- This topic has 15 replies, 1 voice, and was last updated 10 years, 6 months ago by paraHO.
29th October 2010 at 12:52 #64854bilalGuest
I want to know if a mobile is turned off and then turned on in the same Location area would it do a Location update when turned on?29th October 2010 at 12:55 #64855bilalGuest
and if it does then what is the point of storing the last LAI in the sim?1st November 2010 at 04:59 #64856Junior RF ManGuest
It will do1st November 2010 at 08:09 #64857bilalGuest
Thanks for th ereply Junior RF Man but where have you seen/studied it?1st November 2010 at 08:10 #64858BrotherGuest
when u turn off it will detach imsi, whenever someone calls no need paging, system knows ur mobile is off,1st November 2010 at 09:11 #64859bilalGuest
yes i agree IMSI will be detached but when you turn your mobile on, it will attach again but will the location update happen as HLR already knows ur last LAI
thank you1st November 2010 at 09:45 #64860korgiGuest
When you turn your mobile on if it is not detached from MSC/VLR no need to do LA update. But if you over the time (I mean if you keep the mobile off mode more than detach timer value) then MS do LA Update.
Korgi1st November 2010 at 09:57 #64861BrotherGuest
i think in HLR there is IMSI and VLR info,
in VLR TMSI and LAI
so HLR doesnt contain LAI1st November 2010 at 12:04 #64862bilalGuest
HLR does have the Lac plus Sim also have the last LAC stored in it1st November 2010 at 12:33 #64863korgiGuest
If you know the subject why did you ask question bilal?
If you know better than member of this forum so let’s listen you.
By the way, HLR does not have LAI! It has VLR number. When it needs LAI information it checks the VLR number for subscriber and goes related VLR and gets it.
BR1st November 2010 at 15:58 #64864paraHOGuest
GSM Networks: Protocols, Terminology,
12.1 Location Update
12.1.1 Location Update in the BSS
An MS performs LU on several occasions: every time it changes the location area, periodically, when a periodic location update is active, or with IMSI attach/ detach switched on at the time when it is subsequently turned on again.1st November 2010 at 19:10 #64865pixGuest
yes, when ms is turned on, it will do the IMSI ATTACH. The IMSI ATTACH is a normal Location Update procedure, only with one extra information that says “IMSI ATTACH”.
Basically, the MS does a LU with IMSI ATTACH. Therefore, as for a normal LU, VLR will update the LAI linked to that TMSI.
I don’t know why MS keeps the LAI after being switched off. It is perhaps used to speed up the cell selection. But it will NOT prevent the MS to do a Imsi Attach.
I believed that the information TMSI/LAI in the VLR would be erased when the MS does the IMSI DETACH. But you are suggesting that VLR keeps this information for a time = purge timer… Are you sure about it?
pix1st November 2010 at 21:12 #64866paraHOGuest
LU – Part 1
The MS requests a control channel from the BSC. The BTS decodes the CHAN_REQ, calculates the distance MS«BTS (timing advance), and forwards all this information to the BSC. Please note that the CHAN_REQ already indicates which service the MS requests (Location Update, in this case).
After the CHAN_RQD is received and processed, the BSC informs the BTS which channel type and channel number shall be reserved (CHAN_ACT).
The BTS confirms with a CHAN_ACT_ACK that it received and processed the CHAN_ACT.
The BSC sends the IMM_ASS_CMD, which activates the previously reserved channel. The BTS sends this information over an AGCH to the MS. The MS finds “its” IMM_ASS_CMD by means of the request reference, which is already contained in the CHAN_REQ.
Layer 2, the LAPDm connection is activated only now. The MS sends a SABM to the BTS, which (differently from LAPD) already contains data (LOC_UPD_REQ in this case).1st November 2010 at 21:14 #64867paraHOGuest
LU – Part 2
The BTS confirms that a LAPDm connection was established by sending an UA message, which repeats the LOC_UPD_REQ.
The BTS passes LOC_UPD_REQ to the BSC. Although this is a transparent MM message, the BSC still processes the LOC_UPD_REQ in parts, because the BSC amongst others, requires the Mobile Station Classmark information. The BSC packs LOC_UPD_REQ, together with the current LAC, and CI into a CL3I message (Attention: the LOC_UPD_REQ from the MS contains the old LAC!) and then sends this within a SCCP CR
message to the MSC. The CR message carries not only the LOC_UPD_REQ to the MSC, but also requests establishment of an SCCP connection.
If the MSC is able to provide the requested SCCP connection,then the CR is answered with a CC. A logical connection from the MS to the MSC/VLR exists from this point in time on. The MSC/VLR answers the LOC_UPD_REQ with an AUTH_REQ This message is conveyed to the BSC via the established SCCP connection.
BSC and BTS transparently forward the AUTH_REQ to the MS. Most important content is the random number parameter (RAND). The MS (more precisely the SIM) calculates the result SRES by feeding RAND and Kj into the algorithm A3, then transparently sends SRES in an AUTH_RSP message to the MSC/VLR. The VLR compares SRES with the value provided by the HLR.1st November 2010 at 21:15 #64868paraHOGuest
LU – Part 3
The MSC/VLR switches on ciphering, if the result from the authentication is correct. For this purpose, the MSC/VLR sends information to both, the MS and the BTS.
The BTS extracts its part form the ENCR_CMD message, which is Kc and sends the rest in a CIPH_MOD_CMD message to the MS. The CIPH_MOD_CMD message only contains the information, which cipher algorithm (A5/X) shall be used. The MS confirms, by sending a CIPH_MOD_COM message that ciphering was activated.
If Equipment Check is active, then the MSC/VLR requests the MS to provide its IMEI. This is done in an IDENT_REQ message, which is transparent for the BSS. Please note that the IDENT_REQ message also allows to request the TMSI or the IMSI. The equipment check may be performed at almost any time during the scenario, or in other words, is not tied to this place of the scenario.
The MS transparently transmits its IMEI in an IDENT_RSP message to the MSC/VLR, where it is checked by means of the EIR, whether that equipment is registered stolen or not approved.
The MSC/VLR assigns a TMSI, which is used instead of the IMSI in order to make tracking of subscribers more difficult. TMSI_REAL_CMD is also a transparent message between MSC/VLR and MS. The most important content of this message is the new TMSI. Please note that the assignment of a TMSI may also take place at the end within the LOC_UPD_ACC.
The MS confirms with a TMSI_REAL_COM that the new TMSI was received and stored. If the new TMSI is assigned with a LOC_UPD_ACC, then the TMSI_REAL_COM is obviously sent only after the LOC_UPD_ACC.