[engaom]

Dear Experts;

I just want to share with you this case and your reply is highly appreciated.

The case is that I have to cells neighbor to each other and the inter BSS handovers sometimes fail causing call drop during DT (in both directions).

Here is the investigation steps that I did:
1- Tune the handover margin from the source cell to the target to fast the handovers (No Effect)

2-Frequency tuning.(No Effect)

3- From BSS call traces I found the following:
1- Very bad uplink on the target Cell
3-the msc trigger the handover to the target cell correctly and all messages between BSCs occurs until
T200 Expiry (so L2 connection not established).

Finally;do think that the uplink is the main cause of this issue; specially that I disabled the Uplink power control on the target cell and the Uplink Quality improved or mainly disappeared

Thanks & Regards

[Pix]

Hi Engaom,

During the DT, Which layer 3 messages does the MS receive ?

The HO Command ?

If no : then problem in your MSC database.

If yes : then resume reading…

Look inside this HO command :
you should see the frequency and TS of the target cell on which the MS should connect.
Are they correct ? Is it indeed the target cell towards which the MS should go ?

If yes : then it means the MS tries to connect to the right cell, but with wrong parameters.
On top of my head:
1/ problem of clock in the target cell ?
2/ problem of ciphering ? are both sides using the same ciphering mode ? (A5/1 ? A5/0 ? A5/3 ?)

Cheers
pix
Regards
pix

[engaom]

Thank Pix “great Expert”

After check both BSCs have the same ciphering Alg A5/1

Regarding Target cell; I got the which is the target cell

“SYNCH CHANNEL MESSAGE”
========================
MS1
Synch Channel Information

Time : 12:34:02.04
Vendor Header
ARFCN : 58 (E-GSM)
FrameOffset : 174078
QuarterBitOffset : 914
BSIC : 4-6
T1 : 824
T2 : 8
T3′ : 0
spare : 0
Message dump (Hex):
99 9C 20 00

Fianlly;there is no something clear about the clocking

Thanks & Regards

[pix]

hi,

the synch message does not show any problem, IMO. Could you copy & paste the content of the HO COMMAND received by the MS in DL in the serving cell, and the contents of the CHANNEL REQUESTs sent just after from MS to the target cell ?

Thanks,
Pix

[Author]

Posts