As more voice-controlled Internet of Things (IoT) devices start to arrive in homes and commercial environments, Verizon is enabling voice traffic on its nationwide LTE Cat-M IoT network.

Verizon is initially enabling fixed IoT voice services -- providing voice access to IoT units such as alarm units -- with the carrier adding mobile hand-off capabilities during the coming months. (See Verizon Takes IoT Network Nationwide.)

Verizon Communications Inc. (NYSE: VZ), like AT&T Inc. (NYSE: T), has started its 4G IoT deployment with Cat-M, with NB-IoT to follow. T-Mobile US Inc. has started with NB-IoT and with deploy Cat-M later. (See US Carriers Place Bets on Cat M & NB-IoT and AT&T Buckles Down to Deploy NB-IoT in 2019.)

Verizon's deployment of voice, however, illustrates one of the major differences between Cat-M and NB-IoT -- it's all down to the data packet sizes supported by the LTE variants.

"NB-IoT is designed for such small packets it does not support voice," a Verizon spokesperson told Light Reading. "That's why having voice on Cat-M is such a great addition, so that smaller IoT solutions have an option for voice now."

NB-IoT delivers 20 Kbit/s over 180KHz LTE, in the guard channels used to divide traditional 4G consumer services, while Cat-M supports up to 1 Mbit/s over 1MHz channels. Both Cat-M and NB-IoT use much less battery power than standard 4G LTE.

— Dan Jones, Mobile Editor, Light Reading