Handover

Possible causes :

1. Channel type combination not supported or invalid data
rate;

2. or CIC is present for SDCCH connection;

3. or CIC is missing for a TCH connection;

4. or Cell identifier for target cell is not present for a Multicell
BSS;

5. or IE identifier is inconsistent (i.e. missing mandatory
field, Encryption Information, Classmark Information 1 or
2, or Cell Identifier (Serving cell));

6. or erroneous IE contents (Encryption Information);

7. or only one among OIEs “Group Call Reference” and
“Talker Flag” ist present

By comparing the HO REQUIRED, HO REQUEST and HO COMMAND (and more) on each side, you should be able to detect exactly where is located your problem.

As for the timer expiry : which timer ? If you know which timer is expiring, you will know which message the MSC or BSC is waiting and not receiving. And you’ll know exactly what is going wrong.

External HO problems are very interesting to solve, because you must work with QoS, OMC and NSS people.

i think it is in regards with “group calls”, which i doubt is widely used…

Hi Rajiv Gujral,
Please check message flows for your vendor. You could find witch timer is expired. I saw sometimes, that for Siemens equipment, if expires timer T7, there is problem with wrong definition of CGI in source/target BSC/MSC. It is possible to see in counters.
That my recommendation: At firs check if there are right definitions of handovers. Not only in BSC (target cells), but also in MSC (outer cells) in both directions.
BR Tomar

Hi Pix,
In our network we have a problem with inter BSC handovers, we tried to do TEMs drives and we have isolated 1 BSCs which is giving us inter BSC Handover problems. Iam getting T200 expiry

hello,

if external cells are correctly defined, then it’s a mismatch between the BSC and the MSC.

ZTE -> external cells is not working, it means:
1/ either the iBSC does not manage to “contact” these cells -> HO COMMAND is not sent to the MS. HO is not triggered, there is no HO failure.

2/ the iBSC understands those cells are neighbors, a HO CMD is sent to the MS, but the MS cannot access the external cells. HO FAILURE occurs.

Which case is it ?
Case 1 i suppose ?
therefore you should perform an A INTERFACE trace. Do you see a HO REQUIRED from iBSC to MSC ?
do you see a HO REQUEST from MSC to target BSC ?
and so on…
find where is the “missing” message. If the HO REQUIRED is missing, it means the problem is in the iBSC.
if the HO REQUEST is missing, the problem lies in the MSC.

Initial check, before traces:
in OMCR ZTE, the external cells are defined
in MSC, the neighbor cells of iBSC are well defined.

Regards,
Pix

ok, thanks 🙂