Baseband behavior on IMSI change¶
With "Proactive SIM" REFRESH command¶
According to ETSI TS 101 267 / 3GPP TS 11.14 section 18.104.22.168 "EF IMSI changing procedure", after changing EF-IMSI,
valid REFRESH qualifiers are
- "SIM Initialization and File Change Notification"
- "SIM Initialization and Full File Change Notification"
- "SIM Reset"
1 "SIM Initialization and Full File Change Notification"¶
1.1 ATT == 1 (Channel Description: Attach = yes)¶
- Samsung Galaxy phone displays "Refreshing SIM" (notification bubble on display, probably annoying to the user)
- immediate IMSI Detach
- some seconds delay of being detached: Samsung Galaxy S4m = 15s; NOKIA 1100 = 8s
- Location Updating (IMSI Attach) with previous TMSI (!)
- MSC has forgotten the TMSI due to IMSI detach (OsmoMSC peculiarity, usually an MSC should still have the TMSI)
- Identity Request & Response yields new IMSI
1.2 ATT == 0 (Channel Description: Attach = no)¶
1.2.1 ATT == 0, Nokia 1100¶
- omits IMSI Detach
- Nokia 1100 sends Location Updating (Periodic) immediately = changes identity at MSC immediately
1.2.2 ATT == 0, Samsung Galaxy S4m¶
- omits IMSI Detach
- does not send Location Updating = stays on previous TMSI = keeps old identity
- even after periodic LU period expired, still uses previous TMSI = still keeps old identity
(due to omitted IMSI Detach, OsmoMSC still knows the TMSI; if we implement that OsmoMSC forgets the TMSI, the periodic LU should ask for the IMSI and change identity)
2 "SIM Reset"¶
3 "SIM Initialization and File Change Notification"¶
Phones Keep the TMSI¶
Even though the IMSI has changed, the Baseband uses the last TMSI, and hence looks as if it remained completely unchanged, keeps using the previous identity.
After a power cycle, it also uses the last TMSI.
When the MSC has forgotten the last TMSI (e.g. due to IMSI Detach), the Identity Request is answered with the new IMSI, and the phone has thus switched to the new identity.
- Needs to make sure the MSC forgets the TMSI.
Investigate whether we can make the SIM forget the TMSI.implemented
Without "Proactive SIM" REFRESH command¶
Just for your info, we should not omit the REFRESH.
|phone||directly when writing new IMSI to SIM file||on CM Service Request||after periodical LU period||after flight mode / phone restart||on Identity Request|
|Nokia||no reaction||uses previous TMSI||uses previous TMSI||uses previous TMSI||returns new IMSI|
|Samsung Galaxy S4m||no reaction||uses previous TMSI||uses previous TMSI||uses previous TMSI||returns new IMSI|