What is BGCF (Breakout Gateway Control Function)?

It is an IMS element that chooses the network where PSTN breakout occurs. It is used to route call signaling to and from the most appropriate soft switch/ S-CSCF. The S-CSCF controls PSTN services through the use of soft switches and a BGCF. The soft switch comprises an MGCF (Media Gateway Control Function) and an MGW (Media Gateway) and the BGCF has functionality in order to route traffic and signaling to the correct soft switch.