NAS Overview
NAS(non-access stratum) it is a Layer 3 signaling protocol and it is a highest stratum of the control plane between UE and MME at the radio interface Main functions of the protocols that are part of the NAS are:NAS Protocol Functions:
Main functions of the protocols that are part of the NAS are:
-the support of mobility of the user equipment (UE); and
-the support of session management procedures to establish and maintain IP connectivity between the UE and a packet data network gateway (PDN GW).
-NAS security (e.g. integrity protection and ciphering of NAS signalling messages.)
For the support of the above functions, the following procedures are required,
-elementary procedures for EMM(EPS mobility management)
-elementary procedures for ESM(EPS session management)
Linkage between the protocols for EPS mobility management and EPS session management
During the EPS attach procedure, the network activates a default EPS bearer context. Additionally, the network can activate one or several dedicated EPS bearer contexts in parallel. To this purpose the EPS session management messages for the default EPS bearer context activation are transmitted in an information element in the EPS mobility management messages. The UE and the network execute the attach procedure, the default EPS bearer context activation procedure, and the dedicated EPS bearer context activation procedure in parallel. The UE and network shall complete the combined default EPS bearer context activation procedure and the attach procedure before the dedicated EPS bearer context activation procedure is completed. The success of the attach procedure is dependent on the success of the default EPS bearer context activation procedure. If the attach procedure fails, then the ESM procedures also fail.
Except for the attach procedure, during EMM procedures the transmission of ESM messages shall be suspended.
NAS(non-access stratum) it is a Layer 3 signaling protocol and it is a highest stratum of the control plane between UE and MME at the radio interface Main functions of the protocols that are part of the NAS are:NAS Protocol Functions:
Main functions of the protocols that are part of the NAS are:
-the support of mobility of the user equipment (UE); and
-the support of session management procedures to establish and maintain IP connectivity between the UE and a packet data network gateway (PDN GW).
-NAS security (e.g. integrity protection and ciphering of NAS signalling messages.)
For the support of the above functions, the following procedures are required,
-elementary procedures for EMM(EPS mobility management)
-elementary procedures for ESM(EPS session management)
Linkage between the protocols for EPS mobility management and EPS session management
During the EPS attach procedure, the network activates a default EPS bearer context. Additionally, the network can activate one or several dedicated EPS bearer contexts in parallel. To this purpose the EPS session management messages for the default EPS bearer context activation are transmitted in an information element in the EPS mobility management messages. The UE and the network execute the attach procedure, the default EPS bearer context activation procedure, and the dedicated EPS bearer context activation procedure in parallel. The UE and network shall complete the combined default EPS bearer context activation procedure and the attach procedure before the dedicated EPS bearer context activation procedure is completed. The success of the attach procedure is dependent on the success of the default EPS bearer context activation procedure. If the attach procedure fails, then the ESM procedures also fail.
Except for the attach procedure, during EMM procedures the transmission of ESM messages shall be suspended.
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