UMTS Protocol stack
This tutorial on UMTS covers protocol stack of UMTS system.
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.
For CS functions it consists of CM(connection management) and MM(Mobility Management) layers. CM layer takes care of CC(Call Control), SM(supplementary Services) and SMS(Short Message Service). This is for UMTS CS control plane stack. For UMTS CS user plane stack NAS part do not include CM and MM layers but it includes application data layer protocol end to end (between UE-NodeB-RNC-MSC-Remote user).
For PS functions if consists of SM(session Management) and GMM(GPRS Mobility Management) layers. This is for UMTS PS control plane stack. For PS user plane stack, AS part incorporates PDCP(Packet Data Convergence) and NAS part incorporates packet protocol data(IP/PPP/..) and packet data applications(FTP/HTTP/..). PDCP does compression of IP headers, it may or may not exist in the UMTS protocol stack.