# 5G Support for Industrial IoT Applications--Challenges, Solutions, and Research Gaps
## 2 IoT Requirements--Critical and Mass  
The high level expectations of market actors on 5G are not as detailed as the 3 GPP recommendation. Although the high level requirements were gathered from various sources, one of the earliest standards on that was ITU-R M.2083-0 [2]. When describing the importance of key capabilities in different usage scenarios, this standard was the first to define those three types of key communication scenarios: eMBB, URLLC, and MMTC. Their characteristics are summarized by Figure 1, which already shows the major requirements for mass IoT or MMTC traffic as (i) network energy efficiency and (ii) connection density; whereas, for URLLC traffic, mobility and latency. Figure 1: The importance of key capabilities in different usage scenarios [2]. Although the mass IoT or MMTC do not have high throughput expectation (when compared to eMBB), there are connection density requirements appear as high as 1 million endpoints per km\({}^{2}\). This is not far from broadband access requirements in a crowd (half million users per km\({}^{2}\)), as Table 1 shows whirl providing examples of eMBB scenarios. When discussing the requirements of industrial IoT applications, the requirements for real-time (low-latency) operation, high security, system interoperability and integrability, effective deployment and engineering, and proactive maintenance emerge [4]. The recommendation 3 GPP TS 22.104 [5] details the requirements for cyberphysical control applications in vertical domains further. The level of detail for this quasi-standard is convincing: the standardized values for latency (0.5 ms to 500 ms at different scenarios), high reliability (starting from 99.999% up to 99.999999%), and long-term reliability (with mean time between failures ranging from 1 day to 10 years) must ensure the wide applicability of 5G. This 3 GPP TS 22.104 recommendation covers various performance requirements for both periodic and aperiodic deterministic communication (as well as nondeterministic communication), mixed traffic, clock synchronization, positioning performance, and network operation. The requirements are also elaborated on a per-scenario basis, covering various use-cases within factories of the future, electric power distribution, central power generation, as well as connected hospitals, and medical facilities (indeed, including clear requirements for robotic surgery, among others). While Vehicle to Everything (V2X) communication is also expected to be the \"killer application for 5G\"--and the respective requirements are detailed in 3 GPP TS 22.186 [6]--this area falls out of the focus of this paper, targeting Industrial IoT. Similarly, although rail communications have their own strict requirements elaborated in 3 GPP TS 22.289 [7], this paper does not focus on the specific issues of this transport domain. The rest of the paper is organized as follows. Section 3 provides a brief overview of 5G and some of its core technologies. Section 4 discusses 5G support for IIoT applications, especially those that utilize robotics. Section 5 introduces the current challenges and solutions in the Mobile Edge Cloud. Section 6 deep dives into the next architectural element and data center back-ends, whereas Section 7 surveys the general issues in virtualization network functions (VNFs). As a mandatory element of IIoT, security considerations are discussed in Section 8 The latest conceptual interworking in the field are blockchains with IIoT and the utilization of Artificial Intelligence in 5G--these are addressed in Sections 9 and 10 respectively. The private campus network is a sensible manifestation concept for