It seems that H323v4 is support in j323v5.0.0 as you can see in
CHANGES file in j323 package :
Changes J323 Engine v4.7.7 -> v4.8.1
but in j323 features page ,it is writen that H323v2 has been supported .
I wander what features of H323v4 are functional in j323v5.0.0 ?