The EPC network may decide to enable two or more ProSe-enabled WLAN-capable UEs to directly communicate using WLAN technology. This decision can be taken, for example, when the EPC network supports EPC-level ProSe discovery and becomes aware that two or more UEs are in close proximity, when the EPC network knows that UE-A requests to communicate with UE-B which is in close proximity of UE-A, etc.
Figure 5.6.2-1 shows how the EPC network enables UE-A and UE-B to directly communicate in WLAN direct mode. This is accomplished by triggering the two UEs to establish a WLAN direct group and providing them with assistance information which enables the EPC network to control and to expedite the establishment of the WLAN direct group.
With the procedure shown in Figure 5.6.2-1 the EPC network can (i) control when a WLAN direct group can be established, (ii) authorize the UEs that can become members of this group (and thus communicate with each other in WLAN direct mode) and (iii) control the operating parameters of the WLAN direct group e.g. the SSID, the security keys, etc.
The ProSe Function shown in Figure 5.6.2-1 is the network function that triggers and controls the establishment of a WLAN direct group between one or more UEs.
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Figure 5.6.2-1: Signalling flow for EPC support for WLAN direct communication
The ProSe Function sends a WLAN Direct Group Setup Request (Assistance Information) to UE-A. The Assistance Information is a set of parameters which can expedite the establishment of the WLAN direct group and enables the EPC network to control the operating parameters of the WLAN direct group. The Assistance Information content depends on the WLAN technology. If UE-A accepts the request and the offered Assistance Information, it responds with a WLAN Direct Group Setup Response. This response may include parameters for the WLAN direct group proposed by UE-A (e.g. an operating channel).
The ProSe Function sends also a WLAN Direct Group Setup Request (Assistance Information) to UE-B. The Assistance Information in the request may take into account the parameters proposed by UE-A in step 2b.