The fate of voice, SMS in LTE networks

New spec, SDK could keep prime services humming during net transition

Industry analysis by expert Joanie Wexler, plus links to the day's wireless news headlines

When mobile networks first become all-IP networks, they will not be inherently outfitted to support IP-based voice and short-message service. Yet today, circuit-switched voice and SMS are among the most popular services, not to mention the mobile operators' two biggest cash cows.

In Long-Term Evolution (LTE) networks, for example, the current 3GPP-standard mechanism for supporting these services is to fall back to the circuit-switched network. This approach requires users to stop what they're doing on the data network to handle a voice call or send/receive an SMS message.

Some see this as less than desirable. So a group called the Voice over LTE via Generic Access (VoLGA) Forum has published a set of specifications for delivering mobile voice and SMS messaging over LTE networks. And member Kineto Wireless has  released a VoLGA SDK based on the specs. The VoLGA scheme could serve as an affordable interim way for operators to keep delivering these popular services until IP Multimedia Subsystem (IMS) telephony has been fully defined and widely deployed.

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When mobile networks first become all-IP networks, they will not be inherently outfitted to support IP-based voice and short-message service. Yet today, circuit-switched voice and SMS are among the most popular services, not to mention the mobile operators' two biggest cash cows.

In Long-Term Evolution (LTE) networks, for example, the current 3GPP-standard mechanism for supporting these services is to fall back to the circuit-switched network. This approach requires users to stop what they're doing on the data network to handle a voice call or send/receive an SMS message.

Some see this as less than desirable. So a group called the Voice over LTE via Generic Access (VoLGA) Forum has published a set of specifications for delivering mobile voice and SMS messaging over LTE networks. And member Kineto Wireless has  released a VoLGA SDK based on the specs. The VoLGA scheme could serve as an affordable interim way for operators to keep delivering these popular services until IP Multimedia Subsystem (IMS) telephony has been fully defined and widely deployed.

Franz Seiser, head of core network architecture at Deutsche Telekom, the parent of T-Mobile units around the world, explains the operator conundrum from his own point of view. He says next-generation mobile networks are being driven by an increase in data traffic, although data is currently "not a money-making machine." Meanwhile, the plan for supporting VoIP and SMS on all-IP networks has been IMS. But IMS has been kicking around for nearly 10 years, and Seiser fears it might not be defined and aggressively deployed until at least 2025.

With data usage going up but operator revenues going down, he says, operators find it difficult to make a business case to deploy next-gen networks that won't have voice and SMS built in. Aside from the inelegant user experience, using the circuit-switched fallback technique to continue delivering the services means "you can't shut down the old network," which is cost-prohibitive, he says.

The VoLGA interim solution would allow operators to build and use the all-IP mobile access networks as soon as possible but retain the legacy call control engine, "which is very stable," in the network core until IMS becomes pervasive, Seiser says.

He notes that Deutsche Telekom hasn't even decided if it will be deploying LTE or not. "But we believe [the VoLGA approach] would be a smoother and lower-risk way" to transition than the circuit-switched fallback mechanism, Seiser says.

Read more about wireless & mobile in Network World's Wireless & Mobile section.

Joanie Wexler is an independent networking technology writer/editor in Silicon Valley.