Paging issue using TMSI

[tek74]

Hi expert,

I have core Huawei and E******* BSS. We tried to change paging strategy from IMSI to TMSI in the core huawei but after this change paging UEs in this area was not possible anymore (100% paging failure).
Has anyone an idea about what could be the cause ?

Thanks.

[Muhammad Imran Rafique]

Maximum of NWs are using TMSI, b/C they cant afford to have IMSI.
its surely configuration issue, not implemented properly.

BR//
Imran

[tek74]

Thanks for your answer Muhammad.
I am not sure i understood completely your answer though. I am not a core expert.
What do you mean with "Maximum of NWs are using TMSI, b/C they cant afford to have IMSI." ?

What type of bad configuration could explain that it is not possible to page with TMSI ?

Thanks.
Tek

[Muhammad Imran Rafique]

Hi,

TMSI is always updated in periodic or LAC change, so NW should always have correct tract of Ue via TMSI.
regarding your query, of IMSI vs TMSI.

IMSI exactly take double the capacity, so in order to avoid wastage of precious resources over radio interface, all big operators cant afford IMSI paging.

Moreover, i can see many NWs now which are even using TMSI for 2nd page. So no paging with IMSI at all.

BR//
Imran

[william.dg08]

Besides, for security reasons is better to use TMSI.
Check the following note (Page 33. BOOK "Radio Access Networks for UMTS -- Principles and Practice__Chris_Johnson__edWiley_y2008")

" A UE in RRC Idle mode can be identified by its International Mobile Subscriber Identity (IMSI),
Temporary Mobile Subscriber Identity (TMSI) or Packet Temporary Mobile Subscriber Identity
(P-TMSI). An IMSI is fixed for a specific USIM and is not allocated by the network during registration.
A TMSI can be allocated by the CS core network whereas a P-TMSI can be allocated by the PS core
network. ATMSI is unique within a location area. The MCC, MNC and Location Area Code (LAC) are
specified in combination with the TMSI to ensure that the UE identity is unique globally. A P-TMSI is
unique within a routing area. The MCC, MNC, LAC and Routing Area Code (RAC) are specified in
combination with the P-TMSI to ensure that the UE identity is unique globally. The TMSI and P-TMSI
are used in preference to the IMSI to help protect the confidentiality of the UE identity. The TMSI and
P-TMSI are less vulnerable to malicious attacks because they are not fixed. It is usual to reallocate the
TMSI as part of the location area update procedure and to reallocate the P-TMSI as part of the routing
area update procedure "

Try to check if the LAC/RAC config is the same in RAN and CORE

[tek74]

NRI size in LST POOLINFO should be 5. If not, E******* will not recognize TMSI (it will cut it). NRI size in both E******* and Huawei should be the same.