Signaling when higher ARP bearer is to be established while EUTRAN is loaded?

Question

I understand that eNB kicks off the bearers with lower priorities(based on ARP), during high load condition, in order to accommodate higher priority bearers. What is the exact signaling involved here?

Answer 1

There might be two scenarios to establish a new bearer to deliver high QoS.
1. UE originated.
2. Network triggered.

In any of above cases. Core network establishes bearer first and then eNB.
** For core network point of view. NAS, GTP, Diameter signalling messages exchanged.
Here I would like to explain only 2 (UE originated).

1. UE can send either BearerResourceAllocationRequest or BearerResourceModificationRequest message NAS message to MME. Both the messages reached till MME via following messages.

   UE-----UE Information Transfer ---> eNB-------Uplink NAS transport-------->MME

2. MME sends Bearer Resource Command GTP message to SGW and SGW sends to PGW.

   MME---- Bearer Resource Command-----> SGW ---- Bearer Resource Command -----> PGW.

3. PGW/PCEF sends CCR(Credit Control Request) Diameter to PCRF and PCRF responds back to PCEF with CCA(Creadit Control Answer) diameter message.

   PGW/PCEF -------------------Credit Control Request---------------- PCRF.
   PCRF ------------------------- Credit Control Answer ----------------- PCEF/PGW.

4. If PCEF gets positive response from PCRF to create a new bearer. PGW/PCEF sends Create bearer request to SGW and SGW sends the same GTP message to MME.

   PCEF/PGW --------- Create bearer Request ------> SGW------------------ Create Bearer Request--->MME.

5. MME sends ERAB Setup Request S1AP message to eNB with SGW tunnel endpoint identifier.

   MME----------------ERAB setup Request ------------->eNB.

6. if eNB evaluates that to add this bearer it has to release lower priority bearer(s). eNB do the same thing and send RRC connection Reconfiguration message with the drbtoadd/drbtorelease list. UE responds back with RRC connection Reconfiguration Complete

   ENB-----------------RRCConnectionReconfiguration------------->UE.
   UE------------------ RRCConnectionReconfigurationComplete----->ENB.

7. ENB prepares ERAB SETUP response for successful established bearer to MME. ENB sends ERAB release Indication s1ap message to MME.

   ENB---------------------- ERAB SETUP RESPONSE Message ----------------> MME.
   ENB---------------------- ERAB Release Indication message----------------> MME.

8. MME send Create bearer Response to SGW and SGW to PGW/PCEF for established bearer. And send Delete bearer Command to SGW and SGW to PGW for the deleted one.

MME---- Create Bearer Response -----> SGW ---- Create Bearer Response -----> PGW.
MME---- Delete bearer command -----> SGW ---- Delete bearer Command -----> PGW.

1. PGW/PCEF send CCR to PCRF and PCRF responds back to PCEF with CCA

PGW/PCEF--------------Credit Control Request------------------->PCRF.
PCRF--------------------- Credit Control Answer -------------------->PCEF/PGW.