This feature helps to priorities the active and nonactive VoLTE calls over the normal calls. The priority is for the recovery of calls due to the failure of the User Plane.

Relationship

This feature is related to VoLTE Support in CUPS.

There are two types of sessions in the User Plane:

• Normal Session

• Prioritized session

Prioritized session - The MP (message priority) bit set in PFCP header received from the Control Plane during the Sx Session establishment/modification request. The prioritized sessions take precedence in case of recovery. Normal calls recover only after the completion of the recovery of the prioritized calls.

The Control Plane sets the message priority (upper nibble of the 16th octet) in the PFCP header along with the MP (second bit of the first Octet). Currently for EMPS calls, Message Priority is 1. Similarly, message priority is 2 for VoLTE active calls and Message priority is 3 for VoLTE nonactive calls. Following figure describes the message priority in PFCP header format for the various calls.

On receipt of SX Session establish/modification request, the User Plane marks the session as prioritized session. The priority is based on nonzero (EMPS=1, VoLTE Active=2, VoLTE nonactive =3) value of the message priority filled in the PFCP header.

This feature supports the following aspects for the Priority Recovery of VoLTE calls.

On Control Plane: (P-GW, S-GW, SAE-GW, GGSN)

• VoLTE call configuration under APN

• Sets the MP priority Bit and Message Priority in the PFCP header of SX session establishment request

• Sets MP priority Bit and Message Priority in the PFCP header of SX session modification request

On User Plane:

• Checks the Message Priority of the PFCP header for the earlier messages

• If the message priority is nonzero, mark the session as priority session.

• These prioritized sessions are recovered before the nonprioritized sessions after SR /ICSR.

The following call flows explain about the:

• Session Establishment Handling

• Session Modification Handling

Session Establishment Handling Call Flow

The following call flow explains about the Session Establishment.

Session Modification Handling Call Flow

The following call flow explains about the Session Modification.

Following are the configurations for the Pure-P/Collapsed calls and Pure-S calls.

Configuring Pure-P or Collapsed Calls

Following are the configurations to mark the calls as VoLTE in Control Plane for Pure-P/Collapsed calls.

configure 
            context ingress 
               apn vrf.com 
               qci1 ims-media 
               end 

Configuring Pure-S Calls

Following are the configurations to mark the calls as VoLTE in Control Plane for Pure-S/Collapsed calls.

configure 
            apn profile apn_1 
            qci1 ims-media 
configure 
   operator-policy name intershat 
   apn default-apn-profile apn_1 
   end 
configure 
   lte-policy 
   subscriber-map map_name 
      precedence 1 match-criteria all operator-policy-name intershat 
   end 
configure 
   context ingress 
   sgw-service sa_sgw_service 
   associate subscriber-map map_name 
   end 

This section provides information on CLI commands that are available for monitoring and troubleshooting for priority recovery of VoLTE calls.

This section provides information about show CLI commands that are available in support of priority recovery of VoLTE calls in User Plane.

show session subsystem facility sessmgr instance 1 debug-info

AAA TCP Connect Succeeded with   : 0    Retries 
fetched_from_aaamgr                       : 1    pror_to_audit                    : 1         
passed_audit                              : 1    calls_recovered                  : 1         
calls_recovered_by_tmr                    : 1    calls_recovered_by_med           : 0         
priority_calls_recoverd_by_med            : 0    non_priority_calls_ignored_by_med: 0

show session subsystem facility aaamgr instance 1 debug-info

1 Current recovery archives 1 Current valid recovery records
1 Current valid priority recovery records