## 6 Use Case of One Smart Building and Its Applications
One of the most prominent SB solutions employing large-scale IP technology is VoIP calling within the condominium or between buildings (which may be federated within the same architectural complex). This is implemented using SIP client devices (see Table 1). The virtual concierge adopts IoT technology with integrated microphones and speakers, enabling audio and video connection with the CCO or OCC; see the call flow in Figure 8. Within the SB, an IP-PBX/SIP server controls call admission and addressing between IoT devices and SIP clients (e.g., extensions 01-999) and IP phones using or not IoT devices together (replacing traditional TDM intercom systems). As detailed in Section 5, this study incorporates quality of experience (QoE) and quality of service (QoS) metrics. To ensure adherence to established benchmarks, this study utilizes standards and metrics promulgated by organizations such as ITU-T and IETF. The subsequent four metric groups (1-4) are specifically tailored for SB use cases and can be extended to federated SB architectures with Fog or Cloud (SDN could be included):  
1. _Latency._  
ITU-T G.114 [55] recommends the following latency thresholds: less than or equal to 150 ms, acceptable latency for bidirectional conversation without perceptible impact; a range of 150-300 ms, acceptable but may cause degradation in user experience; and finally, greater than 300 ms, severe impact on real-time communication and interaction. Typical Applications: VoIP and video calls: Ideally, latency should be less than 150 ms. Furthermore, control of IoT devices in Smart Buildings: Latency less than 100 ms is recommended for real-time actuation. 2. _Jitter_:  
ITU-T G.1020 [56]/IETF RFC 3550 [57] standards recommend the following: Less than or equal to 30 ms: acceptable jitter for real-time applications (VoIP, video conferencing and SB automation); jitter greater than 50 ms may cause perceptible degradation in multimedia transmissions. So, the Impact on SB: Lighting and/or climate control: Jitter less than 30 ms is recommended. Video streaming and VIoT: Jitter between 10 and 30 ms is recommended to avoid distortions and audio/video interruptions. 3. _Packet Loss_:  
The ITU-T G.1010 [58] and IETF RFC 2680 [59] standards recommend the following for IoT devices and other clients: less than or equal to 1%, acceptable communication for VoIP and streaming; less than 3%, perceptible impact on audio and video; greater than 5%, VoIP conversation and video conferencing become unintelligible. Examples in Smart Buildings (SBs):  
Critical automation control and sensors: Less than 0.5% is recommended to ensure reliable communication. Video streaming (CCTV, video conferencing): Less than 1% is recommended. 4. _User Satisfaction Ratings_ (QoE scores) [41]:  
MOS (Mean Opinion Score) - ITU-T P.862 and P.862.2:  
5 = Excellent (no perceptible distortion);  
4 = Good (minor glitches);  
3 = Fair (some perceptible distortions);  
2 = Poor (difficulty in understanding);  
1 = Unacceptable. Other subjective metrics exist, such as the QoE Score ITU-T P.1501 [60]. This latter standard measures perceived video quality. Another interesting feature is the centralized billing procedure, managed within the database and accessed by the Operational Center administrator. This billing information is sent to the condominium residents from the CCO, detailing water, electricity and gas consumption, separated by unit and measured by control devices over IoT (meters and sensors) in each condominium unit. The CCO automatically generates and sends monthly electronic invoices to each resident's email address using their system credentials (AD users). The important choice of adopting an IEC or Fog computing approach in the simplified SB follows the solutions chosen during the research and outlined in Table 1, along with its evolution concerning the types of IoT devices, 5G-IoT [7], VIoT, SDN, gateways, containers, deployment of security-assurance processes, etc.