If only a single processor, do you really mean single core assigned? That may be that system is underpowered in this case. What is the speed.
Generally speaking I think you may need at least 4 cores in this case assigned in that case as a BKM. There is some info on sizing in the release guide, but I don't know the last time that was changed (table 1):
www.dialogic.com/.../release_guide.pdf
Jeff