Arriving in Beijing from HK by CA108 at 1355hours and departing for Ulaanbaatar by CA955 at 1515hour

Hi, please guide me if the time gap is enough to catch the connecting flight.
Do I need to do all the formalities in the same Terminal (3)- customs & security check before catching the connecting flight?
Or the Airlines - being the same will take care of my luggage transfer?
Thanks!