LTE: What is the role of policy and charging rule function (PCRF) during the attach procedure ?

Question

How the signalling messages flow between network nodes of inter PLMN ?
Assume a scenario, in which LTE UE is connected to its home network and handed over to another network due to mobility.

Answer 1

Once the IP address is allocated by PGW ,it's PCRF who is in the charge to control the policies for the default bearer.
So first we will see what is policy ?
QOS is associated with another term known as Gating, which determine whether or not packet are allowed to travel through SDF. Each SDF is associated with Gate status, which can be either open or closed. Together Gating and QOS make a concept know as policy .
LTE uses 2 types of PCC rules
1- predefined pcc rules which are permanently stored by the network and are only referenced by the PCRF
2- dynamic pcc rules which the PCRF compose on the fly.
Each SDF(service data flow) is associated with one of these pcc rules and it's PCRF who decides which SDF will receive which PCC rules.
So in the attach procedure our motive is to establish a EPS session and to do so , PGW will send subscription profile (QOS profile)of the user to PCRF,
So PCRF will define the PCC policy for that particular EPS session.

If you have any other doubt please let me know