AT&T: VoLTE needed to support voice roaming with CDMA carriers in 700 MHz band

AT&T Mobility (NYSE: T) said it will need to wait until it deploys Voice over LTE nationwide to support CDMA voice roaming on its 700 MHz spectrum.

In a filing with the FCC, AT&T clarified comments it made to the commission in a progress report last month on its efforts to support interoperability between Band Class 17 and Band Class 12 in the 700 MHz band. In that report, AT&T said it continues to have discussions with several Band 12 operators "to stay aligned technically to support LTE data roaming and when appropriate we will schedule Band 17/12 interoperability testing. It may be necessary for some operators to wait until Voice over LTE (VoLTE) roaming is available before operationalizing LTE data roaming."

The FCC's staff asked for clarification on the VoLTE part of that comment. AT&T replied that because CMDA-based carriers use traditional circuit-switched voice on their 2G networks, AT&T will not be able to support voice roaming on its 700 MHz LTE network until it deploys VoLTE.

"For CDMA operators, we would be able to support LTE Data Roaming but since voice is handled on the 2G CDMA network, there is no opportunity for AT&T to offer voice roaming until we support VoLTE," Joseph Marx, assistant vice president of AT&T Services, wrote in the filing. "The staff also asked about SMS Texting while roaming on LTE data only and at this point it isn't clear that we'd be able to support SMS while roaming on the LTE data network."

In December, AT&T announced that it had deployed VoLTE in parts of the District of Columbia, Georgia, Illinois, Indiana, Maryland, Michigan, Minnesota, Nevada, North Carolina, Ohio, Oregon, Pennsylvania, South Carolina, Texas, Utah, Virginia, Washington and Wisconsin. The carrier has said it will continue to roll out VoLTE on a market-by-market basis but AT&T has not said when it will launch VoLTE nationwide.

Verizon Wireless (NYSE: VZ) and AT&T are currently working to ensure VoLTE calls made by customers on the different carriers can interconnect with one another. The two carriers have said they are going to enable VoLTE-to-VoLTE connections sometime in 2015.

T-Mobile US (NYSE:TMUS), the largest 700 MHz A Block/Band 12 spectrum holder, currently has VoLTE deployed nationwide. U.S. Cellular (NYSE:USM) is one of the largest Band 12 operators after T-Mobile and has said it is currently conducting VoLTE trials but has not said when it will launch he service commercially.

In its progress report last month, AT&T said that in the first half of this year it will bring devices to market that are fully capable of interoperating between Band 12 and Band 17. AT&T agreed to develop, implement and deploy throughout its network multi-frequency band indicator (MFBI) capabilities that will let its network operate simultaneously in both Band 12 and Band 17 and support devices in both band classes. AT&T said it has completed lab testing of the MFBI feature with all of its Radio Access Network vendors. The carrier expects to deploy the feature in its network by the deadline of Sept. 30, 2015.

For more:
- see this FCC filing
- see this Wireless Week article
- see this Light Reading article

Related Articles:
AT&T makes progress on 700 MHz interoperability, likely benefiting T-Mobile
T-Mobile hopes to deploy LTE in all of its 700 MHz A Block spectrum this year
AT&T unveils LTE phones that support 700 MHz spectrum it got from Qualcomm
AT&T, Dish, CCA cheer FCC's official stamp on 700 MHz interoperability deal
AT&T's Donovan: Work with Qualcomm, network vendors made 700 MHz interoperability possible
AT&T does an about-face, will support 700 MHz interoperability

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