There was one interesting feature in Release 7 that dint
make it to LTE in Release 8, however it has introduced as part of Release 9. I
am talking about Location Reporting feature.
A PGW/GGSN needs to know the exact location of UE/MS so that
it can do location based charging. Other reason why PGW/GGSN needs the exact UE
location could be for lawful intercept. Any more reasons?
Anyway the UE location is propagated by MME/SGSN to PGW/GGSN
over ULI IE (User Location Information). Whenever a UE changes a cell or
routing area or tracking area MME/SGSN may inform the PGW/GGSN about the same
using location change reporting feature. In pre-release 7 if the UE moves from
one routing area to other that is under same SGSN then there is no message over
Gn interface towards GGSN. So how will SGSN send the User location information
IE with new RAI to GGSN? There is a GTPv1 message called “MS Info Change
Notification Request” that SGSN may send to GGSN indicating the UE location.
GGSN, based on this, can do location based charging.
This feature is missing in Release 8. Oh shoot! We completely
forgot about it. Lets put in Release 9.
In LTE the location reporting may be achieved in following
way. First if MME/PGW supports location reporting then MME will ask eNB to
report UE location. So, as and when UE moves from one TAI to other or from one
cell to cell eNB will send Location Update message to MME. But how to propagate
this info all the way to PGW? According to release 8, there is now way to do
it. MME has to wait for the next available GTP message to send this information
to SGW/PGW. Which means a cell change may never be reported to PGW or you need
to have a eNB with just one cell under it and that is just covering one TAI, so
that when UE moves from once cell to other there can be a handover and MME can
send Modify bearer request to SGW with the ULI. This is little too much. So
3GPP Release 9 brought back the support
for “Change Notification Request”. If UE moves from one cell to cell, MME may
now send Change Notification Request that can be propagated all the way to PGW
and PGW may further send UE location to PCRF or charging server. Thus bringing
back location based charging.
Refer to 3GPP TS 23.401 v 9.9.0 Section 5.9.2 which was
missing in Release 8.
Release 7 equivalent is in 3GPP TS 23.060 Section 15.1.3.
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