Thursday, September 8, 2011

Location Reporting!

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.


RaduS said...

Nice post! Welcome back

Santosh said...

Hey thanks!

Ravi said...

Just adding one more point to the update,the "TEID" value used in the Change Notification Request/Response messages shall always be zero.

Santosh said...

Thanks Ravi for the pointer! It makes sense as Imsi is mandated in Request/Response

Zhe said...

Thanks for the post! It is much clearer to me now

Toshiba nb505 said...


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Anonymous said...

I believe PDN-GW can request MME to enable the Change reporting feature for a particular subscriber through Change Reporting Action IE in Create Session Response. So, if PDN-GW has not enabled the feature, will MME still send change notification request.

Santosh said...

Correct, but only valid in rel 9.