In a comment to a previous blog post on new mobiles now supporting GPRS to LTE Reselection during ongoing data transfers there was a comment that this was a network and not a device feature. The answer to this is quite interesting so I decided to make a post out of the response rather than just post an answer in the comments section.
It's in the nature of 3GPP to have several options for a feature and this one is no exception. Reselection from GPRS to LTE during data transfer is optional, it can be implemented as a device only feature or the device can signal to the network that it is capable to make LTE measurements during an ongoing GPRS data transfer and let the network decide what to do. Which of these options are supported are sent to the network during the GPRS attach process:
Message: ATTACH REQUEST
Information Element: GERAN to E-UTRA support in GERAN packet transfer mode
Possible Values:
- 0 0 (0): None
- 0 1 (1): E-UTRAN Neighbour Cell measurements and MS autonomous cell reselection to E-UTRAN supported
- 1 0 (2): CCN towards E-UTRAN, E-UTRAN Neighbour Cell measurement reporting and Network controlled cell reselection to E-UTRAN supported in addition to capabilities indicated by '01'
- 1 1 (3): PS Handover to E-UTRAN supported in addition to capabilities indicated by '01' and '10'
I've checked a number of recent mobiles and all of them either don't support the feature at all or support the autonomous cell reselection option without involvement of the network (like it is the case for GSM to UMTS reselection today as well).
That doesn't mean there are no networks and mobiles that support a network variant but I wonder if network operators are really interested in the feature when the autonomous variant works quite well!?
For details see 3GPP TS 24.008, Table 10.5.146 and search for "GERAN to E-UTRA support in GERAN packet transfer mode".