Transit Function
As described in 3GPP TS
2
3. 228, a Transit Function may be used by an Application Server (AS) if the AS does not support routing capabilities. Under these circumstances, an AS may forward an originating request to the Transit Function and the Transit Function will route the session initiation request to the destination.3GPP allows the Transit Function to reside in a stand-alone entity or to be combined with the functionality of an MGCF, a BGCF, an S-CSCF, or an IBCF. In the context of the IMS-based NG9-1-1 Service Architecture, the Transit Function may be used, as an operator option, to support transfer scenarios where an AS has to initiate signaling toward a Secondary PSAP that is outside of the IMS-based Next Generation Emergency Services Network.