aling with extremely small data packets, setting up the connection for a short trans- mission has a significant impact on the overall connection time and power consumption. To reduce this overhead, control-plane CloT EPS optimization specifies a mechanism to include user data packets within signaling messages. By including the payload in the signal- ing message, the overhead is significantly reduced [11]. As shown in Fig. 6.3, in the control-plane CIoT EPS optimization, the uplink data is trans- ferred from the eNB (CIoT RAN) to the MME. At that point, the data may either be trans- ferred via the S-GW to the P-GW, or to the service capability exposure function (SCEF). The latter is only possible for non-IP data packets. From these nodes, the data is ultimately forwarded to the application server (CIoT services). The downlink data is transmitted over the same route in the reverse direction. However, there is no data radio bearer setup and data packets are instead sent on the signaling radio bearer (SRB). This solution is suitable for transmission of infrequent and small data packets. The SCEF is a new network entity introduced to enable machine-type communications. It is used for delivery of non-IP data over control plane and provides an abstract interface for the network services; that is, authentication and authorization, discovery and access network capabilities. With the 752 Chapter 6 user-plane CloT EPS optimization, the data is transferred in the same way as the conven- tional data traffic; that is, over radio bearers via the S-GW and the P-GW to the application server. Therefore, it introduces some overhead upon setting up the connection; however, it facilitates the transmission of a sequence of data packets. This solution supports both IP and non-IP data transfer [11]. The access network architecture for NB-IoT is similar to that of LTE. The eNBs are connected to the MME and S-GW via S1 interface, with the difference of carrying the NB-IoT messages and data packets. Even though there is no handover defined