Dear;
If you are using the DBS3900, the UBBP board is used to connect to the RRU. And there is an antenna cable in the RRU which is ussd to connect to the antenna. The CPRI ports on the UBBP are connected to the RFU. And the UMPT board is used to connect to the OMC and it is used for commissioning and maintenance. The two boards UMPT and UBBP are connected in a built in link known as SCTP link.