9.2.5 Preservation Procedures

23.0603GPPGeneral Packet Radio Service (GPRS)Release 17Service descriptionStage 2TS

By sending a RAB Release Request or Iu Release Request message to the SGSN, an Iu mode RAN initiates the release of one or more RABs. The preservation procedure allows the active PDP contexts associated with the released RABs to be preserved in the CN, and the RABs can then be re-established at a later stage, see clause 9.2.5.2 and clause 9.2.3.5.

An Iu mode RAN uses the Iu Release Request to request release of all RABs of an MS, and the RAB Release Request in other cases.

9.2.5.1 Release of RABs Triggered by an Iu mode RAN

9.2.5.1.1 RAB Release Procedure

An Iu mode RAN initiates a RAB release procedure to release one or several RABs. The RAB Release procedure is described in clause 12.7.2.

9.2.5.1.2 Iu Release Procedure

An Iu mode RAN initiates an Iu release procedure to release all RABs of an MS and the Iu connection. The Iu Release procedure is described in clause 12.7.3.

9.2.5.2 Re-establishment of RABs

The procedure for re-establishment of RABs allows the SGSN to re-establish RABs for active PDP contexts that don’t have an associated RAB.

The MS initiates the re-establishment of RABs by using the Service Request (Service Type = Data) message. This is described in the clause "MS Initiated Service Request Procedure". SGSN shall not establish RABs for PDP contexts with maximum bit rate for uplink and downlink of 0 kbit/s. For these PDP contexts including a TFT with packet filter(s) set by the MS, the MS shall perform a MS-initiated PDP Context Modification or Deactivation procedure. For PDP contexts including a TFT with packet filter(s) set by the network only, the MS does not re-establish the RABs (see clauses 9.2.3.4 and 9.2.3.5).

When RABs for an MS that has no RRC connection needs to be re-established, the CN must first page the MS. The clause "Network Initiated Service Request Procedure" describes this.

When RAB(s) are released in S4 SGSN, the received downlink data packet(s) for the preserved EPS bearer(s) may be buffered in the Serving GW. In this case, at reception of the first downlink data packet for one of those EPS bearers, the Serving GW sends a Downlink Data Notification message to the S4 SGSN. When RABs for a UE in PMM-IDLE needs to be re-established, the S4 SGSN must first page the UE. When RAB(s) need to be re-established for a UE that already has an active RRC connection, the S4 SGSN initiates the re-establishment of RABs for all the preserved PDN connections by using the RAB assignment procedure.