BLE or Bluetooth Low Energy Release 5 is also a top league contender in IoT technologies. It had a head start, and built on the success of the classic Bluetooth standard (or Basic Rate, as defined by the standard) as a short-range radio connectivity. It promptly addresses the shortcomings of the venerable Bluetooth standard, and these include power consumption, and to some extent, security.
While the BLE design targets focus on low power consumption, the aim is to maintain the same type of coverage, roughly 100 meters in clear scenarios, that is, outdoors, which may stretch up to 400 meters for the release 5 in the lower data rates, at the expense of increased power consumption. IoT Mesh network configuration extends the range of a single link, as they are operating in a mesh mode. By definition, BLE remains a technology that provides peer-to-peer communications over a short distance.
BLE is not fully backwards compatible beyond its 4.0 release, as there have been several changes, in the physical aspects of the standard that prevent such compatibility (for instance, in modulation, Basic Rate using GFSK modulation, while Low Energy also uses, for instance, π/4-DQPSK and 8DPSK).
A major strength for BLE protocol is the massive installed base in use, and the wide range of accessories that can be connected to them.