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LTE networks fall back to 3G for voice

Those lucky enough to be carrying the iPhone 5 this week may not be able to resist the urge to call friends to share the news, but they won’t be making those calls on LTE networks. Like other LTE phones, the iPhone 5 finds a 3G or 2G network when its user makes a voice call using the cellular network. And any data application running at the time will also switch back to the slower network when a voice call is initiated. (In the case of the iPhone, only the AT&T model can handle voice and data simultaneously on the 3G network. The Verizon and Sprint versions must use WiFi to handle data during voice calls.)

For operators, the preferred method of moving subscribers back to the 3G network is called circuit switched fallback (CSFB). Solutions that support this protocol are getting a lot of intention as service providers anticipate a sharp increase in traffic on their LTE networks with the rollout of the new iPhone. Today Mavenir Systems introduced a CFSB solution that it says operators can deploy in as little as 60 days, independent of their mobile switching center. The company says its CSFB technology does not require service providers to make additional investments in their legacy networks, and can integrate with future 4G technologies. “This is the first step for many operators, but they can easily leverage this Mavenir CSFB investment along the path to SRVCC and VoLTE,” says Pardeep Kohli, president and chief executive officer of Mavenir Systems.

Most analysts agree that VoLTE (voice over LTE) is at least a year away, and that widespread deployment will take even longer. A recent survey of mobile operators found that three quarters expect to see VoLTE deployed within three years. In the interim, circuit switched fallback is sure to become much more important to operators as they activate more devices on their LTE networks.

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Martha DeGrasse
Martha DeGrasse
Martha DeGrasse is the publisher of Network Builder Reports ( At RCR, Martha authored more than 20 in-depth feature reports and more than 2,400 news articles. She also created the Mobile Minute and the 5 Things to Know Today series. Prior to joining RCR Wireless News, Martha produced business and technology news for CNN and Dow Jones in New York and managed the online editorial group at Hoover’s Online before taking a number of years off to be at home when her children were young. Martha is the board president of Austin's Trinity Center and is a member of the Women's Wireless Leadership Forum.

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