How will the estimated 6.4 billion Internet of Things (IoT) devices by 2020 get connected? The question remains to be answered, as competing IoT connectivity solutions based on low-power wide-area (LPWA) networks emerge.

So far, connectivity hasn't been a big part of the mainstream IoT conversation. That's not surprising, given that most of the IoT devices available today, such as smart microwaves and connected coffee makers, use short-range WiFi networks or Bluetooth to connect.

Going forward, however, service providers will need to solve two major connectivity challenges that traditional wireless networks can't handle, in order to add new types of "things" to the Internet. Those challenges are connecting devices over long distances and accommodating low-power hardware.

Existing solutions on this front fall into two basic categories. The first centers on LPWA networks that use unlicensed spectrum. SigFox, a French company, and the LoRA Alliance, a collaboration of industry partners building a protocol called LoRaWAN, are the main contenders in this arena.

The second major set of IoT connectivity solutions networking comprises standards based on the 3GPP specification. Implementations include LTE-M, NB LTE-M, and NB-IOT. These standards are essentially cellular networking optimized for IoT devices, which makes them a natural fit for cellular providers.

Supporters of the 3GPP-based protocols have sought to promote their solutions as more enterprise-friendly because they are based on an open specification. Shane Rooney, executive director of the GSMA, a global association that represents mobile operators, says that networks that use licensed spectrum "are not proprietary, so they give customers a choice and don’t lock them into a technology or a particular supplier as their business changes." He notes that unlicensed spectrum "has restrictive data message lengths and availability.”

The carriers that GSMA represents have good reason to defend 3GPP-based solutions against networking newcomers like SigFox and LoRa. On May 4, SigFox announced that it will expand its IoT network to 100 U.S. cities by year's end. The company's network is already well established in much of Western Europe, and it has plans to expand to Brazil and parts of the Middle East as well. SigFox's growth means a much broader set of organizations will have ready access to LPWA networks that do not rely on 3GPP-based solutions.

Another important difference between LPWA networks using licensed and unlicensed spectrum involves virtualization. So far, the 3GPP standard is the only area where virtualization innovations are emerging. Network functions virtualization (NFV) for the 3GPP standard remains incomplete, but the 3GPP designers are giving virtualization increasing weight. "NFV in 3GPP continues to progress as planned," Rooney says, adding that NFV-based solutions for tasks such as configuration management and performance management will comprise part of 3GPP Release 14, which is currently under development.

For now, SigFox says it has no plans to add virtualization to its network. SigFox spokeswoman Kristi Mason says it is instead focused on providing low-cost connectivity without introducing the complexity of virtualization.

According to Mason: “SigFox technology and networks have the lowest TCO [total cost of ownership], which is the main driver for virtualization.” Because the company already believes its service costs are low, she says, it sees no need to introduce NFV or SDN at this time.

But Godfrey Chua, an analyst with Machina Research, says that may eventually change. "I can see virtualization being the natural next step" for SigFox, he says, though the company is likely to wait until it has finished establishing its basic network before moving onto the NFV stage.

That's because IoT traffic currently remains minimal compared to other types of data, according to Chua. As a result, there is no pressing need for providers such as SigFox or LoRA to implement virtualization as a way of optimizing IoT data delivery. "NFV and  SDN bring a whole new level of economics, flexibility, and scalability" to the network, says Chua, but IoT is not likely to become a big part of the SDN picture in the near future, because "we don't have an IoT data tsunami" yet.

Chua also says it's worth bearing in mind that IoT connectivity is not an either/or proposition. IoT constitutes a broad category of devices, which demand many different types of networking needs. There is no reason to assume that the LPWA networking solutions that currently compete with one another will not end up coexisting by catering to different niches.

"IoT is not a single thing," Chua says, adding that, at any rate, he expects short-range technologies like WiFi to account for the vast majority of IoT connectivity solutions for the foreseeable future. But LPWA networks will no doubt become an increasingly important part of the IoT scene as IoT device offerings expand beyond those that can get online from the comfort of a WiFi-enabled home or office.