On Tue, Nov 23, 2010 at 8:54 PM, Jesse Wang <[email protected]> wrote: > Hi guys > The TMSI gets changed when the phone performs a location update right? Does > the phone update the TMSI when changing cells or changing location areas? In > the latter case, what is the chance of a phone changes its TMSI in a large > shopping centre? Isn't extremly unlikely, as a shopping centre would > probably be covered by only 1 location area? > Regards, > Jesse Wang
Regarding the size of location areas, this can also vary greatly from one network to another. In my neck of the woods, the GSM operators are AT&T and T-Mobile USA, and they seem to have drastically different location area strategies. Specifically, T-Mobile's location areas are quite large while AT&T has a ton of smaller location areas (in the same geographical region). Also, in my area, the "maximum time between location updates" timer is set to one hour on T-Mobile's network and 54 minutes on AT&T's network. However, I am led to believe that this value is configurable on a per-cell basis, so if your shopping centre has an in-building coverage system fed from a separate BTS (as opposed to over the air from a macrocell), mobiles in the centre could have a different timeout than those in the surrounding area. In this case, the operator could also assign a different location area to the BTS feeding the in-building system, if they wished to segregate the in-building paging traffic from the surrounding area. I am not sure whether this is a common practice though. (This timer is called T3212, and is measured in decihours. It's broadcast on the BCCH as part of the system information type 3 message. I _think_, but am not sure, that the timer is reset any time there is voice or SMS activity on the mobile - so if the mobile in question is being actively used, it would reduce the likelihood of a TMSI change due to T3212 expiration.) Cheers, Rusty D _______________________________________________ A51 mailing list [email protected] http://lists.lists.reflextor.com/cgi-bin/mailman/listinfo/a51
