Movistar, Orange and Vodafone. This was followed deployments in Korea – KT, LGU+, SK Telecom, Germany – Vodafone, T-Mobile and US – MetroPCS. More and more operators across the world are getting on the Joyn bandwagon. Trials are ongoing for Video over LTE, with the ultimate goal of providing an integrated super-app that provides a unified VoLTE, Video over LTE and RCS functionality.

Roadmap and conclusion

Operators have adopted different approaches to migrate from the full circuit-switched voice + data to full LTE voice and data. From a high-level perspective, there are three categories. The first category includes operators who have gone ahead and launched the VoLTE service even though the LTE coverage is spotty (using CSFB for voice calling). The second category of operators is planning to adopt the SRVCC to fall back to 2G/3G where there is no LTE coverage. The last group includes more conservative carriers who are busy rolling-out the LTE data-only service so that they initially provide the same coverage as their existing 3G network and then deploy VoLTE for LTE-only handsets. But CSFB, SVLTE and SRVCC are expensive interim solutions; operators will have to quickly migrate to full VoLTE-only solutions in order to provide the carrier-grade user experience.

After my talk at the IEEE meeting, there was a healthy discussion as to when this will all become a reality. There were also some concerns as to whether the operators will keep their promise. I think the next couple of years will be very critical for VoLTE, with an increasing number of LTE and VoLTE-enabled handsets shipping. Some of the major tier-1 mobile operators are already doing VoLTE trials and are gearing up to launch VoLTE later this year or early next year. For example, Verizon and AT&T plan to launch VoLTE phones by end of this year in the US, and ZTE has partnered with Imagination to announce the availability of VoLTE on commercial handsets.

Finally, I’d like to thank IEEE for organizing the event and look forward to their next talk and future events. You can download the presentation from the IEEE website by clicking on this link.

Follow us on Twitter (@ImaginationTech) for the latest news and events from Imagination and its partners.

Saraj Mudigonda

Saraj Mudigonda

Saraj Mudigonda is a director of segment marketing at Imagination Technologies. Previously he was a business development manager for Imagination's HelloSoft V.VoIP products. He has 15 years of experience in the telecommunication industry in Wireless LAN, V.VoIP, and Wireless Communications and started his career as a DSP (Digital Signal Processing) engineer developing, implementing, and optimizing the assembly code for several DSP architectures. He also managed multiple V.VoIP customer projects and was the primary liaison between customers and engineering teams.

1 thought on “VoLTE or VoIP over LTE – Who is the ultimate winner?”

  1. Until the carriers break out of their silos and fully embrace digital/packet voice VoLTE will be an issue. This starts with the carrier allowing to designate wifi offload of voice and sms to solve the indoor coverage problem. If they don’t do that they will still be substandard compared with OTT. This will have the added benefit of freeing up outdoor capacity and reducing capex. They can then further on focusing on VoLTE ubiquitously in the macro cellular (wide area) coverage market.


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