User Plane

The user plane, sometimes referred to as the connectivity layer (see Figure 35), could be seen as a layer of distributed resources managing user data (and signaling) flows. The user plane’s functions are primarily handled by the GGSNs and the MGWs, located at the edges of the core network. The MGW carries out the processing of end user data such as speech coding and also acts as an access switch/router to the backbone network. The MGW also sets up the bearer connections carrying the user data flows in the user plane.

The MGWs are controlled by the MSC and SGSN servers via the H.248 gateway control protocol. The resources needed for a call/session may be distributed over multiple MGWs. For Circuit mode communications the user data processing is primarily allocated to the MGW on the boarder of the ISDN/PSTN.

For interconnecting the network elements in the user plane, different transport technologies may be used.