Application Server assisted Direct Mode Offload
Original Publication Date: 2016-Aug-17
Included in the Prior Art Database: 2016-Aug-17
This paper describes a method for application server assisted direct mode push to talk calls. 3GPP ProSe  defines methods for LTE UEs to communicate in direct mode. This paper describes a method where PTT server is aware of a direct mode graph for each PTT group. This graph consists of UEs that are affiliated to the group which can communicate with each other either directly or through other UEs in the graph acting as a relay for this communication. When PTT Server determines that all call participants are in a connected graph for the PTT communication, PTT server instructs all the required devices in the graph to switch to direct mode, setup the communication session and on completion, resume network connected mode of operation. The communication may be for 1-1 or group PTT calls. This paper further describes how UEs that communicate over diverse technologies such as LMR direct mode can be included in the graph. Such UEs are bridged by converged (multi-mode) devices and/or collaborative devices (LMR and LTE device collaborating over a bluetooth link) that support both capabilities. This enables direct mode communication between LMR and LTE devices.