Section: 5.3.6A PDN GW Pause of Charging procedure
Content: The PDN GW Pause of Charging procedure is optionally supported by the Serving GW and PDN GW and has the purpose to limit a mismatch between PDN GW and Serving GW charging volume and packet counts. Generally, it aims for the PDN GW charging and usage monitoring data to more accurately reflect the downlink traffic actually sent to the E-UTRAN. NOTE 1: A consequence of using this procedure is that PDN GW charging data does not correspond to the volume that traversed the PDN GW, and it is therefore not possible to count the downlink packets dropped between the PDN GW and the E-UTRAN. The Serving GW may indicate support of this function to the PDN GW when the PDN connection is activated or when a new/target Serving GW is used for a PDN connection. This is indicated to the PDN GW by a "PDN Charging Pause Support Indication" in the Create Session Request during PDN activation/Attach and in the Modify Bearer Request in procedures with a change of Serving GW. NOTE 2: It is assumed that Pause of PGW Charging is not invoked by SGW that is performing extended data buffering. The PDN GW may indicate if the feature is to be enabled on a per PDN connection basis, if the current Serving GW supports the feature and the operator's policy is to enable the feature. This is indicated to the Serving GW by a "PDN Charging Pause Enabled" Indication in the Create Session Response during PDN activation/Attach and in the Modify Bearer Response in procedures with a change of Serving GW. This is an indication to the Serving GW that when the criteria for pause of PDN GW charging are met (as described further down in this clause) the PDN GW charging can be paused. NOTE 3: PDNs where this function applies are based on an operator policy in the PDN GW. What enters into that policy is operator specific but may be based on for example if the PDN uses SDF based charging, UE is in home or visited network, APN employed, UE is configured for NAS signalling low priority, Charging Characteristics value etc. The PDN GW shall stop any charging and usage monitoring actions for the PDN connection upon receiving a "PDN Charging Pause Start" Indication in a Modify Bearer Request. When the PDN GW receives a Modify Bearer Request for a PDN connection for which charging has been stopped previously and, if the Modify Bearer Request contains a "PDN Charging Pause Stop" Indication or does not contain a "PDN Charging Pause Start" Indication, then the PDN GW shall continue charging for the PDN connection. NOTE 4: In addition to the Service Request Procedure, the PDN GW charging is also unpaused during mobility procedures involving the Serving GW based on Modify Bearer Request messages without "PDN Charging Pause Start" indication or during mobility procedures involving the Gn/Gp SGSN based on Update PDP Context Request messages. NOTE 5: A Delete Bearer Command or Delete Bearer Request or Delete Bearer Response for a dedicated bearer does not unpause a previously paused PDN charging. When bearers become suspended for a UE (see TS 23.272[ Circuit Switched (CS) fallback in Evolved Packet System (EPS); Stage 2 ]  [58]), the PDN GW charging is no longer paused and the PDN GW continues charging for the PDN connection after suspended bearers are resumed. NOTE 6: The PDN GW discards packets received for a suspended UE as described in TS 23.272[ Circuit Switched (CS) fallback in Evolved Packet System (EPS); Stage 2 ]  [58]. While the PDN GW charging is currently paused and the UE is in ECM-IDLE (for ISR case the device is at same time in PMM-IDLE or STANDBY in UTRAN/GERAN accesses) the following applies: - The PDN GW shall not perform charging and usage monitoring actions for downlink traffic on this PDN. NOTE 7: The Serving GW charges anyway only for the amount of transmitted downlink traffic as described in clause 5.7A. - Based on operator policy/configuration in the PDN GW, the PDN GW may limit the rate of downlink traffic sent to the Serving GW. Based on operator policy/configuration in the Serving GW, the Serving GW may discard rather than buffer the downlink user plane packets for this PDN connection while the PDN GW charging is paused. This is to avoid delivery of user plane packets to the UE that were not counted in the PDN GW for charging and usage monitoring purposes. Regardless of operator policy/configuration, the downlink user plane packets received from PDN GW at the Serving GW shall trigger Downlink Data Notifications as described in clause 5.3.4.3. When the Serving GW receives a Modify Bearer Request or Modify Access Bearers Request for a PDN connection triggering a Modify Bearer Request towards the PDN GW, the Serving GW shall consider the PDN charging as being unpaused if it has been paused previously. Figure 5.3.6A: PDN GW Pause of charging procedure 1. The Serving GW receives downlink data packets for a UE known as not user plane connected (i.e. the Serving GW context data indicates no downlink user plane TEID for the eNodeB) as described in clause 5.3.4.3 step 1, i.e. the packets are buffered or discarded in Serving GW based on operator policy. 2. Based on operator policy/configuration the Serving GW triggers the procedure to pause PDN charging. Triggering criteria are based on Serving GW operator policy/configuration. Example of such policy may be: a. Operator specified criteria/threshold (e.g. number/fraction of packets/bytes dropped at Serving GW in downlink since last time the UE was in ECM-CONNECTED state (or for ISR case PMM-CONNECTED state)). b. Recent indication of "Abnormal Release of Radio Link" (see clause 5.3.5) or a recent Downlink Data Notification Reject (clause 5.3.4.3) without UE shortly re-entering ECM-CONNECTED state (or for ISR case without also re-entering PMM-CONNECTED state). 3. Serving GW sends a Modify Bearer Request (PDN Charging Pause Start) message to the PDN GW. PDN Charging Pause Start indicates that PDN GW charging shall be paused. 4. PDN GW confirms with a Modify Bearer Response message.