LTE service lacks support for voice and SMS messaging

Many telecommunications experts have touted the benefits of 4G Long Term Evolution (LTE) mobile cellular technology and its promise of an era of high-speed mobile broadband that will enable smooth video streaming and fast Web browsing. But what about those mundane voice and SMS text messaging services? Surprisingly, LTE supporters have not yet agreed on a single method to support voice and text messaging. This article looks at the competing alternatives and eventual implications for 4G LTE services for enterprise users.

Many telecommunications experts have touted the benefits of 4G Long Term Evolution (LTE) mobile cellular technology,

and this Internet Protocol (IP)-based technology promises to usher in an era of high-speed mobile broadband that will enable smooth video streaming and fast Web browsing. But what about those mundane voice and SMS text messaging services that generate more than 85% of the worldwide mobile services market? Surprisingly, LTE supporters have not yet agreed on a single method to support voice and text messaging. This article looks at the competing alternatives and eventual implications for 4G LTE services for enterprise users.

Data-only LTE service

Although data generates only 25% of the average revenue per user (ARPU) for most operators, it is the fastest-growing segment of the wireless industry. Because of this, some operators may choose to initially deploy a data-only LTE service. In this case, the operator will provide LTE data cards and USB dongles that connect laptops, netbooks and other consumer electronic devices to the data-only network. Users benefit from LTE's higher throughput speeds and from the ability to run voice over IP (VoIP) services such as Skype. But these VoIP services will not support inter-operator roaming and will not fall back to traditional circuit-switched voice service when the subscriber leaves an LTE coverage area.

Circuit-switch fallback

Another approach uses the LTE packet-switched network for data communications and the 2G/3G circuit-switched network for voice communications. In this case, when the handset needs to make a voice call (or is receiving a voice call), it establishes a circuit-switched connection to the 2G/3G network. When the voice call is complete, the handset disconnects from the 2G/3G network. The benefit of this approach is that users retain all of the voice and SMS text messaging capabilities they have now while gaining the benefits provided by a high-speed data service. The drawbacks include the fact that call-setup times may be longer and battery life shorter. In addition, this approach may delay the deployment of an IP multimedia subsystem (IMS)-based solution. An IMS-based solution (see OneVoice, below) will most likely become the long-term voice solution for LTE.

Voice over LTE Generic Access (VoLGA)

Voice over LTE Generic Access (VoLGA) is a combination circuit-switched and packet-switched approach that uses the Unlicensed Mobile Access/Generic Access Network (UMA/GAN) protocol for voice communication. Unlike the circuit-switched fallback approach, a voice call uses both the LTE and the 2G/3G networks simultaneously to establish an end-to-end voice connection. Kinteo Wireless originally created this technology to provide Wi-Fi access to 3G networks. The technology eventually became a Third Generation Partnership Project (3GPP) standard and was deployed by T-Mobile for its @Home service.

This approach enables an LTE device to look like a GSM/UMTS device from the perspective of the 2G/3G network. The voice call is carried over the LTE network using VoIP and over the GSM/UMTS network using circuit-switched technology. Calls pass through a gateway that converts between circuit-switched and packet-switched voice, and vice versa. The service supports roaming from LTE to GSM/UMTS and from GSM/UMTS to LTE. The benefit of this approach is that it enables subscribers to use LTE for voice and data while simultaneously supporting 2G/3G roaming. The drawback is that it may delay the deployment of an IMS-based solution.

IMS-based solution (One Voice)

Six mobile operators (including Verizon Wireless and AT&T), along with a number of equipment manufacturers, defined a voice over IMS profile called One Voice. IMS is a complex architecture designed to provide IP-based multimedia services over the mobile cellular network. IMS was designed and standardized by the 3GPP. The major criticism of IMS is that it is overly complex and costly to deploy.

One Voice does not create a new standard. Instead, it refers to existing voice over IMS standards and selects from among hundreds of IMS options to create a simplified voice over IMS profile. The benefit of this approach is that it takes advantage of existing IMS standards to create a simplified long-term solution. The drawback is that it requires mobile operators to deploy a complex and unproven architecture that may delay the timely deployment of LTE services.

4G LTE enterprise implications

Someone once quipped, "The great thing about standards is that there are so many to choose from." Having many choices for voice over LTE is not good for enterprise users because it is very likely that wireless operators will choose different methods.

4G LTE services have the following implications:

  • It may be impossible to roam from one operator's LTE network to another without dropping and reestablishing a voice call.
  • It may not be possible to send an SMS text message from a user on one operator's LTE network to a user on another network.
  • Handset vendors will have to support more than one approach in order to sell their handsets to various network operators. This would probably increase the cost to manufacture a device because handset vendors will not be able to achieve the economies of scale that a single, worldwide standard would provide.
  • The confusion over how to support voice over LTE may cause some network operators to delay their deployment of LTE, thus forcing enterprises to use 3G data services.

Statements made by wireless executives and industry pundits make it appear that 4G LTE services are right around the corner. But the lack of a single approach to support voice and SMS raises serious questions about the readiness of this technology for widespread enterprise adoption.

About the author: Paul DeBeasi is a senior analyst at the Burton Group and has more than 25 years of experience in the networking industry. Before joining the Burton Group, Paul founded ClearChoice Advisors, a wireless consulting firm, and was the VP of product marketing at Legra Systems, a wireless-switch innovator.

This was first published in November 2009

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