Wireless Oom

RRC is the main AS control protocol.
RRC performs
1. establishment, modification and release of RRC conncetions
RRC connections are used to transfer RRC signal messages and be used to transport higher layer NAS protocol messages.
2. establishment, modification and release of RAB (radio access bearer ), user plane data connection.
3. radio mobility functions, etc.

UMTS protocols are divided into two different strata (See Fig):
1. NAS (non access stratum)
2. AS  (access stratum)
UE (User Equipment) and CN (Core Network, MSC for circuit switched service, SGSN for packet switched service) need to talk!
NAS protocols support the talk between UE and CN.
It does not care below access method (could be UTRAN, GSM/GPRS).
Some examples [...]