Disable Ciphering causing high drop

[wael]

Dear expert

I have strange issue in our network , after disable the ciphering( to reduce the call setup time ) we noticed that the DCR ( release indication , connection failure and handover ) increased in all BSC’s , is there any explain for this behavior

[srinivasan]

Hi,

you mean DCR in SDCCH . as there is no possibility in DCR TCH.

secondly chiper happens before call setup. so i feel this can't cause HO fail.

[gprastomo]

It can be increase the DCR, if the chipering on MSC Level is activated.
But please make sure when you disable the Chipering, you have to disable the chipering on the MSS/MSC Level as well, since the MSS also control the chipering code to be used by UE/BSC.

br


Dear expert

I have strange issue in our network , after disable the ciphering( to reduce the call setup time ) we noticed that the DCR ( release indication , connection failure and handover ) increased in all BSC’s , is there any explain for this behavior

[wael]

Yes th DCR on the TCH not sdcch , and Ciphering was disabled im MSC side only .if I disable it from the BSS side this will solve the problem can you explain

[zeezzoo]

one thing i have to ask : how you are able to disable ciphering ? it reflects a bad image for the operator you are working in ?
the challenge is not to disable ciphering , it is to enhance the call setup with the ciphering enabled .

[srinivasan]

HI,

to reduce call setup time and as its a feature of MSC ( causing additional cost) in our N/w its not used.

I feel chipering comes into picture during call setup once TCH is established the chipering role is not there. so TCH DCR can't be linked to Chipering.

chipering if disabled it should be done in MSC and BSC side also.

[gprastomo]

Hi,

Im not sure, since it needs call traces to proof.
The chipering works based on the preference on the MSS/MSC, which preference to be the first and second, and then BSC should follow, which chipering capability should the BSC have.
So if you disable it only on 1 entity (MSS only or BSS only), it will be problem.

And i think it is not a dropcall, should be blocked call.
Or may be if it is drop call, the call drop should be during multi call.

br

[gprastomo]

Hi,

I think to optimize the cipering, its better not to disable it. Just to reduce the number of authentication times, you can modify this on the MSS level.
You can try, during 10 call, 1 call is Authenticated, or 100 over 1 etc.

Better rather than disable it.

[srinivasan]

HI Wael,

Is the TCH drops increasing in that praticular BSC sites are to all MSC connected BSC sites.

[wael]

TCH drop incresed in most cells in all BSC .Especially the BSC's that having high traffic

[mohyedeen_alkousy]

there is one possibility to the cause of this problem :
the Ms is moving from BSC that support Cyphering to another BSC that doesn't support Cyphering , the handover never happened because the requested cyphering from MSC is not supported by BSC , because the handover didnt happen the mobile dragged till it made call drop

i have similar experience about this before in Siemens vendor and the solution was to apply batch in the BSCs that doesn't support the new Cyphering A5/3

[scorpion]

Check whether Anchor & Target BSC support A5/0 (i.e. No ciphering) if not enable it, this will help.

Anchor BSC Should give options of various Ciphering Algorithms, at least one of them should be Supported by Target BSC.Then the criteria will match.

[zhanglw268]

What's your ciph_mode_rej_allowed settings in your BSCs?

It's better to get MSS's log to see whether they really disabled the ciphering for all your BSCs.
Another thing is to check your BSC's ciphering setting by command "disp_a5_alg_pr", make sure that you have the same ciphering across all BSCs;
Thirdly, make sure that MSC send the "HANDOVER COMMAND" with "Cipher Option" in it, otherwise it may cause handover failure if you have different ciphering settings between different BSCs.

[wael]

What's your ciph_mode_rej_allowed settings in your BSCs?

It's better to get MSS's log to see whether they really disabled the ciphering for all your BSCs.
Another thing is to check your BSC's ciphering setting by command "disp_a5_alg_pr", make sure that you have the same ciphering across all BSCs;
Thirdly, make sure that MSC send the "HANDOVER COMMAND" with "Cipher Option" in it, otherwise it may cause handover failure if you have different ciphering settings between different BSCs.

Hi zhanglw
Hope you are fine , actually our vender right now is Huawei and ********
In Huawei BSC’s the TCH drop increased on ( release indication and Handover and connection failure and Error indication ) and the Ciphering is A50 and A51 in all BSC’s
In ******** BSC the TCH DROP increased in RF losses and Handover and the Ciphering is A50 and A51 in all BSC’s
We have 3G Net but the IRAT from the 2G to 3G is disable.

About the Handover it get little degradation in most the BSC ‘s