What is UMTS and its layers?
UMTS protocol stack consists of Access Stratum(AS) and Non Access Stratum(NAS) . Access Stratum supports OSI-layer 1 to 3. It consists of PHY(layer 1), MAC(layer 2),RLC(layer 2) and RRC(layer 3). NAS or core network part is divided based on circuit switched(CS) or packet switched(PS) functionalities.
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