LTE General Architecture Overview Part-2

LTE General Architecture Overview Part-2
http://beyond-3g-wireless.blogspot.com/

2G/3G Network Architecture
Please take a look at above picture for comparing LTE Architecture with 2G/3G network Architecture.
Let us continue the discussion on the EPC network elements listed in the previous topic
S-GW primary function is to manage the user plane mobility.It maintains the data path between eNodeB's and PDN GW. When UE moves around eNodeBs in E-UTRAN network, the S-GW servers as a anchor for local mobility. The data packets are routed via S-GW during E-UTRAN mobility or when UE moves from E-UTRAN network to other 3GPP network(GSM,UMTS etc.)
PDN GW servers as an anchor for sessions towards the external packet data networks.
MME performs signalling and control functions to manage the UE access to network connections, assignment of network resources,paging,roaming,handovers etc.
In short the control & signalling path in LTE are managed by MME whereas the user data path is managed by S-GW.
Regarding PCRF not much idea but in general it supports flow based charging.