## 3 5G and TSN Integrated Networks for VPP
### Semi-Persistent Scheduling with Reserved Bandwidth Sharing and Pre-Emption
#### 4.2.2 Semi-Persistent Scheduling with Reserved Bandwidth Sharing and Pre-Emption Mechanism  
In traditional networks, TT flows typically have higher priorities and stricter delay limits than ET flows. However, in VPP systems, ET flows have higher priority and more strict delay requirements than TT flows. Due to the special characteristics of VPP traffic, this section designs a scheduling mechanism based on semi-persistent scheduling with reserved bandwidth sharing and pre-emption (SPS-RBSP). The traditional dynamic access process of the 5G system is complex and it cannot guarantee to meet strict delay requirements. By reserving resources for traffic in advance, the access delay of traffic in the 5G system can be significantly reduced. Reserving resources can also ensure that time-critical traffic is not disturbed by other traffic. It ensures the reliability of time-critical traffic. The traffic in the VPP system can be divided into three categories: (1) ET flow, triggered by events, has the highest priority and target delay requirement (50 ms), including three types of traffic: fast frequency regulation, regular frequency regulation, and emergency demand response; (2) TT flow, with periodic arrival, has lower delay requirements, including peak regulation and normal demand response traffic; and (3) best effort (BE) flow has the lowest priority and delay requirements (second level), including power trade market traffic. Because the arrival times of ET flows are unpredictable, it will cause a serious waste of resources if it only reserves resources for ET flows. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**VPP Service** & **Bandwidth** & **Target Delay** & **Reliability** & **Priority in TSN** & **5 QI (Priority)** \\ \hline Fast frequency regulation & 4.8 Mbps (100 Terminals/km\({}^{2}\)) & \textless{}50 ms & 99.999\% & 7 & 82 (19) \\ Regular frequency regulation & 4.8 Mbps (100 Terminals/km\({}^{2}\)) & \textless{}50 ms & 99.99\% & 6 & 82 (22) \\ Peak regulation & 0.82 Mbps & \textless{}6 s & 99.99\% & 5 & 6 (23) \\ Emergency demand response & 16 Mbps (100 Terminals/km\({}^{2}\)) & \textless{}50 ms & 99.999\% & 4 & 84 (24) \\ Normal demand response & 2.74 Mbps (150 Terminals/km\({}^{2}\)) & 500–1100 ms & 99.999\% & 3 & 76 (56) \\ Power trade market & 1.33 Mbps (1000 trade members) & \textless{}10 s & 99.99\% & 0 & 8 (80) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: VPP service traffic and corresponding TSN priority and 5 QI. Considering the highest priority and event-triggered characteristics of ET flows, in each semi-persistent scheduling period \(T_{S}\), a set of fixed numbers of RBs are reserved for possible ET flows. The reserved RBs are sufficient for ET flows. Because the period of TT flows in the VPP system is very long and the delay requirement is low, the setting of the SPS period is based on the minimum event interval of the ET flow \(T^{event}\), i.e., \(T_{S}=T^{event}\). The minimum event interval of ET flows is generally equal to their delay requirement. In the SPS-RBSP, this set of fixed reserved RBs can be shared with TT flows when there are no arriving ET flows. It improves the resource utilization when the event interval of ET flows is long. The transmission period of TT flows \(T^{time}\) in the VPP system is in the order of seconds or minutes, which is several times \(T^{event}\), that is, \(T^{time}=nT^{event}\). In shared scheduling, the transmission order of frames is determined based on the delay requirement of traffic. Regardless of whether there is traffic occupying resources at present, high-priority ET flows will immediately obtain transmission resources when they arrive. This ensures the low latency and reliable transmission of time-critical ET flows. TT flows can be transmitted using idle reserved RBs when they arrive. If the reserved RBs are insufficient, the remaining TT flows and BE flows are orderly carried by by dynamic RBs through the dynamic access process. Figure 3 shows the basic principle of the proposed SPS-RBSP mechanism. Each square represents one RB.