4G-LTE Basic Architecture!! Part II: Evolved Packet Core MME!!!

Evolved Packet Core (EPC) many things evolved in 4G-LTE network. Observe this topology:basic-architecture
and the legend:
1. UE: User Equipment
2. E-NodeB: Evolved NodeB
3. E-UTRAN: Evolved UMTS Terrestrial Radio Access Network
4. MME: Mobility Management Entity
5. SGW: Serving Gateway
6. PGW: PDN Gateway, Packet Data Network Gateway
7. HSS: Home Subscriber Subsystem
8. PCRF: Policy and Charging Rules Function
9. IMS: IP Multimedia Subsystem
10. UMTS: Universal Mobile Telecommunication Service

Now, I will tell let you know about EPC.
Evolved Packet Core, yes this is packet core which has evolved. hahaha.
Consists of:
1. MME
2. SGW
3. PGW
4. HSS
5. Billing and Charging

1. MME (read: emem i)
Mobility Management Entity, it manages UE mobility in idle state.
based on its RRC connection availibility, UE has two states in LTE.
rrc-con-stt-digrm

figure: RRC Connection State Diagram

when UE doesn’t have data flow for a certain time, e-Node B will release the RRC connection, and UE’s state become idle. In this idle state, UE will be under MME’s watch. UE mobility will be handled by MME only.
in connected mode, UE handled by both eNB and MME, MME know which eNB does the UE attached, while in idle state, both eNB and MME wouldn’t know if UE mobile and required handover. the solution is as follow:
tracking-area

figure: Tracking area

TA stands for tracking area, every cell in LTE has been allocated in code, tracking area code. every cell sends its tracking area code in its cell broadcast information. periodically or when UE mobile to area that has different tracking area code, UE triggered RRC connection and sends its new tracking area code to MME in NAS message and releases its RRC connection. (this process called tracking area update (TAU)) that’s why MME always has latest information about UE’s tracking area. while idle state, UE context (UE currently used services) maintained by MME.
the next task is handling NAS signalling and NAS security, and manage bearer for the UE. bearer is the least resource that should available to serve certain service.

that’s for now.

thanks!

 

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