Protection enables the SGSN to avoid overcharging the subscriber if/when
a loss of radio coverage (LORC) occurs.
When a mobile is streaming
or downloading files from external sources (for example, via a background
or interactive traffic class) and the mobile goes out of radio coverage,
the GGSN is unaware of such loss of connectivity and continues to
forward the downlink packets to the SGSN.
Previously, upon loss
of radio coverage (LORC), the SGSN did not perform the UPC procedure
to set QoS to 0kbps, as it does when the traffic class is either
streaming or conversational. Therefore, when the SGSN did a Paging
Request, if the mobile did not respond the SGSN would simply drop
the packets without notifying the GGSN; the G-CDR would have increased
counts but the S-CDR would not, causing overcharges when operators
charged the subscribers based on the G-CDR.
Now operators can accommodate
this situation, they can configure the SGSN to set QoS to 0kbps,
or to a negotiated value, upon detecting the loss of radio coverage.
The overcharging protection feature relies upon the SGSN adding
a proprietary private extension to GTP LORC Intimation IE to messages.
This LORC Intimation IE is included in UPCQ, DPCQ, DPCR, and SGSN
Context Response GTP messages. One of the functions of these messages
is to notify the GGSN to prevent overcharging.
The GGSN becomes aware
of the LORC status by recognizing the message from the SGSN and
discards the downlink packets if LORC status indicates loss of radio
coverage or stops discarding downlink packets if LORC status indicates
gain of radio coverage for the UE.