Читать книгу Mobile Communications Systems Development - Rajib Taid - Страница 69

The GTP has the control as well as the user plane protocols. The tunnel management is taken care of by the so‐called GPRS tunneling Control Protocol, whereas the user IP data packets/payload is transported using the GTP‐User Plane T‐PDU (tunneled PDU) as shown later in Figure 8.1. GTP is used in a couple of interfaces in GPRS, UMTS, LTE/EPS, and 5G CN. For more information on the GTP control and user plane protocol, refer to TS 29.060 [67], 29.274 [70], and TS 29.281 [72].

At the LTE/EPC end, the user plane of the eNodeB, S‐GW, and P‐GW consists of the GTP‐user plane [12] to tunnel user data on top of the UDP/IP transport network. Figure 3.8 also shows the respective user plane logical interfaces, i.e. S1‐U and S5/S8, for carrying user data between two network elements of an LTE/EPS network.

From Figures 3.7 and 3.8, it is observed that in the LTE system, the radio interface protocol layers – PDCP, RLC, and MAC, are available in both the control plane and the user plane protocol stack. In the user plane protocol stack, the application and IP layers terminate at the CN, P‐GW, which transfers user data packets to the external network. Examples 3.5 and 3.6 describe two typical protocols consisting of control plane and user plane protocol.