Core Network: Architecture and Signaling Procedures

If the network deploys dynamic PCC, the PCRF triggers the bearer deactivation by sending a Diameter Re-Auth-Request (RAR) message over the Gx interface to the PCEF, which is collocated in the P-GW. The message removes authorized PCC rules and instructs the PCEF to delete the specific SDF filters of the bearer that the network deactivates. The message carries these AVPs: the Session-Id, the Auth-Application-Id, set to the vendor-specific Gx Application ID 16777238, the Re-Auth-Request-Type, set to AUTHORIZE_ONLY, and the Charging-Rule-Remove. The Charging-Rule-Remove AVP encapsulates the Charging-Rule-Name or the Charging-Rule-Base-Name, which identify the rules to deactivate.

The P-GW acknowledges the policy modification command by returning a Diameter Re-Auth-Answer (RAA) message to the PCRF. This message shows that the PCEF accepted the rule removal request and starts the bearer deactivation on the access network. The message carries the Session-Id, the Origin-Host, the Origin-Realm, and the Result-Code, set to DIAMETER_SUCCESS, to confirm a successful transaction.

The P-GW maps the removed PCC rules to the related bearer context and sends a GTPv2-C Delete Bearer Request message to the S-GW over the S5/S8 interface. The message starts the deallocation of the downlink S5/S8-U transport parameters and identifies the bearer that the network deactivates. The message carries these IEs: the EPS Bearer IDs, which identify the specific dedicated bearer to delete, or the LBI, if the network deactivates the complete PDN connection, the PTI, which correlates the message with a UE-initiated modification if applicable, and the Cause. The Cause IE carries the specific release trigger, for example "Regular deactivation" or "RAT changed from 3GPP to Non-3GPP".

After processing the request of the P-GW, the S-GW starts the release of its local S5/S8-U user-plane tunnel resources and forwards the GTPv2 Delete Bearer Request message to the MME over the S11 interface. The message prompts the MME to start the E-UTRAN resource release and the NAS signaling to the UE, and carries the EPS Bearer IDs with the target EBI, the PTI, and the Cause.

To terminate the logical S1-U connection and the radio resources of the bearer, the MME starts the S1AP E-RAB Release procedure and sends an S1AP E-RAB Release Command message to the eNodeB. The message instructs the eNodeB to release the radio resources on the Uu interface and the uplink user-plane tunnels on the S1-U interface, and carries the MME UE S1AP ID, the eNB UE S1AP ID, and the E-RAB To Be Released List, which contains the E-RAB To Be Released Item with the target E-RAB ID and the Cause. The message also carries a NAS-PDU, which encapsulates the NAS Deactivate EPS Bearer Context Request message. The embedded NAS ESM message carries the EPS bearer identity, the PTI, and the ESM cause, for example ESM Cause #36, "regular deactivation", or ESM Cause #39, "reactivation requested".

The eNodeB maps the received S1AP E-RAB release information to the radio bearer parameters and sends an RRC Connection Reconfiguration message to the UE over the Uu interface. The message requests the UE to release the physical layer resources, the MAC layer resources, and the RLC layer resources of the designated DRB, and carries the rrc-TransactionIdentifier and the radioResourceConfigDedicated container. This container carries the drb-ToReleaseList with the assigned DRB identity to release. The message also carries the dedicatedInfoNASList, which contains the NAS Deactivate EPS Bearer Context Request message.

The UE tears down the physical radio resources, removes the uplink packet filters in its TFT that match the deactivated EPS bearer, and returns an RRC Connection Reconfiguration Complete message to the eNodeB over the air interface. The message carries the rrc-TransactionIdentifier and confirms that the UE reconfigured the radio sub-layers.

After confirming the successful deallocation of the S1-U tunnel endpoints and of the Uu interface radio resources, the eNodeB sends an S1AP E-RAB Release Response message to the MME over the S1-MME interface. The message carries the MME UE S1AP ID, the eNB UE S1AP ID, and the E-RAB Release List, which encloses the E-RAB Release Item with the E-RAB ID, together with the User Location Information with the ECGI and the TAI of the serving cell. If the network releases secondary RAT resources, the message also carries the Secondary RAT Usage Report List.

The NAS layer of the UE builds the ESM response that acknowledges the bearer context deactivation and encapsulates this response in an RRC Direct Transfer message, which the UE sends to the eNodeB over the control-plane signaling link. The message carries the rrc-TransactionIdentifier and the dedicatedInfoNASList, which contains the NAS Deactivate EPS Bearer Context Accept message. This NAS message contains the Protocol discriminator, the EPS bearer identity, and the PTI.

The eNodeB extracts the encapsulated NAS-PDU from the RRC Direct Transfer message and forwards the NAS-PDU without changes to the MME, inside an S1AP Uplink NAS Transport message that delivers the final ESM confirmation from the UE to the core network. The message carries the Message Type, the MME UE S1AP ID, the eNB UE S1AP ID, the NAS-PDU with the Deactivate EPS Bearer Context Accept message, the ECGI, and the TAI of the serving cell.

When the MME receives both the S1AP E-RAB Release Response message of step 8 and the Uplink NAS Transport message with the NAS Accept of step 10, the MME deletes the local bearer context and acknowledges the bearer deactivation to the S-GW with a GTPv2 Delete Bearer Response message over the S11 interface. The message carries the Cause, set to "Request accepted", the EPS Bearer ID, which is grouped in the Bearer Contexts IE, the ULI with the ECGI and the TAI, and the RAN/NAS Cause, which indicates the release cause of the access network. If the data is available, the message also carries the Secondary RAT Usage Data Report.

After processing the response of the MME, the S-GW deallocates its downlink user-plane tunnel resources, that is the S1-U F-TEID, and its uplink S5/S8-U tunnel resources, and forwards the GTPv2 Delete Bearer Response message to the P-GW over the S5/S8 interface. This message confirms the end-to-end deactivation of the user-plane resources in the EPC and carries the Cause, the EPS Bearer ID, which is grouped in the Bearer Contexts IE, the ULI, and the Secondary RAT Usage Data Report.

If dynamic policy rules triggered the bearer deactivation, the PCEF in the P-GW reports the successful enforcement of the PCC rule removal to the PCRF by sending a Diameter Credit-Control-Request (CCR) message with the CC-Request-Type set to UPDATE_REQUEST. The message synchronizes the session state of the PCRF with the actual state of the core network and reports the charging identifiers and the location information. The message carries the Session-Id, the CC-Request-Type, set to UPDATE_REQUEST, the CC-Request-Number, and the Charging-Rule-Report, which contains the Charging-Rule-Name and the PCC-Rule-Status, set to INACTIVE. The message also carries the Access-Network-Charging-Identifier-Gx, the RAN-NAS-Release-Cause, and the 3GPP-User-Location-Info.

The PCRF acknowledges the rule deactivation report of the PCEF and closes the policy modification transaction by sending a Diameter Credit-Control-Answer (CCA) message to the P-GW. The message carries the Session-Id, the Origin-Host, the Origin-Realm, and the Result-Code, set to DIAMETER_SUCCESS.