Interworking Security Between EPS and Other Systems
In this chapter, we describe how the EPC can interwork with other 3GPP access technologies like GERAN and UTRAN, but also how EPC supports interworking with non-3GPP access technologies like cdma2000®HRPD, WiMAX and WLAN. Interworking is important as LTE allows different deployment options for the operators. Clients supporting multiple-access technologies, including LTE, need to have continuous access to the network for good user experience. For example, a client using 3G data may enter an LTE hotspot and thus be handed over to it for a higher data throughput.
We start by describing the interworking with GSM and 3G in section 11.1 and move then to the non-3GPP interworking part in section 11.2.
11.1 Interworking with GSM and 3G Networks
Here we describe intersystem idle state mobility and handovers between 3G or GSM and EPS. This is particularly interesting as there are multiple cases for handling the security context depending on the originating system and mobility mode (handover or idle state mobility). Refer to section 7.4 for detailed definitions relating to security contexts. A process called mapping of security contexts from 3G or GSM to EPS, and vice versa, is applied in intersystem mobility. This mapping means that a 3G or GSM originated security context is used to derive an EPS security context, and vice versa. In handovers, the mapping of security contexts is always applied for efficiency reasons even if a native ...