EPC will be having below elements:
MME : Mobility Management Entity
S-GW : ServingGateway
P-GW : PDNGateway
HSS : HomeSubscriberServer
PCRF : Policy Control and Charging Rules Function
We shall see in brief functionality of all the elements
Mobility Management Engine [MME] Functions:
1. It handles all the signaling information between UE and EPC or eNB and EPC.
2. The signaling is known as NAS signaling as it is done through NAS protocol.
3. MME connects to eNB through s1-AP interface.
It has following functions:
1. Authentication: It will authenticate UE to the LTE network by exchanging authentication information between UE and HSS
2. Mobility Management: It will allow subscribers mobility with in the network or across network.
3. Location Update: It keeps track of subscribers location.
4. Bearer Establishment
5. Handover Support: It will enable handover between eNB’s.
6. It will support lawful interception of signaling.
S-GW : ServingGateway
1. S-GW handles mobility between LTE and other CS network
2. When UE in idle state, S-GW maintain UE’s context, and generate paging request when UR receives down-link data.
3. It also performs replication of traffic for lawful interception.
P-GW : PDNGateway
Below are the functionality of P-GW:
1. IP routing and forwarding
2. Per user packet filtering
3. UE IP address allocation
4. PCEF functions
5. Charging
6. It ensures the UE connectivity to external PDN.
7. One UE can connect to more than 1 P-GW to access multiple PDN’s.
HSS : HomeSubscriberServer
It is used to provide user authentication information and user profiles to the MME
Some of the functions include:
1. User Authentication
2. Access authorization.
PCRF : Policy Control and Charging Rules Function
It is a combination of the Charging Rules Function (CRF) and the Policy Decision Function (PDF)
It will also specify the service policy and the quality of service information.