What is Policy charging and Rules Function (PCRF)? entity in LTE

PCRF is an important entity in the LTE core network domain, initially introduced in 3gpp rel 5. It is mainly responsible for making policy and control decisions. In simple words, if a user needs better quality of service (lets suppose in case of VoLTE ) then it is the responsibility of PCRF to initiate QoS with instructions from IMS. The functionality is listed below

• Provide QoS information to packet gateway 
• Dynamically manage and control data sessions. Example: For VoIP session, PCRF will initiate dedicated bearer dynamically
• Enforce minimum QoS parameters
• Determine charging policy for packets