I have got few more questions
Ques.1) For PRACH procedure, how does the eNB calculate the UPLINK GRANT(required for msg3 transmission from UE) size in case if UE has transmitted preamble from Group B.
As per the spec. 36.321: eNB can know the msg3 size of GroupA preamble based on messageSizeGroupA. Based on this eNB calculates UL grant, but for Group B preamble, how the eNB gets the input for UL grant calculation.
Ques.2) Is it that all possible msg3 have only 2 possible sizes, hence specs specify only 2 groups. Group A and Group B ? Actually, i want to know what is motivation for having 2 groups?
Ques.3) Which msg3 (for ex. RRC connection request, RRC_connection_reestablishment) types, fall in Group A and which all under Group B?
Ques.4) How the PRACH mask Index is used?