There is a single MAC instance within the UE.
In the network, usually a single MAC instance for each UE exists.
However, multiple MAC instances for a single UE may happen (e.g., one in a CRNC and one in an SRNC)
S-RNTI is assigned by the SRNC.
It is uniquely identified within the SRNC.
It is 20 bits.
This id is used by UE, SRNC, DRNC.
In the Cell_DCH, the UE location is known to
1. cell level by the UTRAN
2. serving RNC by the CN
Active set is the set of cells to which the UE is simultaneously connected during soft handover.
Due to soft handover, the classification of SRNC and DRNC occurs:
1. SRNC: Serving Radio Network Controller
2. DRNC: Drift Radio Network Controller
SRNC is the RNC which combines signals from multiple node Bs and sends them to CN (SGSN for PS, MSC for CS).
