E1 = 2048Kbps transmission channel/trunk
Fractionalised E1= 31 timeslots X 64Kbps for Data Tx
30B+D (for PBX) refers to PRI or primary rate ISDN (intergrated services digital network)= 31 X 64Kbps where 1 X 64 Kbps = D channel,used for signalling and 30 X 64 Kbps B channels used usually for voice but can include data and video too.