LTE core network also called EPC in SAE is responsible for the complete control of the UE and the creation of media. The main logical nodes LTE EPC are:
• PDN Gateway (P-GW)
• Serving Gateway (S-GW)
• Mobility Management Entity (MME)
PCRF of LTE Core Network
The political control and charging rules is responsible for control policy making, as well as flow control functionality based charging enforcement function Control Policy (PCEF), which is the P-GW.PCRF provides QoS authorization (QoS class identifier [QCI] and bit rates), which decides how a particular data stream will be treated PCEF and ensure that it is in accordance with the user’s subscription profile.
HSS of LTE Core Network
Home Subscriber Server database subscription includes SAE users such as EPS subscribed QoS profile, as well as any restrictions on access for roaming. He also holds information on PDNs which users can connect. This could be in the form of an access point name (APN) (which is a label according to DNS naming conventions describing the access point PDN) or PDN address (indicating the subscriber’s IP address (es)). In addition HSS has dynamic information such as the identity of the MME user is already logged in or registered. HSS can also integrate, authentication center (AUC), which generates vectors authentication keys and security.
P-GW of LTE Core Network
PDN Gateway is responsible for allocating IP UE and the application QoS and flow based charging in accordance with the PCRF. It is responsible for filtering user downlink IP packets in different QoS-based carriers. This is done based on traffic patterns (TFTs) .P-GW performs application QoS guaranteed bit rate (GBR) bearers. It also serves as the anchor for mobility for interworking with non-3GPP technologies such as CDMA2000 and WiMAX networks.
S-GW of LTE Core Network
All user IP packets are transferred via Gateway service, which serves as the local mobility anchor data carriers if the UE moves between eNodeBs. It retains also information carriers when the UE is at rest (known as the “EPS Connection Management – IDLE” [ECM-IDLE]) and buffers downlink data temporarily while the MME initiates paging UE to restore carriers. In addition, S-GW performs certain administrative functions in the visited network, such as the collection of information load (ie the amount of data sent or received by the user) and lawful intercept. It also serves as a mobility anchor for interworking with other 3GPP technologies such as packet radio service (GPRS) and UMTS.
MME of LTE Core Network
Mobility Management Entity (MME) is a control node that processes the signaling between the UE and CN. Protocols running between the UE and CN are known as Non-Access Stratum (NAS) protocols.