Protection helps in avoiding charging the subscribers for dropped downlink
packets while the UE is in idle mode. In some countries, it is a regulatory
requirement to avoid such overcharging, so it becomes a mandatory feature for
operators in such countries. Overall, this feature helps ensure subscriber are
not overcharged while the subscriber is in idle mode.
This feature is
supported on the P-GW, and S-GW. Overcharging Protection is supported on the
SAEGW only if the SAEGW is configured for Pure P or Pure S functionality.
P-GW will never be
aware of UE state (idle or connected mode). Charging for downlink data is
applicable at P-GW, even when UE is in idle mode. Downlink data for UE may be
dropped at S-GW when UE is in idle mode due to buffer overflow or delay in
paging. Thus, P-GW will charge the subscriber for the dropped packets, which
isn't desired. To address this problem, with Overcharging Protection feature
enabled, S-GW will inform P-GW to stop or resume charging based on packets
dropped at S-GW and transition of UE from idle to active state.
If the S-GW supports
the Overcharging Protection feature, then it will send a CSReq with the PDN
Pause Support Indication flag set to 1 in an Indication IE to the P-GW.
If the P-GW supports
the Overcharging Protection feature then it will send a CSRsp with the PDN
Pause Support Indication flag set to 1 in Indication IE and/or private
extension IE to the S-GW.
Once the criterion
to signal "stop charging" is met, S-GW will send Modify Bearer Request (MBReq)
to P-GW. MBReq would be sent for the PDN to specify which packets will be
dropped at S-GW. The MBReq will have an indication IE and/or a new private
extension IE to send "stop charging" and "start charging" indication to P-GW.
For Pause/Start Charging procedure (S-GW sends MBReq), MBRes from P-GW will
have indication and/or private extension IE with Overcharging Protection
When the MBReq with
stop charging is received from a S-GW for a PDN, P-GW will stop charging for
downlink packets but will continue sending the packets to S-GW.
P-GW will resume
charging downlink packets when either of these conditions is met:
- When the S-GW (which had earlier sent
"stop charging" in MBReq) sends "start charging" in MBReq.
- When the S-GW changes (which indicates
that maybe UE has relocated to new S-GW).
This feature aligns
with the 3GPP TS 29.274: 3GPP Evolved Packet System (EPS); Evolved General
Packet Radio Service (GPRS) Tunneling Protocol for Control plane (GTPv2-C)
Protection feature is configured at both P-GW service and APN, configuration at
APN takes priority.