The longer mobile operators delay offering their own voice services over Long Term Evolution (LTE), the more vulnerable they could be to over-the-top (OTT) voice over IP (VoIP) service providers, finds a recent Heavy Reading Insider report.

Operators are not in a hurry to deliver voice services over LTE networks, says Robert Poe, author of the Heavy Reading 4G/LTE Insider report, "Voice Over LTE: More Pitfalls Than Promise for Now." This is because they can use their 3G or 2G networks to deliver voice services, reserving the packet-based LTE network for data services, a technique called "circuit-switched fallback." (See LTE TDD: In Mobile, Size Matters.)

But if operators wait too long, they could face some negative consequences. (See Google Gives Telcos a Wakeup Call.)

"The main one is that over-the-top VoIP providers -- like Skype Ltd., fringland Ltd., and Nimbuzz Group -- could offer voice services over the speedy new LTE connections," says Poe, adding that such services represent a significant threat to operators' existing voice revenues because they would probably be cheaper and could even offer better quality with high-definition voice technology.

"So the period in which operators have deployed LTE networks but are not delivering voice services over them represents a window of vulnerability for them," says Poe.

One operator facing that window of vulnerability is TeliaSonera AB, with its commercial LTE networks in Norway and Sweden. The operator's CTO of mobility services, Lars Klasson, told Light Reading Mobile in a recent interview, "We're not in a rush to put voice onto the 4G networks."

But when the Swedish operator is ready to put voice over its LTE networks, it will use IP Multimedia Subsystem (IMS)-based VoIP, Klasson said. (See TeliaSonera First to Go Live With LTE.)

However, over-the-top VoIP doesn't have to be a threat to mobile operators. It's possible for operators to use these services to their advantage, finds the Heavy Reading report, either by offering their own over-the-top VoIP services, or by partnering with VoIP service providers.

The IMS dilemma
The standards-based way to deliver voice services over LTE is to use an IMS architecture in the network, an option driven by the One Voice industry initiative and which became the 3rd Generation Partnership Project (3GPP)'s voice over LTE (VoLTE) specification.

But, according to the report, there is a disconnect between IMS and LTE deployments. Operators are deploying IMS and LTE independently, so the technologies may not be rolled out at the same time or in the same place. (See Operators Rally Round IMS for LTE Voice and Voice Over LTE & the 'IMS Gap'.)

This situation has had two results: First, there will be a need for alternatives to IMS-based LTE voice services; and second, there has been an acceleration of some operators' IMS plans specifically to enable LTE voice services.

The alternative approaches for LTE voice services include circuit-switched fallback, VoLGA (voice over LTE via generic access), Nokia Siemens Networks's fast-track VoLTE, and over-the-top VoIP. (See New Specs Deepen LTE Voice Dilemma, NSN Goes Solo for LTE Voice, and T-Mobile: Voice Discord Threatens LTE.)

— Michelle Donegan, European Editor, Light Reading Mobile