question about "inter-RAT cell reselection"

[a19997104]

im reading from 3GPP 25.331:

8.3.8 Inter-RAT cell reselection to UTRAN
8.3.8.1 General
The purpose of the inter-RAT cell reselection procedure to UTRAN is to transfer, under the control of the UE and to some extent the source radio access technology, a connection between the UE and another radio access technology (e.g. GSM/GPRS, but not UTRAN) to UTRAN.
8.3.8.2 Initiation
When the UE makes an inter-RAT cell reselection to UTRAN according to the criteria specified in [4], it shall initiate this procedure. The inter-RAT cell reselection made by the UE may use system information broadcast from the source radio access technology or UE dedicated information.
If the NAS procedures associated with inter-system change specified in [5] require the establishment of an RRC connection, the UE shall:
1> set the variable ESTABLISHMENT_CAUSE to "Inter-RAT cell reselection";
NOTE: This value of ESTABLISHMENT_CAUSE has priority over the cause requested by upper layers.
1> initiate an RRC connection establishment procedure as specified in subclause 8.1.3;
1> after initiating an RRC connection establishment:
2> release all resources specific to the other radio access technology.
If the NAS procedures associated with inter-system change specified in [5] do not require the establishment of an RRC connection, the UE shall:
1> enter idle mode in the target cell without accessing the cell; and
1> release all resources specific to the other radio access technology.

how can we know if the source technology is GSM or LTE?

[tharinduwije]

What do you mean by "How do we know which source RAT?".Normally Target RAT info & Priorities sent on SIB messages.Not clear enough

[a19997104]

when you go to 3G, due to the procedure of "inter RAT cell reselection" , how can you check in L3 if the user is returning to 3G from 2G or LTE ?? thats my question, thank you

[s52d]

Without looking into papers/traces etc: When terminals do RA update, they report previous RA. I guess TA as well.
If not: I guess HLR/HSS/SGSN/MME traces should tell teh story.

BR, HNY