Functionally of EPC in LTE

• EPC ( Evolved Universal Terrestrial Radio Access Network)
• Functionally the EPC is equivalent to the packet switched domain of the existing 3GPP networks.
• EPC consist of:
  –MME (Mobility Management Entity)
  –SAE GW represents the combination of the two gateways , Serving Gateway(S-GW) and Packet Data Network Gateway (P-GW)
  –Home Subscriber Server (HSS)
  –Policy and Charging Rules Function (PCRF)
• Mobility Management Entity (MME)
  –MME is a controller at each node on the LTE access network. At UE in idle state (idle mode) ,MME is responsible for tracking and paging procedure which includes retransmission therein.
  –MME is responsible for selecting SGW (Serving SAE Gateway) which will be used during initial attach EU and the EU time to do intra-LTE handover.
  –Used for bearer control,a different view R99/4 which is still controlled by the gateway
• Policy and Charging Rules Function (PCRF) - In order to handle QoS as well as control rating and charging, and billing
• Home Subscriber Server (HSS) - For management and security subscriber, combination AUC and HLR
• Serving SAE Gateway (SGW) 
• Set the path and forwards the data in the form of packets of each user
• As an anchor / liaison between the UE and the eNBat the time of the inter handover
• As a liaison link between the 3GPP LTE technology with the technology
  (in this case the 2G and 3G)
• Gateway Packet Data Network (PDN GW)
  -Provides for the UE 's relationship to the network packet-Provide a link relationship between LTE technology with technology non 3GPP (WiMAX) and 3GPP2 (CDMA 20001X and EVDO)