Look at the following chart
UE is NB-IOT equipment, the UE data to the application server has three road can go
The first, the UE, a base station, MME, SCEF, application server, the CP mode is also called control plane, also known as signaling radio bearer plane, also called control plane bearer, is called a lot. Second, this path is specially made for the NB-IOT. Because the control data into the user data (in particular the NAS layer) made along the inside, so called control plane data go. But this only supports the Non-IP data.
Second, the UE, a base station, MME, S-GW, P-GW, the application server, this is the CP mode, also called control plane, also known as signaling radio bearer plane, also called bearer control plane, the user data is into control plane data (NAS particular layer) which sent out. Benefit is less data when the transmission speed. The second benefit is not established third line.
Third, the UE, the base station, S-GW, P-GW, an application server, that is UP mode, also called user plane, also called data plane, also called data radio bearer. The user data and control data separate from user data only go this route, the benefits are fast transmission of data and more time. Basically this is the phone line.
To sum up the above, the current NB-IOT and more taking the second route, an analogy, that is, the establishment of a large highway, compared to a bicycle user data, control data, compared to the car, then use the second route, which means that I built a road, bicycles and cars can go together. Third line, which means that a road bike repair, automobile repair a road, the same road two parallel routes, but go a bicycle and car separately. So NB-IOT with a second way, then I can just repair a road.