2G/2.5G: 2G connectivity remains a prevalent and viable IoT connectivity option due to the low cost of 2G modules, relatively long battery life, and large installed base of
2G sensors and M2M applications.
* 3G: IoT devices with 3G modules use either Wideband Code Division Multiple Access (W-CDMA) or Evolved High Speed Packet Access (HSPA+ and Advanced HSPA+) to achieve data transfer rates of 384Kbps to 168Mbps.
* 4G/Long-Term Evolution (LTE): 4G/LTE networks enable real-time IoT use cases, such as autonomous vehicles, with 4G LTE Advanced Pro delivering speeds in excess of
3Gbps and less than 2 milliseconds of latency.
* 5G: 5G cellular technology provides significant enhancements compared to 4G/LTE networks and is backed by ultra-low latency, massive connectivity and scalability for IoT devices, more efficient use of the licensed spectrum, and network slicing for application traffic prioritization.

Application (Layer 4 or L4): This layer loosely corresponds to Layers 5 through 7 of the OSI model.
Transport (Layer 3 or L3): This layer corresponds to Layer 4 of the OSI model.
Internet (Layer 2 or L2): This layer corresponds to Layer 3 of the OSI model.
Network Access (Layer 1 or L1): This layer corresponds to Layers 1 and 2 of the OSI model

Explanation
A directory service is a database that contains information about users, resources, and services in a network.

Originally designed as a tool to assist organizations with compliance and industry-specific regulations, security information and event management (SIEM) is a technology that has been around for almost two decades