LTE call flow beyond PGW

                       Basic LTE Call Flow beyond PGW.

Here are the call flow from PGW to PCRF on Gx interface.

During Initial Attach procedure, PGW check for the APN/Charging Characterstics received in Create session request for whether dynamic Policy(configured in PCRF) or Static policy(configured on PGW) should be applied. Depending upon the configuration, PGW forwards the request to PCRF for providing PCC Rule for the UE attach request.

PCC rules consist of:

• Rule name - This is to be used to reference a PCC rule in communication between PCEF and the PCRF . 
• Service data flow filters - shall be used to select the type of traffic that passes through the bearer on which the rule applies.
• precedence : Determines the precedence of the bearer on which the rule is applied when data is received uplink or downlink for a particular type UDP/TCP etc.  
• QoS parameters - Includes QoS Class Identifier (QCI), also the Allocation and Retention Priority (ARP) and GBR,MBR for uplink and downlik.
• Charging type - Defines whether online,offline or both or none charging is applied.

  PGW sends CCR(Init) to PCRF to get the PCC Rule from PCRF.
  PCRF has primarily two entities. PDT (Policy Derivation table) and PCT (Policy and
  Configuration table).
  In PCT, PCRF has number of PCC Rules configured.
  In PDT, PCRF has the selection criteria based upon which PCRF sends the selected PCC Rules in 
  CCA.
  Selection criteria- Can be IMSI,APN name, QCI, MBR/GBR etc. means if CCR request contains 
  the given value of IMSI or QCI and so then particular PDT is applied. 
  For Example: In CCR (Init), PCRF receive IMSI 122334455667001. Based upon this IMSI, PCRF
  has PDT configured in which PCRF applies two PCC Rules let suppose PCC1 and PCC2.
 
  Upon getting successfull PDT matched PCRF sends successfull CCA (Init) to PGW.
  Now, upon getting of successfull CCA (Init) PGW sends CCR (Update) to confirm the PCRF that  
  the Rule is applied  successfully on the particular bearer (in this case default bearer) and also
  inform the ip address of the UE.Then PCRF acknowlege with CCA(Update) success.

  Now PGW has already applied the Rule(Qos,filters,MBR,GBR etc) received from PCRF to
  the requested bearer, it sends Create Session Response to SGW and then the Default session created
  successfully.
 
Similar Procedure follows for dedicated bearer also.
  In dedicated bearer creation/updation/deletion, PGW sends CCR Update to PCRF.PCRF 
  acknowledge the request with CCA Update.
 

Note: CCR (Init) send by PGW only once for a UE session i.e on default bearer creation.