How Procedures Non-access (NAS) in LTE

NAS procedures, especially procedures for managing connections, essentially similar to UMTS. Main change UMTS is that the EPS allows the union of certain procedures to ensure a more rapid establishment of communication and media. MME creates a context of the UE, when the UE is turned on and attaches to the network. It allocates a unique short UE temporary identity called SAE-temporary mobile subscriber identity (S-TMSI), which identifies the UE context in the MME. This context UE keeps the user’s subscription information downloaded from the HSS.
Local storage subscription MME help improve the execution of procedures such as the creation of a one-way, since it removes the need to consult HSS every time. Furthermore, in the context of UE also has the dynamic information such as a list of media that are installed and the terminal capabilities.
To reduce overhead in E-UTRAN and handle a UE, UE all information related to the access network can be released for prolonged periods of data inactivity. UE then ECM-standby state. MME UE context and saves the information about the installed media during these periods.
To allow the network to contact ECM-IDLE UE, UE updates the network as a new location when it comes out of its current tracking area (TA); This procedure is called “tracking area update. MME is responsible for tracking the location of the user, while the UE is in ECM-IDLE. When there is a need to deliver the downlink data ECM-IDLE UE, the MME transmits a paging message to all eNodeBs in its current TA and eNodeBs page UE via the air interface. Upon receiving the paging message, UE performs a service request that causes the displacement of the UE to the ECM-connected state.
UE-related information thus generated in the E-UTRAN and the carriers to be restored. MME is responsible for the renovation and restoration of radio channels in the context of the UE eNodeB. This transition between the UE states is called ‘Idle to active transition. To speed up the idle to active transition and bearer establishment, EPS NAS supports connection and AS5 bearer activation procedure.
Some of the relationship between the NAS and how the protocols used intentionally to ensure procedures run concurrently rather than sequentially, as in the UMTS. For example, the bearer establishment procedure may be executed in the network without waiting for the completion of the security.
Safety functions are managed by MME for signaling and user data.
When the UE joins the network, mutual authentication is performed UE and the network between the UE and MME / HSS. This authentication function also provides security keys are used to encrypt media.
NAS also handles emergency calls to IMS, which UE, without regular access to the network (ie without terminal Universal Subscriber Identity Module (USIM) or RAO UES in limited service mode) have access to the network with ’emergency attach procedure, it bypassing the security requirements, but only allows access to emergency P-GW.

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