# Prediction-Based Energy Saving Mechanism in 3 GPP NB-IoT Networks
## 4 Prediction-Based Energy Saving Mechanism
### Network Architecture with PBESM.  
Figure 11 shows the NB-IoT network architecture that includes proposed mechanism. It is basically the same as the conventional network architecture and interface structure, but considers two new entities, namely, the packet inspection entity (PIE) and packet prediction entity (PPE).  
The PIE, which is logically located on the MME, determines the session type from the packet header inspection, e.g., protocol type, port number, and IP address. Then, the PIE predicts the occurrence of the uplink response message with strategy as o the paging delay in the PSM.  
Table 1. Moreover, it measures the response time for each session and sends this information to the PPE, which operates in the base station. The PIE is located on the MME because the paging delay in the PSM may pull the predictive processing delay in the wrong direction, and the MME can prevent this case. The estimated information is transmitted through the existing S1-MME interface in the downlink packets. Though the response message of the NAS and transport protocol (e.g., DTLS, CoAP, and transmission control protocol-TCP) can be predicted in the PIE, it is difficult to predict the application response due to message encryption and customized protocols. Therefore, the application server should support the prediction of uplink occurrence to profit from the PBESM. For prediction from the application server, the information about packet occurrence is trustable only due to the paging delay in the PSM.  
The PPE organizes the received uplink occurrence information and response time for each session. Using these data and the proposed algorithm, it predicts the processing delay, which is the time difference between the downlink transmission and uplink packet generation. Then, the eNB generates a prescheduling command that contains the uplink transmission time and modulation scheme, and the command is sent to the UE in a downlink packet via the NPDSCH. When the UE receives the command, it holds the uplink packet for the specified time without a scheduling request procedure.  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Packet Type** &
\begin{tabular}{l} **Prediction** \\ **Entity** \\ \end{tabular} & **Strategy** \\ \hline RLC protocol & PPE & Prediction of RLC ACK packet though poll bit transmission \\ RRC protocol & PPE & Prediction of RRC response message through a REQUEST message type \\ NAS protocol & PIE & Prediction of NAS response message through a REQUEST message type \\ Transport & PIE & Prediction for DNS, DTLS, etc. through packet header inspection \\ layer protocol & Application & Application server can analyze application message type \\ response & Server, PIE & Application server can analyze application message type \\ \hline \hline \end{tabular}
\end{table}
Table 1: Predictable packet types.  
Figure 11: Network architecture with prediction-based energy saving mechanism (PBESM).  
Predictable Packet Type  
There are five types of predictable packets, namely, RLC ACK, RRC and NAS signaling messages, transport layer response (e.g., TCP ACK and DTLS response), and application response. Table 1 lists the prediction entities and strategies for each packet type.